Doctoral Degrees (Botany)

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Abscisic acid and other hormonal effects on growth in Spirodela.
(1969) Van Staden, Johannes.; Bornman, Chris H.
The effects of abscisic acid In particular, as well well as gibberellic acid and the cytoklnlns, 6-benzyladenine, kinetin, and 6-dlmethylal lalylamlnopurine, on the growth of Spirodela oligorrhiza were investigated. Abscisic acid effectively arrested growth permanently at concentrations down to 10¯¹ mg/I. Normal growth tended to be resumed at concentrations of 10¯² and 10¯³ mg/l between nine and twelve days after treatment. A concentration of 10[-8] mg/l, however, resulted in a significant increase in dry weight at both eight, nine and twelve days after introduction into the culture medium. It is suggested that the resumption of growth twelve days after treatment at those concentrations which inhibit growth up to nine days, was due to a possible progressive inactivation of abscisic acid resulting in a lowering of its concentration to a level that is promotive. It was furthermore found that the growth response of Spirodela in terms of dry weight production over a period of eight days is proportional to the log[10] concentration of abscisic acid. It is suggested that this curve can be used as a relatively reliable and easily performed bioassay to detect amounts of abscisic acid as low as 10[-5] μg. The assay is more reliable over the range 0.01 to 10,000 μg and appears not to be affected by gibberellin, benzyladenine and kinetin. The inhibitory effect of abscisic acid on growth in Spirodela was shown to be reversed by benzyladenine, kinetin and dimethylallalylaminopurine, although they were not equally effective in doing so. Benzyladenine at 1.0 mg/l was the most effective In overcoming growth inhibition by abscisic acid. Gibberellic acid, however, proved ineffective in reversing the inhibitory effect of abscisic acid on Spirodela oligorrhiza. The apparent Increases in growth obtained in some cases may have resulted more directly from gibberellic acid stimulation than from the Interaction of gibberel lie acid with abscisic acid.
Achene biology and the chemical control of Chromolaena odorata.
(1985) Erasmus, Daniël Jacobus.; Van Staden, Johannes.
Abstract viewable in PDF document.
The actions of, and interactions between, auxins and cytokinins and their effect on in vitro rooting of selected Eucalyptus clones.
(2011) Nakhooda, Muhammad.; Watt, Maria Paula Mousaco Deoliveira.; Mycock, David John.
Clonal propagation of Eucalyptus spp. and its hybrids allows for competitiveness in the commercial forestry industry through the propagation and preservation of superior/elite genotypes. Vegetative propagation through rooted cuttings is the industry‟s standard and the choice of clones selected for plantations are determined by their rooting ability. However, as many potentially valuable genotypes are recalcitrant to adventitious rooting, micropropagation is the only effective means of propagating them. Micropropagation results in high plantlet yields, achieved primarily through the empirical use of the key plant growth regulators (PGRs) cytokinins and auxins, for shoot and root production, respectively. Their selection for use in vitro is driven by their effects on percent rooting rather than root quality. Little is known regarding the quality of the roots of the plantlets ex vitro, but there is some evidence that they are different from those of seedlings and cuttings. It was therefore hypothesized that the properties of exogenous PGRs and their interaction with other exogenous and endogenous PGRs, influenced root development and subsequent root quality. This was tested in vitro using a good-rooting E. grandis (TAG31) and two poor-rooting E. grandis x nitens hybrid clones (GN155 and NH58). In the former, the auxins supplied during the pre-rooting culture stages (multiplication and elongation) were sufficient for 100% rooting in an auxin-free rooting medium. Different combinations of PGRs in the two pre-rooting stages, followed by rooting without auxins, revealed a direct relationship between the stability of the supplied auxin and the rooting ability of TAG31. Gas chromatographymass spectrometry (GC-MS) analyses indicated that endogenous shoot levels of indole- 3-acetic acid (IAA) influenced graviperception. Also, low IAA content was associated with atypical starch grain accumulation or its absence from root tips (53.1 nmol IAA gˉ¹ DW compared with 325.7 nmol IAA g-¹ DW in gravisensing roots). The specific roles of the natural auxins IAA and IBA on root morphogenesis were then investigated using 2,3,5-triiodobenzoic acid (TIBA; inhibits IAA transport), ρ-chlorophenoxyisobutyric acid (PCIB; inhibits auxin signal transduction), and the auxin antagonist kinetin in the rooting medium, following root induction. After 3 weeks, the mean root diameter was significantly reduced from 552.8μm (control) to 129.2μm (with PCIB) and 278.6μm (with kinetin). TIBA increased root diameter to 833.4μm, decreased Δ root length, increased root vasculature and resulted in agravitropism. Hence, whereas rooting could be induced by IBA, IAA was necessary for the maintenance of vascular integrity and graviperception. This critical role of IAA in root development is of importance as IBA, owing to its higher stability, has been traditionally relied upon for root induction in the majority of micropropagation protocols. The potential of incorporating IAA into the media formulations of in vitro protocols for poor-rooters that do not respond well to IAA was then investigated, using GN155 and NH58. While PCIB in the rooting medium of GN155 completely inhibited rooting, the addition of dihydroxyacetophenone (DHAP), an inhibitor of auxin conjugation, to the rooting medium, did not significantly increase % rooting in the presence of 0.1 mg 1ˉ¹ IBA (i.e. 50% rooting with 2mM DHAP and IBA, compared with 45% with IBA alone). The results suggested that the inability of some eucalypts to induce roots easily in vitro was not due to a deficiency in auxin signal transduction or to auxin conjugation. Instead, rooting was inhibited by an accumulation of kinetin within shoots during the pre-rooting culture stages. The endogenous levels of PGRs in shoots of GN155 and NH58 showed a strong relationship (R² = 0.943) between the shoot kinetin:auxin and shoot rootability. Substituting kinetin with the relatively less stable natural cytokinin trans-zeatin in the elongation stage resulted in a significant increase in % rooting in both clones, from 19% to 45% (GN155) and from 31% to 52% (NH58), with 0.1 mg 1ˉ¹ IAA in the rooting medium. However, omitting all cytokinins from the elongation medium, resulted in over 95% and 75% rooting of shoots of GN155 and NH58, respectively, with 0.1 mg 1ˉ¹ IAA. These results suggest that IAA is a requirement for root development and cannot be substituted by its analogues in certain root developmental events. Hence, IAA should be the preferred auxin for eucalypt micropropagation. As fundamental research, the approach taken in this study circumvents the empirical method used in improving micropropagation protocols. The importance of the properties and the interactions between endogenous and exogenous PGRs in regulating root morphogenesis, and the practical implications of these findings is emphasised.
Adventitious rooting in stem cuttings of Eucalyptus grandis Hill ex Maid.
(1988) Wilson, Philip John.; Van Staden, Johannes.
Adventitious rooting in stem cuttings of Eucalyptus grandis Hill ex Maid. was thought to be influenced by a putative inhibitor. In previous studies it has been usual to infer the presence of putative rooting inhibitors and promoters from the mung bean bioassay, but the possibility was raised that treatment responses in this assay could be mediated more by the concentration of the treatment solution than by the chemical identity of the solute. This appeared to be so: several solutes, including hydrochloric acid and common salt, were found to promote the rooting of mung bean cuttings when present in the treatment solution at an apparently injurous concentration. The concept of promoters and inhibitors of adventitious rooting, as constituted at present, was considered to be an unfavourable approach for further studies. Stem cuttings must contain a morphogen, broadly defined, which operates the 'switch' from stem to adventitious root. The leaves and buds of E.grandis stem cuttings did not appear to be sole sources of a morphogen (as is often assumed), but nevertheless the activity of the leaves and buds was good for rooting. This activity was reflected in the pattern of root emergence. A slight preponderance emerged from the leaf trace sectors of the stem, suggesting that the leaves and buds cause a morphogen (of unknown origin) to circulate in the cutting. The existence of a vascular morphogen was confirmed and it proved to be very mobile in the stem, suggesting that it is well distributed circumferentially at the base of the cutting rather than confined to the leaf trace sectors. It appeared to be super-abundant at the base of easy-to-root cuttings, but it was not possible to tell to what extent the morphogen was rendered accessible to the sites where roots initiate. In general, the rate of efflux from the transporting tissues, the rate of attenuation of the morphogen after efflux, and the number of potential sites for root initiation must interact on a small scale to determine rooting ability. The relative prominence of these groups of factors would be expected to vary with circumstances, for example at different locations within a single stem cutting, so the traditional concept of a limiting morphogen ('rhizocaline') is unhelpful in its simplest form. Nevertheless, the rhizocaline concept provides a starting point towards a more comprehensive view of adventitious rooting, which is required in order to predict and improve rooting ability. This view remains a remote objective because many of the factors which could be important have recieved very little attention and will be difficult to elucidate.
The application of the heat pulse velocity technique to the study of transpiration from Eucalyptus grandis.
(1994) Olbrich, Bernard Wolfgang.; Pammenter, Norman William.
This thesis examines the application of the heat pulse velocity technique (HPV) to plantation-grown Eucalyptus grandis in the Eastern Transvaal, South Africa. The work addresses the application of the technique per se and is ultimately focused on improving the prediction of the hydrological impact of afforestation, to assist in the equitable management of South Africa's limited water resources. The verification of the HPV technique on E. grandis against the cut-tree method showed that the technique accurately reflected the water uptake in four three-year-old trees and a sixteen-year-old tree. It was found that accurate measurement of wound size and probe separation was essential for accurate water use estimates. The optimal probe allocation strategy for accurate measurements of transpiration in individual trees and stands of trees was examined. Stratifying the depths of implanted probes resulted in greater precision and repeatability in the HPV-derived estimates of sap flow in E. grandis. Given a limitation in the number of probes available to estimate stand transpiration, the results showed that sampling many individuals with a low sampling intensity (few probes per tree), rather than sampling few individuals intensively, improved the estimate of stand transpiration. An examination of the influence of tree age and season on transpiration rates showed that the transpiration rate per unit leaf area of E. grandis declined with age. Also, transpiration rates were higher in summer than under equivalent conditions of evaporative demand in winter. A seasonal change in the response of transpiration to VPD was implicated as the primary cause of this shift. A number of models were derived to predict transpiration from E. grandis. The variables vapour pressure deficit (VPO) and photosynthetically active radiation (PAR) were found to account for a large proportion of the observed variation in transpiration from the age sequence of trees studied. The models developed are applicable to trees of varying age, but are valid only for conditions where minimal soil water stress is experienced. The derived models were tested against two sets of independent data. This confirmed that a simple linear multiple regression adequately describes the relationship between transpiration and the two driving meteorological variables, PAR and VPO, in E. grandis. The application of a selection of the developed models on a sample data set from Sabie showed that transpiration from a three-year-old stand of E. grandis in summer may be more than double that for a sixteen-year-old stand under the same conditions. Simulated results also showed that transpiration in summer was about 25 to 50% higher than that from the same stand during winter conditions. Simulated transpiration rates from the young E. grandis stands were high, suggesting that further validation of the estimated rates is required before the models are applied. It is concluded that the HPV method is an ideal technique to estimate water use in E. grandis trees. The models developed represent a major advancement on previous models used to predict the hydrological impact of afforestation on mountain catchments.
Aspects of structure, growth and morphogenesis in a new filamentous red alga (Ceramiaceae, Rhodophyta)
(1993) Stirk, Wendy Ann.; Van Staden, Johannes.
Pteroceramium, a descriptive name given to an undescribed winged species closely related to Ceramium, has uniaxial filamentous thallus construction with pseudodichotomous branching. Alternate branches become dominant. This pattern of growth is referred to as cellulosympodial growth. All growth is from an apical cell which cuts off subapical cells. The subapical cells develop into axial cells. Each axial cell cuts off six pericentral cells in a ring around its apical pole. The pericentral cells divide further to form the cortical band. Pc1 always forms on the outer face of the thallus as determined by the preceding pseudodichotomy and gives rise to the larger outer wing which is a lateral expansion of the cortical band. The smaller inner wing forms from Pc6 on the inner face. The other pericentral cells give rise apically to uniseriate spines. The pericentral cells also give rise to rhizoids and adventitious lateral branches. Each axial cell has a large central vacuole with a few peripheral chloroplasts, mitochondria and floridean starch granules. The smaller wing cells have a much denser cytoplasm with fewer small vacuoles, many chloroplasts which are more closely packed together and more floridean starch granules than axial cells. Chloroplasts have a typical Rhodophyta ultrastructure with single, evenly spaced thylakoids with phycobilisomes. Pit connections have a plug core but no plug cap. Pteroceramium has a typical Polysiphonia-type triphasic life history. The carposporophyte is naked and tetraspores are produced in a characteristic decussate cruciate arrangement. The effect of a number of physical and chemical factors on growth and morphogenesis was investigated. Pteroceramium grew best at irradiance levels between 79 μmol m⁻² S¯¹ and 129 μmol m⁻² S¯¹ with growth being limited at 30 μmol m⁻² S-I. The largest axial cells and wings were obtained from the material grown at 79 μmol m⁻² S¯¹ and the smallest measurements for material grown at 129 μmol m⁻² S¯¹. Monochromatic light fields of red, green and blue caused reduced growth rates compared to the control replicates grown in a white light from both incandescent and fluorescent lights. Light quality had no effect on morphogenesis. The critical daylength for maximum rates of cell elongation was 10 hours or longer, although 16 hours light caused a decrease in final axial cell volume. Optimum temperatures for growth of Pteroceramium were between 20°C and 25°C with growth decreasing at 15°C and 30°C. Axial cell volume was reduced and wing size was stunted at these two extreme temperatures tested. Scouring by sand caused axial cells to decrease in volume although the wings were unaffected. Smothering by sand did not prevent growth although axial cells and wings were greatly decreased in size, with the wings consisting of only one or two other cells. Tumbling to disrupt gravity did not affect the angle of each pseudodichotomy. Decreased levels of nitrogen and phosphorus limited growth but had little effect on axial cell volume and wing development. Pteroceramium was stenohaline with maximum growth at 34°/[00] and reduced growth at 300/[00] and 40°/[00]. Pteroceramium grew best at pH 7.5 and pH 8.5 with decreased growth at pH 6.5 and pH 5.5. The various pHs tested had little effect on morphogenesis. The best photosynthetic responses were obtained from material preconditioned at 80 μmol m⁻² S¯¹ compared with that at 30 μmol m⁻² S¯¹ and 150 μmol m⁻² S¯¹. There was a decrease in pigment content with increasing irradiance at which the alga was grown. Phycoerythrin was the dominant pigment. Exposure to a high irradiance (3000 μmol m⁻² S¯¹) for 30 minutes or longer inhibited photosynthesis. Plants did not fully recover even 24 hours later, indicating that this damage was permanent. Pteroceramium was able to acclimatize slowly over a week to temperature changes within the range of 15°C to 25°C. Rapid increases of 5°C within this temperature range increased photosynthetic performance and a rapid drop of 5°C decreased photosynthetic performance. However, a 10°C increase or drop reduced Pteroceramium's photosynthetic performance. Photosynthetic rates were decreased in alkaline conditions and increased in acidic conditions. Pteroceramium has well defined developmental patterns with basal band growth of axial cells and tip growth in the rhizoids. The pericentral cells are formed in a set sequence similar to Ceramium species with Pcl forming on the outer face, Pc2 and Pc3 forming on the lower and upper surface nearest to Pel respectively, Pc4 and PcS forming on the lower and upper surface respectively farthest from Pel, and Pc6 forming on the inner face. This sequence is unaffected by the direction of illumination or gravity. Exogenous application of plant hormones (IAA, GA3 and kinetin) in the concentration range of 10[-9] M to 10[-5] M had no effect on growth and morphogenesis in Pteroceramium. Application of polyamines and their precursors caused a decrease in growth and a reduction in cell size at concentrations higher than 10[-4] M. Polyamine inhibitors caused a reduction in growth and cell size at concentrations higher than 10[-5] M. Arginine increased growth at concentrations 10[-5] M and 10[-6] M. High power liquid chromatography (HPLC) separation of Pteroceramium extracts indicated that spermidine was present in Pteroceramium at approximately 38 μg spermidine g¯¹ fresh weight. The apical tip exerts an apical dominance effect on the subordinate branches, suppressing their elongation. Removal of the dominant apical tip increased adventitious branch formation. This effect was not reversed by application of exogenous IAA at concentrations of 10[-9] M to 10[-4] M.
Aspects related to the germination of Themeda triandra seed.
(1996) Baxter, Brent J. M.; Van Staden, Johannes.
Themeda triandra is a grass species of economic importance in Southern and Eastern Africa, and Australia. The species is being lost from grasslands and savannas in these areas due to poor agricultural practice, rangeland degradation, opencast mining and increased afforestation. Based on the poor re-establishment of the species from seed in sub-climax grasslands, dogma holds that T. triandra can not be re-established from seed. Recent research has, however, highlighted the potential to establish this species from seed, but the use of seed of T. triandra in re-vegetation of disturbed areas is limited by poor understanding of the seed biology of the species and low seed availability. In this Thesis ways to maximise the use of available seed are reported. Areas investigated include optimisation of seed storage conditions, overcoming primary seed dormancy, promoting germination of available seed and pre-treatment of seed to improve germination. The Thesis closes with an investigation of the environmental limits of tolerance of seedlings from the T. triandra ecotypes studied, when grown under field conditions at reciprocal sites. Two altitudinally and geographically distinct populations of T. triandra were studied; a high altitude grassland population at Cathedral Peak (Drakensberg: 1800 m) and a low altitude savanna population from the Umfolozi Game Reserve (Zululand: 90 m). At seed shed T. triandra seed is dormant. The depth and duration of primary seed dormancy varies between populations, but appears to reflect severity of the winter period experienced. More than 95% of T. triandra seed from the Drakensberg population was dormant at seed shed, compared to 55% of seed from the Zululand population. In both populations dormancy is lost during dry after-ripening. At seed shed T. triandra seed displays a high level of seed viability (> 80%). Seed temperature range -15°C to 70°C, was achieved at 25°C (± 2°C), at which temperature seed was held for 40 months. During this period viability decreased from over 80% to 50% and dormancy was lost through dry after-ripening within four (Zululand) to eight (Drakensberg) months. Loss of dormancy can be accelerated at higher temperatures, but is accompanied by rapid loss of seed viability. In contrast, viability can be maintained in storage at sub zero temperatures, but loss of dormancy is retarded. Loss of dormancy coinsides with the onset of spring. Dormant seed is capable 'of germination at a narrow range of constant temperatures (25 ° C to 40 ° C). With after-ripening, the range of temperatures at which germination takes place increases (15 ° C to 40 ° C) and the optimum temperature for germination decreases from 30 ° C in both populations to 25 ° C. After-ripened seed is capable of germination at lower water potentials than dormant seed. Similarly, seed from the low altitude population is capable of germination at lower water potentials (-1.0 MPa dormant: -1.5 MPa after-ripened) than seed from the high altitude population (-0.5 MPa dormant: -1.0 MPa afterripened). Dormancy in seed from the high altitude population is overcome by prolonged stratification (30d). In contrast, seed from the low altitude population responds to short duration stratification (5d) with longer periods proving detrimental to seed germination. Germination of dormant and non-dormant seed of T. triandra does not differ significantly in the light or dark. Neither does photoperiod, or red / far-red light exposure significantly affect germination. Seed response to light and temperature, as characterised under controlled conditions, was verified in a field seed burial experiment undertaken at the high altitude Drakensberg site during winter. Burial in soil does not affect the response of T. triandra seed to light or temperature. Loss of dormancy is accelerated in buried seed. After-ripened seed germinates over a wider range of temperatures than dormant seed. The mechanisms governing T. triandra seed dormancy and germination appear to be universal between ecotypes. Dormancy is enforced, in part, by the seed covering structures (glumes) which impose a mechanical restraint to radicle emergence. Approximately 85% of dormant seed, however, contains a dormant embryo. Embryo dormancy is enforced at seed shed by compounds inhibitory to seed germination. The germination process in T. triandra appears to be governed by endogenous gibberellins. Bioassay results reveal that endogenous gibberellin synthesis commences up to six hours sooner in after-ripened seed than in dormant seed and that the level, or concentration, of gibberellin-like compounds is substantially lower in after-ripened seed than in dormant seed. Similarly, the concentration of applied gibberellic acid required to achieve maximum germination of T. triandra seed decreased from 500 mg.l ¯¹ (8 week old seed) to 50 mg.l ¯¹ (78 week old seed) as dormancy is lost during after-ripening. Contrary to previous reports, boron does not promote T. triandra seed germination. Plant-derived smoke significantly promotes T. triandra seed germination (5% to 43% for dormant seed from the Drakensberg population). The effectiveness of smoke in promoting germination increased with increasing seed imbibition suggesting smoke action at a metabolic level. This suggestion is reinforced by the ability of smoke to bring about the germination of seed which had failed to germinate in water. Moreover when smoke is applied in combination with gibberellic acid the final level of seed germination following combined treatment is significantly greater than the level of germination achieved in the presence of either smoke or gibberellic acid alone. A similar result is achieved with joint application of smoke and kinetin, although the results were not statistically significant. Furthermore, smoke treatment reversed ABA-induced inhibition of germination of non-dormant T. triandra, wheat, radish and sunflower seed to a level equal to or greater than that achieved using GA[3] or kinetin. The possibility that smoke promotes seed germination by mimicking, or promoting the synthesis of endogenous gibberellins was investigated. Bioassay results revealed that smoke had no effect on increasing the level of endogenous gibberellin-like activity in T. triandra caryopses. The mechanism by which smoke acts to promote seed germination remains elusive, however results presented suggest that smoke may act to remove an ABA-induced block to seed germination. Consequently, it is suggested that smoke plays a permissive role in promotion of T. triandra seed germination by removing a block to the seed germination process thereby allowing endogenous gibberellins to act. Treatments which significantly improved the level of T. triandra seed germination were evaluated as seed pre-treatments. Significant improvement in germination was obtained following smoke (aq) and gibberellic acid (100 mg.l ¯¹) pre-treatment of seed. The effects of pre-treatment were evident on germination of seed for up to 21 days after pre-treatment. Seed pre-treatment with smoke had no affect on subsequent seedling growth, but gibberellic acid pre-treated seedlings developed abnormally. In contrast, short duration exposure of dormant seed to high temperature (70 0 C for 7 days) increased germination, seedling height and tiller number. Priming of seed in polyethylene glycol (PEG 8000) for 7 days significantly improves the level of T. triandra seed germination. The use of seed pre-treatment to maximise germination of T. triandra seed is discussed. Reciprocal transplanting of seedlings from both the Drakensberg and Zululand populations confirmed that the T. triandra populations under investigation are distinct ecotypes. Field transplant gardens were established in the Drakensberg, Zululand and at an intermediate altitude in Pietermaritzburg (800m). Less than 10% of planted seedlings died at any site. With increasing altitude of the field site, tiller number increased, but tiller allocation to reproduction decreased. Similarly, for both Zulu land and Drakensberg seedling transplants the time taken to reach anthesis increased with increasing altitude and the proportion of transplants which flowered decreased. These data are consistent with the climate of the field sites where the high altitude site experiences a short growing season and harsh winter while the Zululand site experiences a prolonged growing season and mild winter period. These data indicate that T. triandra ecotypes are tolerant of a wide range of environmental variables. The application of the data presented in this Thesis, in maximising the use of available seed of T. triandra for use in re-vegetation, is discussed.
Aspects relating to the occurrence of an inhibitor of tissue plasminogen activator in Erythrina caffra thunb. plants and in vitro cultures.
(1990) Meyer, Hendrik Johannes.; Van Staden, Johannes.
A double sandwich enzyme-linked immunosorbent assay (ELISA) was developed to quantify the proteinaceous inhibitor of tissue plasminogen activator (t-PA) which occur in the tissue of Erythrina caffra Thunb. Using the ELISA the t-PA inhibitor could be detected in nanogramme quantities on the micro titer plate. The concentration of the t-PA inhibitor was determined in different tissues of Erythrina caffra. t-PA inhibitor concentrations in the order of 1 000 microgrammes per gramme protein were found in the seeds. Relatively small quantities of t - PA inhibitor, in the order of 10 to 50 microgrammes per gramme protein, occurred in root, shoot, leaf and living bark material. The t-PA inhibitor was found to accumulate in a similar way to the storage proteins in developing seeds. The accumulation of the inhibitor is at a relatively low level during the early period of seed development but increases exponentially just before the seeds reach their maximum size. The t-PA inhibitor content of the cotyledons decreased drastically during the process of germination and subsequent seedling development. The disappearance of the inhibitor be the result of total degradation of the molecule can or partial proteolysis with the modified molecule still being present in the tissue. An attempt was made to increase the t-PA inhibitor content of excised leaves of Erythrina caffra with protein inducing substances such as polyamines, precursors of ethylene and phytic acid. The protein inducing compounds included cell wall hydrolysates of Erythrina caffra, the marine alga Ecklonia maxima Osbeck (Papenfuss) as well as Lycopersicon esculentum Mill which induced the, synthesis of proteinase inhibitors suggested to be involved in the defense mechanism of plants. None of the substances used, increased the t-PA inhibitor content of excised leaves or in vitro cultures of Erythrina caffra. It is suggested that the t-PA inhibitor is probably not involved in a defense mechanism of Erythrina caffra. A callus and suspension culture derived from shoot tissue was developed to determine the occurrence of the t-PA inhibitor in vitro. The optimal nutrient medium for the growth of callus was the salts and vitamins of MURASHIGE and SKOOG (1962). The medium was supplemented with 3 % sucrose, 0. 1 gramme per litre meso - inositol, 10 micromoles per litre benzyl adenine and 5 micromoles per litre 2,4- dichlorophenoxyacetic acid . Different auxins and cytokinins had a similar growth stimulatory effect on the growth of callus derived from a number of organs of Erythrina caffra. The callus from different organs did however, grow at different rates on the same nutrient medium. Callus derived from leaf, shoot, and cotyledonary tissue grew at similar rates on the nutrient media of MURASHIGE and SKOOG (1962), SCHENK and HILDEBRANDT (1972) and B5 (GAMBORG, MILLER and OJIMA, 1968) despite large differences in the concentration of the nutrients in the three nutri.ent media. The source of nitrogen and ratio of nitrate to ammonium was critical to the growth of callus cultures . The optimal concentration of nitrate and ammonium was 30 millimoles per litre . The growth of callus from different organs was significantly affected by the concentration of sucrose in the nutrient medium. A concentration of 3% was optimal for callus growth. Temperature had a significant effect on the growth of callus. The optimal temperature for callus growth was 25 °C. A shoot cell suspension culture was established and maintained at the same temperature and on the same medium as the callus cultures but with a ten times lower concentration of growth regulators. A low shake speed was essential for the growth of the suspension culture. Maximum growth was obtained at a shake speed of 60 rpm. Relatively low quantities of t-PA inhibitor, in the order of 1 to 5 microgrammes per gramme protein, was detected in the suspension cultures. An attempt was made to increase the t-PA inhibitor content of the suspension cultures with the pro te in i nduc i ng compounds used on excised leaves, but without success. However, the t-PA inhibitor content of the suspension culture was significantly increased with a ten times increase in the sulphate content of the nutrient medium.
Assessment of a process-based model to predict the growth and yield of Eucalyptus grandis plantations in South Africa.
(2005) Esprey, Luke John.; Smith, Colin William.; Pammenter, Norman William.; Sands, Peter.
It is believed that the process-based model 3-PG (Physiological Principles Predicting Growth; Landsberg and Waring, 1997) can potentially play a useful role within South African forestry, both as an operational and a strategic tool. Strategic applications may include the prediction of potential productivity on a site-by-site basis; broadscale productivity estimates based on remote sensing and the spatial application of 3-PG; identification of production constraints; and estimation of carbon fluxes to help address sustainability issues. Operationally, 3-PG could complement empiricallybased models or be used in conjunction with them as a hybridised product. The challenges of this study were therefore to see whether it is possible to adapt 3-PG to predict the growth and yield of E. grandis under South African conditions, test that model predictions are consistent with observed growth data and are biologically reasonable, and to assess the practicality of using 3-PG as either a strategic or operational tool. The main emphasis of this study was to understand the internal logic of 3-PG and how physiological processes are represented, and to develop methods to objectively parameterise and initialise the model. Thereafter a detailed model validation study was performed, ending off with selected potential applications of 3-PG within the South African context. The sensitivity of predicted stand volume (SV) and leaf area index (LAI) to the values of the species-specific parameters in 3-PG was examined. These analyses enabled the development of three distinct parameter sensitivity classes: insensitive parameters (i.e. those that can be varied widely without affecting the outputs studied), sensitive parameters (i.e. those whose value strongly affects the outputs, and non-linear parameters (i.e. those for which the outputs depend in a non-linear manner on the parameter value). Minimum data requirements for the parameterisation and initialisation of 3-PG are considered in detail. Conventional methods used for the parameterisation of models, specifically 3-PG, are reflected upon. An automated parameter estimation technique was examined and used for the estimation of selected parameters. Species-specific parameters were categorised according to data source estimation and sensitivity classes. Parameters describing allometric and age-dependent relationships were assigned values using observed data from biomass harvests. Critical parameters that could not be directly assigned using observed data were the ratio of foliage to stem allocation (i.e. P2 and p2o), allocation of net primary production (NPP) to roots (TJRX and T]Rn), optimum temperature for growth (7^,) and maximum canopy quantum efficiency (acx)- These were estimated using Parameter ESTimation, by fitting model output to corresponding observed growth data. As well as species-specific parameter values, mandatory inputs required by 3-PG include weather data, site-specific factors such as site fertility (FR) and physical properties of the soils, and stand initialisation data. Objective techniques to determine these site-specific factors and the initial values for the biomass pools were proposed. Most of these data are readily available for sites where experimental trials exist, or where monitoring networks are in place. However, this is the exception rather than the rule, so alternative data and information sources are required. These, together with the need for accurate weather inputs (especially monthly rainfall) and physical properties (especially soil texture, maximum available soil water and FR) of the sites being modelled were explored. 3-PG was validated using four simple tests by comparing predicted versus observed SV. Results showed that 3-PG predictions are relatively consistent with observed stand data. Analyses performed using time-series data showed model predictions accurately tracked observed growth in response to erratic and fluctuating weather conditions. Results from the initial model validation showed production on high and low productivity sites was under- and over-predicted, respectively. Further results presented here show a similar, but less marked trend (i.e. over- and under-predictions are not as extreme), and individual biases are less than those from predictions made using another locally developed parameter set. The application of 3-PG showed that the model is able to make estimates of tree growth that are consistent with those used within the forestry site classification. This showed the considerable potential 3-PG has for strategic planning by the forest industry (i.e. projected wood supplies etc) and in research planning (refining existing site classifications). The model could be useful in predicting growth in various areas where E. grandis is not grown, assisting in future decision making. 3-PG was able to identify growth constraints on a site-by-site basis and distinguish among them, and was able to identify environmental and site limitations to plantation growth, and how they vary in space and time. These results together with predictions of site productivity demonstrate the potential for 3-PG to be used to improve existing forest site classifications. The model comparison study between empirically-based models and 3-PG showed that although the empirical models made accurate predictions of volume under static climatic conditions, under fluctuating weather conditions empirical estimates of volume were less accurate than those made with 3-PG. 3-PG can therefore be used operationally with minimum input data to predict growth using enumeration data. This is useful in saving time and cutting costs. The use of process-based models (PBMs) in general, and 3-PG in particular, needs to be "championed'' to the South African forest industry. This is necessary for two reasons. Firstly, the model and the manner with which it describes physiological processes of growth need to be explained in layman's terms. This will demonstrate how and why a process-based model can work better in a fluctuating environment than empirically based models. Secondly the comparison between 3-PG and the local empirical models needs to be presented as an example of how 3-PG can be applied on an operational basis. It is accepted that much convincing is still required.
Automatic classification and ecological profiles of South-Western Transvaal Highveld grassland.
(1973) Morris, Jeffrey William.; Villiers, T. A.
Abstract available in PDF file.
The biochemical and cytokinin changes in the developing and germinating seeds of Podocarpus henkelli stapf.
(1981) Dodd, Malcolm Caulton.; Van Staden, Johannes.
A review of the literature revealed that there is a lack of depth in our knowledge of gymnospermous seeds with regard to the development and germination processes. The phytohormones, particularly the cytokinins have been implicated in these processes. The seeds of Podocarpus henkelii were thus selected as experimental material for studying the biochemical and cytokinin-like changes associated with development and germination. The development of these seeds was also followed at the ultrastructural level. These studies revealed that cellular detail within the female gametophyte only began .to form in December (early summer), approximately six weeks after fertilization had taken place. At this time some reserve protein was evident and the embryo sporophyte consisted of only a few pro-suspensor and pro-embryo cells. Concurrently, the cytokinin levels were fairly high in the female gametophyte but low in the epimatium. In both seed components two cytokinin- like compounds predominated which co-chromatographed with the free base cytokinin zeatin and its ribonucleoside. The second sample was taken in late January (mid-summer) by which time the embryo sporophyte had developed rapidly into a readily distinguishable seed component. The cellular detail indicated that much cell division had recently taken place and that the cells were currently increasing in size and accumulating starch and lipid. In the female gametophyte the soluble sugars were at the maximum level recorded during these experiments and the level of starch was increasing. The extractable cytokinin content of the seed was high at this time, particularly in the embryo sporophyte. In all three seed components cytokinin-like compounds which co-chromatographed with zeatin and ribosylzeatin were present. These high levels of cytokinin coincided with the rapid increase in both fresh and dry mass of the embryo sporophyte and female gametophyte. Ultrastructural studies of the third sample collected in mid-March (early autumn) showed that cellular changes were associated mainly with increases in cell size and the accumulation of food reserves, particularly starch. The cytokinin levels had decreased in all three seed components at this time. There was an increase in the cytokinin which co-chromatographed with glucosylzeatin in the female gametophyte. The seeds matured in late April (autumn) and had the unusual features of not drying out during maturation. Fresh seeds collected from the ground had a moisture content of ca. 62 per cent. The main food reserve was starch with relatively small amounts of protein and lipid also present. The seeds of Podocarpus henkelii germinated readily after scarification in the absence of water provided that their moisture content remained ca. 60 per cent. Seeds in which the moisture content had fallen below ca. 54 per cent required additional water for germination. The moisture content of the seeds fell rapidly under natural conditions and viability was lost below a moisture content of ca. 34 per cent. Unscarified seeds of 52 per cent moisture content placed under moist conditions at a constant 25°C took 23 weeks to achieve 68 per cent germination. These experiments showed that although the epimatium limited water uptake by the seeds it did not prevent moisture loss to the atmosphere. This appears to be the main factor contributing to the seed's inefficiency as a propagule. A small degree of after-ripening was recorded with the embryo sporophyte increasing in size with storage. This appeared to contribute to the increased rate of germination of the scarified seeds. An interesting feature of the seeds of Podocarpus henkelii is that they have the ability to fix atmospheric carbon, which is subsequently translocated from the epimatium to the female gametophyte and embryo sporophyte. The mature seeds were stored at 4°C for six weeks during which time little change had occurred at the ultrastructural level. Protein vacuoles in the embryo sporophyte had disappeared and in all three seed components cytokinin levels were low. Three days after scarification and the start of incubation, little change in cellular detail was apparent as limited rehydration was necessary due to the high moisture content. The cytokinin levels in the embryo sporophyte and epimatium had increased, whilst the levels in the female gametophyte had decreased at this time. In the embryo sporophyte lipid mobilization had commenced with these reserves apparently being metabolized within vacuoles. The rate of respiration measured in terms of increases in CO[2] evolution, increased 60 hours after the start of the incubation period, just 12 hours before ten per cent germination was recorded. Germination was accompanied by a large increase in the levels of cytokinins in the female gametophyte and embryo sporophyte. The cytokinins detected co-chromatographed with the free base cytokinin zeatin and its riboside, ribosylzeatin. Concurrently, marked ultrastructural changes were recorded with increases in the amounts of dictyosomes, endoplasmic reticulum and the formation of polyribosomes, all of which are indicative of increased metabolic activity. Similar increases in the female gametophyte were ofa lower order and occurred only after nine days of incubation. By this time the levels of cytokinins had decreased considerably. After 12 days of incubation 65 per cent of the seeds had germinated. As much of the food reserves in the female gametophyte and embryo sporophyte remained, it is suggested that these reserves are utilized for subsequent seedling establishment rather than for germination. The actual role that cytokinins play in the development and germination of these seeds is not clear. High levels of this phytohormone coincide with periods of food deposition and mobilization suggesting that they play an important part in these processes. The results of the biochemical, cytokinin and ultrastructural studies are discussed in relation to the developmental and germination processes and are compared to the data of other seeds.
Biochemical, physiological and agronomic response of various sweet potato cultivars/varieties to drought stress in rainout shelters and field conditions.
(2014) Laurie, Robert Naylor.; Van Staden, Johannes.; Finnie, Jeffrey Franklin.
Drought is and will always be an issue in the cultivation of plants. Some plants have the ability to withstand a drought conditions to a certain degree while others, with other useful attributes, fail dismally. The value of testing genotypes for the ability to tolerate drought cannot be underestimated and will enhance the progress in the selection of drought tolerant genotypes. Thus, the objective of this study was to investigate the physiological, biochemical and agronomical reaction of sweet potato plants to drought and the procedures which could be used to test for sweet potato drought tolerance in the field. This was made possible through the creation of an environment at ARC-Roodeplaat in which sweet potato plants could be subjected to drought stress conditions. Thirty five sweet potato genotypes were planted in three trials in rainout shelters and open fields to analyze their physiological, biochemical and agronomical responses to drought stress. The majority of the genotypes were selected breeding lines with some cultivars from America, Peru and South Africa. These genotypes were chosen due to their range of traits for incorporation in crosses in the sweet potato breeding programme of the Agricultural Research Council (ARC). Drought stress conditions on the plants were induced through selective irrigation practices. In Trial 1 control plants were cultivated at field capacity while drought stressed plants received 60% and 30% of the amount of water of the control, respectively. In Trial 2, genotypes were planted in the field and under rainout shelters respectively. The field plantings acted as the control and received normal rain and irrigation while the rainout shelter planting received irrigation corresponding to 30% of field capacity. The plants in Trial 3 were subjected to control and drought conditions with the drought stressed plants receiving 30% of the water of the control. Leaf harvesting and phenotypical measurements were conducted twice during the trial period i.e. 60 and 120 days after planting. The drought stress impacted the growth of the sweet potato plants significantly. Canopy cover and stem length were severely influenced by the drought stress and resulted in huge declines of the respective values in all trails. Canopy cover values declined by more than twice compared to the control while stem length values were reduced by up to 10 times compared to the control. Antioxidant systems with particular reference to ascorbate peroxidase (AP), super oxide dismutase (SOD) and glutathione reductase (GR) reacted to the stress imposed and increased significantly. It was observed that values of the respective antioxidant enzyme systems increased sharply in the latter part of the trial and that the increase was also more intense at severe stress. The analysis of the antioxidant system made it possible to distinguish between the genotypes regarding their reaction to the stress. Results for carbon discrimination experiments in all the trials indicated that a significant decline in values took place as the drought stress increased. The decline appeared to be slightly more pronounced as the stress progressed. Also, as in the case of the antioxidant systems, it was possible to distinguish between genotypes even in the control treatments. The plants responded to the drought stress to the effect that a similar trend, (compared to the antioxidants), was observed with regards to stomatal conductance although genotypical differentiation was not possible in any of the stress conditions. It was demonstrated in the trials that the relative water content (RWC) values in the leaves of plants subjected to drought stress declined significantly between water treatments. Drought stress in the three trials had a severe impact on the nitrate reductase (NR) activity in the leaves of the plants. The decline in values were substantial but no significant differences could be detected between the genotypes except for the breeding line 2005-1-16 and cultivars Purple Sunset, Beauregard and Zapallo. Slight non-significant differences were observed between the genotypes at mild stress conditions but the severe stress conditions proved too harsh. Significant increases in the proline content of the sweet potato plants subjected to drought stress resulted in differentiation between the genotypes in Trial 1 and Trial 2, especially during the latter stages of the trials and at severe stress. Large reductions, up to 97%, of root yield were detected in the three trials. It appeared that the severe stress treatment proved too harsh to accomplish significant differences between the genotypes in all the trials. In Trial 1 the genotype Resisto differed significantly from the other genotypes and seemed to tolerate the drought the best in the mild stress conditions. Water use efficiency (WUE) values did allow for discrimination between the genotypes in Trial 1. A large decline in WUE values were observed in Trial 2 in general, although a few breeding lines 2005-7-4, 2006-4-4 and ix 2006-7-7 were prominent with high WUE values and could be recommended for use in a breeding programme. In Trial 3 the cultivar Bophelo and 199062.1 also exhibited higher WUE values which correlate well with yield data obtained from the same Trial. This could also prove valuable in the selection process. Due to the fact that multiple traits make a valuable contribution to the decision-making process in the selection for possible screening methods, statistical correlation was undertaken to establish possible relationships between traits. Good correlation was found between yield, stomatal conductance and WUE in Trial 1. This confirmed the assumption that a drop in stomatal conductance will result in lower root yield. Proline correlated also very well with the antioxidant enzyme levels of GR and AP which indicates that while the antioxidant enzymes play a role in combatting oxidants proline aid in possible prevention of moisture loss and stabilization of cell membrane structures. In Trial 2 good correlation was observed between yield, LAI, NR and CCI and to a lesser extent carbon-13 discrimination. This confirmed the belief that a decrease in LAI and CCI should have a negative effect on the yield due to less canopy cover and less chlorophyll for the capture of sunlight for photosynthesis. Results from Trial 3 also indicated good relationships between proline, GR and AP, as well as good relationships between yield, WUE, carbon discrimination and stomatal conductance (gs). It can hereby be concluded that the reaction of sweet potatoes to drought stress revealed results that can be of help for use in the future to successfully establish a protocol whereby successful selection of genotypes can be made in a biochemical, physiological and agronomical way. The study also provided proof that some of the approaches and procedures used in these trials can be successfully implemented in the drought screening of sweet potato.
Biological activity of traditional medicinal plants used against venereal diseases in South Africa.
(2006) Buwa, Lisa Valencia.; Van Staden, Johannes.
Throughout the history of mankind, many infectious diseases have been treated with plant extracts. Venereal infections are one such group and are regarded as conditions that are highly responsive to traditional treatment. Aqueous, ethanol and ethyl acetate extracts of 13 plants used in South Africa for the treatment of venereal diseases were screened for in vitro antibacterial, antifungal, mutagenic and antimutagenic activities. Antibacterial activity was evaluated using the disc-diffusion and microdilution assays to determine the minimal inhibitory concentration (MIC) values of the extracts. The extracts were tested against the Gram-positive bacteria Bacillus subtilis and Staphylococcus aureus, and the Gram-negative bacteria Escherichia coli and Klebsiella pneumoniae. Among the plants tested, Gunnera perpensa, Harpephyllum caffrum, Hypoxis latifolia and Ledebouria ovatifolia showed the best antibacterial activity. The aqueous rhizome extract of Gunnera perpensa displayed good activity against Gram-negative bacteria with an MIC value of 0.78 mg/ml, and against S. aureus (0.78 mg/ml). Aqueous and ethanol extracts of H. caffrum bark were active against both Gram-positive and Gram-negative bacteria. Hypoxis latifolia aqueous corm extracts exhibited very good MIC values against K. pneumoniae (0.78 mg/ml), E. coli and S. aureus (1.56 mg/ml). Ethanol and ethyl acetate bulb extracts of Ledebouria ovatifolia displayed good activity against Bacillus subtilis bacteria with MIC values of 0.78 mg/ml and 0.39 mg/ml respectively. Antifungal activity was evaluated using the microdilution bioassay. Good activity was shown by the ethanolic bark extracts of Bersama lucens and Harpephyllum caffrum against Candida albicans. Only in the case of Harpephyllum caffrum did aqueous extracts have activity against Candida albicans. In the Ames test, all plant extracts showed a negative genotoxic response except for ethanol and ethyl acetate bulb extracts of Cyrtanthus obliquus which induced mutations in TA98. Moderate antimutagenic activity was observed with the ethyl acetate extract of G. perpensa and the ethanolic extract of H. latifolia. High antibacterial and antifungal activity detected with Harpephyllum caffrum bark extracts resulted in an investigation on seasonal and geographical variation of this inhibitory activity. Seasonal variation in antibacterial and antifungal activities was investigated in order to determine the best collection time to ensure potential high medicinal activity in plant preparations. The highest inhibitory activity was detected with plant material collected in June and December 2003, with a decline in activity when collections were made in September 2004. The chemical profiles of TLC chromatograms were compared and little variation was found, particularly in the case of plant material obtained from the Botanic Garden of the University of KwaZulu-Natal and a 'Muthi' Shop in Pietermaritzburg. Identification of active compounds from G. perpensa and H. caffrum was not successful due to insufficient amounts of isolated fractions.
The biology of pollination and seed dispersal in Clivia (Amaryllidaceae)
(2019) Kiepiel, Ian.; Johnson, Steven Dean.
Pollinator shifts have been implicated as drivers of angiosperm diversification. The hypothesis that a transition from bird to butterfly pollination took place in Clivia was tested, and floral traits investigated to determine which may have mediated the putative shift. Linking pollination systems with available phylogenies indicated a shift occurred from bird to butterfly pollination, accompanied by the evolution of upright trumpet-shaped flowers, scent emission and nectar volume reduction, whilst floral colouration and nectar chemistry remain unmodified. Results support the idea that pollinator shifts may explain major floral trait modifications during plant diversification. Breeding systems of Clivia were investigated, with the aims of demining the site and functional consequences of putative late-acting self-incompatibility (LSI). Results suggest that Clivia species are largely self-sterile as a result of LSI or severe inbreeding depression, but ovule discounting caused by self-pollination is not a major limitation on fecundity, and seed production appears to be mostly resource limited. Clivia miniata is pollinated virtually exclusively by butterflies. Functional significance of C. miniata floral traits were examined, with the aim of determining butterfly floral preferences and the functional basis of traits responsible for butterfly pollination. Colour is a key advertising signal, with orientation facilitating alighting, whilst size, scent, and shape also influence butterfly attraction. Dispersal mechanisms of numerous fleshy seeded Amaryllidaceae have been an enigma as seeds are unorthodox, toxic and unable to survive ingestion, yet packaged in brightly coloured fruits suggestive of animal dispersal. Dispersal and germination of Clivia miniata seeds was investigated. Results indicated consumption of fruit by primates which disperse seeds through non-ingestive spitting behaviour. The short distance of seed dispersal by primates is predicted to lead to restricted gene flow and genetic subdivision of populations. I conclude that shifts in pollination systems and the associated modification of suites of functional floral traits led to floral diversification in Clivia. Self-infertility in Clivia highlights pollinator dependence and pollination syndrome conformity reflects functional advertising signals. Gene flow appears to be governed by pollen flow and facilitated by pollinators rather than seed dispersal. Mating and breeding system evolution are likely a consequence of adaptation to isolated forest habitats.
The biosynthesis and production of hypoxoside in Hypoxis hemerocallidea Fisch. and Mey. in vivo and in vitro.
(1989) Bayley, Arlene Diane.; Van Staden, Johannes.
Hypoxoside, a phenolic diglucoside, with a diarylpentane-type structure, is thought to be the medicinally active constituent of corm extracts of Hypoxis hemerocallidea Fisch. & Mey. which are reputed to alleviate the symptoms of prostate hypertrophy and urinary infections. The biosynthes is and production of this unique phytochemical were investigated in H. hemerocallidea using both in vivo and in vitro systems. It was found, in root-producing callus, that [l4]C-phenylalanine and [14]C-t-cinnamic acid were efficient precursors for hypoxoside in comparison to [14]C-sodium acetate and [14]C-acetyl coenzyme-A, which were not incorporated into the phenolic compound. Thus, at least one aryl moiety of hypoxoside was derived, via phenylalanine and t-cinnamic acid, from the shikimate pathway. The acetate pathway did not appear to be involved in the biosynthetic process. The data supports the hypothesis that the molecule is formed from two cinnamate units with the loss of a carbon atom, in opposition to the proposal that the molecule is derived from head-to-tail condensation of acetate units onto a propenylic moiety. Despite the structural similarities between hypoxoside and caffeic and p-coumaric acids, these two hydroxycinnamic acids were not efficient precursors for hypoxoside in vivo or in vitro. A number of reasons are put forward to explain this finding. It was found that the greatest concentration of hypoxoside was located in the corms of intact plants. The major biosynthetic site of the molecule was also found to be located in this organ. Since the roots did accumulate the phytochemical to a small extent, the biosynthetic potential of these organs has not been disregarded. That of the leaves has been, however. The report by PAGE (1984) that the upper region of the corm contained a greater con cent ration of hypoxoside than the lower portion, is substantiated in this study, where this region was found to be more biosynthetically active than the lower half. Light microscopic and electron microscopic studies revealed that starch storing cells, which accumulated phenolics in their vacuoles, contained seemingly synthetically active tubular endoplasmic reticulum in their cytoplasm. A greater number of these cells were concentrated in the upper region as opposed to the lower half of the corm. It is postulated that these cells are the site for biosynthesis and accumulation of hypoxoside. The shikimate pathway, from which the precursors for hypoxoside are derived, was found, through the exposure of intact plants to [14]C-carbon dioxide, to be located mainly in the leaves. It is postulated from the above study and one in which [14]C-phenylalanine, [14]C-t-cinnamic acid, [14]C-p-coumaric acid and [14]C-caffeic acid were applied to intact plants, that phenylalanine and/or cinnamic acid are the transported form of the shi kimate derivatives. p-Coumaric and caffeic acids, which are metabolically more stable, are envisaged to be the sequestering forms. The investigation of the seasonal production of hypoxoside revealed that most of the synthesis and accumulation occurred after the corms had broken winter dormancy and after the flush of leaf growth had slowed down. During dormancy the production of hypoxoside appeared to cease. The in vjtro studies, where the effects of light, temperature, nutrients, plant growth regulators and supply of potential precursors, on hypoxoside production by root-producing callus were investigated, indicate that this metabolite is not simply a "shunt" metabolite. A number of factors other than precursor availability enhanced, or reduced the jn vjtro production of this phytochemical. Furthermore, production of the phytochemical and growth were not always antagonistic. Hypoxoside, the biosynthesis of which requires a more thorough investigation, is, however, according to this investigation, a typical secondary metabolite in many respects.
Cape elements on high-altitude corridors and edaphic islands.
(2004) Carbutt, Clinton.; Beckett, Richard Peter.; Edwards, Trevor John.
Common to the temperate floras throughout sub-Saharan Africa is a group of taxa with strong ties to the Cape Floristic Region (CFR) (≈ Cape elements). Their distribution is limited to the eastern escarpment of Africa (e.g. the Drakensberg Alpine Centre - DAC), on nutrient-rich humic soils, as well as on isolated sandstone outcrops of low elevation, on nutrient-poor soils (e.g. the Pondoland Centre - PC), suggesting that intrinsic soil fertility is not the primary determinant of their distribution. The principal aim of this study was to determine which aspect of the edaphic environment of the DAC is most influenced by temperature, that may indirectly render it nutrient-poor and therefore provide suitable niches for Cape elements, as in the PC. A multidisciplinary approach involving aspects of plant biogeography, plant ecology, plant ecophysiology and soil chemistry was therefore adopted. The study regions were the DAC, PC and the KwaZulu-Natal Midlands. The flora of the DAC was resurveyed for this study, and is richer than previously thought: 2818 native taxa, most of which (2520) are angiosperms. The phytogeography of the DAC and PC is discussed, and comparisons are made with the floras of KwaZulu-Natal and the CFR. Their climatic environments, as well as those for the CFR and Sneeuberge, were compared using rainfall and temperature data from a range of sources. These climatic regimes were correlated with the floristic patterns of Cape elements for the high-altitude regions of South Africa and Lesotho. Altitude and rainfall increased, and temperature decreased, as the number of Cape elements increased towards the DAC. This study provided a contemporary inventory of the Cape elements of the DAC and PC. A total of 89 genera are recognised as Cape elements, of which 60 (c. 67%) are shared between the two regions. The highest number of Cape elements recorded for the eastern escarpment was the DAC (72 genera), with the highest number from all sites analysed being the PC (77 genera). The most Cape elements are contributed by the Asteraceae, Scrophulariaceae, Iridaceae, Fabaceae, Orchidaceae and Restionaceae, partly due to the success of annual aerial parts and their geophytic growth forms, which are convergent in these families. Further compartmentalisation into life and growth forms shows that most Cape elements of the DAC and PC are either ericoid (and sclerophyllous) or mesic herbs and shrubs. The ecological and ecophysiological aspects of this study involved the use of reciprocal pot experiments established along a gradient of altitude from coastal hinterland to mountain, that investigated the interactions between altitude, temperature and substrate on plant productivity in sites known either to support or to exclude Cape elements. Three soils were used at each site, representative of the DAC, PC and KwaZulu-Natal Midlands. The interactions between 'soil' and 'site' (≈ the climatic environment) were quantified using a temperate test taxon (Diascia) that has a strong Cape-centred distribution. Plant characters relating to morphology and nutrient content, and soil characters relating to fertility, were used as the basis for comparing treatment effects (soil-site interactions). Soil nitrogen availability was assayed using pot experiments with Eragrostis curvula (Schrad.) Nees. Wheat pot experiments revealed no Al³⁺ toxicity in 'Drakensberg' soil. Non-metric multidimensional scaling (NMDS) and redundancy analysis (RDA) indicated that all soil-site interactions were significant contributors to biomass differences, and that the Cape taxon performed poorly in the nutrient-rich Drakensberg soil at low altitude. Soil samples indicated that Drakensberg soil was the most nutrient-rich, and Pondoland soil the most nutrient-poor. Although total nitrogen in Drakensberg soil was six times higher than Pondoland soil, both soils mineralised similar low levels of nitrogen at their respective spring temperatures. The result for Drakensberg soil (simulated so as to include the effect of altitude) meant that only 1.7% of its total nitrogen was mineralisable at 12°C (its mean spring temperature). These findings suggest that nitrogen mineralisation rate is a key growth-limiting factor in the DAC, exacerbated by a number of complex interactions with soil pH and organic matter. It is hypothesized that Cape elements are preadapted to high-altitude habitats. These habitats are nutrient-deprived due to low temperatures, which reduce metabolic rates and the movement of ions in cold soils. This constraint imposes nutrient-related stresses similar to those of the CFR and PC. Taxa that are adapted to the nutrient-poor soils of the CFR are preadapted to the temperature-induced 'nutrient-poor' soils of the DAC and vice versa. This 'compatibility' has allowed the reciprocal exchange of taxa between regions, as suggested by cladistic biogeographical analyses using Cliffortia, Disa, Moraea and Pterygodium. The strong overlap of Cape elements between the CFR and PC is a product of similar nutritional niches and ancient floristic continuity. The result therefore is a high number of Cape elements common to the DAC and PC.
Carbohydrate metabolism in Parthenium argentatum Gray.
(1991) Kelly, Kathleen Mary.; Van Staden, Johannes.
The metabolism of carbohydrates in guayule is a subject which has not been considered with respect to its role in cis-polyisoprene synthesis, It has been suggested that acetate or sucrose act as the distal, and isopentenylpyrophosphate as the immediate precursor of the isoprenoid biosynthetic pathway. Application of radioactive precursors to the leaves of guayule plants in Winter and Summer showed that the fate of the carbohydrate depends on the chemical structure of the carbohydrate and the time of application. [[14]C] Sucrose was incorporated into the acetone (resin) fraction during the Summer and petroleum ether (rubber) fraction during the Winter. The amount of radioactivity that was translocated in Winter and Summer was similar. The loss of leaves during Winter reduced the area for photosynthesis, while the loss of carbon from the leaves during Summer, probably due to photorespiration, decreased the amount of available photosynthates. These two phenomena did not disadvantage the plant as far as the allocation of carbon was concerned. No plant components were acting as sinks during the Winter. The pith of the crown area incorporated the most radioactivity in Summer. [[14]C] Fructose was more readily translocated than [[14]C] sucrose during a 12 hour experiment. When fructose was applied and plants were left for 48 hours, more radioactivity was translocated to the stems and roots during the Summer. The [[14]C] from fructose was incorporated into the acetone (resins) rather than the petroleum ether (rubber) fraction in Winter therefore apparently having a different fate to [[14]C] sucrose. The principal reserve carbohydrates in guayule are fructans. Two types of fructans were detected and are referred to as water-soluble or ethanol-soluble fructans. The ethanol-soluble fructan polymers apparently played an active role in metabolism of guayule and showed cyclic patterns of accumulation. The water-soluble fructans seem to be true reserve carbohydrates, depolymerizing when the carbon supply decreased at the end of Winter, and the demand for carbon increased at the inception of bud break. Fructans provide carbon for budbreak and exposure of plants to longer days and higher temperatures did not seem to alter this role. It is proposed that fructans are providing carbon for budbreak and renewed growth and are utilized for flowering when required. Starch production occurs during the warmer months in the leaves and young stems. Starch is synthesized from the immediate photosynthetic supply and it is this source of carbon which is utilized for the synthesis of cis-polyisoprene (rubber). Sucrose in the cytosol is sequestered for cis-polyisoprene synthesis while fructose, which can enter the plastid, is providing carbon for the synthesis of isoprenoids. Compartmentation of resin and rubber production ensures that the supply of carbon is adequate for both processes. As cis-polyisoprene synthesis occurs at a time when the plant is not disadvantaged by insufficient carbon , induction of rubber transferase enzymes would not depend on excess substrate, but would use a more reliable cue like temperature or daylength. Any attempt therefore to increase the carbon supply in guayule during the winter months would not necessarily lead to partitioning into cis-polyisoprene, but may be stored as fructan to ensure that, at bud break, the plant has an adequate and utilizable carbon supply.
The causes and consequences of Seriphium plumosum L. encroachment in semi-arid grassland communities of Gauteng province, South Africa.
(2021) Pule, Hosia Turupa.; Tedder, Michelle Jennifer.; Tjelele, Julius Tlou.
Abstract available in PDF.
Characterisation and role of sugarcane invertase with special reference to neutral invertase.
(2000) Vorster, Darren James.; Botha, Frikkie Coenraad.; Huckett, Barbara Isobel.
The relationship between extractable invertase activities and sucrose accumulation in the sugarcane (Saccharum spp. hybrids) culm and in vivo invertase mediated sucrose hydrolysis was investigated to determine the significance of invertases in sucrose utilisation and turnover. In vitro activities were determined by assaying the soluble acid invertase (SAI), cell wall bound acid invertase (CWA) and neutral invertase (NI) from internodes three to ten in mature sugarcane plants of cultivar NCo376. Extractable activities were verified by immunoblotting. In vivo invertase mediated sucrose hydrolysis was investigated in tissue discs prepared from mature culm tissue of the same cultivar. Sugarcane NI had a higher specific activity than SAI (apoplastic and vacuolar) in the sucrose accumulating region of the sugarcane culm. CWA was also present in significant quantities in both immature and mature tissue. Sugarcane NI was partially purified from mature sugarcane culm tissue to remove any potential competing activity. The enzyme is non-glycosylated and exhibits catalytic activity as a monomer, dimer and tetramer. Most of the activity elutes as a monomer of native Mr ca 60 kDa. The enzyme displays typical hyperbolic saturation kinetics for sucrose hydrolysis. It has a Km of 9.8 mM for sucrose and a pH optimum of 7.2. An Arrhenius plot shows the energy of activation of the enzyme for sucrose to be 62.5 kJ.mol-1 below 30°C and -11.6 kJ.mol-1 above 30°C. Sugarcane NI is inhibited by its products, with fructose being a more effective inhibitor than glucose. Sugarcane NI is significantly inhibited by HgCI2, AgNO-3, ZnCI2, CuSO4 and CoCI2 but not by CaCI2, MgCI2 or MnCI2. Sugarcane NI showed no significant hydrolysis of cellobiose or trehalose. When radiolabelled fructose was fed to sugarcane internodal tissue, label appeared in glucose which demonstrates that invertase mediated hydrolysis of sucrose occurs. A combination of continuous feeding and pulse chase experiments was used to investigate the in vivo contribution of the invertases and the compartmentation of sugars. Sucrose is synthesised at a rate greater than the rate of breakdown at all stages of maturity in sugarcane culm tissue. The turnover time of the total cytosolic label pool is longer for internode three than internode six. A higher vacuolar:cytosolic sugar molar ratio than previously assumed is indicated. Developmentally, the greatest change in carbon allocation occurs from internodes three to six. The main competing pools are the insoluble and neutral fractions. As the tissue matures, less carbon is allocated to the insoluble and more to the neutral fraction. The neutral fraction consists mainly of sucrose, glucose and fructose. The compartmented nature of sugarcane storage parenchyma carbohydrate metabolism results in a system that is complex and difficult to investigate. A computer based metabolic flux model was developed to aid in the interpretation of timecourse labelling studies. A significant obstacle was the global optimization of the model, while maintaining physiologically meaningful flux parameters. Once the vacuolar:cytosolic molar ratio was increased, the model was able to describe the internode three and six labelling profiles. The model results were in agreement with experimental observation. An increase in the rate of sucrose accumulation was observed with tissue maturation. Only the internode three glucokinase activity was greater than the experimentally determined limit. The rate was however physiologically feasible and may reflect the underestimation of the in vivo rate. SAI and NI contributed to sucrose hydrolysis in internode three but not in internode six. The rates in internode six were set to fixed low values to enable the model to fit the experimental data. This does not however preclude low levels of in vivo SAI and NI activity, which would prove significant over a longer time period. The flow of label through the individual pools, which comprise the experimentally measured composite pools could be observed. This provides insight into the sucrose moiety label ratio, SPS:SuSy sucrose synthesis ratio, and the rate of 14CO2 release. The model provides a framework for the investigation and interpretation of timecourse labelling studies of sugarcane storage parenchyma.
Characterization and control of micropropagation problems in aloe, devil's claw and banana.
(2008) Bairu, Michael Wolday.; Van Staden, Johannes.; Stirk, Wendy Ann.
The development of the science of micropropagation from the very initial concept of totipotency to the modern day advancement and sophistication has been affected by a wide range of problems such as hyperhydricity, shoot-tip necrosis and somaclonal variation. These problems are largely the result of the obvious fact of trying to grow plants in an environment that is different from the one plants are used to naturally. The extent of these problems ranges from minor technical inconvenience to significant economic loss. Characterization and control of micropropagation problems has been one of the priorities of plant tissue culture research due to the enormous contribution of this discipline for plant production, improvement and conservation. The prevalence and severity of these tissue culture problems varies widely among plant species. The rationale of this research project was therefore, to identify plant species most affected by the problems studied, characterize the problem and find mechanism(s) to control or minimize the damage caused by the problem. The literatures reviewed provide sufficient background information for the experimental chapters. Due to the different nature of the problems and variation in the plant species they affect, the model plant, the methodologies used and parameters analysed were also different. The findings of these investigations, in their own different way, addressed certain problems that individually and collectively pose difficulties to the micropropagation industry. The difference in the content of the experimental chapters is therefore the result of the broader objective of the research project to tackle such difficulties. The success and failure of tissue culture system greatly depends on the choice of PGR’s. This choice can be made based on comparative study of their biological activity. Some promising reports on the role of topolins in micropropagation led to the idea of testing these cytokinins for their potential in tissue culture. As a prerequisite to subsequent investigations, the biological activity of some selected topolins and BA derivatives was tested using the soybean callus bioassay. The activity of the cytokinins tested varied significantly. The results demonstrated that the structure of a cytokinin dictates its activity. Modifications of side-chain improved the activity of oT but had no effect on pT. The presence of the methyl group had an enhancing effect on cytokinin activity of topolins or at least it did not reduce it. BA derivatives BA9THP (conjugated at N9 position), 3FBA and 2Cl6(3OHBA)R (halogenated derivatives) also showed good cytokinin activity and hold good promise for future research. In an attempt to alleviate hyperhydricity in Aloe polyphylla and optimize the micropropagation protocol, meta-topolin and its derivatives were tested at various concentrations together with BA and zeatin. Of all the cytokinins tested mT produced the best results in terms of shoot and root growth. Five μM was found to be the optimum concentration at which complete control of hyperhydricity was achieved without compromising shoot and root growth. Plantlets rooted in a multiplication media. BA generally had a negative effect on growth and development both in vitro and ex vitro. Acclimatization of plantlets was achieved easily by initially transferring plantlets to a mist house (for three weeks) followed by transfer to the greenhouse. The type of cytokinin also had an effect on ex vitro growth with BA-treated plants producing the lowest shoot and root biomass. Various experiments were conducted to characterize and control factors affecting STN in Harpagophytum procumbens. Media type and strength, PGR, carbon sources, sub-culturing, calcium and boron were tested. Results indicated that all of the tissue culture components tested affected STN. From the different media types tested, half strength was MS found to be the preferred medium. Increasing cytokinin concentration increased the incidence of STN and the problem was aggravated by the addition of auxin to the multiplication medium. Optimum shoot multiplication was achieved by omitting auxin and using the cytokinin mTR. Plantlets produced basal callus which interfered with rooting. The quantity of this basal callus was minimum when mTR was used. Sub-culturing plantlets onto fresh medium every two weeks helped minimize STN. Off all the sugars tested 3% sucrose was optimum. Other sugars either aggravated STN or inhibited growth when compared at equi-molar concentration. Increasing the concentration of either Ca or B prevented the development of necrotic shoots. When the concentration of both elements is increased simultaneously negative effects on both growth and STN were observed. Using 6 mM Ca in half strength MS medium was optimum. B was toxic at higher concentrations. Plantlets rooted readily in half strength cytokinin-free MS media supplemented with 2.5 μM IAA. Rooted plantlets produced using the optimized protocol were acclimatized successfully by transferring directly to a greenhouse in a 1:1 ratio of sand and soil mixture. The effect of meta-toplins on micropropagation and somaclonal variation of banana was investigated. Tissue cultured explants of cultivars ‘Williams’ and ‘Grand Naine’ were cultured in MS media containing the cytokinins BA, mT, MemT, MemTR and mTR at various concentrations. Results of the investigation revealed that superior multiplication and lower abnormality index was recorded from the mTR and mT treatments at 22.2 μM concentration. These treatments, however, had an inhibitory effect on rooting. The effect of these treatments (22.2 μM mT and mTR) in comparison with equi-molar concentration of BA on somaclonal variation of ‘Williams’ banana was tested using RAPD-PCR at the 7th multiplication cycle. No significant difference was found between the treatments. It should however be highlighted that cultures were initially maintained for three multiplication cycles in media containing BA. The inherent stability and initial effect of BA could have influenced the results.

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