Browsing by Author "Aremu, Adeyemi Oladapo."

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Pharmacological and phytochemical evaluation of seven plants used for microbial-related ailments in South African traditional medicine.
(2018) Vambe, McMaster.; Aremu, Adeyemi Oladapo.; Finnie, Jeffrey Franklin.; Van Staden, Johannes.
Since antiquity, man has always believed in the healing properties of plants. The age-old practice of phytotherapy is now justified by numerous phytochemical and pharmacological studies which substantiate the presence of biologically active compound(s) in some medicinal plants. Quite often, ethnopharmacological studies provide important leads for the development of different types of plant-based therapeutic drugs. New effective antibiotics are urgently needed to combat multiple and extensively drug-resistant bacterial strains that are currently threatening public health globally. The rich floral diversity in southern Africa and the resultant extensive chemical diversity provide encouraging prospects for discovering novel pharmacologically important phytocompounds within this region. Against this background, the current study was designed to evaluate the in vitro antibacterial properties, phenolic profiles and mutagenic potentials of extracts obtained from seven South African plants used traditionally to manage bacterial infections and where the active principles were unknown. The study also aimed at identifying the principal antibacterial compound(s) in selected plants that demonstrated potent and broad-spectrum antibacterial properties. Aqueous and organic solvent extracts of the seven selected plants namely Bolusanthus speciosus, Cucumis myriocarpus, Ekebergia capensis, Protea caffra, Prunus africana, Searsia lancea and Solanum panduriforme were screened for antibacterial (minimum inhibitory concentration, MIC) properties against a panel of seven bacterial strains (Enterococcus faecalis, Escherichia coli, Klebsiella pneumoniae, multiple drug-resistant (MDR) E. coli, MDR K. pneumoniae, drug-sensitive Staphylococcus aureus and penicillin-resistant S. aureus) using the microdilution technique. The extracts were also screened for antigonococcal properties using microdilution and agar disk-diffusion techniques. In addition, combinations of the different plant extracts, as well as plant extracts with four antibiotics (ampicillin, cefotaxime, chloramphenicol and penicillin) were evaluated for antibacterial synergistic interactions against MDR Gram-negative bacterial strains (E. coli and K. pneumoniae) using the checkerboard titration and time-kill bio-assays. Preliminary phytochemical analyses for phenolics in aqueous methanol (50% MeOH) plant extracts were conducted using spectrophotometric methods. In addition, specific phenolic acids in 80% MeOH extracts of the plants were quantified with the use of ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The mutagenic properties of plant extracts that demonstrated noteworthy antibacterial activities (MIC<1 mg/ml) were assessed using the Ames Salmonella/Microsome assay involving two tester strains, TA98 and TA102 (without S9 metabolic activation). The most potent antibacterial activities were exhibited by the MeOH bark extracts of B. speciosus which yielded MIC values of 0.039 and 0.078 mg/ml against S. aureus (penicillin-resistant and drug-sensitive strains, respectively). Dichloromethane (DCM) leaf extracts of S. lancea yielded an MIC value of 0.63 mg/ml against five of the seven test bacterial strains including MDR E. coli and MDR K. pneumoniae. B. speciosus bark (MeOH and DCM), P. caffra seeds (DCM) and twigs (MeOH) also demonstrated broad-spectrum antibacterial activities. B. speciosus MeOH bark extracts, as well as the DCM leaf extracts of P. africana and S. lancea demonstrated moderate antigonococcal properties (MIC range: 0.31-0.63 mg/ml). The checkerboard assay detected antibacterial synergistic interactions in combinations of chloramphenicol with each of B. specious leaf MeOH extracts, P. africana leaf MeOH and DCM extracts against MDR E. coli (fractional inhibitory concentration index ≤ 0.5). However, the time-kill assay did not detect any significant synergistic interactions in any of these three aforementioned combinations. Total phenolic content in the plant extracts investigated ranged from 2.38 to 62.73 mg gallic acid equivalents (GAE)/g dry matter. Variations in the quantities of flavonoids, condensed tannins, hydroxybenzoic and hydroxycinnamic acids among these plant extracts were also observed. In generally, higher levels of phenolic compounds were detected in S. lancea (leaves), P. africana (leaves) and P. caffra (leaves, twigs), while lower levels were detected in B. speciosus (barks), C. myriocarpus (fruits) and S. panduriforme (fruits, leaves, roots, stem). Based on the Ames test, all test plant extracts were non-mutagenic against Salmonella typhimurium tester strain TA98 and TA102 (without S9 metabolic activation). S. lancea leaves and P. caffra twigs demonstrated broad-spectrum antibacterial properties and as a result, a detailed analysis of their phytochemical constituencies was conducted. Antibacterial activity directed fractionation led to the isolation of two compounds from the aqueous (80%) MeOH leaf extracts of S. lancea. The isolated compounds were characterised using NMR data and both of them demonstrated noteworthy antibacterial activities (MIC range: 0.016-0.25 mg/ml) against E. faecalis and S. aureus. 1-Tetracosanol (43.98%), 1-nonadecanol (37.5%), eicosane (7.67%), 1,7-di-iso-propylnaphthalene (4.23%), 1-pentadecanol (3.04%), 2,6-di-iso-propylnaphthalene (1.96%) 1,3-iso-propylnaphthalene (1.62 %) were identified by GC-MS in an active S. lancea leaf ethyl acetate sub-fraction. The sub-fraction inhibited the growth of both E. faecalis and S. aureus at an MIC value of 0.25 mg/ml. 1-Tetracosanol and 1-nonadecanol, which accounted for more than 80% of the total phytochemical constituents of the fraction, are known antibacterial compounds which most likely contributed to the antibacterial properties of S. lancea leaves. Gas chromatography-mass spectrometry (GC-MS) analysis also revealed the presence of 15 compounds in three fractions obtained from a methanolic P. caffra twig extract. Two of the identified compounds, 1-adamantanecarboxylic acid and levoglucosan, are often incorporated into antimicrobial moieties to improve the efficacy of the therapeutic molecule, or as carbon skeletons. Two known antibacterial compounds, namely 1-heptacosanol and 1-nonadecanol were also among the compounds detected in the methanolic P. caffra twig extract. Overall, the present study reaffirmed that botanical medicines can potentially be used to manage drug-sensitive and drug-resistant bacterial infections often prevalent in humans. The study also provided the scientific rationale for the use of P. caffra, C. myriocarpus and S. panduriforme in South African folk medicine.
Pharmacology and phytochemistry of South African plants used as anthelmintics.
(2009) Aremu, Adeyemi Oladapo.
Traditional medicine in South Africa is part of the culture of the people and has been in existence for a long-time. Although animal components form part of the ingredients used, plant material constitutes the major component. South Africa is endowed with vast resources of medicinal and aromatic plants which have been employed for treatment against various diseases for decades. A large number of South Africans still depend on traditional medicine for their healthcare needs due to its affordability, accessibility and cultural importance. Helminth infections are among the variety of diseases treated by traditional healers. These infections are regarded as neglected tropical diseases (NTDs) due to their high prevalence among the economically disadvantaged living in rural areas in different regions of the world.
Physiological and biochemical effect of biostimulants on Abelmoschus esculentus (L.) and Cleome gynandra (L.)
(2021) Makhaye, Gugulethu.; Tesfay, Samson Zeray.; Amoo, Stephen Oluwaseun.; Aremu, Adeyemi Oladapo.
Abelmoschus esculentus (L.) and Cleome gynandra (L.) are neglected plants, often collected from the wild, with dual benefits of nutritional and medicinal values, especially in rural communities. Biostimulants are well-known for their stimulatory effect on plant physiological processes, from germination to full maturity. In the current study, the effect of biostimulant application was investigated on the germination, growth, yield and biochemical quality of selected A. esculentus and C. gynandra genotypes, as a tool for improving their physiological and biochemical aspects. The study involved two biostimulants [Kelpak® (1:100, 1:40 and 1:20, dilutions)] and plant growth promoting rhizobacteria = PGPR (1:5, 1:10 and 1:15, dilutions)] as well as their interaction effect on the different genotypes of A. esculentus (Okra PB1, PB2, PB3, PB4 and PB5) and C. gynandra (TOT10212, TOT8420, Cleome 3, CleomeMaseno and Cleome Arusha). The parameters evaluated were seed germination, vegetative growth, yield, biochemical (ꞵ-carotene, vitamin C, total phenolic, flavonoids and condensed tannins) and mineral elements content (Ca, Fe, K, Mg, Na and Zn). Germination of A. esculentus and C. gynandra was influenced by different genotypes and biostimulants. Okra PB2 and Okra PB4 had significantly enhanced Final Germination Percentage (FGP), Germination index (GI) and Germination Rate Index (GRI). Similarly, genotype TOT10212 had significantly increased FGP, GI and GRI while Cleome 3 had least FGP, GI, GRI and Coefficient of Velocity of Germination (CVG). The effect of Kelpak® treatments on FGP, GI, Mean Germination Time (MGT) and GRI was significantly comparable to that of control. The effect of PGPR treatments on FGP, GI and GRI significantly increased with increasing PGPR dilutions. In A. esculentus, the interaction of Kelpak® (1:100) and genotype OkraPB1 significantly improved germination parameters (FGP, GI and GRI) while no stimulatory effect was observed on the interaction of biostimulants and Okra PB2, PB3, PB4 and PB5. In C. gynandra, the biostimulants especially PGPR (1:5, 1:10 and 1:15), inhibited germination parameters (FGP, GI and GRI) of genotype TOT10212. A. esculentus genotypes showed different growth parameters. For instance, Okra PB5 had significantly higher plant height while Okra PB4 had least plant height. Biostimulants further influenced the vegetative growth and yield of A. esculentus and C. gynandra genotypes. Plant height, chlorophyll content and stem diameter of A. esculentus genotypes was significantly enhanced by PGPR (1:5, 1:10 and 1:15) application. The yield (number of pods, total fresh weight and total dry weight) of A. esculentus was enhanced by PGPR (1:5, 1:10 and 1:15) application. Plant growth promoting rhizobacteria (1:5, and 1:10) enhanced the chlorophyll content, stem diameter and yield (total fresh and total dry weight of leaves) of C. gynandra genotypes. No inhibitory effect was observed on the growth and yield of A. esculentus and C. gynandra genotypes following biostimulant treatments. Interaction of biostimulants with A. esculentus and C. gynandra genotypes had no significant effect on growth and yield parameters. The biochemical and mineral elements content of A. esculentus and C. gynandra genotypes was influenced by genotype and biostimulant (both Kelpak® and PGPR dilutions) application. In C. gynandra, biostimulants enhanced the ꞵ-carotene, total flavonoid and total phenolic content. Okra PB4 had significantly enhanced vitamin C and total phenolic content while Okra PB5 had significantly higher total flavonoid content. Genotype TOT10212 had significantly increased Ca, Fe, Mg and Na content. However, the content of condensed tannins together with Fe and Mg of C. gynandra genotypes was inhibited by biostimulants application. Application of PGPR-1:5, Kelpak®-1:40 and Kelpak®-1:20 significantly enhanced total phenolic, total flavonoid and condensed tannins of A. esculentus genotypes. Furthermore, biostimulants had varying effects on the mineral element content. A significant increase was observed on Fe content when A. esculentus genotypes were treated PGPR (1:10). Application of Kelpak® (1:100 and 1:40) caused a significant decrease on the Ca content of A. esculentus genotypes. The interaction effect of biostimulants application and genotypes significantly inhibited the mineral elements of C. gynandra genotypes while significantly enhancing the vitamin C and condensed tannins of Okra PB3. The current study demonstrated the differential effect of biostimulants application (Kelpak® and PGPR) on A. esculentus and C. gynandra genotypes. The application of biostimulants can therefore, be used to enhance germination, growth, yield, biochemical content and mineral elements, depending on the crop genotype, and hence assist in combatting food insecurity in food insecure communities.
The role of meta-topolins on the physiology of micropropagated 'Williams' bananas (Musa spp. AAA)
(2012) Aremu, Adeyemi Oladapo.; Van Staden, Johannes.; Finnie, Jeffrey Franklin.; Bairu, Michael Wolday.
Banana production ranks fifth behind cereals as a food crop and has potential, along with other major crops, to feed the world's increasing population. Globally, continuous efforts and techniques including the use of plant tissue culture (PTC) have been devised for increasing the production of several Musa species. The choice of cytokinin (CK) is one of the most critical factors in developing a successful PTC protocol. Since the discovery of topolins as naturally occurring aromatic CKs, they have emerged as genuine alternatives to the long serving CKs (benzyladenine = BA, zeatin = Z and kinetin = KIN) in PTC. Globally, the past 15 years has witnessed a surge in the use of topolins and their derivatives in research laboratories. Topolins have demonstrated great potential during culture initiation and protocol optimization as well as for counteracting various in vitro induced physiological disorders in some species. In terms of general physiology (growth, phytochemical and photosynthetic pigment contents as well as genetic fidelity), the topolins were compared with BA using 'Williams' bananas with minimal residual exogenous CK carry-over effects. The five topolins tested were meta-Topolin (mT); meta-Topolin riboside (mTR); meta-Methoxy topolin (MemT); meta-Methoxy topolin riboside (MemTR) and meta-Methoxy topolin 9-tetrahydropyran-2-yl (MemTTHP). Based on evidence of potential CK- and auxin-like activity of smoke-water (SW) and karrikinolide (KAR1) at low concentrations, a similar comparative study involving both compounds and mT was performed. For a further understanding of banana physiology in vitro, the effect of supplementing either mT- or BA-requiring cultures with roscovitine (a cyclin-dependent kinase and N-glucosylation inhibitor) and INCYDE (an inhibitor of CK degradation) on the endogenous CK profiles was investigated. In addition, greenhouse experiments geared towards improving the acclimatization competence of tissue-cultured banana plantlets via application of different concentrations of SW and vermicompost leachate was conducted. Sterile shoot-tip explants were cultured on modified Murashige and Skoog (MS) media supplemented with 10, 20 or 30 μM of the tested CKs for 42 days while rooting experiments involved the use of classic auxins as well as SW and KAR1. Apart from 10 μM BA and 30 μM MemTTHP treatments, the number of shoots produced with all the CK treatments were significantly higher than the control. Treatment with 30 μM mT resulted in the highest number of shoots (7.3±1.0) which is an indication of the requirement of exogenous CK for increased shoot proliferation in 'Williams' bananas The use of 10 μM MemTTHP had the least root inhibitory effect during the shoot proliferation phase. As an indication of the toxicity of applied CK, MemT- and MemTR-regenerants were the most deformed while mTR-regenerated plantlets demonstrated the best quality across all the CKs tested. In mT- and BA-derived shoots, SW and KAR1 significantly increased the number and length of roots compared to the control. During the rooting phase, topolin treatments produced more off-shoots than BA-treated ones which inevitably improved the overall number of regenerated shoots. Total phenolic levels were highest in 10 μM mT- and 30 μM MemTTHP-treated plantlets detected in the aerial and underground parts, respectively. It is interesting that in the underground parts, 10 μM mT resulted in the production of the highest amount of proanthocyanidins which was approximately five-fold higher than in the control plants. On the other hand, 10 μM MemTTHP-treated plantlets had significantly higher total flavonoids within the aerial parts. In view of the stimulation of secondary metabolites in the majority of the CK-treated plantlets, the current results indicate the role of the type and concentration of applied CK as potential elicitors in PTC. Generally, the maximum photosynthetic pigment content was attained between 40-50 days. The control plantlets had the highest pigment content (1150 μg/g FW) while 10 μM MemTTHP had the best pigment stimulatory effect among the tested CKs. Nevertheless, in vitro propagation of banana devoid of CKs is not a practical option due to low shoot proliferation rates. Scanning electron microscopy (SEM) of the foliar surface showed that the stomatal density was highest in 10 μM MemTTHP-treated and lowest in 10 μM MemTR-treated plantlets. Prolonging the culture duration as well as increasing CK concentrations reduced the pigment content. However, the drastic breakdown in chlorophyll pigments beyond 50 days was slightly inhibited by the presence of mT, mTR, MemTTHP and BA compared to the control. Current findings indicate the potential anti-senescence activity of the topolins such as mT, mTR and MemTTHP under in vitro conditions. This study articulates that the right choice and concentration of CKs applied during in vitro propagation may alleviate photomixotrophic-induced physiological stress that usually accompanies the transfer of plantlets to ex vitro conditions. Findings indicate that the effect of subculturing contributed significantly to the higher rate of variation in 'Williams' bananas in vitro. The presence of CK in the culture media apparently aggravated the stress on the explants as indicated in the relatively higher percentage polymorphic bands compared to the controls. Among the tested CKs, the use of mTR and MemTTHP caused the least detrimental effect on the regenerants while mT-treated plantlets had the most polymorphic bands. Hence, it is recommended that subculturing cycles from the initial explant establishment should be limited to a maximum of five. The use of SW and KAR1 improved the level of photosynthetic pigment and phenolic compounds in the micropropagated bananas. However, they had a negative effect on shoot proliferation; hence their inclusion is more desired when used at the rooting phase of micropropagation. Perhaps, these compounds could be used in conjunction with auxin to increase the number of roots prior to the acclimatization stage. The enhanced photosynthetic pigment level resulting from addition of SW and KAR1 would also play a vital role during acclimatization of the micropropagated plants. The present finding serves as an alternative approach, available to researchers for improving the quantity of secondary metabolites in micropropagated plants. The highest regeneration rate (93%) was observed in BA + roscovitine treatment while mT + INCYDE-treated plantlets produced most shoots. Treatment with BA + roscovitine had the highest shoot length and biomass. Although not significant, there was more proanthocyanidins in BA + roscovitine treatments compared to the treatment with BA alone. On the contrary, total phenolics were significantly higher in mT + roscovitine treatment than in the mT-treated regenerants. The presence of roscovitine and/or INCYDE had no significant effect on the photosynthetic pigments of the banana plantlets. Forty-seven aromatic and isoprenoid CKs categorized into nine CK-types were detected at varying concentrations. The presence of mT + roscovitine and/or INCYDE increased the levels of O-glucosides, while 9-glucosides remained the major derivative in the presence of BA. Generally, the underground parts had higher CK levels than the aerial parts; however the presence of INCYDE increased the level of CK quantified in the aerial parts of both CK treated plantlets. Apparently, the presence of INCYDE serves to enhance transportation of the CK towards the aerial regions. From a practical perspective, the use of roscovitine and INCYDE in PTC could be crucial in the alleviation of commonly observed in vitro-induced physiological abnormalities. Soil drenching with SW significantly increased the root length (1:1000 and 1:500 dilutions) as well as fresh and dry weight (1:1000; 1:500 and 1:250 dilutions) when compared to foliar application. Vermicompost leachate (1:10 and 1:5 dilutions) significantly enhanced the shoot length, root length, leaf area and dry weights. Vermicompost leachate (1:20; 1:10 and 1:5 dilutions) also significantly increased the number of off-shoots. The positive effect on rooting is beneficial for acclimatization and establishment of tissue-cultured banana plantlets in nurseries and subsequent transfer to the field. However, field trials will be necessary to substantiate the effects demonstrated by these compounds. In an attempt to contribute to improving banana micropropagation, the current findings provide additional evidence on the increasing advantage of topolins over BA. Nevertheless, some detrimental physiological effects observed with some of the topolins (for example, MemT and MemTR) are clear indication that they should not be taken as a panacea in PTC. Besides optimizing efficient PTC protocols through stringent choice of CKs, other associated physiological and metabolic events taking place in culture during the optimization process need more in-depth investigation. In addition to contributing towards the better understanding of the mode of action of these CKs, such an approach will help solve associated physiological and developmental problems in vitro.
The role of nutritional status of soils from grassland and savanna ecosystems on the biochemical and physiological responses of Vigna unguiculata L. (Walp)
(2022) Makaure, Brenda Tsungai.; Magadlela, Anathi.; Aremu, Adeyemi Oladapo.
Most arable soils in sub–Saharan Africa savanna and grassland ecosystems are acidic and nutrient deficient with nitrogen and phosphorus being the most limiting and this poses a huge threat to agricultural productivity. To overcome soil nutrient deficiency and increase crop yields, farmers have resorted to high inputs of synthetic fertilizers, which are expensive and may cause environmental degradation. Use of legumes is an important alternative as they help enhance soil nutrition through biological nitrogen fixation. Vigna unguiculata L. (Walp), a highly nutritious legume crop that could be incorporated in small scale cropping systems to improve soil nutrition. However, there is limited information on the physiological and biochemical strategies enabling the growth of V. unguiculata under acidic and nutrient stress conditions. In this study it was hypothesized that symbiotic association between V. unguiculata and rhizospheric microbes affects the growth, nutrient assimilation and phytochemicals of the grain legume grown in nutrient stressed soils. Firstly, this study evaluated the physicochemical properties, microbial composition and soil enzymes activities of soils from four geographically distinct regions of KwaZulu-Natal representing savanna and grassland ecosystems. Secondly, the study investigated how the tripartite symbiosis of V. unguiculata, arbuscular mycorrhizal fungi and nodulating bacteria affect phosphorus and nitrogen nutrition, and the growth of V. unguiculata grown under acidic and nutrient stress conditions. Then, the study investigated how four V. unguiculata varieties regulated their phenolic acids and antioxidants to enhance their growth in acidic and nutrient stressed soils conditions. The four soil types were acidic with low mineral nutrients, with Bergville being the most acidic. The soils were significantly different in their physicochemical and microbial composition. Most bacterial strains identified in the soils belonged to genera Lysinibacillus, and Bacillus while the most identified fungal strains belonged to Fusarium and Trichoderma genera. There were variations in soil lignin degrading, C, N and P cycling enzyme activities. The identified soil enzymes included β-D Phosphatase, L-asparaginase, β-glucosaminidase, β-cellobioside, catalase and lacasse. The availability of this rich pool of soil microbes and soil enzymes is a great opportunity as these can be used to regulate nutrient cycling and enhance nutrient availability for crop production in the savanna and grassland ecosystems. Four V. unguiculata varieties (IT18, Batch white, Brown mix, Dr Saunders) were grown in these acidic and nutrient poor soils. These V. unguiculata varieties were nodulated by several bacterial strains including those of genera Bradyrhizobium, Rhizobium, Bacillus and Paenibacillus. The V. unguiculata fixed more than 60% of its total nitrogen from the atmosphere across all soil treatments. Interestingly, V. unguiculata plants which were nodulated by non-rhizobial bacteria strains effectively fixed significantly high amounts of atmospheric nitrogen. Vigna unguiculata also developed symbiotic association with arbuscular mycorrhizal fungi (AMF) as evidenced by high root mycorrhizal fungi colonization ranging from 58-100%. Variations were observed on growth kinetics, nutrient assimilation and utilization among the four V. unguiculata varieties. Vigna unguiculata was able to switch N source preferences utilizing both soil and atmospheric nitrogen. These findings revealed that V. unguiculata has the capacity to adapt to nutrient poor ecosystems by establishing symbiotic interaction with naturally occurring soil bacteria and AMF and through its ability to switch N source preferences; by using soil N and atmospheric N2 through biological nitrogen fixation. There were variations in the response of the four V. unguiculata varieties to different levels of soil acidity and nutrient stress with regards to phenolic acid concentration and antioxidant capacities. The most abundant phenolic acids were vanillic acid and protocatechuic acid and these constituted 22.59% and 17.22% respectively of the total phenolic acids in the plants. More so, there were differences in correlations between the phenolic acids and plant biomass, plant nutrition, soil nutrition and AMF infection. There was negative correlation between phenolic acids protocatechuic acid and syringic acid, and concentration of plant nutrients N and P. Varieties IT18 and Batch white had relatively lower concentrations of phenolic acids but these had the highest plant biomass. These results confirm that low phenolic acid concentrations have stimulatory effects on growth and nutrient uptake by plants while high concentrations may inhibit plant growth and development. There were variations among the V. unguiculata varieties with respect to oxygen radical absorbance capacity (ORAC) across the four soil types. Overall, the study demonstrated that V. unguiculata is adaptable to acidic and nutrient poor ecosystems as it has the capacity to regulate its phenolic acids which enhance nutrient uptake, promote legume-microbe symbiosis, and help scavenge radical oxidative species due to their antioxidant properties.