Browsing by Author "Ndhlovu, Nqobile Truelove."

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DNA barcoding of KwaZulu-Natal afromontane forest parmelia (parmeliaceae) species: a molecular approach to accurate specimen identification and sensitivity to climate change.
(2018) Ndhlovu, Nqobile Truelove.; Willows-Munro, Sandi.; Beckett, Richard Peter.
Accurate species identification is challenging, especially in groups with subtle taxonomically diagnostic characters such as lichens. Molecular-based techniques have shown to be a valuable tool for accurate specimen identification in fungi, in particular the use of DNA barcoding has become popular. Specifically, the internal transcriber spacer (ITS) region has been shown to successfully discriminate a broad range of fungal species. In this study, the utility of the ITS DNA barcode for use as a species diagnostic tool in the cosmopolitan lichen-forming fungus, Parmelia (Parmeliaceae) was investigated. Sixty-eight ITS sequences were generated from specimens collected from five sites around the province of KwaZulu-Natal and analysed. Phylogenetic analysis indicated that unlike European Parmelia species that form strong monophyletic clades, what appeared to be morphologically very similar Parmelia species in KwaZulu-Natal are paraphyletic or polyphyletic. No barcode gap was detected between the intra and interspecific distances. This suggests that the taxonomy of Parmelia lichens in South Africa needs to be thoroughly revised. The molecular data presented in this study provides evidence of previously hidden species-level diversity in Parmelia and as such contributes to the knowledge and understanding of the biodiversity of lichenized fungi in South Africa. The thermotolerance of Parmelia collected from different sites along an altitudinal gradient around Kwa-Zulu Natal was invesigated Chlorophyll fluorescence was used to assess the performance of lichen photobionts following stress, while ion leakage that of the mycobiont. For heat tolerance, results suggested that tolerance was correlated with the climatic conditions in which the lichens grow. Material from the coastal site of Hawaan were more heat tolerant than that from the three Midlands sites. Counter to our expectations, the coastal collections were more cold tolerant than those from the other sites. However, the genus clearly contains genetic variation with respect to stress tolerance, suggesting that it may have the potential to adapt to climate change.
The role of secondary metabolites in protecting lichens from climate change induced stress.
(2022) Ndhlovu, Nqobile Truelove.; Beckett, Richard Peter.
Lichen secondary metabolites play a great diversity of roles in lichen biology by acting as UV screens, antimicrobials, herbivore deterrents or allelopathic compounds. The main aim of the work described in this thesis was to test the potential roles of secondary metabolites in the tolerance of lichens (twelve species) to a variety of abiotic stresses. The first stress considered was that of tolerance to high levels of photosynthetically active radiation (PAR). Photosynthetic organisms possess a great diversity of mechanisms to protect themselves from the potentially stressful effects of high PAR. In addition to non-photochemical quenching and antioxidant mechanisms, it has been suggested that lichens use secondary metabolites for photoprotection. A few studies have shown that even faintly pigmented or unpigmented lichen substances can reduce photoinhibition. Here, the acetone rinsing technique was used to harmlessly remove secondary metabolites from all lichen thalli and then the chlorophyll fluorescence technique was used to measure their tolerance to photoinhibition in desiccated and hydrated states. Results showed that colorless lichen substances can increase the tolerance of lichen photobionts to photoinhibition when thalli are hydrated, apparently by increasing reflectance. Interestingly, substances can also photoprotect lichens in the dry state, while having no effect on reflectance. The acetone rinsing technique was also used to compare the relative importance of lichen substances in photoprotection in sun and shade collections of four species of Afromontane lichens. Results showed that lichens collected from sunny microhabitats have higher tolerance to photoinhibition than those from shaded locations. Furthermore, removal of lichen substances increases sensitivity to photoinhibition much more in sun than shade collections. Results further emphasized the importance of lichen secondary metabolites in photoprotection. This study also considered whether melanins, a pigmented secondary metabolite can cause problems with using fluorimetry techniques for e.g., to measure NPQ. A dissecting technique was used to remove the lower cortices and medullas of two lichen species so that NPQ could be measured from the underside of the thallus with an imaging PAM. Results confirmed that NPQ can be satisfactorily assessed with a standard fluorimeter by taking measurement from above using intact thalli. However, interestingly, photobionts from the bottom of the photobiont layer tended to have slightly lower rates of photosynthetic activity and lower NPQ than those at the top, i.e., display mild “shade” characteristics. The results presented in the final chapter looked at the protective role of secondary metabolites against desiccation-induced stress. It was hypothesized that secondary metabolites may act as antioxidants that protect lichens from desiccation-induced stress. Unfortunately, the findings of this part of the work did not present a consistent story, but rather indicated that according to species, the secondary metabolites can act as antioxidants or prooxidants. Nevertheless, taken together, the work presented in this thesis clearly shows that lichen secondary metabolites, whether pigmented or unpigmented, play important roles in photobiont photoprotection.