Comparison of Antioxidant Enzyme Activities between Tylosema esculentum and Tylosema fassoglense in Response to Water Deficit

Africa – like the rest of the world – periodically experiences drought, which may become further exacerbated because of climate change, leading to severe impacts on crop production and food security in the region. The genus Tylosema consists of five distinct species, namely T. humifusum, T. argentum, T. angolense, T. esculentum, and T. fassoglense. Tylosema fassoglense (Schweinf.) Torre & Hillc. has the widest distribution across Africa in diverse habitats, while Tylosema esculentum (Burch.) A. Schreib. is limited to arid regions in southern Africa. T. fassoglense holds unique nutritional composition and bioactive properties, and thus could offer unique uses that are not found in T. esculentum. Consequently, enhancing drought tolerance in T. fassoglense can contribute to food security and sustain its medicinal applications and thus mitigate the impacts of climate change on vulnerable populations in the region. The present study aimed at comparing the physiological and biochemical responses between the two species to elucidate the underlying mechanisms of differences in drought tolerance between T. esculentum and T. fassoglense. We compared water status, growth performance, oxidative stress levels as well as the responses of selected antioxidant components under water deficit in the two species. Our results showed that the water deficit caused higher reductions in leaf water potential and relative water content in T. fassoglense than in T. esculentum, which translated to a higher loss of leaf and root fresh weights in T. fassoglense than in T. esculentum. A higher increase in free proline content, hydrogen peroxide content and lipid peroxidation level were observed in T. fassoglense when compared to T. esculentum. Distinct differences were observed in the antioxidant enzyme activities for superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase between these two species in response to water deficit. The observed differences in antioxidant enzyme responses demonstrate their role in the differences in water deficit tolerance between the two species. Further detailed ‘omics’-based analyses will aid in understanding the molecular basis of drought responses in these two species and potentially towards improving drought tolerance in T. fassoglense.