Title : Mineral nutrient acquisition and antioxidant enzyme activities in two accessions of cowpea under drought stress
Abstract:
The significance of water stress in modulating nutrient acquisition and antioxidant enzyme activity was assessed in cowpea (Vigna unguiculata Walp). This study hypothesised that water deprivation will facilitate nutrient acquisition to upregulate antioxidant enzyme activities by altering root proliferation to encounter mineral nutrient at a distant wetter region in the soil. Two cowpea cultivars (Bechuana White (BW) and Dr. Saunders (DS) were grown either under well-watered (control) or water stress conditions. At physiological level, drought-exposed DS plants exhibited 1.3-folds higher relative water content (RWC), 1.6-folds higher chlorophyll a (Chl. A), 1.6-folds higher chlorophyll b (Chl. B) and 1.7-folds higher total chlorophyll compared than well-watered plants (control). Despite showing comparable values of root hydrogen peroxide (H2O2) and root proline, DS plants grown under drought conditions attained a significantly higher leaf H2O2, leaf MDA, leaf cell death leaf APX, leaf CAT, leaf proline as well as root MDA, root APX and root CAT compared to control plants. Additionally, although Mg levels were statistically similar to those of well-watered plants, drought exposed DS plants accumulated higher tissue nutrient contents including Ca, P, Mn, Fe, Cu, Zn, and K. Contrastingly, under water stress, BW plants exhibited lower RWC, lower photosynthetic pigments, higher H2O2, higher oxidative damages, lower antioxidant enzyme activities and lower nutrient acquisition and translocation. Overall, under drought conditions, DS genotype alters gene expression that upregulates mineral nutrient acquisition and enzymatic antioxidant activities, thus indicating enhanced drought stress tolerance.
