Drought stress induces alterations in photosynthesis, hormonal balance, water potential, and metabolomic profiles in cowpea (Vigna unguiculata)

Drought is a significant abiotic stress affecting the growth, development, and overall crop yield worldwide. Cowpea is a drought tolerant legume widely cultivated in arid and semi-arid regions, but its physiological and metabolic responses to severe water stress are not well understood. This study investigates how cowpea responds to drought stress induced by polyethylene glycol 6000 (PEG6000) at concentrations of 0% (0 g/100 mL), 8% (8 g/100 mL), and 16% (16 g/100 mL) at morphological, physiological, and biochemical levels. Our findings revealed that drought stress significantly induced a decrease in leaf number, shoot height, root length, and shoot number. Significant reduction in photosynthetic pigments (6.21 ± 0.61), carotenoids (2.08 ± 0.071), indole acetic acid (4.08 ± 0.341), and an increase in antioxidant biomarkers such as catalase (0.0087 ± 0.00047) and superoxide dismutase (1.41 ± 0.010) were also recorded. Drought stress induces the reduction of indole-3-acetic acid content (20.57 ± 0.23 µg/mL) in both 8% (12.18 ± 0.27 µg/mL) and 16% (4.08 ± 0.34 µg/mL) PEG-induced drought. Metabolomic profiling revealed a significant expression of both secondary and primary metabolites based on fold change analysis and a two-sample t-test. Expression of osmoprotectants such as proline, glycine betaine, soluble sugars, and antioxidant secondary metabolites were observed. Alterations in metabolic flux affecting several pathways, such as amino acid, hormone, glutathione, and plant secondary metabolites, were observed in drought-exposed seedlings. Overall, the study highlights the ability of this plant to respond to drought stress by modifying growth parameters, altering biochemical reactions, and several metabolic pathways.