Elucidation of drought tolerance mechanisms of different mungbean genotypes based upon physiological, biochemical and genetic mechanisms

Drought is a major problem to mungbean (<i>Vigna radiata</i> L.) productivity, necessitating the identification of tolerant genotypes and the exploration of their adaptive mechanisms. This study evaluated seven mungbean genotypes 'BARI Mung-8', 'BMX-010015', 'K851', 'L-92', 'BARI Mung-1', 'FH-18', and 'PDM-139' under control and drought treatments to characterize their physiological, biochemical, and molecular responses. Physiological traits, including chlorophyll content, photosynthesis rate (Pn), cell membrane stability (CMS), and relative water content (RWC), varied significantly (p≤ 0.05). Under drought, 'BARI Mung-8', 'BMX-010015', and 'K851' maintained chl content of 1.85-2.10 mg g^-1 FW and Pn of 138-145 μmol m^-2 s^-1, compared to 1.25 mg g^-1 FW and 78 μmol m^-2 s^-1 in 'BARI Mung-1'. These tolerant lines also retained high RWC (89-92%) and CMS (84-86%). Biochemically, they accumulated greater osmolytes, proline (38.7-42.1 µg g^-1 FW) and glycine betaine (118-132 µg g^-1 FW), and depicted enhanced antioxidant enzyme activities, including SOD (39.8-41.2 U mg^-1 protein) and CAT (14.5-15.2 U mg^-1 protein). Principal component analysis (PCA) and heatmap clustering grouped tolerant genotypes with these key adaptive traits, illustrating combined stress-response processes. Gene expression profiling showed significant upregulation (2.5-4.8 fold) of osmotic adjustment genes (<i>VrP5CS1</i>, <i>VrBADH</i>), antioxidant defense genes (<i>VrSOD1</i>, <i>VrCAT1</i>, <i>VrPOD1</i>), water transport gene (<i>VrPIP2-1</i>), and stress signaling genes (<i>VrDREB2A</i>, <i>VrLEA3</i>). The aquaporin gene <i>VrPIP2-1</i> was associated with higher RWC, while <i>VrCHLH</i> stability supported chl retention. Integration of physiological, biochemical, and molecular data proved that drought tolerance in mungbean is regulated by coordinated cellular hydration, osmotic regulation, ROS detoxification, and transcriptional activation. "BARI Mung-8', 'BMX-010015', 'K851', and 'L-92' emerged as eminent candidates for breeding programs targeting drought-prone environments, and the identified genes provide potential markers for selection of genotypes in climate-resilient legume improvement.