Nitric oxide confers drought tolerance through integrated morphological, physiological, biochemical and metabolomic responses in common bean (Phaseolus vulgaris L.)

The ongoing change in the climatic dynamics is contributing significantly to events attributing drought-like conditions that pose a serious threat to the overall growth and development of crops and, as such, to their productivity worldwide. The present study aims to explore the differential tolerance potential of five common bean cultivars (BR-39, BR-104, BR-303, VL-63 and VL-125) exposed to polyethene glycol (15% PEG) induced drought stress. Various growth, physiological, and biochemical processes were assessed 30 days after sowing. Drought stress negatively affected the growth of common bean cultivars by reducing photosynthesis via increased oxidative stress. Among the cultivars, BR-104 exhibited the highest tolerance, while BR-303 was the most sensitive. Based on its superior performance, BR-104 was further selected to evaluate the role of gaseous signaling molecule, nitric oxide (NO; applied as100µM sodium nitroprusside, SNP) for its potential in ameliorating drought stress in common bean following analysis of the morphological, physio-biochemical parameters, and changes in the metabolic profile. Drought stress resulted in a significant reduction in the growth and biomass of common bean, associated with a decrease in Rubisco activity and PS-II efficiency, and consequently in photosynthesis. It proceeds with a decrease in the nitrogen content and its associated enzyme activities and a subsequent increase in the proline metabolism. Additionally, it was found that increasing the accumulation of oxidative stress biomarkers, such as hydrogen peroxide (H2O2) and thiobarbituric acid reactive substances (TBARS), was observed. Simultaneously, supplementation of NO exerted positive effects on the overall growth and development of plants by mitigating the impacts of drought stress. Together, the study highlights the importance of NO (both endogenous and exogenous) in conferring tolerance to drought stress in common bean by improving photosynthetic efficiency and antioxidant defense through the modulation of nitrogen assimilation and proline metabolism.