Biochemical and physiological characteristics of tropical mung bean (Vigna radiata L.) cultivars against chronic ozone stress: an insight to cultivar-specific response

Surface-level ozone (O₃) has been regarded as one of the most significant phytotoxic pollutants worldwide. Investigations addressing adverse impacts of elevated O₃ on mung bean (Vigna radiata L.), an important leguminous crop of the Indian subcontinent, are still limited. The present study analyzed the differences on the foliar injury, reactive oxygen species (ROS) generation, antioxidative defense system, physiology, and foliar protein profile of two tropical mung bean cultivars (HUM-2 and HUM-6) exposed to elevated O₃ under near-natural conditions. Both cultivars were negatively affected by the pollutant, but the response was cultivar-specific. Results revealed that elevated O₃ induced higher levels of ROS (O₂ ^·− and H₂O₂) and lipid peroxidation leading to greater foliar injury in HUM-2 compared to HUM-6. Photosynthetic pigments, photosynthetic rate, stomatal conductance, and photochemical efficiency reduced under elevated O₃ exposure and the extent of reduction was higher in HUM-2. Principal component analysis revealed that photosynthetic performance and quantum yield were drastically affected in HUM-2 as compared to HUM-6. Activities of antioxidative enzymes were also stimulated, suggesting generation of oxidative stress under elevated O₃. HUM-6 showed higher induction of antioxidative enzymes than HUM-2. One-dimensional gel electrophoresis analysis showed drastic reductions in the abundantly present ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) large and small subunits and the decrease was higher in HUM-2. Altogether, results suggested that higher accumulation of ROS and limited induction of antioxidant defense system led to more leaf injury and impairment of photosynthesis in HUM-2 than HUM-6 depicting its higher sensitivity towards elevated O₃.