On the interaction of UV‐B radiation (280–315 nm) with water stress in crop plants

Cowpea (Vigna unguiculata L. Walp.) seedlings (3‐day‐old) were subjected to 4 kinds of experimental treatments: (1) control without exposure to any stress (−D‐UV), (2) moderate water stress with no UV‐B irradiation (+D‐UV), (3) no water stress but to UV‐B radiation (−D+UV). and (4)moderate water stress and exposure to UV‐B (+D+UV). UV‐B and drought stress in the combined form elicited beneficial effects on the morphological and growth characteristics, and a few additive inhibitory effects in some functional processes. An increase in the specific leaf weight (SLW) was observed in the combination of stresses, which could be a defence mechanism against UV‐B. The combination of stresses promoted the synthesis of anthocyanins and phenolic compounds. The responses of plants to the combination of stresses indicate that during simultaneous exposure of plants to multiple stresses, one form of stress could minimize the damage by the other. The enhancement of superoxide dismutase (SOD) and catalase activities appear to serve as acclimation mechanisms to scavenge the toxic, free radicals of oxygen produced under stress conditions. However, the inhibition in nitrate metabolism was greater in the combined stresses than in either of the stresses imposed separately. The results of this study illustrate that the interaction of stresses during simultaneous multiple stress conditions brings out certain beneficial effects.