Adjustment to Low Light Intensity Enhances Susceptibility of Bean Leaves to Oxidative Stress

Abstract

Summary We studied the effect of a short term shading on the activity of the antioxidative system in primary leaves of Phaseolus vulgaris (cv. Pinto) and the response of the shaded beans to subsequent oxidative stress. Shaded bean leaves demonstrated a 35 % decrease in activity and concentration of glutathione reductase (GR, EC 1.6.4.2) and reduced glutathione (GSH) and a 30 % decrease in concentration of chloroplastic CuZn-superoxide dismutase (SOD, EC 1.15.11). No difference was observed in activities of ascorbate peroxidase (APX, EC 1.11.1.11) and catalase (EC 1.11.1.6) and the concentration of cytosolic CuZn-SOD. Two days shading (20 % of that of daylight) of bean plants resulted in increased sensitivity to methyl viologen and SOZ as compared to unshaded control plants but there was no difference in the sensitivity to ozone. Shaded leaves suffered smarked increase in ion leakage and water losses, and developed more necrotic lesions as compared to the control leaves. Our results show that in beans, even a short transition of plants from high to low light intensity, decreases the activity of chloroplastic antioxidative mechanisms that are needed to counteract subsequent oxidative stress.