Effects of enhanced UV-B radiation on the activity and expression of alternative oxidase in red kidney bean leaves

An increase in ultraviolet (UV) B radiation on the earth's surface is a feature of current global climate changes. It has been reported that alternative oxidase (AOX) may have a protective role against oxidative stress induced by environmental stresses, such as UV-B. To better understand the characteristic tolerance of plants to UV-B radiation, the effects of enhanced UV-B radiation on the activity and expression of AOX in red kidney bean (Phaseolus vulgaris) leaves were investigated in the present study. The results show that the total respiration rate and AOX activity in red kidney bean leaves increased significantly during treatment with enhanced lJV-B. However, cytochrome oxidase (COX) activity did not change significantly. The H2O2 content was also markedly increased and reached a maximum of 4.45 mmol . L-1. g(-1) DW (dry weight) at 24 h of UV-B treatment, before dropping rapidly. Both alternative pathway content and alternative pathway activity were increased in the presence of exogenous H2O2- Immunoblotting analysis with anti-AOX monoclonal antibody revealed that expression of the AOX protein increased in red kidney bean leaves under enhanced UV-B radiation, reaching a peak at 72 h. In addition, AOX expression in red kidney bean leaves was induced by exogenous H2O2. These data indicate that the increase in AOX activity in red kidney bean leaves under enhanced UV-B radiation was mainly due to H2O2-induced AOX expression.