EFFECTS OF ETHYLENEDIUREA AND OZONE ON THE ANTIOXIDATIVE SYSTEMS IN BEANS (PHASEOLUS-VULGARIS L)

To study the biochemical mechanism of EDU protection against ozone inj ury, peroxidase, ascorbate-dependent peroxidase, and catalase activiti es, and the contents of ascorbic acid, dehydroascorbic acid, malondial dehyde and soluble protein were measured in Phaseolus vulgaris L. cv. LIt exposed to ozone and ethylenediurea (EDU) in open top chambers. Pl ants not treated with EDU showed foliar bronzing due to ozone, while E DU-treated plants were not affected. EDU application modified the reac tion of biochemical parameters to ozone. Soluble protein content was e levated by EDU. Peroxidase activity increased with ozone exposure in u ntreated plants only, while ascorbate-dependent peroxidase activity wa s lower in EDU treated plants. Catalase activity decreased in EDU-untr eated plants. The ratio of ascorbic acid to dehydroascorbic acid was s ignificantly increased in EDU treated plants. These results suggest th at EDU might induce ascorbic acid synthesis and therefore provide the plant with a very potent antioxidant. Or the content of hydrogen perox ide was reduced due to oother unknown processes and caused a delay in foliar senescence, regardless of wheether these processes were ozone-i nduced or due to natural ging processes.