Superoxide Dismutase: A POSSIBLE PROTECTIVE ENZYME AGAINST OZONE INJURY IN SNAP BEANS (PHASEOLUS VULGARIS L.)

An experimental chemical N-[2-(2-oxo-1-imidazolidinyl)ethyl]-N'-phenylurea (EDU), is an effective protectant against acute and chronic foliar injury due to ozone (0(3)) when sprayed on intact leaves or supplied to the plants through soil application. An 0(3)-sensitive snap bean cultivar (Phaseolus vulgaris L. ;Bush Blue Lake 290') was systemically treated with EDU (0, 25, 50, and 100 milligrams per 15-centimeter diameter pot) to determine if EDU-induced or activated protective oxyradical and peroxyl scavenging enzymes. EDU-enhanced tolerance to O(3) injury always correlated with increases in superoxide dismutase (SOD) and catalase activities in the leaves. Peroxidase levels correlated more closely with foliar injury. Greater SOD levels in young leves compared to older leaves were associated with lower ozone sensitivities in these tissues.Polyacrylamide slab gel electrophoresis separations and specific determinations of SOD activity showed that EDU-treated plants possessed markedly greater SOD activity than non-treated plants. Tolerant plant tissues may have enhanced enzyme scavenging capabilities for the protection against toxic oxyradicals. Experimental confirmation for the oxyradical theory for O(3) phytotoxicity and SOD involvement in the detoxification process are presented.