OXIDATIVE DAMAGE IN PEA-PLANTS EXPOSED TO WATER-DEFICIT OR PARAQUAT

The application of a moderate water deficit (water potential of -1.3 M Pa) to pea (Pisum sativum L. cv Lincoln) leaves led to a 75% inhibitio n of photosynthesis and to increases in zeaxanthin, malondialdehyde, o xidized proteins, and mitochondrial, cytosolic, and chloroplastic supe roxide dismutase activities. Severe water deficit (-1.9 MPa) almost co mpletely inhibited photosynthesis, decreased chlorophylls, beta-carote ne, neoxanthin, and lutein, and caused further conversion of violaxant hin to zeaxanthin, suggesting damage to the photosynthetic apparatus. There were consistent decreases in antioxidants and pyridine nucleotid es, and accumulation of catalytic Fe, malondialdehyde, and oxidized pr oteins. Paraquat (PQ) treatment led to similar major decreases in phot osynthesis, water content, proteins, and most antioxidants, and induce d the accumulation of zeaxanthin and damaged proteins. PQ decreased ma rkedly ascorbate, NADPH, ascorbate peroxidase, and chloroplastic Fe-su peroxide dismutase activity, and caused major increases in oxidized gl utathione, NAD(+), NADH, and catalytic Fe. It is concluded that, in cv Lincoln, the increase in catalytic Fe and the lowering of antioxidant protection may be involved in the oxidative damage caused by severe w ater deficit and PQ, but not necessarily in the incipient stress induc ed by moderate water deficit. Results also indicate that the tolerance to water deficit in terms of oxidative damage largely depends on the legume cultivar.