Role of Hydrogen Peroxide in Senescence of Excised Leaves of Rice and Maize

Abstract

Incubation of excised leaves (55 to 65 days old) of rice (Oryza sativa L. cv. Jaya) and maize (Zea mays L.) with different concentrations (10-3, 10-4 and 10-5 M) of H2O2 and glycolate hastened senescence by accelerating the loss of chlorophyll and protein and increasing the activities of RNase and protease. Both the chemicals induced much faster rate of senescence in rice than in maize leaf segments. Endogenous level of glycolate declined more markedly when incubated in the dark than in the light. There was a marked rise in the glycolate oxidase activity in the light. H2O2 content decreased and catalase activity significantly increased in the light, and the opposite was the case in the dark. Such changes were more prominent in rice than in maize leaves. Infiltration with antioxidants like ascorbic acid, 1-cysteine, reduced glutathione and ferrous sulphate for 30 tnin markedly retarded senescence. Such delaying effect of antioxidants was more prominent in rice than in maize. It was concluded that the sensitivity of leaf tissues to H2O2 and glycolate in inducing senescence was different in rice and maize where the endogenous levels of these two substances were also different and that the antioxidants could delay senescence probably by destroying the endogenous H2O2.