Leaf Senescence in Submerged Rice Plants

Abstract

Leaf senescence in the rice (Oryza sativa) cultivars FR13A and IR42 under submergence was assessed in terms of changes in total chlorophyll, soluble amino acids and protein concentrations and peroxidase activity in crude extracts. The objective was to determine whether delay in leaf senescence was related to the submergence tolerance of a rice cultivar. Submergence induced senescence and its extent was notably different in the two cultivars. Results indicated a reduction in chlorophyll and protein concentrations in leaves during submergence but an increase in amino acid concentration and peroxidase activity. These relative changes were more pronounced in submergence intolerant IR42 than in tolerant FR13A even at four days after complete submergence. When plants were desubmerged and returned to standard irrigated conditions after 10 days of complete submergence the rate of recovery was different for the two cultivars. FR13A showed a greater protein and chlorophyll restoring ability compared with the intolerant IR42. The differences observed between the responses of FR13A and IR42 to submergence were likely to be due to differences in proteolysis. Senescence of leaves due to submergence was similar to the senescence of non-submerged excised leaves. Results demonstrate that, in the two cultivars studied, leaf senescence is an important biochemical mechanism in plants under submergence and its slower development in tolerant cultivars is, in part, responsible for submergence tolerance.