Leaf senescence in submerged rice plants

Leaf senescence in the rice (Oryza sativa) cultivars FR13A and IR42 under s ubmergence was assessed in terms of changes in total chlorophyll, soluble a mino acids and protein concentrations and peroxidase activity in crude extr acts. The objective was to determine whether delay in leaf senescence was r elated to the submergence tolerance of a rice cultivar. Submergence induced senescence and its extent was notably different in the two cultivars. Resu lts indicated a reduction in chlorophyll and protein concentrations in leav es during submergence but an increase in amino acid concentration and perox idase activity. These relative changes were more pronounced in submergence intolerant IR42 than in tolerant FR13A even at four days after complete sub mergence. When plants were desubmerged and returned to standard irrigated c onditions after 10 days of complete submergence the rate of recovery was di fferent for the two cultivars. FR13A showed a greater protein and chlorophy ll restoring ability compared with the intolerant IR42. The differences obs erved between the responses of FR13A and IR42 to submergence were likely to be due to differences in proteolysis. Senescence of leaves due to submerge nce was similar to the senescence of non-submerged excised leaves. Results demonstrate that, in the two cultivars studied, leaf senescence is an impor tant biochemical mechanism in plants under submergence and its slower devel opment in tolerant cultivars is, in part, responsible for submergence toler ance.