SENESCENCE IN SUBMERGED AQUATIC ANGIOSPERMS: CHANGES IN INTACT AND ISOLATED LEAVES DURING AGING

Abstract

SUMMARYEvents during the senescence of intact and isolated leaves of two submerged aquatic angiosperms, Vallisneria spiralis L. and Hydrilla verticillata (L.F.) Royle, were studied. Mature leaves were the most active metabolically in both the plants. The decline in chlorophyll, protein and dry wt and increase in tissue permeability was, in general, age‐related in Vallisneria but not so in Hydrilla. Changes in the chlorophyll a: b ratio did not follow a consistent pattern as leaves aged. In general, an increase in the activities of protease, RNase, and acid pyrophosphatase and a decrease in alkaline pyrophosphatase activities were noted in aging leaves of Vallisneria. Catalase activity was, however, highest in mature and lowest in young leaves. In Hydrilla, a similar trend in the activities of the enzymes, with the exception of acid pyrophosphatase and catalase, was noted. Both acid pyrophosphatase and catalase activities showed a general decline with age of the leaves. A higher ratio of acid: alkaline pyrophosphatase was observed in both species as leaves aged. The senescence pattern of isolated leaves of the two species showed a general decline in cell components and dry wt, and an increase in tissue permeability. A rise in the activities of degradative enzymes and a decline in alkaline pyrophosphatase and catalase activities were also noted during aging of isolated leaves. The ratio of acid: alkaline pyrophosphatase increased with aging. Kinetin treatment delayed the loss of cell components and dry wt, and the rise in tissue permeability, and lowered the activities of catabolic enzymes and thus effectively deferred senescence in both the species.