Changes in the Activities of Ribulose 1,5-Bisphosphate and Phosphoenolpyruvate Carboxylases in Submersed Aquatic Angiosperms during Aging

Changes in the activities of ribulose-1,5-bisphosphate carboxylase (RuBPcase) and phosphoenolpyruvate carboxylase (PEPcase) during aging and senescence of leaves of submersed aquatic angiosperms, Potamogeton pectinatus L., Vallisneria spiralis L., and Hydrilla verticillata (L.f.) Royle were studied. The activity of RuBPcase decreased with both aging and senescence in three species. PEPcase activity increased from young to mature leaves in all three plants and also in old leaves of Hydrilla. The ratio of RuBPcase to PEPcase activity was lowest in mature and highest in old leaves, and increased with aging of isolated mature leaves in Potamogeton and Vallisneria, but decreased markedly in Hydrilla with aging and senescence. Kinetin treatment (0.23 mm) increased RuBPcase activity in three species and PEPcase activity in Potamogeton and Vallisneria, but decreased PEPcase activity in Hydrilla. Treatments with 2-chloroethylphosphonic acid (Ethrel, 0.69 mm) and abscisic acid (ABA, 0.075 mm) showed almost an opposite trend.