STIMULATION OF H-TRANSPORT ACTIVITY OF VACUOLAR H+-ATPASE BY ACTIVATION OF H+-PPASE IN KALANCHOE-BLOSSFELDIANA()

In Kalanchoe blossfeldiana cv. Tom Thumb the initial rate of ATP-depen dent H+-transport into tonoplast vesicles was stimulated up to three t imes if the H+-ATPase (EC 3.6.1.3) was energized a few minutes after p re-energization of the H+-PPase (EC 3.6.1.1). H+-PPase-activated ATP-d ependent H+-transport was observed in plants of K. blossfeldiana culti vated in short day (SD) or long day (LD) conditions expressing differe nt degrees of crassulacean acid metabolism (CAM), However, based on th e higher activity and protein amount of H+-PPase and H+-ATPase present in the vacuolar membrane of SD plants the maximum H+-transport activi ty in the stimulated mode of the H+-ATPase was significantly higher in tonoplast vesicles of SD plants than of LD plants. Hence, a co-ordina ted action of the H+-PPase and H+-ATPase at the tonoplast of Kalanchoe could allow a higher transport capacity at the vacuolar membrane when plants perform high CAM. Immunoprecipitation experiments with an anti serum raised against the A-subunit of the vacuolar H+-ATPase of Mesemb ryanthemum crystallinum L. showed that in SD and LD plants of K. bloss feldiana the H+-PPase was co-precipitated with the vacuolar H+-ATPase holoenzyme. The co-percipitation of the two transport proteins indicat es a close structural localization of the H+-PPase and the A-subunit o f the vacuolar H+-ATPase.