The Adaptive Changes Of The Activities Of H～+-ATPase In Vacuolar Membranes From The Roots Of Tomato Seedlings Under Phosphate Starvation

The paper has studied the effects of phosphate starvation on growth state and the change of Pi contents from tomato seedlings and the adaptive changes of H⁺-ATPase activity in tonoplast vesicles under phosphate starvation by different days (5d, 7d, 9d, 11d, 13d) sampling from the roots of tomato seedlings. The results are as follows:1. The average height of the seedlings decreased to a certain degree under phosphate starvation, while the main roots of the seedlings were obviously longer than those of the controls. In addition, the early days of phosphate starvation had no obvious effect on the fresh weight (FW) accumulation of the seedlings gradually became markedly less than the control. Phosphate starvation also decreased the dry weight (DW) accumulation of the seedlings.2. Under Pi-Starved conditions, the Pi contents of main root and overground seedlings decreased continually while the late days of phosphate starvation and were obviously less than the control.3. Tomato seedlings distinctly increased their Pi uptake rates that were much higher than the controls after 7d of Phosphate starvation.4. The hydrolytic activity of H⁺-ATPase in tonoplast vesicles from the roots of tomato seedlings was increased under phosphate starvation. The hydrolytic activity was highest to phosphate starvation for 7 days. Therefore the hydrolytic activity that of the controls was unchanged. Kinetic analysis of the tonoplast H⁺-ATPase from the roots of tomato seedlings showed that phosphate starvation obviously lowered the Km value, which indicated that phosphate starvation increased the affinity of the enzyme to its substrate, but had no significant effect on the V_max value of the enzyme. In addition, phosphate starvation did not alter the optimum pH of the ATPase. The optimal pH for H⁺-ATPase activity was 7.5.5. The properties of proton pumping activity of H⁺-ATPase in tonoplast vesicleswere studied by acridine orange fluorescent quenching measured at 22°C. the proton pumping activity of H+-ATPase was increased under phosphate starvation. The results in the study showed that salinity stimulated the increase of the pump efficiency of the V-H+-ATPase from roots.To a certain degree, these results suggest that the V-ATPase was involved in the induction of high-affinity phosphate transport systems by phosphate starvation.