磷饥饿时番茄幼苗根系质膜H+-ATP酶活性

磷饥饿提高了番茄幼苗质膜H+-ATP酶活性并促进了番茄幼苗根部的H+分泌。动力学分析表明，磷饥饿使番茄幼苗根部质膜H+-ATP酶的Km值明显降低，亦即提高了该酶对其底物的亲和力，但对该酶的Vmax影响不大。另外，磷饥饿并不改变ATP酶的最适pH值(最适pH值为6.5)。钒酸盐显著抑制番茄幼苗根部质膜ATP酶的活性以及H+分泌，也显著抑制番茄幼苗的Pi吸收。与对照相比，上述抑制作用在饥饿处理的植物中表现得更强。以上结果表明，磷饥饿时高亲和性Pi传递系统的诱导很可能包含质膜H+-ATP酶的参与。

The Relationship Between Phosphate Uptake and Changes in Plasmale-mma H +- ATPase Activities from the Roots of Tomato Seedlings DuringPhosphate Starvation

Phosphate starvation increased the activity of PM H+-ATPase fromtomato seedlings and enhanced the extrusion of H + from the roots of the seedlings (Figs. 1,2). Kinetic analysis of the PM H+-ATPase from the roots of tomato seedlings showed that phosphate starvation obviously Iowered the Km value,which indicated that phosphate starvation increased the affinity of the enzyme to its substrate, but had no significant effect on the Vmax value of the enzyme (Fig.4). In addition, phosphate starvation did not alter the optimum pH ( i. e. , 6.5 ) of the ATPase ( Fig. 3 ).Vanadate, a specific inhibitor of PM H+-ATPase,strongly inhibited not only phosphate uptake (Table3 ) but also PM ATPase activity from (Table 2) and H+-extrusion (Table 1 ) by the roots of tomato seedlings. These results demonstrated that the PM H +-ATPase is involved in the induction of high-affinity phosphate transport systems by phosphate starvation.