水分胁迫对玉米幼叶生长区细胞质膜H^+-ATPase活性的影响

The Stimulative Effect of Water Stress on the Plasma Membrane ATPase Activity in the Growing Zone of Maize Leaves

PEG/Hoagland(-0.1 MPa)溶液根际胁迫处理5叶期玉米幼苗24h,明显刺激第5幼叶生长区细胞H?的分泌,比对照高约1.5倍,钒酸钠对此过程有强烈抑制作用。用水溶性多聚物(PEG4000/Dextran T 500)两相分配法分离玉米第5幼叶生长区的质膜,胁迫处理增加了质膜H^+—ATPase对底物的亲和力,K_m降低到对照的?;活力增加约1.5倍。亚胺环己酮对胁迫处理引起的质膜H^+—ATP_(ase)活性增加没有抑制作用,不同程度的胁迫处理会导致膜制剂磷脂/蛋白比率的变化,其比率在0.83～1.05之间时.随比率的增加,质膜 H^+—ATP_(ase)活性迅速上升;比率在1.05～1.37之间时,随比率值增加,活性迅速下降。暗示质膜的磷脂含量变化可能是胁迫导致质膜 H^+—ATP_(ase)活性增加的主要原因。

After the roots of intact maizeseedling were treated with PEGHoagland's solution with an osmoticpotential of -- 0. 4 MPa for 24 h, therate of H^+ extrusion increased marked-ly in thc growing zone of thc 5thleaves. The increase of H^+ was almostcompletely inhibited by Na_3VO_4. 0. 1mmol/L (Table 1). It Has been sug-gested that the increase of the H^+ ex-trusion may be the result of plasmamembranc ATPase acitvity increasecaused bv water stress. Plasma membrane (PM ), Puri-fied by two phase partition with aque-ous polymer from growing zone ofmaize seedling leaves, possessed theATPase activity with an optimum pHof 6. 5 (Fig. 1) and was strongly in-hibited by vanadate. K^+ and Na^+stimulatcd its activity markedly (Fig.2). Water stress treatment increasedplasma membrane ATPase activity by1. 5 times (Table 2), and decreasedthe K_m of PM ATPase from 0. 33mmol/L to 0. 11 mmol/L (Table 3,Fig. 3). It was showed that waterstress treatment increased the affinityof PM ATPase for substrate ATP, and?_(max) rose from 0. 35 umol mg ~1 min 1to 0. 87 umol mg^(-1) min^(-1) (Table 3).When the roots of intact maize seedlingwere treated by different water stress-es, the ratio of phospholipids to pro-teins in PM changed (Fig. 4). TheATPase had the maximun activitywhen the ratio was 1. 05 (Fig. 5). The treatment with cycloheximideat 0. 1 mmol/L did not decrease thePM ATPase activity, even increased itslightly (Table 4). It was suggestedthat some protein which interfered inPM ATPase activity had been removedfrom plasma membranes.