缺水對大豆白化幼苗蛋白質合成的影響

Abstract

用Polyethylenegiycol(PEG)調配成不同滲透勢的緩衝液(28)，以滴降法測定緩衝液的滲透勢為-5.4bars時，相當大豆白化幼苗（生長二天，約6.5cm長）的等張溶液，若滲透勢比-5.4bars小時，大豆白化幼苗就開始缺水了。 大豆白化幼苗一旦處於缺水環境下，會引起生長停頓，觀察其蛋白質合成的機制，有快速與劇烈的改變：(1)細胞核內RNA合成的酵素—核糖核酸聚合?Ⅰ及Ⅱ的活性降低；(2)合成蛋白質的所在—多核糖體轉變成單核糖體(3)以3H-leucine標示蛋白質的合成，發現缺水還不太嚴重時(-6.75bars)攝入蛋白質的量只有輕微抑制的現象，低於-6.75bars時，則其攝入量會隨著滲透勢的降低而顯著降低。由以上可證明正常蛋白質合成速率，在缺水狀況下會顯著下降。 若缺水在-8bars時，再給予正常供水，核糖核酸聚合?Ⅰ及Ⅱ活性?升，多核糖體合量也會增高，3H-leucin的攝入量在6小時後亦可見?升，即蛋白質的正常合成功能可?復，也就是說在凋萎點之內缺水對大豆白化幼苗的效應是可逆的。 抽取缺水的大豆白化幼苗之全蛋白質，經SDS/12.5%Polyacrylamide膠體電泳分析和放射顯影術，發現在膠體上之全蛋白質的類型，沒有改變，即看不出有特殊新蛋白質的合成，可能大豆白化幼苗對缺水的效應與熱效應不同。

When the incubation medium contained various concentration of osmoticant, polyenthylene glycol (PEG), 2-day old etiolted seedlings (Ca. 6.5 cm long) were found to be equivalent to -5.4 bars. So the water potential less than -5.4 bars was considered as stressed conditions. Water stress inhibited growth and protein synthesis by a rapid change of polyribosomes into monoribosomes as shown by the others (16, 23, 30). At -6.75 bars when water stress is not serious, 3H-leucine incorporation into protein was slightly inhibited, however, the inhibition of 3H-leucine incorporation was obviously decreased if water potential was less than -6.75 bars. Similarly the in vitro RNA polymerase I and II activities for RNA synthesis by isolated nuclei from water stressed seedlings declined dramatically at -8 bars. When seedlings were transfered back to -5.4 bars for recovery from stress at 8 bars for 1 hr, 3H-leucine incorporation increased slightly and likewise the level of polyribosomes during 4 hr recovery period. RNA polymerase I and II activities by isolated nuclei, however, recovered to almost the initial level. So the effect of water stress at -8 bars was reversible and beyond this stress no recovery of protein synthesis was observed. 3H-labeled proteins from soybean seedlings under various water potentials were analyzed by SDS/ 12.5% polyacrylamide gel electrophorysis and fluorography. The patterns of protein bands in gels were found without any noticeable differences. The effect of water stress on protein synthesis was not as dramastic as heat shock effect and they are possibly different.