Ca^(2+)/CaM介导生长素对小麦胚芽鞘细胞NAD激酶的刺激作用

The Effect of IAA on NAD Kinase in Wheat Coleoptile Is Mediated by Ca^(2+) /Calmodulin Complex

外源ＩＡＡ 处理可以显著增加小麦胚芽鞘细胞ＮＡＤ 激酶的催化活性，钙离子可以增强ＩＡＡ 的作用效果，而钙离子通道抑制剂ＬａＣｌ３ 则起强烈的抑制作用，但在存在钙离子的条件下，这种抑制作用可以被钙离子载体Ａ２３１８７ 消除；钙调蛋白能够在离体条件下激活经过ＤＥＡＥ 纤维素柱纯化的小麦胚芽鞘ＮＡＤ激酶，经过ＩＡＡ 处理的胚芽鞘细胞中能够刺激ＮＡＤ 激酶活性的钙调蛋白含量明显增加，ＩＡＡ 的这一作用受ＬａＣｌ３ 的抑制。上述结果表明Ｃａ２＋ ／ＣａＭ 复合物介导了生长素对小麦胚芽鞘细胞ＮＡＤ 激酶活性的促进作用。

NAD kinase (NADK) catalyzes the only known biochemical reaction leading to the phosphorylation of NAD + to form NADP +,which is a rate limiting factor in many reactions in plants and plays a key role in the control of metabolism. Enhanced by calcium, exogenous IAA increased NADK activity in etiolated wheat coleoptile segments(Figs.1, 2). LaCl 3, a potent calcium ion channel blocker, could inhibit effectively the IAA induced activity of NADK(Fig.3). The inhibitive effect of LaCl 3 could be reversed by the calcium ionophore A23187(Fig.4). Calmodulin could activate in vitro the NADK purified by anion exchange chromatography from wheat coleoptile segments(Fig.5). LaCl 3, however, almost completely abolished the IAA induced increase in NADK dependent calmodulin content in wheat coleoptile(Fig.6). All these results suggest that IAA induced activation of NADK is mediated by Ca 2+ and calmodulin.