Chemical structure and function of phototropism-regulating substances in plants

向光性是植物对环境反应的一个典型例子。大量的研究表明，向光性是由于光诱导的生长抑制物质在光照面和阴影面的不均匀分布影响了生长素的活性，甚至在生长素水平不变的情况下（Bruinsma-Hasegawa theory，1990）。蓝光诱导的生长抑制剂是从光生长的玉米胚芽鞘中分离出来的，根据其^H NMR谱鉴定为DIMBOA和MBOA。化学分析表明，向光性刺激诱导玉米胚芽鞘中的DIMBOA葡萄糖苷转化为活性DIMBOA，然后代谢为活性较低的MBOA。从光生长的拟南芥下胚轴中分离得到吲哚-3-乙腈（IAN），经鉴定为蓝光诱导的生长抑制剂。IAN增加在野生型向光性刺激后，而它没有表现出变化的突变体，显示没有向光性反应。这些结果表明IAN在拟南芥下胚轴向光性中起着重要作用。

Phototropism is a typical example of an environmental response in plants. From many accumulated findings it is suggested that phototropism is caused by the unequal lateral distribution of light-induced growth inhibitor(s) in the illuminated and the shaded sides affecting the auxin activity at unchanged, even auxin level (Bruinsma-Hasegawa theory, 1990).In the present study, we investigated chemical structure and formation of phototropism-regulatming substances in plants. Blue light-induced growth inhibitors were isolated from light-grown maize coleoptiles, and identified as DIMBOA and MBOA from their ^1H NMR spectra. From chemical analyzes, it can be concluded that phototropic stimulation induces conversion of the inactive DIMBOA glucoside into the active DIMBOA, which plays the essential role in the phototropism of maize coleoptiles, and then metabolizes into MBOA, which has a lower activity.From light-grown Arabidopsis thaliana hypocotyls, indole-3-acetonitrile (IAN) was isolated and identified as a blue light-induced growth inhibitor. IAN increased in the wild type upon phototropic stimulation, whereas it showed no change in the mutant that shows no phototropic response. From these results it is suggested that IAN plays an important role in the phototropism of Arabidopsis hypocotyls.