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，光诱导生长抑制物(S)在光照侧和阴侧的分布不均匀，从而影响生长素活性，从而导致植物向光性(Bruinsma-Hasegawa理论，1990)。从光培养玉米胚芽鞘中分离得到蓝光诱导生长抑制物，经1H核磁共振谱鉴定为DIMBOA和MboA。化学分析表明，光致刺激诱导玉米胚芽鞘向光性中起重要作用的非活性DIMBOA糖苷转化为活性DIMBOA，然后代谢成活性较低的MBEA。从光培养的拟南芥下胚轴中分离到吲哚-3-乙腈(Ian)，并鉴定为蓝光诱导生长抑制物。野生型的Ian在光致刺激下增加，而突变体中没有表现出光致反应的变化。这些结果表明，Ian在拟南芥下胚轴向光性中起重要作用。

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.