METABOLIC FATE OF SECONDARY METABOLITES : INVOLVEMENT OF CELL WALLS

在禾本科植物燕麦和模式植物拟南芥中研究了次生代谢物的代谢命运。在燕麦中，已经证明它们的植物毒素，燕麦，被结合到细胞壁中。详细了解了这些化合物的合成过程，并对其代谢产物进行了研究。燕麦叶片中存在由过氧化物酶作用产生的燕麦黄原胺代谢物。对它们的化学结构进行了分析，结果表明它们是除草剂的脱氢二聚体。光谱分析表明，它们具有天然产品中没有的独特的碳骨架。在拟南芥中，吲哚-3-羧酸(ICA)被发现与细胞壁结合。我们发现，感染甘蓝型油菜的叶片中ICA的含量增加。利用稳定同位素标记的假定前体和显示色氨酸代谢改变的突变体来分析ICA的生物合成途径。首先，用标记色氨酸饲喂拟南芥叶片，接种油菜分生孢子。叶片用甲醇提取，用LC-MS/MS分析了色氨酸在ICA中的掺入，标记的色氨酸有效地掺入到ICA中，表明ICA在受感染的叶片中从头合成。接下来，我们分析了改变色氨酸代谢的多个品系的ICA含量。突变系pAD-3细胞壁内ICA含量增加。PAD 3行百灵鸟体内吲哚类植物保卫素、骆驼蓬蛋白的积累。因此，这一发现有力地表明，ICA不是直接来自Camalexin，ICA的生物合成途径与Camalexin的合成途径是相同的。

The metabolic fates of secondary metabolites were investigated in gramineous plants, oats, and a model plant Arabidopsis thaliana.In oats, it has been demonstrated that their phytoalesxins, avenanthramides, are incorporated into cell walls. lb know the incorporation processes in detail, the metabolites that are derived from avenanthramides were investigated. The avenanthramide metabolites that are genrerated by the action of peroxidase were found to be present in oat leaves. The analysis of their chemical structures revealed that they are dehydrodimers of avenanthramides. The spectroscopic analysis revealed that they have unique carbon skeletons that have not been found in natural products. These compounds are considered to be units for the incorporation of avenanthramides into cell walls.In Arabidopsis thaliana, indole-3-carboxylic acid (ICA) has been indicated to bound to the cell walls. We found that the amount of ICA increases in the leaves infected by A. brassicicola. The biosynthetic pathway of ICA was analyzed by using stable isotope labeled putative precursors and mutants that exhibit modified tryptophan metabolism. First, Arabidopsis leaves were fed with labeled tryptophan and the conidia of A. brassicicola were inoculated. The leaves were extracted with methanol and the incorporation of tryptophan into ICA was analyzed by LC-MS/MS. The labeled tryptophan was effectively incorporated into ICA, indicating de novo synthesis of ICA in the infected leaves. Next, we analyzed ICA contents in multiple lines that have altered tryptophan metabolism. The increase of the amount of ICA in the cell walls was found in pad 3 mutant line. pad 3 line larks the accumulation of indolic phytoalexin, camalexin. Thus, this finding strongly suggests that ICA is not directly derived from camalexin, and that the biosynthetic pathway of ICA is shared by the pathway for camalexin.