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产物的代谢命运。在燕麦中，已经证明它们的植物毒素燕麦生物碱被掺入细胞壁。在详细了解掺入过程的基础上，研究了燕麦生物碱衍生的代谢产物。燕麦叶片中存在着由过氧化物酶作用产生的燕麦生物碱代谢物。化学结构分析表明它们是燕麦生物碱的脱氢二聚体。光谱分析表明，它们具有天然产物中未发现的独特碳骨架。在拟南芥中，吲哚-3-羧酸（indole-3-carboxylic acid，伊卡）与细胞壁结合。结果表明，感染A.芸苔属。伊卡的生物合成途径进行了分析，通过使用稳定同位素标记的推定的前体和突变体，表现出修改色氨酸代谢。首先，用标记的色氨酸和A. brassicicola接种。用甲醇提取叶片，并通过LC-MS/MS分析色氨酸掺入伊卡中。标记的色氨酸有效地掺入伊卡中，表明在感染的叶片中伊卡从头合成。接下来，我们分析了伊卡内容在多个线，改变色氨酸代谢。pad 3突变体细胞壁伊卡含量增加。垫3线云雀积累吲哚植物抗毒素，camalexin。因此，这一发现强烈表明伊卡不是直接来源于Camalexin，伊卡的生物合成途径与Camalexin的途径共享。

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.