Müller A, Weiler E W
Lehrstuhl für Pflanzenphysiologie, Ruhr-Universität, Bochum, Germany.
Planta. 2000 Nov;211(6):855-63. doi: 10.1007/s004250000353.
The tryptophan auxotroph mutant trp3-1 of Arabidopsis thaliana (L.) Heynh., despite having reduced levels of L-tryptophan, accumulates the tryptophan-derived glucosinolate, glucobrassicin and, thus, does not appear to be tryptophan-limited. However, due to the block in tryptophan synthase, the mutant hyperaccumulates the precursor indole-3-glycerophosphate (up to 10 mg per g FW). Instability of indole-3-glycerophosphate leads to release of indole-3-acetic acid (IAA) from this metabolite during standard workup of samples for determination of conjugated IAA. The apparent increase in "conjugated IAA" in trp3-1 mutant plants can be traced back entirely to indole-3-glycerophosphate degradation. Thus, the levels of neither free IAA nor conjugated IAA increase detectably in the trp3-1 mutant compared to wild-type plants. Precursor-feeding experiments to shoots of sterile-grown wild-type plants using [2H]5-L-tryptophan have shown incorporation of label from this precursor into indole-3-acetonitrile and indole-3-acetic acid with very little isotope dilution. It is concluded that Arabidopsis thaliana shoots synthesize IAA from L-tryptophan and that the non-tryptophan pathway is probably an artifact.
拟南芥（Arabidopsis thaliana (L.) Heynh.）的色氨酸营养缺陷型突变体trp3-1，尽管L-色氨酸水平降低，但仍积累了色氨酸衍生的芥子油苷——葡萄糖硫苷，因此似乎不存在色氨酸限制。然而，由于色氨酸合酶的阻断，该突变体过度积累了前体吲哚-3-甘油磷酸（高达每克鲜重10毫克）。在用于测定结合态吲哚-3-乙酸（IAA）的样品标准处理过程中，吲哚-3-甘油磷酸的不稳定性导致该代谢物释放出吲哚-3-乙酸（IAA）。trp3-1突变体植物中“结合态IAA”的明显增加完全可追溯到吲哚-3-甘油磷酸的降解。因此，与野生型植物相比，trp3-1突变体中游离IAA和结合态IAA的水平均未检测到明显增加。使用[2H]5-L-色氨酸对无菌培养的野生型植物的茎进行前体饲喂实验表明，该前体的标记物以非常低的同位素稀释率掺入吲哚-3-乙腈和吲哚-3-乙酸中。得出的结论是，拟南芥的茎从L-色氨酸合成IAA，并且非色氨酸途径可能是一种假象。
