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Indolic constituents and indole-3-acetic acid biosynthesis in the wild-type and a tryptophan auxotroph mutant of Arabidopsis thaliana
Authors:A Müller  E W Weiler
Institution:Lehrstuhl für Pflanzenphysiologie, Ruhr-Universit?t, Universit?tsstr. 150, 44801 Bochum, Germany, DE
Abstract: 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. Received: 1 March 2000 / Accepted: 10 April 2000
Keywords::   Arabidopsis (tryptophan mutant) –  Auxin biosynthesis –  Indole-3-glycerophosphate –  Mutant (Arabidopsis) –  Nitrilase            Tryptophan synthase
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