EVIDENCE THAT TRYPTOPHAN IS NOT A DIRECT BIOSYNTHETIC INTERMEDIATE OF CAMALEXIN IN ARABIDOPSIS-THALIANA

Camalexin, a phytoalexin produced by Arabidopsis thaliana, is an indole compound substituted at the C-3 position with a thiazole. As part of a program to determine the camalexin biosynthetic pathway, the ability of tryptophan to serve as a precursor of camalexin was tested. Two complementary methods were employed-the analysis of camalexin accumulation in tryptophan-deficient mutants and the incorporation of radiolabelled compounds into camalexin. Both sets of experiments indicate that anthranilate but not tryptophan served as a biochemical precursor of camalexin. Therefore, we concluded that the camalexin biosynthetic pathway originates with an intermediate of the tryptophan pathway that lies between anthranilate and indole. © 1993 Academic Press, Inc.