Auxin biosynthesis in maize kernels

Auxin biosynthesis was analyzed in a maize (Zen mays) kernel culture system in which the seeds develop under physiological conditions similar to the i n vivo situation. This system was modified for precursor feeding experiment s. Tryptophan (Trp) is efficiently incorporated into indole-3-acetic acid ( IAA) with retention of the 3,3' bond. Conversion of Trp to IAA is not compe ted by indole. Labeling with the general precursors [U-C-13(6)]glucose and [1,2-C-13(6)]acetate followed by retrobiosynthetic analysis strongly sugges t that Trp-dependent IAA synthesis is the predominant route for auxin biosy nthesis in the maize kernel. The synthesis of IAA from indole glycerol phos phate and IAA formation via condensation of indole with an acetyl-coenzyme A or phosphoenolpyruvate derived metabolite can be excluded.