The biosynthetic pathway for indole-3-acetic acid changes during tomato fruit development

Phytohormone metabolism during fruit ripening is critical to the control of this developmental process, yet we know little about pathways for the production of many of these signaling compounds. Using stable isotope labeling in both an in vitro aseptic tomato fruit culture system and detached greenhouse-grown tomato fruit, we have shown by mass spectral analysis that tomato uses the tryptophan-independent pathway to produce IAA from anthranilate or indole. We also show that there is a developmental switch from tryptophan utilization to tryptophan-independent production that occurs between mature green and red-ripe stages of fruit development. Moreover, this pathway switch does not appear to be associated with ripening per se in that fruit from neverripe tomato plants also utilize the tryptophan independent pathway.