INDOLE-3-LACTIC ACID IS A WEAK AUXIN ANALOG BUT NOT AN ANTIAUXIN

Indole-3-lactic acid (ILA) is a naturally occurring indole derivative, preferably detected in soil bacteria and fungi and only in low amount s in plants. T-DNA gene 5 of Agrobacterium tumefaciens was found to be involved in the synthesis of ILA in transformed plant tissues, but th e physiologic relevance for ILA production in plants is unclear. The r elated molecular structure of ILA to the natural auxin indole-3-acetic acid (IAA) makes ILA a good candidate for an auxin analogue. We exami ned the possible auxin activity of ILA on elongation, proliferation, a nd differentiation in Pisum sativum L. Results presented in this paper indicate that there are no or only weak effects of ILA toward the act ivity of auxins when used in the physiologic concentration range. Furt hermore, no antagonistic effects of ILA were found. Biochemical analys is using the equilibrium dialysis binding system resulted in no high a ffinity ILA binding to an enriched protein fraction containing auxin-b inding protein (ABP(44)), whereas 1-naphthaleneacetic acid exhibited h igh affinity auxin binding.