Evaluation of evidence for the presence of indole-3-acetic acid in marine algae.

Using a two-dimensional thin layer chromatography system (TLC) we have been unable to detect endogenous indole-3-acetic acid (IAA) (as an Ehrlichpositive spot on TLC plates) in the acidic, ether-soluble fraction of alkaline hydrolysates of 10 species of marine algae. Exogenously added IAA, admixed with algal extracts, was completely separated on chromatograms from other Ehrlich-positive compounds which were present in the extracts. Several regions of auxin-like activity were located on chromatograms of Fucus extracts. From experiments on the recovery of exogenously added IAA from algal extracts, we calculate that if IAA is present in algae, the levels are below 0.1 μg IAA/g fresh weight. The claim by previous workers that IAA is present in marine algae is critically discussed.