Catabolism of indole‐3‐acetic acid to indole‐3‐methanol in a crude enzyme extract and in protoplasts from Scots pine (Pinus sylvestris)

Abstract

The catabolism of radiolabelled indole‐3‐acetic acid was investigated in a crude enzyme extract and a protoplast‐rich fraction from Scots pine (Pinus sylvestris L.). Analysis by ion‐pair reverse‐phase and normal‐phase high performance liquid chromatography indicated that [14C]‐indole‐3‐methanol was a major catabolite of [2‐14C]‐indole‐3‐acetic acid in the crude enzyme system. This was confirmed by combined gas chromatograpby‐mass spectrometry which demonstrated the conversion of [2, 4, 5, 6, 7‐2H5]‐indole‐3‐acetic acid to [2H]‐indole‐3‐methanol. In addition to indole‐3‐methanol, the enzyme system converted indole‐3‐acetic acid to a number of other catabolites. Feeds with [1‐14C]‐ and [2‐14C]‐mdole‐3‐acetic acid suggest that, with the exception of two minor components, these catabolites result from decarboxylation. The effects of 2, 4‐dichlorophenol, phenol and hydrogen peroxide upon the reaction rate and product formation in the crude enzyme system were also investigated. Phenols favoured the formation of indole‐3‐methanol and enhanced the reaction rate. In contrast to the enzyme extract [14C]‐indole‐3‐methanol was only a minor product when P. sylvestris protoplasts were incubated with [2‐14C]‐indole‐3‐acetic acid.