L‐Tryptophan metabolism in wound‐activated and Agrobacterium tumefaciens‐transformed potato tuber cells

Abstract

The in vivo metabolism of L‐tryptophan in wound‐activated and Agrobacterium tumefaciens, strain C 58, transformed tissues of white potato tubers (Solanum tuberosum L. cv. Saskia) was investigated. The following metabolites of L‐tryptophan were identified in both tissues by co‐chromatography with authentic standards in several thinlayer chromotography (TLC) and high pressure liquid chromatographic (HPLC) systems: indole‐3‐acetic acid (IAA), indole‐3‐acetaldehyde, indole‐3‐ethanol, indole‐3‐acetamide and tryptamine. Labelled indole‐3‐acetaldoxime was only found in transformed tissue. Crown gall tissue generally incorporated [14C]‐L‐tryptophan into precursors of IAA at a distinctly higher rate than did wound tissue. Tryptamine and indole‐3‐ethanol accumulated about ten‐fold more label in crown gall cells than in cells from wounded tissue. The incorporation of radioactivity into indole‐3‐acetamide as determined by 2 consecutive TLC systems followed by HPLC analysis was rather low, though consistently observed in both tissues. An indole‐3‐acetamide hydrolyzing enzyme, the putative product of gene 2 on the T‐DNA, could be extracted from the transformed tissue only. The indole‐3‐ethanol level was 4.3 nmol (g dry weight)−1 and 41 nmol (g dry weight)−1 for wounded tissue and primary crown gall tissue, respectively, as determined by HPLC with a [14C]‐labelled internal standard. The experiments are critically discussed in relation to recent reports on a T‐DNA encoded enzyme of IAA biosynthesis in crown gall tumors.