Biosynthesis of phenolic acids in tomato plants infected with <i>Agrobacterium tumefaciens</i>

Abstract

Tomato plants 21 days old were inoculated with Agrobacterium tumefaciens, the causative organism of crown gall, and 72 h later [3- 14 C]cinnamic or [carboxyl- 14 C]benzoic acid was administered by wick-feeding to these and to uninfected control plants. After a further 48 h both groups were examined for incorporation of label into phenolic acids. The pattern of incorporation into bound phenolic acids of the controls was in accord with biosynthetic pathways previously demonstrated in normal plants, but qualitative and quantitative divergence from this pattern was observed in the bound phenolic acids of the infected plants. The data suggest interference by the pathogen with β-oxidation of at least two phenylpropanoid acids of the lignification pathway. In infected plants, lowered incorporation of 14 C from cinnamic acid into phenylpropanoid acids of the lignification pathway and their β-oxidation products was accompanied by the appearance of labelled o-coumaric acid, consistent with some diversion of cinnamic acid metabolism toward ortho-hydroxylation. Incorporation of 14 C from benzoic acid into gentisic and especially salicylic acid of infected plants was much lower than in the controls.