Changes in Amino Acid and Amine Contents of Susceptible Tomato Cultivars Infected with Alternaria alternata Tomato Pathotype or Treated with AL-toxin.

Abstract

The changes in amino acid and amine contents of susceptible and resistant tomato cultivars infected with Alternaria alternata tomato pathotype or treated with its host-selective AL-toxin were investigated. AL-toxin has been known as a potential inhibitor of aspartate carbamoyltransferase (ACTase) in susceptible tomato plants. Inhibition of ACTase should result in the accumulation of aspartic acid in the susceptible plant treated with AL-toxin. In this study, however, no difference was observed in the amount of aspartic acid and other amino acids between toxin-treated and non-treated leaves of the susceptible and resistant cultivars until at least 24hr after treatment. In the susceptible tomato plants inoculated with spores at the base of the stem, amino acid contents in leaflets showing necrotic symptom were similar to that in corresponding leaflets without symptom. Aspartic acid content in symptom-developed leaflets was rather lower than that in symptom-less ones. These results do not support the hypothesis that AL-toxin inhibits ACTase. On the other hand, two amines, ethanolamine and phosphoethanolamine, markedly accumulated in susceptible tomato leaves 12 to 24hr after toxin treatment, but not in resistant ones. The increase in these amines was also observed in symptom-developing leaflets but not in symptomless ones of plants inoculated with the spores of the pathogen. These results suggest that AL-toxin induces disorder of metabolism related to these amines in susceptible tomato cells.