Inhibitory Effect of AL-toxin Produced by Alternaria alternata Tomato Pathotype on the Biosynthesis of Phopshatidylethanolamine in Tomato Leaves Susceptible to the Fungus.

Abstract

AL-toxin, a host specific toxin produced by Alternaria alternata tomato pathotype, had been reported to cause accumulation of ethanolamine (EA) and phosphoethanolamine (PEA) in susceptible tomato leaves. In this connection, the effect of AL-toxin on the metabolism of phospholipids, particularly on the biosynthetic pathway of phosphatidylethanolamine (PtdEA) was investigated. [14C] EA was fed in leaf discs in both susceptible and resistant cultivars, Mie First and Saturn, respectively. The incorporation of [14C] EA into both tomato leaf discs similarly increased with incubation time, regardless of AL-toxin treatment, while significant inhibition of its incorporation into PtdEA was only found in susceptible leaf discs treated with the toxin. In a comparative study on the effect of AL-toxin on the biosynthesis of phosphatidylcholine (PtdC), the inhibition of incorporation of [14C] choline into PtdC in susceptible leaf discs was very low as compared to that of [14C] EA into PtdEA. Results from the present work indicate that AL-toxin have a greater inhibitory effect on the biosynthesis of PtdEA through EA in the leaves of susceptible cultivar, but not in resistant one.