FORMATION OF N-MALONYL-L-TRYPTOPHAN IN WATER-STRESSED TOMATO LEAVES

Excised tomato (Lycopersicon esculentum Mill, cv. Castlemart) leaves s ubjected to water loss of 20 to 30% of their fresh weight increased dr amatically both tryptophan and N-malonyl-L-tryptophan (M-L-Trp) conten t. The identity of M-L-Trp was confirmed by chiral TLC, by oxidation o f the released Trp residue with L-amino acid oxidase, and by mass spec trometry. Wilted leaves administered exogenous D- or L-Trp formed the corresponding malonyl-conjugate. N-malonyl-D-tryptophan (M-D-Trp) or M -L-Trp, respectively. Crude leaf extracts were able to N-malonylate bo th L- and D-Trp in vitro. The activity was higher in mature leaves tha n in immature leaves and was increased by water stress. Since most of the previous reports have assumed that all endogenous MTrp is M-D-Trp without actual chiral identification, our present results suggest that the current literature concerning the natural occurrence of M-D-Trp n eeds to be re-examined.