Branched Chain Amino Acid Metabolism in the Biosynthesis of <i>Lycopersicon pennellii</i> Glucose Esters

Abstract

Lycopersicon pennellii Corr. (D'Arcy) an insect-resistant, wild tomato possesses high densities of glandular trichomes which exude a mixture of 2,3,4-tri-O-acylated glucose esters that function as a physical impediment and feeding deterrent to small arthropod pests. The acyl moieties are branched C(4) and C(5) acids, and branched and straight chain C(10), C(11), and C(12) acids. The structure of the branched acyl constituents suggests that the branched chain amino acid biosynthetic pathway participates in their biosynthesis. [(14)C]Valine and deuterated branched chain amino acids (and their oxo-acid derivatives) were incorporated into branched C(4) and C(5) acid groups of glucose esters by a process of transamination, oxidative decarboxylation and subsequent acylation. C(4) and C(5) branched acids were elongated by two carbon units to produce the branched C(10)-C(12) groups. Norvaline, norleucine, allylglycine, and methionine also were processed into acyl moieties and secreted from the trichomes as glucose esters. Changes in the acyl composition of the glucose esters following sulfonylurea herbicide administration support the participation of acetohydroxyacid synthetase and the other enzymes of branched amino acid biosynthesis in the production of glucose esters.