REGULATION OF TRIACYLGLUCOSE FATTY-ACID COMPOSITION - URIDINE-DIPHOSPHATE GLUCOSE FATTY-ACID GLUCOSYLTRANSFERASES WITH OVERLAPPING CHAIN-LENGTH SPECIFICITY

UDP-glucose (UDP-Glc):fatty acid glucosyltransferases catalyze the UDP -Glc-dependent activation of fatty acids as 1-O-acyl-beta-glucoses. 1- O-Acyl-beta-glucoses act as acyl donors in the biosynthesis of 2,3,4-t ri-O-acylglucoses secreted by wild tomato (Lycopersicon pennellii) gla ndular trichomes. The acyl composition of L. pennellii 2,3,4-tri-O-acy lglucoses is dominated by branched short-chain acids (4:0 and 5:0; app roximately 65%) and straight and branched medium-chain-length fatty ac ids (10:0 and 12:0; approximately 35%). Two operationally soluble UDP- Glc:fatty acid glucosyltransferases (I and II) were separated and part ially purified from L. pennellii (LA1376) leaves by polyethylene glyco l precipitation followed by DEAE-Sepharose and Cibacron Blue 3GA-agaro se chromatography. Whereas both transferases possessed similar affinit y for UDP-Glc, glucosyltransferase I showed higher specificity toward short-chain fatty acids (4:0) and glucosyltransferase II showed higher specificity toward medium-chain fatty acids (8:0 and 12:0). The overl apping specificity of UDP-Glc:fatty acid glucosyltransferases for 4:0 to 12:0 fatty acid chain lengths suggests that the mechanism of 6:0 to 9:0 exclusion from acyl substituents of 2,3,4-tri-O-acylglucoses is u nlikely to be controlled at the level of fatty acid activation. UDP-Gl c:fatty acid glucosyltransferases are also present in cultivated tomat o (Lycopersicon esculentum), and activities toward 4:0, 8:0, and 12:0 fatty acids do not appear to be primarily epidermal when assayed in in terspecific periclinal chimeras.