PLANT PHYSIOLOGY , Vol 115, Issue 4 1581-1587, Copyright © 1997 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Regulation of Triacylglucose Fatty Acid Composition (Uridine Diphosphate Glucose:Fatty Acid Glucosyltransferases with Overlapping Chain-Length Specificity)
J. P. Kuai, G. S. Ghangas and J. C. Steffens
Department of Plant Breeding, 252 Emerson Hall, Cornell University, Ithaca, New York 14853-1901
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-tri-O-acylglucoses secreted by wild tomato (Lycopersicon pennellii)
glandular trichomes. The acyl composition of L. pennellii
2,3,4-tri-O-acylglucoses is dominated by branched short-chain acids (4:0
and 5:0; approximately 65%) and straight and branched medium-chain-length
fatty acids (10:0 and 12:0; approximately 35%). Two operationally soluble
UDP-Glc:fatty acid glucosyltransferases (I and II) were separated and
partially purified from L. pennellii (LA1376) leaves by polyethylene glycol
precipitation followed by DEAE-Sepharose and Cibacron Blue 3GA-agarose
chromatography. Whereas both transferases possessed similar affinity 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 overlapping 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 unlikely to be controlled at
the level of fatty acid activation. UDP-Glc:fatty acid glucosyltransferases
are also present in cultivated tomato (Lycopersicon esculentum), and
activities toward 4:0, 8:0, and 12:0 fatty acids do not appear to be
primarily epidermal when assayed in interspecific periclinal chimeras.