PLANT PHYSIOLOGY , Vol 109, Issue 2 409-420, Copyright © 1995 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Microsomal Lyso-Phosphatidic Acid Acyltransferase from a Brassica oleracea Cultivar Incorporates Erucic Acid into the sn-2 Position of Seed Triacylglycerols
D. C. Taylor, D. L. Barton, E. M. Giblin, S. L. MacKenzie, CGJ. van den Berg and PBE. McVetty
National Research Council of Canada, Plant Biotechnology Institute, 110 Gymnasium Place, Saskatoon, Saskatchewan, Canada S7N 0W9 (D.C.T., E.M.G., S.L.M.)
Developing seeds from Brassica oleracea (L.) var botrytis cv Sesam were
examined for the ability to biosynthesize and incorporate erucic acid into
triacylglycerols (TAGs). Seed embryos at mid-development contained a high
concentration of erucic acid in diacylglycerols and TAGs, and substantial
levels were also detected in free fatty acids, acyl-coenzyme A (CoA),
phosphatidic acid, and phosphatidylcholine. Homogenates and microsomal
fractions from seeds at mid-development produced [14C]eicosenoyl- and
[14C]erucoyl-CoAs from [14C]oleoyl-CoA in the presence of malonyl-CoA and
reducing equivalents in vitro. These fatty acids were incorporated into
TAGs via the Kennedy pathway. However, unlike most Brassicaceae, the B.
oleracea was able to insert significant erucic acid into the sn-2 position
of TAGs. It was shown that the lyso-phosphatidic acid acyltransferase
(LPAT) incorporated erucic acid into the sn-2 position of lyso-phosphatidic
acid. The erucoyl-CoA:LPAT activity during seed development and the sn-2
erucic acid content of the TAG fraction in mature seed were compared to
those in B. napus, Tropaeolum majus, and Limnanthes douglasii. There was a
correlation between the in vitro erucoyl-CoA:LPAT activity and the sn-2
erucic acid content in seed TAGs. To our knowledge, this is the first
member of the Brassicaceae reported to have an LPAT able to use
erucoyl-CoA. This observation has important implications for efforts being
made to increase the erucic acid content in B. napus, to supply strategic
industrial feedstocks.