PLANT PHYSIOLOGY , Vol 113, Issue 2 549-557, Copyright © 1997 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Characterization of the Glycerolipid Composition and Biosynthetic Capacity of Pea Root Plastids
L. Xue, L. M. McCune, K. F. Kleppinger-Sparace, M. J. Brown, M. K. Pomeroy and S. A. Sparace
Plant Science Department, McGill University, Macdonald Campus, 21111 Lakeshore Road, Ste. Anne-de- Bellevue, Quebec, Canada H9X 3V9 (L.X., L.M.M., K.F.K.-S., M.J.B., S.A.S.)
The glycerolipid composition of pea (Pisum sativum L.) root plastids and
their capacity to synthesize glycerolipids from
[UL-14C]glycerol-3-phosphate were determined. Pea root plastids primarily
consist of monogalactosyldiacylglycerol, triacylglycerol,
phosphatidylcholine, digalactosyldiacylglycerol, and diacylglycerol.
Maximum rates of total glycerolipid biosynthesis were obtained in the
presence of 2.4 mM glycerol-3-phosphate, 15 mM KHCO3, 0.2 mM
sodium-acetate, 0.5 mM each of NADH and NADPH, 0.05 mM coenzyme A, 2 mM
MgCl2, 1 mM ATP, 0.1 M Bis-Tris propane (pH 7.5), and 0.31 M sorbitol.
Glycerolipid biosynthesis was completely dependent on exogenously supplied
ATP, coenzyme A, and a divalent cation, whereas the remaining cofactors
improved their activity from 1.3- to 2.4-fold. Radioactivity from
glycerol-3-phosphate was recovered predominantly in phosphatidic acid,
phosphatidylglycerol, diacylglycerol, and triacylglycerol with lesser
amounts in phosphatidylcholine and monoacylglycerol. The proportions of the
various radiolabeled lipids that accumulated were dependent on the pH and
the concentration of ATP and glycerol-3-phosphate. The data presented
indicate that pea root plastids can synthesize almost all of their
component glycerolipids and that glycerolipid biosynthesis is tightly
coupled to de novo fatty acid biosynthesis. pH and the availability of ATP
may have important roles in the regulation of lipid biosynthesis at the
levels of phosphatidic acid phosphatase and in the reactions that are
involved in phosphatidylglycerol and triacylglycerol biosynthesis.
