Phospholipid metabolism in membranes of senescing bean cotyledons

• Published in: Journal of experimental botany 1994-11, Vol.45 (280), p.1513-1522
• Main Authors: Brown, J.H, Chambers, J.A, Ghosh, S, Froese, C.D, Huff, A.M, Thompson, J.E
• Format: Article
• Language: English
• Subjects: Age; Agronomy. Soil science and plant productions; Biological and medical sciences; Catabolism; Cell membranes; Cotyledons; Economic plant physiology; enzyme activity; Enzymes; Fatty acids; Fundamental and applied biological sciences. Psychology; Lipids; lipogenesis; lipolysis; long-chain-fatty-acid-CoA ligase; Metabolism; Metabolism. Physicochemical requirements; microsomes; Nitrogen metabolism and other ones (excepting carbon metabolism); Nutrition. Photosynthesis. Respiration. Metabolism; oleic acid; Phaseolus vulgaris; Phosphatidylcholines; Phosphatidylethanolamines; Phospholipid synthesis; Phospholipids; Plant physiology and development; senescence
• ISSN: 0022-0957; 1460-2431
• DOI: 10.1093/jxb/45.11.1513

Mechanisms underlying the depletion of phospholipid in senescing membranes have been examined using microsomes isolated from bean cotyledons (Phaseolus vulgaris) at various stages of development. As the cotyledons age, microsomal phospholipid levels relative to protein decrease by 93% indicating that phospholipids are selectively depleted from senescing membranes. This reflects active phospholipid catabolism, but can also be attributed to a reduction in phospholipid synthesis. Specifically, the activities of choline phosphotransferase and ethanolamine phosphotransferase, enzymes mediating the terminal step in the synthesis of phosphatidylcholine and phosphatidylethanolamine, respectively, decrease dramatically as the cotyledons senesce. Phosphatidylcholine and phosphatidylethanolamine comprise over 70% of the total phospholipid in these membranes, and this pronounced decline in their synthesis with advancing senescence will lead to phospholipid depletion. There is also a decrease with age in the activity of acyl-CoA synthetase, which generates acyl-CoA for use in phospholipid synthesis. Microsomal phospholipid deacylation-reacylation activity declines as well as the cotyledons senesce, but this can be accounted for in terms of decreased levels of phospholipid available for the reaction. Thus the depletion of phospholipid in senescing membranes can be attributed to active catabolism in the face of declining synthesis.