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Articles

Microsomal Phospholipid Molecular Species Alterations during Low Temperature Acclimation in Dunaliella¹

Department of Botany, The University of Texas, Austin, Texas 78712

A detailed analysis of the low temperature-induced alterations of Dunaliella salina (UTEX 1644) microsomal membrane lipids was carried out. Microsomal membranes were isolated from cells grown at 30°C, from cells shifted to 12°C for 12 hours, and from cells acclimated to 12°C. Fatty acid analyses of the major lipid classes demonstrated significant changes in the fatty acid composition of phosphatidylcholinemine (PE) and phosphatidylglycerol (PG) but not phosphatidylcholine (PC) during the initial 12 hours at low temperature. These changes did not entail enhanced desaturation of linoleic acid. Subsequent to 12 hours, the proportions of linolenic acid increased in all phospholipids.

Molecular species analyses of the phospholipids demonstrated that the most immediate changes following a shift to low temperature were limited to several molecular species of PE and PG. The changes observed in PE included a decrease in C₃₀ species and concomitant increases in C₃₄ and C₃₆ species. Compositional changes associated with PG entailed the emergence of a new molecular species (18:1/18:1) not found at 30°C. The retailoring of molecular species resulted in an increase in the number of species having two unsaturated acyl chains and did not reflect a simple enhancement of desaturase activity as suggested by the fatty acid analysis. We conclude that the initial alterations in response to low temperature stress involve discrete changes in certain molecular species. These and further alterations of molecular species following acclimation to low temperature would appear to augment increases in acyl chain desaturation as a means of modifying membrane properties in response to low temperature stress.

¹ Supported in part by grants from the National Science Foundation (PCM 8200289), the Robert A. Welch Foundation (F-350), and the National Cancer Institute (1 T32 CA09182). D. V. L. was a National Cancer Institute Predoctoral Trainee.