| Summary: | Thesis (M.Sc.)--Memorial University of Newfoundland, 1999. Biology Bibliography: leaves 80-90 The fatty acid composition and fluidity of gill phospholipids and hemocyte membranes of a eurytherrnal bivalve, Placopecten magellanicus, were investigated following a 10°C reduction in acclimation temperature. The time course of the acclimation response from 15 to 5°C was also monitored over a 21-day period. Membrane physical properties were measured by means of an electron spin resonance (ESR) spin-labeling technique, using 5- doxyl stearic acid (5-SASL) as a probe. Changes in the fluidity of gill membranes were analyzed by incorporating 5-SASL into vesicles made from total gill phospholipid (PL). Membrane fluidity measurements showed that cold-acclimated scallop membranes were more fluid than those of wann-acclimated animals. However, the order parameter of 5-SASL was greatest during the first six days of the reduction in temperature, indicating a more rigid gill membrane structure. The fluidity of gill and hemocyte membranes were negatively correlated with the proportion of 20:5n-3 (r = -0.714, P < 0.001, n = 24) and the unsaturated to saturated fetty acid ratio (r = -0.775, P < 0.05, n =8) respectively in the lipids of these tissues. Acclimation to reduced temperature for a prolonged period resulted in an increase in polyunsaturated fatty acid and a decrease in monounsaturated fatty acid content, in particular 20:5n-3 and Qq monoenoic fatty acids. Maximum changes in PL fatty acid levels required 15-21 days following acclimation to 5°C. Scallop gill and hemocyte membranes underwent progressive changes in their membrane fluidity and fatty acid composition, an observation which is consistent with homeoviscous adaptation following a reduction in acclimation temperature.
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