EFFECTS OF TEMPERATURE ON THE MEMBRANES OF DUNALIELLA SALINA

Alterations in the lipid composition of chloroplast and microsomal membrane fractions isolated from the wall-less unicellular green alga Dunaliella salina were monitored during acclimation to low temperature.; Significant changes in the acyl chain compositions of individual phospholipids of the microsomal membranes were observed within 12 hr following a shift in growth temperature from 30(DEGREES)C to 12(DEGREES)C. These rapid changes did not entail enhanced desaturation of linoleic acid, although the proportion of linolenic acid increased during later stages of acclimation.; The phospholipid molecular species were analyzed by capillary column gas chromatography. This permitted the recognition of structural and metabolic relationships not revealed by usual lipid analytical techniques. The most immediate changes following a shift to low temperature were limited to several molecular species. These rapid changes, as well as further retailoring of molecular species during acclimation, resulted in an increase in the number of species having two unsaturated acyl chains and did not reflect a simple enhancement of desaturase activity.; The lipid composition of the chloroplast fraction was less rapidly altered by low temperature. Although the relative proportions of the galactolipid classes changed progressively during acclimation, minimal changes in the acyl chain composition within any one lipid class were observed. More pronounced changes were associated with the phospholipid acyl chains.; During acclimation abrupt changes in the molecular species of phosphatidylglycerol occurred concurrently with a dramatic alteration in the threshold temperature of thermal denaturation of the photosynthetic apparatus, as measured by chlorophyll fluorescence.; The results demonstrate that Dunaliella is well suited as a model for plant membrane lipid studies. Changes in the phospholipid molecular species compositions of both membrane fractions following acclimation to low temperature would appear to augment acyl chain desaturation as a means of modifying membrane properties in response to low temperature stress. Such observations are of interest in light of recent evidence suggesting that the physical properties of plant membranes may be influenced by structural parameters of the lipids other than acyl chain composition per se. The results also suggest an important role for the molecular species of phosphatidylglycerol in modulating the thermal stability of the photosynthetic apparatus.