Chloroplast Phospholipid Molecular Species Alterations during Low Temperature Acclimation in Dunaliella

The alterations in chloroplast phospholipid acyl chain composition and phospholipid molecular species composition of Dunaliella salina (UTEX 1644) were monitored during acclimation to low temperature. Chlorophyll fluorescence yield, an indicator of chloroplast membrane stability, was used as a physical means of following the acclimation process.Minor alterations in phospholipid acyl chain composition were evident within 36 hours of shifting the cells from 30 to 12 degrees C. Between 36 and 60 hours, pronounced changes in the acyl chain composition of phosphatidylglycerol (PG) were observed. Changes in the acyl chain composition of phosphatidylcholine (PC) did not occur until sometime after 60 hours.Alterations in the phospholipid molecular species during acclimation were also examined. The pattern of change observed in PC molecular species, namely a decrease in species having one saturated chain (16:0) paired with a C(18) acyl chain and a concomitant increase in species having two unsaturated C(18) acyl chains, suggests that molecular species changes augment fatty acid compositional changes as a mean of adapting to low temperature. The molecular species of PG were found to change abruptly between 36 and 60 hours following a shift to low temperature. During this time, a dramatic alteration in the threshold temperature of thermal denaturation of the photosynthetic apparatus, as measured by chlorophyll fluorescence, also occurred. Lipid compositional changes other than those associated with PG were negligible during this time. This strongly suggests that a correlation exists between the molecular species composition of PG and the thermal stability of the photosynthetic membrane.