Influence of Warm-Acclimation Rate on Polar Lipids of Ulva lactuca

Abstract

An ability of marine macroalgae Ulva lactuca (L.) to adapt membrane lipid matrix to elevated seawater temperature depending on rate of warm acclimation was studied. Plants were collected in the Peter the Great Gulf of the Sea of Japan in winter at 4°С and acclimated to summer temperature (20°С) at different rates: 16 or 2°С/day. The fatty acid composition and the crystal – liquid crystal thermal transition of glycolipids (monogalactosyl diacylglycerol, digalactosyl diacylglycerol, sulfoquinovosyl diacylglycerol) and betaine lipid 1,2-diacylglycero-O-4'-(N,N,N-tri-methyl)-homoserine (DGTS) from U. lactuca were investigated by GLC, HPLC-MS and differential scanning calorimetry, respectively. The dependence of the results of temperature acclimation on its rate was shown. Thus, rapid warm acclimation induced the decrease of the ratios of n-3/n-6 polyunsaturated fatty acids and unsaturated/saturated fatty acids, as well as the unsaturation index of fatty acid composition of lipids, which corresponded to seasonal changes. However, this trend did not retain, or even reverse changes occurred at lower warming rate. Redistribution of the composition of molecular forms of glycolipids in acclimated algae led not only to maintain the peak maximum temperature of thermal transition (Tmax), but also to phase separation of glycolipids. This contributed to the fit of the thermogram profiles to those of summer samples. The calorimetric transition of DGTS was most effectively changed: even with rapid acclimation, the Tmax value of the summer sample was reached. In general, U. lactuca showed the ability to adapt lipid matrix of membranes at different rates of warming seawater.