Abstract:The composition of molecular species and the positional distribution in fatty acids of phosphatidylglycerol (PG) isolated from poplar ( Populus deltoides cv. Lux 1-69/55 and Poeuramericarla cv.I- 45/51 ) leaves were analyzed by high-performance liquid chromatography (HPLC), enzym hydrolysis and gas phase chromatography (C,C), and the different cold-resistant poplars were compared with respect to the compositions of molecular species of PG isolated from their leaves. The results showed that the fatty acid compositions ( sn- 1/sn-2) of the major molecular species in PCs from poplar leaves were as follows: 18:3/18:2(18:2/18:3), 18:3/16: 1(3t); 18:3/16:0; 18:2/ 16:1 (3t); 16:0/18:2,18:2/16:0; 18: 1/16: l(3t); 16:0/16: l(3t); 18: 1/18: 1,16:0/18: 1( 18: 1/16:0); 16:0/16:0o The positional distribution of fatty acids in lPG from poplar leaves was found that 16:1(30 was exclusively occupied the sn-2 position, whereas 16:0 was present in both the sn1 position and the sn-2 position. The C18 acids were principally localized at the sn-2 position. The relative contents of the unsaturated molecular species of leaf PCs were more than 70% in both coldresistant poplar and cold-sensitive poplar. The ratio of the unsaturated/saturated molecular species of PG isolated from the cold-resistant Ⅰ -45 poplar was 3.10, which was higher than that of the PG from the cold-sensitive cottonwood, which was 2.38. The sum of the relative contents of the disaturated molecular species of the PG from poplar leaves was closely associated with the cold-resistance of plants. The ∑[ 16:0/16:0+ 16:0/16: l(3t) ] of the PG from cottonwood was higher than that of the PG from cold-resistant I -45 poplar. The differences in the compositions of molecular species and the phase transition temperatures of PCs between cold-resistant and cold-sensitive plants were discussed in terms of the pathways and the activities of selective acyhransferases involved in the PG biosynthesis in chloroplast.