CHANGES IN POLAR LIPID FATTY-ACID COMPOSITION DURING COLD-ACCLIMATIONIN MIDIRON AND U3 BERMUDAGRASS

'Midiron' and 'U3' bermudagass were exposed to conditions known to ind uce cold acclimation [e.g., 8/4 degrees C (day/night) temperature, 10- h photoperiod, 250 mu mol m(-2) s(-1) photosynthetic photon flux densi ty (PPFD)]. Tissues (leaves, crowns, and roots) were harvested and sto red frozen until processed. Polar membrane lipids were Isolated by thi n layer chromatography, and fatty acids (FA) were separated and quanti fied by gas chromatography. Different organs from the same plant respo nded differentially to low temperature. Crowns showed the most dramati c changes in total FA content and composition and were the focus of th is study. Overall, greater than 95% of the total FA content was accoun ted for by four PA species: palmitic acid (16:0), stearic acid (18:0), linoleic acid (18:2), and linolenic acid (18:3). Midiron (relatively cold-tolerant) responded more rapidly and to a greater extent than did U3 (relatively cold-sensitive) as illustrated by the nearly four-fold increase of unsaturated FA:saturated PA ratio for Midiron vs. U3, and by the significant difference between the double bond index of the tw o genotypes. These data suggest that specific desaturase enzymes (e.g. , omega-3 and omega-6) are of fundamental importance in controlling me mbrane lipid/fatty acid composition in response to low temperature and ultimately in avoiding the winter damage suffered by bermudagrass alo ng its northern boundary of adaptation.