Changes in fatty acids of leaf polar lipids during chilling and post-chilling rewarming of Zea mays genotypes differing in response to chilling

Changes in fatty acids of leaf polar lipids: monogalactosyldiacylglycerol ( MGDG), digalactosyldiacylglycerol (DGDG), sulfoquinosyldiacylglycerol (SQDG ) and phosphatidylglycerol (PG) in maize seedlings of chiling-sensitive (CS ) CM 7 and Co 151 lines and chilling-tolerant (CT)S 215 and EP 1 lines upon chilling for either 4 or 6 days in the dark and after rewarming for 4 days at original growth conditions were studied. The content of free fatty acid s (FFA) in control leaves as well as alterations in the proportion of major fatty acids, unsaturation ratio (UR), double bond index (DBI) and changes in the proportion of heigh-temperature melting of both phosphatidylglycerol (htm-PG) and sulfoquinovosylglycerol (htm-SQDG) after chilling and rewarmi ng of seedlings were estimated. FFA content in intact leaves was 2-3-fold higher in the chilling susceptibl e CM 7 line than in the other three inbreeds studied. After chilling for 6 days the level of FFA increased only in CM 7 and S 215 Lines by about 30%. Upon rewarming seedlings chilled for 6 days the level of FFA increased abou t twofold in CS Co 151 line and CT EP 1 line and decreased in CS CM 7 line. Limited accumulation of FFAs during chilling and post-chilling rewarming o f maize seedlings, did not correspond to the extent of polar lipid breakdow n (Kaniuga et al 1999b) probably due to the contribution of active oxidativ e systems to the peroxidation of fatty acids under these conditions. During rewarming seedlings chilled for 6 days major changes were observed i n decrease of 18:3 and an increase of 16:0 in all four polar lipids studied with more pronounced changes in CS than CT lines. Similarly, in CS inbreed s a decrease in UR of fatty acids in MGDG, DGDG and SQDG after post-chillin g rewarming was greater than in CT lines. Proportion of htm-fraction in bot h PG and SQDG increased after post-chilling rewarming in all four inbreeds, however to a lesser extent in CT than CS lines. A similar pattern of chang es in DBI in CS and CT maize seedlings was observed in glycolipid and combi ne Lipid classes. More extensive degradation of polar lipids in CS than CT maize inbreeds fol lowing galactolipase action in chloroplasts (Kaniuga et al. 1998) provides FFAs for initiation of peroxidation by LOX which is manifested by decrease of UR and DBI. This sequence of reactions during chilling and post-chilling rewarming appears to be a main route of fatty acids peroxidation responsib le for secondary events involved in chilling injury. In addition, the exten t of these changes differentiates CS and CT inbreeds. Contribution of ester ified fatty acids in thylakoid lipids to direct peroxidation, may be of min or importance.