Fatty acid desaturation in monogalactosyldiacylglycerol of Brassica napus leaves during low temperature acclimation

Brassica napus plants grown at 5°C have the potential to desaturate fatty acids in the major membrane diacylglycerols of leaves at rates much higher than those of plants grown at 30°C. This low temperature-induced desaturation (LTD) is rapidly deactivated if plants grown at 5°C are transferred to 30°C for several hours. By exposure to ¹⁴CO₂ and a computer simulation program, we estimated the rate of desaturation of monogalactosyldiacylglycerol by (ω9-, ω6- and ω3-desaturases of plants grown at 5, 10, 20 and 30°C. Data show that LTD can be induced in mature leaves of plants grown at 20 and 30°C after transfer to 5°C. Full activation of LTD takes several weeks and occurs more rapidly in plants grown at 20°C than 30°C. This activation is largely due to the increased activity of ω9- and ω6-desaturases on C16 fatty acids and ω6-desaturase on C18 fatty acids.