Effect of Low Temperature upon Lipid and Fatty Acid Composition of Roots and Leaves of Winter Rape Plants

When winter rape plants were transferred from favourable temperature conditions (25/20°C day/night temperature) to 5°C, the frost resistance of the leaves was increased whereas the frost tolerance of the roots remained unaffected. This permitted an analysis of the changes in lipid and fatty acid composition both as related to functioning of the plant at low temperature alone (roots) and as related to adaptation to freezing and functioning at low temperature (leaves). — Transfer of the plants to 5°C lead to an increase in the level of linolenic acid in roots and leaves. This increase was most evident in the phosphatidyl choline and ethanolamine fractions of the leaves, and in the neutral lipids and in an unidentified phospholipid from the roots. It was concluded that upon transfer of the plants to 5°C a general and non-specific increase in linolenic acid level contributed to functioning of the rape plants at low temperature; and that parallel but minor increases in linolenic acid level of digalactosyl diglyceride, phosphatidyl inositol and the unknown phospholipid in roots and leaves could only contribute to low-temperature functioning in specific membrane enzyme locations. Combined adaptation of the leaves to freezing tolerance and low-temperature functioning was correlated with a higher level of phosphatidyl choline and ethanolamine, predominantly esterified with linolenic acid.