BIOCHEMICAL-CHARACTERIZATION OF TEMPERATURE-INDUCED CHANGES IN LIPID-METABOLISM IN A HIGH OLEIC-ACID MUTANT OF BRASSICA-RAPA

We have characterized a Brassica rapa mutant (WR586) that has low leve ls of polyunsaturated fatty acids (D. L. Auld et al., 1992, Crop Sci. 32, 657-662). The mutant lacked oleoyl-phosphatidylcholine desaturase (ODS) activity when assayed in 6-day-old seedlings. To further charact erize the mutant, the leaf fatty acid composition and major galactolip ids and phospholipids were characterized in mutant (WR586) and control (cultivar ''Tobin'') plants grown at either 26 degrees C/26 degrees C or 10 degrees C/5 degrees C. Fatty acid profiles show significantly h igher 18:1 levels in WR586 throughout 12 days of germination. The amou nt of saturated fatty acids decreased with a concomitant increase of 1 8:1. Ratios of 18:1/18:2 revealed that WR586 maintains higher mole per cent of 18:1 than Tobin at all times and temperature regimes because o f a lack of desaturation to 18:2. Values for monogalactosyldiacylglyce rol and digalactosyldiacylglycerol 18:1/18:2 ratios indicate a dispari ty in the concentration of 18:1 between WR586 and Tobin grown in eithe r temperature during early germination. The phosphatidylcholine and ph osphatidylethanolamine 18:1/18:2 ratios were higher in WR586 compared to Tobin and remained higher throughout the 12-day period. In WR586, 1 8:1 always accumulated to higher levels in the cooler temperature. In Tobin, 18:1 concentrations paralleled 18:2 in both temperature regimes . These results indicate that the lesion in the mutant WR586 resides a t the ODS locus, 18:1 synthesis is chilling induced, and the microsoma l desaturation pathway is the most prominent in early developing Brass ica seedlings. (C) 1994 Academic Press, Inc.