AUXIN-REGULATED CHANGES OF FATTY-ACID CONTENT AND COMPOSITION IN SOYBEAN ZYGOTIC EMBRYO COTYLEDONS

The present studies were conducted to investigate the effect of exogen ous auxins on zygotic embryo fatty acid content and lipid composition during somatic embryo induction. Immature soybean (Glycine max (L.) Me rr.) cotyledons from two developmental stages were cultured on 2,4-dic hlorophenoxyacetic acid (2,4-D) or alpha-naphthaleneacetic acid (NAA). The presence of 2,4-D or NAA in the medium altered the content and pe rcentage of oleic (18:1), linoleic (18:2) and linolenic (18:3) acids, with less effects on stearic (18:0), palmitic (16:0) or total fatty ac ids in the embryonic cotyledons. Desaturation assays with radiolabelle d fatty acids showed that 2,4-D increased both the ratios of 18:2 to 1 8:1 and 18:3 to 18:2. NAA at 10 mg/l resulted in an increase in the co ntent and percentage of 18:3 but not that of 18:2 in the embryonic cot yledons. Analysis of free fatty acids, triglycerides, phosphatidylchol ine, phosphatidylethanolamine, and glyco lipids (monogalactosyldiacylg lycerol and digalactosyldiacylglycerol) revealed that the increased ra tio of 18:3 to 18:2 occurred in phosphatidylcholine, triglycerides and free fatty acids, but not in glycolipids. Our data suggest that 2,4-D increased the efficiency of the desaturation related processes in ext ra plastidial compartments.