The invention relates generally to methods and compositions concerning desaturase enzymes that modulate the number and location of double bonds in long chain poly-unsaturated fatty acids (LC-PUFA's). In particular, the invention relates to methods and compositions for improving omega-3 fatty acid profiles in plant products and parts using desaturase enzymes and nucleic acids encoding for such enzymes. In particular embodiments, the desaturase enzymes are Primula .DELTA.6-desaturases. Also provided are improved soybean oil compositions having SDA and a beneficial overall content of omega-3 fatty acids relative to omega-6 fatty acids.