Modern diets are often deficient in omega-3 fatty acids and additional dietary sources of omega-3 fatty acids are useful. In order to investigate the molecular basis of the high accumulation of the omega-3 fatty acid, alpha-linolenic acid (18:3), in three different plants, flax (Linum usitatissimum), Dracocephalum moldavica, and Perilla frutescens omega-3 desaturase activity, transcript levels, and 18:3 in-vivo synthesis were examined. The 18:3 content was found to be higher at the later developmental stage of D. moldavica (68%) compared with P. frutescens (59%) and flax (45%) cotyledons. The 18:3 and 18:2 contents in both PC and TAG were determined during various stages of seed development for all three plants in addition to soybean (Glycine max). Northern blot analysis data of three different stages of D. moldavica, flax, and P. frutescens compared with moderately low 18:3 producers, soybean (Glycine max), and Arabidopsis thaliana and Brassica napus, (8-10% 18:3) at a stage of zygotic embryo development of high triglyceride synthesis showed that omega-3 desaturase mRNA levels were higher in all three high 18:3 producers, flax, D. moldavica and P. frutescens. This indicates that the high level of alpha-linolenic acid in TAG may be largely controlled by the level of omega-3 desaturase gene expression. However, the PC versus TAG fatty acid composition data suggested that along with omega-3 desaturase other enzymes also play a role in 18:3 accumulation in TAG, and the high accumulators have a selective transfer of alpha-linolenic acid into TAG.