LIPID-CONTENT AND COMPOSITION OF SOYBEAN SOMATIC EMBRYOS

The extent of morphological similarity between soybean [Glycine max (L.) Merr.] somatic embryos and immature zygotic embryos is often correlated with their ability to germinate and has been used to estimate somatic embryo quality. Biochemical markers, such as the accumulation of seed storage proteins or lipids, offer more objective means of assessing embryo quality than morphological traits alone. The influence of various somatic embryo induction and maturation media on the accumulation and composition of seed storage lipids was determined. Mean lipid concentrations in somatic embryos ranged from 2.4 to 40.3 g kg-1 dry weight and were always much lower than those measured in mature seed (184.6 g kg-1 dry weight). Prior to transfer to maturation media, somatic embryos had significantly higher levels of palmitic acid and linolenic acid than mature seed, but lower levels of oleic acid and linoleic acid than were in the mature seed. Reducing or completely removing auxin during maturation increased germination and also increased the similarity between the lipid compositions of somatic embryos and mature seeds, suggesting that lipid composition may have potential as a diagnostic marker of somatic embryo quality. Differences between somatic embryo axis and cotyledon lipid compositions were identified; however, the differences between the lipid compositions of somatic and zygotic embryos were not fully explained by differences in the relative contribution of axis and cotyledon tissues.