Immature soybean (Glycine max (L.) Merr) embryos, or cotyledons isolated from them, were cultured on modified MS medium containing B5 vitamins and NAA (50 #M) to induce somatic embryogenesis. The effects of media variables, dissection treatments and light conditions were investigated in this system. The efficiency of embryogenesis increased as sugar concentration decreased from 12 to 1.5%; sucrose and glucose were similarly effective as carbon sources. In an examination of the effects of medium pH, values between pH 5.0 and 7.0 gave similar embryogenesis efficiencies, but the frequency of normal embryos was greater in media with low pH values. In buffered medium (10raM MES), a pH of 5.0 was inhibitory to embryogenesis, and most normal embryos were produced at pH 5.5. Under various dissection treatments, embryogenesis efficiency and root and callus production were increased by tissue damage. Somatic embryogenesis was observed both in darkness and in light, although embryo development was impaired under high light (80 pE m-2 S-I) conditions. The ability of somatic embryos to germinate was closely correlated with embryo normality, and was influenced little by the hormone content of germination media. Of various media tested for their ability to support the growth of germinated embryos, a medium based on hydroponic nutrient salts, supplemented with yeast extract, and gelled with Difco-Bacto agar gave the best plantlet growth.
Abbreviations. #E m -2 s-', microEinsteins per square meter per second; NAA, ct-napthalene acetic acid; N50, MS salts with B5 vitamins and 50 #M NAA (Napthalene acetic acid); MES, 2(n-morpholino) ethanesulphuric acid; BAP, benzytamino purine; IBA, indole butyric acid.