Improvement of soybean somatic embryo development and maturation by abscisic acid treatment

Recovery of tissue culture-derived plants through somatic embryogenesis is a useful system for genetic engineering of soybean. The effect of abscisic acid (ABA) on soybean somatic embryogenesis, development, and maturation was investigated. ABA at 1, 10, 50, 100, and 500 µM were applied at different stages of embryo development; namely, at the globular stage in suspension culture, at the development stage and at the maturation stage on solid media. ABA promoted embryo growth and development when applied at the globular stage. Embryo size, after 15 d and after 1 mo on development medium, was significantly greater than that without exposure to ABA. ABA promoted normal embryo morphogenesis and 62% more normal embryos developed when embryos were treated with ABA at the globular stage. ABA treated-embryos showed an increased tolerance to partial desiccation (from 24% to 78%) and exhibited an increased germination capability relative to non-ABA-treated controls (54% versus 8%). Somatic embryos appeared to undergo a decreasing sensitivity to ABA during maturation. ABA did not show an effect when applied during embryo development and maturation stages. A protocol for more normal embryo formation and improved embryo germination is reported. Key words: Glycine max, somatic embryogenesis, in vitro culture