Soybean somatic embryo maturation: composition, respiration and water relations

Abstract

AbstractEmbryogenesis was induced on cotyledons of immature zygotic embryos of soybean (Glycine max(L.) Merrill) placed on solid medium containing 62.5 mmglutamine, soybean seed growth medium salts and vitamins, and 40 mg I−12,4-dichlorophenoxyacetic acid (2,4-D) plus 175 mmmaltose, or 8 mg I−1α-naphthaleneacetic acid (NAA) plus 88 mM sucrose. Somatic embryo development was continued in liquid medium containing 0.16 mg I−1indole-3-butyric acid and 2.64 mg I−1abscisic acid, glutamine and salts as above, and 88–438 mM sucrose in progressively increasing steps. Germination was on solid half-strength Murashige-Skoog medium. During maturation, somatic embryos mimicked zygotic embryos in colour, protein concentration, water and solute potentials, and respiration. Protein and lipid accumulated to 329 and 86 g kg−1dry weight in somatic embryos. Fatty acid composition was similar to that of axes of mature seeds. Before desiccation, the water and solute potentials of maturing somatic embryos declined to −1.13 and −1.99 MPa while turgor increased to 0.86 MPa. Concomitantly, a 60% reduction in activity of the cytochrome oxidase pathway of respiration occurred with somatic embryo maturation at 600 g water kg−1fresh weight. Although small (about 8 mg per embryo), 60% of the somatic embryos formed roots and shoots during germination after maturation without drying and 30% germinated after drying to 60 g water kg−1fresh weight. In the greenhouse, somatic plantlets grew to mature plants with seeds.