A liquid medium-based protocol for rapid regeneration from embryogenic soybean cultures

Soybean [Glycine max (L.) Merrill] somatic embryos of the cultivar Jack underwent histodifferentiation in liquid Murashige and Skoog (MS) medium with 3% maltose, or according to the standard published procedure employing solidified MS media, permitting the recovery of an average of 8.1 and 3.9 embryos/mg of embryogenic tissue, respectively. Cotyledon-stage embryos that developed in liquid medium were ready for desiccation within 4 weeks, while the embryos from the standard procedure required a maturation step for an additional 4 weeks. Comparison of embryo development in MS medium with maltose or FN Lite-based medium without growth regulators and supplemented with maltose or an equimolar amount of sucrose revealed that sucrose promotes faster embryo histodifferentiation and maturation, and allows the recovery of up to 50% more mature, cotyledon-stage embryos within 3 weeks. The use of this liquid-medium-based protocol relative to the standard procedure led to a fourfold increase in the number of cotyledon-stage embryos recovered from other genotypes tested. In many cases, however, the percent germination was lower. Application of this new procedure also made it possible to harvest transgenic seed 9 months following biolistic bombardment, as compared to the 13 months required when the standard solid-medium-based protocol was used.