High frequency conversion of microspore-derived embryos of Brassica napus cv. topas by supplemental calcium and vitamins

Efficient and simple protocols were developed for conversion of embryos derived from microspores in rape. The frequency of embryo conversion was higher than 80% on improved media without pretreatments using ABA, GA3 or desiccation, which had been required before embryos were transferred to solid media for conversion. While on basal media such as 1/2MS, the conversion frequency was no more than 32%. Two groups of embryos at different developmental stages, 7 mm embryos and 3 mm embryos, were used as material to select the most suitable medium. Different components were required for successful conversion of the two groups of embryos. For 7 mm embryos 1/2MS medium with Ca2+ concentration of 900 mg l−1 was optimal, while for 3 mm embryos, 1/2 MSN+V+Ca (half strength MS with 450 mg l−1 CaCl2·2H2O, 100 mg l−1 NH4NO3 and enhanced vitamins) was a suitable medium. The results indicate that calcium may play an important role in the conversion of embryos derived from microspores, and can replace, to some extent, the practice of drying and growth supplements, which have been widely used for maturation, and desiccation of embryos.