High frequency production of embryos from liquid flask cultures of oilseed rape.

As part of the program to scale-up the production of artificial seeds of winter oilseed rape, Brassica napus ssp. oleifera, we established a liquid flask culture system that enables the high frequency production of freely suspended embryos. As many as 4000 embryos could be obtained from 1 mL packed-cell-volume of cells. For initiation of liquid flask cultures, four different types of callus tissues were used. Among them, the most embryogenic cell suspension cultures were obtained from spontaneous callus developed on the surface of secondary embryos precultured in medium supplemented with 2,4-dichlorophenoxyacetic acid (4.52 microM) and kinetin (0.46 microM) (type B callus). Growth curves of the cell suspension were determined and the cell suspension was able to grow in medium without plant growth regulators. Embryos were observed to developed directly from the cells without going through an obvious callus phase. When subcultured to agar medium containing 44.38 microM benzylaminopurine, about 43% of the embryos developed into plants.