Composition of embryogenic suspension cultures of Ipomoea batatas Poir. and production of individualized embryos

Embryogenic suspension cultures of Ipomoea batatas Poir. contain heterogeneous populations of discrete cellular units. In order to optimize embryo production, a study was conducted to identify the embryogenic fraction of such cultures. Suspension cultures were fractionated with sieves of 1000, 710, 500, 355, 250, 180, 125, 90 and 63μm mesh openings and the composition of each fraction was determined. Cellular units larger than 355 μm were primarily calli and made up 75% of the total mass of cultures in the stationary phase of growth. These calli were composed of embryogenic and non-embryogenic subunits, and 98% of the embryogenic subunits measured 355–1000 μm. Calli and embryogenic calli subunits produced clusters of embryos at various stages of development upon transfer to liquid or solidified media without 2,4-D. The 125–355 μm fraction of suspension cultures was composed of cell aggregates of which 20% were embryogenic. The embryogenic cell aggregates produced single globular embryos upon transfer to liquid media containing 0 or 1 μM 2,4-D. The 63–125 μm fraction of suspension cultures contained only 2% of embryogenic cell aggregates. It can be inferred from our results that the embryogenic fraction of cultures was essentially represented in calli, and that proliferation of the embryogenic fraction occurred through the separation of embryogenic cell aggregates from larger calli when cultures approached their stationary growth phase.