Somatic embryogenesis and plant regeneration from suspension cultures of switchgrass

Embryogenic cell suspension cultures represent an enhanced culture type for the selection of mutants, mass propagation, direct delivery of DNA into intact regenerable cells and isolation of totipotent protoplasts, The objectives of this study with switchgrass (Panicum virgatum L.) were to establish embryogenic suspension cultures and to regenerate plants from these cultures. The cultures were initiated from embryogenic callus obtained from young inflorescences. They mere maintained in Murashige and Skoog liquid medium containing 9.0 mu M 2,4-dichlorophenoxyacetic acid (2,4-D), 4.4 mu M 6-benzylaminopurine (BAP) and 30 g L-1 maltose. The suspension was passed through a 210-mu m mesh and was comprised mainly of small, round densely cytoplasmic starch containing cells with distinct nuclei, Somatic embryos developed from these cells directly and were free floating in the medium. A sequence of developmental stages from embryogenic cells to fully developed embryos was observed in the cultures. The embryos had the typical morphology of a grass embryo. Embryogenic calluses were also obtained 4 wk after the suspension was plated onto solid medium containing various combinations of 2,4-D and BAP, Embryos from suspension and suspension-derived callus cultures germinated to produce plants that were successfully established in the greenhouse.