Characterization of an Embryogenic Cell Suspension Culture Derived From Cultured Inflorescences of Pennisetum Americanum (Pearl Millet, Gramineae)

An embryogenic suspension culture was established from cultured inflorescence segments of Pennisetum americanum in Murashige and Skoog's medium supplemented with 2.5 mg/1 2,4‐dichlorophenoxyacetic acid (2,4‐D) and 5% coconut milk. The suspension was composed of two major cell types: 1) small, richly cytoplasmic and starch‐containing cells, generally found in small, compact clumps, here termed embryogenic cells; and 2) elongated, thick‐walled cells with large vacuoles. By manipulating the duration of culture and dilution ratios (cell suspension: fresh medium) at the time of subculture, suspensions consisting predominantly of embryogenic cells were obtained. Suspensions grown for 2‐3 wks were transferred to agar media with reduced amounts of 2,4‐D. This resulted in the production of hundreds of globular and early cotyledonary embryoids. Further development of the embryoids was promoted by their transfer to a medium containing abscisic acid. Many of the embryoids germinated and produced normal green plants. Atypical embryoids, some containing many shoot meristems and a leafy scutellum, were also observed. The relevance of such atypical embryoids in the interpretation of organogenesis and embryogenesis reported in tissue cultures of cereal species is discussed. It is also suggested that somatic embryogenesis occurs in tissue cultures of most, if not all, species of cereals and grasses.