Somatic embryogenesis from leaf callus of mature plants of the gymnospermCeratozamia mexicana var. robusta (Miq.) dyer (Cycadales)

Summary Embryogenic callus was induced from explanted pinnae of newly emerged leaves of mature plants ofCeratozamia mexicana var. Robusta (Gymnospermae, Cycadales) on a modified B5 formulation with 1 mg·liter⁻¹ kinetin and 1 mg·liter⁻¹ 2,4-dichlorophenoxyacetic acid. Proembryos developed on induction medium, but they were more numerous after subculture onto phytohormone-free medium, which also enabled suspensors to elongate. For nearly 1.5 yr after explanting, subsequent development of somatic embryos was not observed as suspensors dedifferentiated to form embryogenic callus on phytohormone-free medium. After this time, cotyledonary somatic embryos developed at the distal end of the suspensors. Somatic embryos have germinated on phytohormone-free medium. This is the first report of regeneration by somatic embryogenesis of a gymnosperm species from a mature tree. This technique has great potential for preservation of the highly endangered cycads.