Effect of In Ovulo Period on the Differentiation and Regulation of Immature Embryos ofZamia Cultured In Vitro

Monnier, M. and Norstog, K. 1986. Effect of in ovulo periodon the differentiation and regulation of immature embryos ofZamia cultured in vitro—J. exp. Bot. 37: 1633–1642. Depending upon excision chronology, undifferentiated embryosof the cycad Zamia exhibited two types of development when culturedin vitro. (1) Early embryos, excised in July shortly after fertilization,showed considerable growth of suspensors but, at first, theembryos at the distal ends of the suspensors remained unchanged.As culture progressed, these embryos grew isodiametncally withoutorganogenesis. (2) Late embryos, excised in September, althoughalso undifferentiated at the time of explantation, directlyentered a period of organogenesis with rapid initiation of twocotyledons. These embryos, therefore, seemed to have receivedan inductive stimulus during their more prolonged stay in theovule which permitted subsequent differentiation. This organogeneticimpulse was also expressed even when the embryo was longitudinallybisected. Each half-embryo regenerated a complete embryo havingtwo cotyledons. In this instance, the independent developmentof each half-embryo was a phenomenon of regulation. However,when the longitudinal bisection was done on an old and well-differentiatedembryo, which already possessed two cotyledons, each half-embryocontinued to develop as if it remained attached to the missinghalf. Thus well-advanced embryos did not exhibit regulationto the same degree as do younger embryos and bisection of theembryo resulted in the formation of two half-embryos. Key words: Regulation, differentiation, embryo culture, Zamia