Effect ofIn OvuloPeriod on the Differentiation and Regulation of Immature Embryos ofZamiaCulturedIn Vitro

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Abstract
Monnier, M. and Norstog, K. 1986. Effect of in ovulo period on the differentiation and regulation of immature embryos of Zamia cultured in vitro—J. exp. Bot. 37: 1633–1642. Depending upon excision chronology, undifferentiated embryos of the cycad Zamia exhibited two types of development when cultured in vitro. (1) Early embryos, excised in July shortly after fertilization, showed considerable growth of suspensors but, at first, the embryos at the distal ends of the suspensors remained unchanged. As culture progressed, these embryos grew isodiametncally without organogenesis. (2) Late embryos, excised in September, although also undifferentiated at the time of explantation, directly entered a period of organogenesis with rapid initiation of two cotyledons. These embryos, therefore, seemed to have received an inductive stimulus during their more prolonged stay in the ovule which permitted subsequent differentiation. This organogenetic impulse was also expressed even when the embryo was longitudinally bisected. Each half-embryo regenerated a complete embryo having two cotyledons. In this instance, the independent development of each half-embryo was a phenomenon of regulation. However, when the longitudinal bisection was done on an old and well-differentiated embryo, which already possessed two cotyledons, each half-embryo continued to develop as if it remained attached to the missing half. Thus well-advanced embryos did not exhibit regulation to the same degree as do younger embryos and bisection of the embryo resulted in the formation of two half-embryos.