(embryogenesis, embry-ony) The development of an embryo, normally from a fertilized egg cell. The first divisions of the zygote are at right angles to the long axis of the archego-nium or embryo sac. In angiosperms and in some gymnosperms and pteridophytes these initial divisions give rise to a chain of cells, the * suspensor. The embryo proper develops from a large cell at the. tip of the suspensor at the end furthest from the micropyle. The pattern of embryo development differs markedly between groups of plants but normally globular, heart-shaped, and torpedo-shaped stages can be recognized. Embryogeny often lags behind the development of other parts of the seed so the embryo may grow at the expense of the previously formed endosperm. Certain cells of the embryo may be polyploid if DNA synthesis outstrips nuclear division. The term embryogenesis is also applied to the development of embryos from diploid somatic cells in suspension cultures. This phenomenon has been described in a number of angiosperm species and demonstrates the * totipotency of cells when removed from the inhibiting influences of the plant body. Such nonzygotic embryos are often termed embryoids to distinguish them from zygotic embryos. However they closely resemble zygotic embryos in their development and if transferred to suitable culture conditions may give rise to normal plants. Embryoids can also be induced to form from pollen grains and subsequently may develop into haploid plants. See also adventive embryony , endoscopic embryogeny , exoscopic embryogeny. |
