Seeds
Embryogenesis occurs naturally as a result of sexual fertilization and the formation of the zygotic embryos. The embryo along with other cells from the motherplant develops into the seed or the next generation, which, after germination, grows into a new plant.
Embryogenesis may be divided up into two phases, the first involves morphogenetic events which form the basic cellular pattern for the development of the shoot-root body and the primary tissue layers; it also programs the regions of meristematic tissue formation. The second phase, or postembryonic development, involves the maturation of cells, which involves cell growth and the storage of macromolecules (such as oils, starches and proteins) required as a 'food and energy supply' during germination and seedling growth. Embryogenesis involves cell growth and division, cell differentiation and programmed cellular death. The zygotic embryo is formed following double fertilisation of the ovule, giving rise to two distinct structures: the plant embryo and the endosperm which together go on to develop into a seed. Seeds may also develop without fertilization, which is referred to as apomixis. Plant cells can also be induced to form embryos in plant tissue culture; such embryos are called somatic embryos.
Following fertilization, the zygote undergoes an asymmetrical cell division that gives rise to a small apical cell, which becomes the embryo and a large basal cell (called the suspensor), which functions to provide nutrients from the endosperm to the growing embryo. From the eight cell stage (octant) onwards, the zygotic embryo shows clear embryo patterning, which forms the main axis of polarity, and the linear formation of future structures. These structures include the shoot meristem, cotyledons, hypocotyl, and the root and root meristem: they arise from specific groups of cells as the young embryo divides and their formation has been shown to be position-dependent.
In the globular stage, the embryo develops radial patterning through a series of cell divisions, with the outer layer of cells differentiating into the 'protoderm.' The globular embryo can be thought of as two layers of inner cells with distinct developmental fates; the apical layer will go on to produce cotyledons and shoot meristem, while the lower layer produces the hypocotyl and root meristem. Bilateral symmetry is apparent from the heart stage; provascular cells will also differentiate at this stage. In the subsequent torpedo and cotyledonary stages of embryogenesis, the embryo completes its growth by elongating and enlarging.
In a dicot embryo, the hypophysis, which is the uppermost cell of the suspensor, differentiates to form part of the root cap. Plant cells can also be induced to form embryos in plant tissue culture; these embryos are called somatic embryos, which are used to generate new plants from single cells.
Read more about this topic: Plant Embryogenesis
Famous quotes containing the word seeds:
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—Stephanie Martson (20th century)
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—Ernest Hemingway (1899–1961)
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—Henry David Thoreau (1817–1862)