Plant embryogenesis
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226076844
2008-07-16T18:51:39Z
BotKung
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{{Refimprove|date=April 2008}}
'''Plant embryogenesis''' refers to the process of development of plant embryos, being either a sexual or asexual reproductive process that forms new plants. [[Embryogenesis]] may occur naturally in the plant as a result of sexual fertilization, and these embryos are called ''[[Zygote|zygotic embryos]]'' and develop into [[seed]]s, which can germinate and give rise to seedlings. Plant cells can also be induced to form embryos in [[plant tissue culture]]; these embryos are called ''[[Somatic|somatic embryos]]''.
An embryo is made up of actively growing [[Cell (biology)|cells]] and the term is normally used to describe the early formation of tissue in the first stages of growth. It can refer to different stages of the [[sporophyte]] and [[gametophyte]] plant.
In both [[gymnosperm]]s and [[angiosperm]]s, the young plant contained in the seed, begins as a developing egg-cell formed after [[fertilization]] (sometimes without fertilization in a process called [[apomixis]]) and becomes a plant embryo.
This embryonic condition also occurs in the [[bud]]s that form on [[Plant stem|stem]]s. The buds have tissue that has differentiated but not grown into complete structures. They can be in a resting state over winter or when conditions are dry, and then commence growth when conditions become suitable. Before they start growing into stem, leaves, or flowers, the buds are said to be in an embryonic state.
==Zygotic embryogenesis==
The zygotic embryo is formed following double [[fertilisation]] of the ovule, forming the plant embryo and the [[endosperm]] which together go on to develop into a seed. Seeds may also develop without fertilization through pathways referred to as [[apomixis]].
==Somatic embryogenesis==
Somatic embryos are formed from plant cells that are not normally involved in the development of embryos, i.e. ordinary plant tissue. No endosperm or seed coat is formed around a somatic embryo. Applications of this process include: clonal propagation of genetically uniform plant material; elimination of viruses; provision of source tissue for genetic transformation; generation of whole plants from single cells called [[protoplast]]s; development of [[synthetic seed]] technology. Cells derived from competent source tissue are cultured to form an undifferentiated mass of cells called a [[callus (cell biology)|callus]]. [[Plant growth regulators]] in the tissue culture medium can be manipulated to induce callus formation and subsequently changed to induce embryos to form from the callus. The ratio of different plant growth regulators required to induce callus or embryo formation varies with the type of plant.<ref>http://www.accessexcellence.org/LC/ST/st2bgplant.html ''Plant Tissue Culture''</ref>
==The stages of embryogenesis==
Zygotic and somatic embryos share a number of characteristic developmental stages; however, the very early steps in their development are not well correlated.
Following fertilization, the zygote undergoes an asymmetrical [[cell division]] that gives rise to a small apical cell that becomes the embryo and a large basal cell (called the suspensor) that functions to provide nutrients from the endosperm to the growing embryo. Asymmetrical cell division also seems to be important in the development of somatic embryos, and while failure to form the suspensor cell is lethal to zygotic embryos, it is not lethal for somatic embryos. From the eight cell stage (octant) in the zygotic embryo, 'embryo patterning' is apparent; however, somatic embryos at this stage may be quite variable, therefore zygotic and somatic embryos become most comparable from the '''globular''' stage.
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 [[cotyledon]]s 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.
==Notes and references==
{{reflist}}
[[Category:Embryology]]
[[Category:Plant reproduction]]
[[es:Embriogénesis vegetal]]
[[th:การเจริญของเอ็มบริโอในพืช]]