Embryogenesis In Pteridophytes

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In Botany , the embryogenesis in pteridophytes is the set of processes physiological leading to the transformation of a single cell, the zygote , in an individual known as complex multicellular sporophyte of pteridophytes (group of plants including ferns). This whole process requires a fine regulation of many elements of development , leading to the development of basic morphologies ( morphogenesis ), the establishment of functionally organized structures ( organogenesis ) and differentiation tissue.
In pteridophytes the male gametes are mobile, pesentan cilia or other appendages to move, so the presence of water is essential for the occurrence of fertilization . The male gametes move to the archegonia and find their way through the neck, and penetrate the egg cell to form the egg cell or zygote.

The first division of the zygote can be horizontal or longitudinal to the axis of the archegonium. In the first case, the embryos can be exoscópicos , if the shoot apex is directed outward (as in Psilotum , Tmesipteris , Equisetum , and some Ophioglossaceae ), or endoscopic , if the shoot apex is directed towards the bottom ...
... of the sporangium . If the division is longitudinal, however, the embryos may have jock , a set of sterile cells that pushes the embryo proper inward (as in Lycopodium , Selaginella , and some members of Marattiaceae ) or not ( Isoetes , some other Marattiaceae and Ophioglossaceae ). If the first division is vertical, the shoot apex grows laterally with respect to the axis of archegonium, and has no hanger (as in the ferns leptosporangiados ).
Usually the embryo of the pteridophytes has three parts: a foot (the portion attached to the prothallus ), the shoot apex and the first root . The embryo is not bipolar like seed plants ( spermatophytes ).

In botany , the embryo is a miniature seedling dormancy or torpor. Is generally formed as a result of fertilization of the oosphere . The double fertilization of angiosperms results in the development of the embryo and endosperm , which is the nutritive tissue of the embryo during germination .
The embryo is formed by the radicle directed towards the micropyle , the hypocotyl which is a short stem, the cotyledons are the first leaves and the plumule or gemmule which is the shoot apex and sometimes some leaf primordia.
In pteridophytes the embryo is unipolar: it only sets the growth pole for the stem, since the roots are adventitious. In contrast, in the spermatophytes , the embryo is bipolar develops a center stem, and at the other, the root . In gymnosperms the embryo usually develops two to several cotyledons, two in the case of Ginkgo and 5 to 18 in the case of Pinus . In the dicot has two cotyledons which may have different appearance, foliaceous as in the pumpkin and castor , fleshy and in peanuts and peas , with the ends twisted as in the tomato , folded in various ways, characteristic for each genus or family. In monocots the embryo has a single cotyledon: its lateral position is, like that of the plumule.

The embryo develops from the zygote. The set of processes physiological leading to the transformation of a single cell, the zygote , in an individual-the more complex multicellular embryo - contained in the seed matures is called embryogenesis . Requires fine regulation of many elements of development , leading to the development of basic morphologies ( morphogenesis ), the establishment of functionally organized structures ( organogenesis ) and differentiation tissue. Furthermore, it must generate the elementary structures of active growth in modular systems that are plants, ie, meristems , and the functions necessary for the subsequent survival of the embryos , such as quiescence and germination . 1
As a model organism of plant physiologists have used the small crucifer Arabidopsis thaliana , which has been widely studied embryogenesis and compartmentalized in conceptual stages: 1
State of the zygote. Initial results from the fusion of oosphere with one of the generative nuclei of the pollen grain .
Globular state. Status of eight cells generated after the first zygotic division asymmetrical.
State cordate. The one where they differentiate actively dividing two places, which will be the future cotyledons.
State torpedo. Because cell elongation in the longitudinal axis of the embryo and by expansion of the cotyledons.
Mature state. After the loss of water and initiation of a quiescent state.

In Botany , the endodermis is a layer of cells of the root , so arranged compact, parenchymatous appearance and is in the innermost part of the cortex , around the vascular tissue. The cells that form the endodermis contain a substance called suberin , which modifies the permeability of the membrane, which allows the plant "filter" the water that enters the vascular tissue. Suberin is available as a band covering four of the six faces of the cell, and is known as Casparian band . Suberin is available across the layer of cells forming the band in the outer part and via apoplast is bounded free space of the root. Thus, water can only flow towards the center of the root through the endodermis. Caspary The band starts with: 2 1) the deposition of films of phenolic substances and fats in the middle lamella between the radial walls of the cells. 2) The primary wall is embedded. 3) The wall thickness increases by the deposition of substances on the inner side. 4) The plasma membrane is tightly bound to the band, forming a barrier that prevents the soil solution to pass through the apoplast, forcing it through the cytoplasm which is selectively permeable (symplast).
The endodermis divides the root apoplast into two compartments, which is very suitable for selective movement of minerals and water. Ions in soil solution can diffuse freely throughout the cortex, but can not cross the Casparian band. To enter the vascular cylinder, ie the transpiration stream must cross the plasma membrane of endodermal cell, and the plant controls which ions pass and what ions are excluded. 2
When growth occurs secondary to the formation of periderm deep, the endodermis is separated from the root cortex. When the periderm is formed on the surface, the endodermis is stretched and squashed or will accommodate the expansion of the vascular cylinder by anticlinal divisions.

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