the Cage of a green plant. A cellular wall

you are: the Cage of a green plant

Cages of plants differ from all other cages that they are concluded in rigid enough ' a case ', are as though placed in a box. About a vegetative cage it is quite possible to tell that she ' lives in a wooden case ' because the number of chemical components of a cellular wall includes also what stiffen wood peculiar to it and durability. At a mature cage the wall, obviously, represents lifeless formation - a product sekretornoj activity of a protolayer, otlagajushchijsja in the form of a number of consecutive layers at various stages of development of a cage. however in a cellular wall is available as well any quantity of fiber, including the fiber possessing fermentativnoj activity. On termination of cellular division first of all otlagaetsja the first layer-median a plate consisting in the beginning mainly from jellylike pectinaceous substances, but later infiltriruemaja more rigid cellulose, different other polisaharidami and, at last, in odrevesnevshih fabrics - ligninom.

Simultaneously with increase in volume of a cage otlagaetsja the following layer - a primary cellular wall. During the growth this primary cellular wall is under pressure from outside cellular contents as by such way it is reached both a stretching of a wall and inclusion in it of a new material.

The Stretching, to a certain extent is reversible (elasticheskim) and partially - irreversible (plastic). The primary cellular wall not only is stretched, but also utolshchaetsja; growth occurs by inclusion of new particles in already existing skeleton (intussustseptsija) and by addition to earlier postponed layers of new layers (appozitsija). In some cages, for example in mezofille, formation of a cellular wall comes to the end, as soon as the cage will reach the maximum size. In other fabrics from the interior of the primary cellular wall which have already finished the growth, otlagaetsja the secondary cellular wall having rigid structure. As the cage thus already does not grow any more, such thickening of a cellular wall reduces protolayer volume; in fibres and traheidah, for example, the cellular wall fills with itself sometimes almost all cage. In such cases the protolayer dies off; There are one only the hollow cylinders of cellular walls which are carrying out basic function or function of the spending fabric.

The Secondary cellular wall is penetrated by a numerous time. In the field of a time the cellular wall is very thin; atop

A median plate and a primary cellular wall any material more any more otlagaetsja (fig. 2.29 and 2.30). In mature live cages, for example in parenhime, a time it is simple the channels connecting an internal part of a secondary cellular wall with an external part primary. Quite often a time meets the whole groups in special thin sites of a cellular wall which carry the name porovyh fields. At coniferous in them traheidah, representing in a mature condition dead cages, a secondary cellular wall hangs over a cavity of a time in the form of a flange, or a bordering; a primary time serving here by a closing film, has linzoobraznoe a thickening, so-called torus. In spending system of a tree such bordered time can play a role of delivery valves as under the influence of pressure difference torus it is displaced and, densely nestling on bordering edges, completely isolates a cage from its environment.

The Cellular wall (secondary and primary) is penetrated also by apertures through which pass cytoplasmatic tjazhi, or plazmodesmy. Protolayers of the next cages communicate these tjazhami in a single whole - simplast. More low we will show that simplast plays the important role as one of ways for transport of materials.

Cellulose fibres form a skeleton both primary, and a secondary cellular wall. Cellulose is the huge polymer consisting of chains collected in bunches gljukana, each of which in turn represents polymer of six-carbon sugar of glucose (fig. 5.3 see). Diameter mikrofibrill cellulose is equal In a primary cellular wall approximately 4 nanometers, in secondary these mikrofibrilly almost in 6 times more thickly. The substances surrounding cellulose fibrilly, fasten them with each other (fig. 2.31). As such cementing material serve gemitselljulozy, glikoproteidy and pectinaceous substances. Gemitselljulozy are the long chains constructed of the rests two pentoz, ksilozy and arabinozy to which the lateral chains presented by others monosaharidami are attached. Pectinaceous substances (the polymers constructed from saharopodobnyh of units) form with water or gels, or viscous solutions. As similar transitions are reversible and connected with changes of temperature and some other conditions, they can make essential impact on a structure of a cellular wall. The main component of a rigid cellular wall - lignin which presence is characteristic for wood. Lignin it is formed as a result of oxidising condensation of typical aromatic spirits of a phytogenesis (koniferilovogo, sinapovogo, kumarovogo). It is steady against various chemical influences and substantially increases rigidity and durability of cellular walls. In those cages,

Which walls are inlaid ligninom, protolayers usually die off; there are one only cellular walls in the form of hollow cylinders. In cages of a bark of a wall are inlaid water-proof suberinom.

Materials for construction of a cellular wall (including polisaharidy, consisting of thousand carbohydrate links, and albuminous molecules) are synthesised in cytoplasm and from here are transported to destination. Phytophysiologists were occupied many years with a question how can take place through plazmalemmu these huge molecules. The newest researches have shown that rough endoplazmatichesky retikulum and diktiosomy participate in synthesis of a material of a cellular wall as functionally uniform membrannoj systems (fig. 2.32).

Polipeptidnye of a chain of the fibers which are a part of a cellular wall, are synthesised on rough endoplazmaticheskom retikulume in the same way, as well as other fibers. However on termination of synthesis these polipeptidy arrive in a gleam Ayr. On it they dvizhutsja to diktiosomam, undergoing in the course of this moving various structural changes. Then fibers together with polisaharidami, synthesised in diktiosomah, are packed in sekretornye vials. Vials go to plazmalemme, merge with it and oporazhnivajutsja, opening outside, i.e. Attaching the contents to a cellular wall. The Fig. 2.32 explains, how there is this process which name the return pinotsitozom. (Usual pinotsitoz is ' zaglatyvanie ' materials a plasmatic membrane in which result of substance arrive in a cage.)

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