Growth and formoobrazovanie at plants. The general review. Differentiation of reproductive bodies

you are: Growth and formoobrazovanie at plants. The general review

One of the vivid examples of sharp change of the form at plants is a transition from vegetative growth to reproductive. At many pokrytosemennyh the plant throughout long time forms only roots, runaways and leaves. Then, at some instant life cycle, rough vegetative growth stops and a number of the transformations leading eventually to occurrence of reproductive bodies begins. first morphological changes are marked in a cone of increase of a stalk which of the narrow cylinder turns in uploshchennyj bugorok. On it bugorke rudiments tsvetkov, containing chashelistiki, petals, stamens and plodolistiki develop now. In stamens and plodolistikah there is an important process - mejoz, coming to the end with formation gaploidnyh cages and sexual generation of a plant - gametofita, having a single set of chromosomes (fig. 3.10). In stamens (man's body) as a result mejoza are formed gaploidnye the microdisputes developing in man's gametofit (pollen grain); in zavjazi (female body), formed from one or several plodolistikov, in process mejoza it is formed gaploidnaja the megadispute, developing in female gametofit (a germinal bag). Man's and female gametofity finally give rise to sexual cages, i.e. spermiju and jajtsekletke. Spermy on a pollen tube gets in semjazachatok and impregnates jajtsekletku. As a result of merge of two sexual cages the sexless generation - sporofit, a having double set of chromosomes is restored.

Last decades biologists managed to study much more full physiology of reproduction of plants and those chemical changes with which transition from vegetative growth to the reproductive is connected. Later we will discuss this important process in more details. Now we will consider system, more simple than pokrytosemennoe a plant, namely zarostok a fern (fig. 3.11). At a fern zarostok the cage of a mature fern - sporofita represents gametofit as its each cage contains twice smaller number of chromosomes, than. At some seaweed, gaploidnoe the generation occupies a considerable part of life cycle while at pokrytosemennyh on its share it is necessary much shorter time interval from mosses and ferns.

Gametofit of a fern is formed as a result of repeated mitoticheskih divisions from monocelled gaploidnoj disputes. Developing on leaves in a sporangium fern disputes represent a product mejoza. After germination from such disputes the thin plate - a layer of cages (on light) is formed by cellular divisions or threadlike structure (in the dark), or. Completely generated zarostok has the heart-shaped form and in an average part consists of several layers of cages from which depart growing into the earth rizoidy (the formations reminding roots). After a while in a fabric zarostka arise both man's, and female genitals - interidii and arhegonii. Anteridy gives rise to group spermatozoidov, and in arhegonii develops one and only jajtsekletka.

What compels cages zarostka to be differentiated a fern in man's and female genitals? It is necessary to search for the answer to this question, apparently, in existence of any special substances stimulating occurrence anteridiev. If disputes of a sensitive kind of fern Onoclea to place on one in the test tubes containing approaching for growth of a fern the synthetic environment zarostki will develop normally in everything, except for one - on them never will appear anteridii. If we grow up these zarostki in the environment where there are much others zarostkov, or we will add, by Wednesday a filtrate kulturalnoj liquids from older zarostkov Onoclea (it is possible to take as well from a related kind, Pteridium) anteridii will appear on zarostkah very quickly. Simple experiences with cultivation show that at the environment from under old zarostkov Pteridium there is any substance capable in unusual way to stimulate differentiation anteridiev on zarostkah, but not rendering some appreciable influence on growth of the last. At addition on Wednesday of considerable quantities of this substance almost each cage mature zarostka can give rise anteridiju.

Detailed studying of a phenomenon about which there is a speech, elicits the curious fact: it appears, by then, when zarostok gets ability to develop the factor stimulating formation anteridiev, it happens already too old that to it to react. Therefore if there is only one zarostok it cannot stimulate formation anteridiev in itself(himself). The natural conclusion from here consists that formation anteridiev in the nature demands simultaneous presence of many zarostkov different age. Old zarostki develop thus the specific factor, capable to cause formation anteridiev at younger zarostkov, but they continue to form arhegonii without preliminary formation anteridiev. Thus, the successful differentiation of genitals leading finally to end of sexual process at this plant, occurs only in that case when zarostki are together. Acquaintance to various families of ferns allows to reveal known specificity in development of the given substance. Usually all members this. Polypo-diaceae react to the factor zarostka Pteridium and appear tolerant to the substances produced by ferns of other families. Similarly gametofity, not belonging to Polypodiaceae, find out tolerance to the factor zarostka Pteridium, but react to the substances produced their own zarostkami. Works on allocation and identification of these active substances have shown that they are related gibberellinam (one of classes of vegetative hormones about which we will speak later).

There is the data confirming that at some seaweed and mushrooms, no less than at the higher plants, any special substances developed by an organism in a certain phase of its life cycle participate in formation of genitals, their maturing, clearing of gametes and, at last, in attraction spermatozoidov jajtsekletkoj. This data speaks well for the concept according to which development consists of a number of stages, and each stage is initiated by that either other chemical or physical process quite often connected with formation of mobile chemical stimulus, or a hormone. At each stage again arisen cages, being differentiated, accept that form which corresponds to their concrete functions. On protjagzhenii all time are invariably supported harmony in an organism and its integrity.