Kinetika of growth. Cellular division, a stretching and differentiation

you are: Kinetika of growth

The Plant is a community of the different cages which have resulted cellular division and the subsequent differentiation actively sharing, or meristematicheskie, the cages concentrated in sites, which are called meristemami (fig. 3.5), keep throughout all life of a plant ability continuously to share and generate new cages. Meristemy are available on tips of roots and on tops of runaways for all plants, and also in bazalnoj parts of leaves and mezhdouzly at some odnodolnyh. Thus, at dvudolnyh the stalk grows at the expense of a top whereas at odnodolnyh growth can occur either at the expense of a top, or for the account bazalnoj parts of a stalk or mezhdouzlija. Knots, i.e. Those sites of a stalk from which leaves depart, also can contain meristematicheskie cages. Between sheet and a stalk, in bosoms of leaves, are put pazushnye kidneys. Pazushnye kidneys, long time not giving runaways, are called as sleeping; Under certain conditions they clear up and from them runaways develop. Development of lateral runaways is subordinated hormonal regulation, and we still will speak about it later. Growth at thickness at stalks and roots dvudolnyh results from tangential division meristematicheskih cages kambija - the educational fabric located single-row: a cylindrical layer, between ksilemoj wood and floemoj barks. Resulting activity kambija cages are differentiated and form secondary floemu (knaruzhi) and secondary ksilemu (knutri).

In a stalk or a plant root, in it vysokoorganizovannom community of the cages, each cage in the development passes (in certain sequence) through a number of phases. Meristematichesky cages - small, thin-walled, approximately cubic form with set small vakuolej and rather big kernel (fig. 3.6).

Cages (basically are extended at length) mainly as a result of water inflow in vakuoli Increase. Each of numerous small vakuolej in process of water inflow grows, and eventually all of them merge in one big central vakuol, limited to a membrane. All other cage together with growth vakuoli too increases; cellular walls are stretched new portions of a material for cellular walls and cytoplasm are synthesised, various cellular organelly share and grow. Thus, growth by a stretching under the control of hormones and increase in crude weight accompanying it occur basically in that zone where cages are extended at length.

Usually in at one time with lengthening of cages, and sometimes after its end there is also a differentiation. Differentiation name process in which result the cages seeming before similar, get morphological distinctions and start to carry out different physiological functions (fig. 3.6 see). This process - one of trudnejshih biology riddles. So far as each cage of a metaphyte arises finally as it is considered to be, as a result of division of the same initial cage - a zygote having a double set of chromosomes, that, obviously, all these cages should have absolutely identical sets of genes. We already know that it not absolutely so; because of infringements which sometimes happen in the course of a mitosis, the number of chromosomes in different cages of the same plant can and not coincide. However between sets of genes in those cages which get eventually absolutely different form, no, probably, nevertheless any qualitative distinctions; In culture it is possible to carry out regeneration of the whole plant from separate cages, whence they were are taken - from sheet, a stalk or a root. So, the differentiation, apparently, does not change the basic genetic information containing in a cage. again arisen cage possesses wide potentialities and can develop (in morphological and physiological sense) on any of several possible ways, depending on physical and chemical influences, and also from spatial parities. Having passed once differentiation in this or that direction, the cage usually more does not come back any more in not differentiated condition and does not pass in other form; however in the conditions of culture of fabrics can occur both dedifferentsiatsija, and redifferentsiatsija. Now it is considered to be that in any cage any part of the general genetic potential is expressed only, i.e. What is the genes in it ' are included ', and others ' are switched off '. The cage nature depends, thus, on what complex of genes appears in it active. The problem, hence, passes in other plane and can be formulated so: what stimulus switches on and off genes?

Getting acquainted with physiology of the higher plants, we can learn to regulate those or other processes of differentiation by means of chemical or physical influences. However such ability is reached by purely empirical way. In effect, we are similar thus to the person who inserts a key into a keyhole and unlocks a door, without knowing anything about the device of the lock. Absolutely clearly that the future successes of experimental biology should depend on detailed studying of those phenomena which occur in an interval between influence of the given specific agent and occurrence of the corresponding changed form appreciably.