the Cage of a green plant. Vakuol

you are: the Cage of a green plant

Vakuol is the extensive central department of cytoplasm surrounded with selectively nontight membrane (tonoplastom) and filled with a water solution of salts and organic substances, and also a various waste of a metabolism. In a young cage there is a set small vakuolej which total amount makes, however, only rather small share from volume of all cage (fig. 2.25). With growth these cages small vakuoli increase as a result of water inflow, and finally merge in one big central vakuol, occupying sometimes over 90% of total amount of a cage. Central vakuol puts pressure upon cytoplasm and cellular walls. This pressure brings the contribution to maintenance of the form of a vegetative organism and giving to it appropriate rigidity.

Tonoplast is formed differently. Often it arises from the preformed membranes endoplazmaticheskogo retikuluma or device Goldzhi (we will describe last more low). Under certain conditions tonoplast, apparently, it is formed as a result of the limited hydration of one of sites of cytoplasm with the subsequent synthesis of a new membrane. In electronic microphotos tonoplast more thickly plazmalemmy also it is painted more intensively. As vakuol strongly differs from cytoplasm on structure of the dissolved substances, it is necessary to conclude, as under permeability characteristics tonoplast and plazmalemma are various. Probably that their ionic pumps-present in membranes the specialised fibers transporting dissolved substances through membrannyj a barrier with use of energy ATR are various also. At bolshej parts of plants rn (see more low) vakuoljarnogo juice fluctuates within 3,5-5,5, but there are also such kinds at which it is equal 1,0 whereas rn cytoplasms it is close to 7,0.

So big difference in concentration of hydrogen ions between vakuoljarnym juice and cytoplasm forces to assume that in tonoplaste there are any pumps which are pumping over ions N + from cytoplasm in vakuol. Most likely, these pumps promote maintenance rn cytoplasms up to the mark. Such control vital as enzymes regulating a metabolism are concentrated mainly in cytoplasm, and activity of enzymes very strongly depends from rn. In vakuoli ions and various substances which otherwise could break a cellular metabolism can be stored and collect, hence. Organic acids or their salts concern such substances (often meets, for example, oksalat calcium), pigments (such, as anto-tsiany) and phenolic connections (for example, tanniny), in particular.

All our modern representations about properties tonoplasta are based, first, on results of ultrastructural researches and, secondly, on revealing of distinctions in structure vakuoli and cytoplasms. Attempts to allocate tonoplast ie other membrannyh fractions had no success up to recent time when at last it was possible to develop a branch technique intaktnyh vakuolej from other cellular contents (fig. 2.26). The first stage of this procedure is reduced to reception of spherical protolayers by fermentativnogo digestion of cellular walls in vysokokontsentrirovannom a solution of any osmotically active substance. Then protolayers transfer to less concentrated (hypotonic) environment. Here they absorb water, bulk up and eventually are broken off, liberating vakuoli. After that differential tsentrifugirovaniem separate vakuoli from organell and from the incubatory environment. The first analyses such isolated vakuolej have shown that in tonoplaste the enzymes regulating transport of salts are concentrated. Now in many laboratories the additional experiments are made, which purpose consists in defining characteristics of permeability and fermental structure tonoplasta; such data considerably would expand our representations about a role tonoplasta in regulation of a cellular metabolism.

Sections