Absorption of mineral substances from soil and transport of ions through cellular membranes. Active transport of ions

you are: Absorption of mineral substances from soil and transport of ions through cellular membranes

Except the diffusion of ions which are carried out through certain sites of a membrane thanks to a gradient of electrochemical potential, ions move also through the specific zones of a membrane named pumps, with an expense of the energy reserved usually in the form of ATR. Thus, unlike diffusion which occurs only on a gradient of electrochemical potential, active transport with use of pumps consists in carrying over of ions against this gradient.

Above it was already discussed that at active transport of any one ion in one direction transmembrannyj the potential changes. However active transport not necessarily should be electrogene. Movement of two ions with an identical charge (for example, To + and N +) in opposite directions or two ions with identical on size, but charges different in a sign (for example, To + and С1-) in one direction represents electroneutral process as the balance kationov and anionov on either side of a membrane thus does not change (fig. 7.9). In roots ions N + often exchange on To +. To + it is absorbed from a soil solution or from a surface of soil particles on which it is adsorbed. As a result of simultaneous export of ions N + the external solution becomes more sour that can promote disintegration of soil particles. Similarly absorption anionov, for example NO3 - is counterbalanced by bicarbonate allocation (NSOZ-) or organic anionov, such, as malat.

Experimentally to establish, whether ions through a membrane by diffusion or by means of active transport move, use substances, ingibirujushchie synthesis ATR. The most simple experiences of this kind spend in the dark. Thus fosforilirovanie in hloroplastah stops, and mitohondrii become the main centres of synthesis ATR. Then to cages add metabolic poisons, such, as 2,4-dinitrofenol, azid sodium, tsianid sodium or m-hlorkarboniltsianidfenilgidrazon, interfering synthesis ATR in mitohondrijah. (At carrying out of similar experiments on light fotofosforilirovanija in hloroplastah it is necessary to apply to prevention additional ingibitory, for example diuron.) If to process a plant effective ingibitorom in corresponding concentration, active transport will stop, as soon as the plant will spend stocks ATR. Diffusion of ions will proceed, apparently, however its share caused by generation of electric potential by active processes, will be lowered. Similar results can be received as well in the dark in atmosphere without О2 as in anaerobnyh conditions oxidising fosforilirovanie in mitohondrijah it is carried out extremely inefficiently. Anaerobnye conditions in korneobitaemoj to a zone of the plants which are grown up on flooded soil, can reduce their ability to absorb ions that, possibly, leads to insufficient supply of plants by mineral substances.

Experiences with the isolated roots placed in salt solutions, have helped physiologists to understand, how function ionye pumps at absorption of salts. Speed of absorption of a certain element which use usually in the form of a radioactive isotope, measure at different concentration of other elements in a solution. Typical experience on oats roots shows that at concentration increase To + with 0 to 0,02 mm speed of its absorption increases linearly, and then this gain becomes slower as concentration To + comes nearer to 0,20 mm (fig. 7.10.

The Majority of other ions is absorbed more slowly, than To +, nevertheless their curve absorption are similar to a curve received for To +. The Particular interest represents that curve absorption of ions have similarity to the schedules characterising dependence of speed fermentativnyh of reactions from concentration of a substratum (see fig. 2.16). Therefore it is possible that membrannye fibers function as the enzymes facilitating movement of ions through a membrane. Thus speed of absorption of a certain ion reaches the maximum when all centres of carrying over in these fibers, intended for the given ion, appear occupied.

When concentration КС1 in an environment becomes above the first ' saturation level ' - from 1 to 50 mm (fig. 7.10,5), speed of absorption To + increases again. However at such high concentration of salt specificity for an ion To + decreases, as its absorption can change under the influence of the diversified ions. It is not established yet, whether participate in absorption of ions To + many carriers of different types (one of them is specific to an ion To +, and others have the active centres which can be occupied by several various kationami) or for all phases of absorption To + one carrier answers.

On plazmalemme cages of a root of oats the enzyme promoting hydrolysis ATR to ADP and R recently has been found out; at presence To +. Besides that activity of this ATR-ELEMENTS raises at presence To + in the environment (fig. 7.11), dependence of such effect on concentration To + has amazing similarity to the schedule v absorption To + intaktnymi oats roots (compare about fig. 7.10).

Obviously, this enzyme operates as a carrier using for transport of ions To + through plazmalemmu energy, formed at disintegration ATR. Though details of the mechanism of active transport remain basically obscure, the available data allows to assume that membrannyj fiber-carrier communicates in the beginning with the specific ion, and then changes the configuration under the influence of ATR. When the carrier eventually splits ATR, its configuration comes back in an initial condition and an ion is liberated, but already on a membrane opposite side (fig. 7.12).