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Biomedical subjects

G A Velikanov

Publications and source records attributed to G A Velikanov.

7 recordsLinked to original sources
PubMed2005

[Diffusional attenuation of proton echo and control of changes in the cytoskeleton hydration level].

Using the pulsed NMR-method with pulse gradient of the magnetic field, a study was made of changes in diffusional attenuation (DA) of proton echo in germs of triticum grains under the influence of agents depolymerizing cytoskeleton elements or inhibiting their ATP-activity. At a short diffusion time, we observed respective alterations of NMR-population in a fraction of cell water molecules contributing to DA at large values of pulse gradient. It is shown that the presence in DA of a site with essentially smaller coefficient of self-diffusion, as compared with basic cell water fraction, is not a consequence of restricted diffusion phenomenon. The observed changes in NMR-population of the appropriate fraction of cell water molecules are interpreted as changes in the level of cytoskeleton hydratation occurring under the influence of the used agents. A hypothesis is proposed for the functional role of similar changes in the level of hydratation of cytoskeleton elements located inside plamodesmata in the mechanism of plasmodesmatal water permeability regulation.

Cytoskeleton↗
PubMed2005

[The role of proton pump and potassium channels of plasma membrane in regulation of cellulose synthesis in plants].

A study was made of the influence of two activators of plasma membrane proton pump [indole-3-acetic acid (IAA) and fusicoccin (EC)] and of the blocker of potassium channels of outward direction [tetraethylammonium chloride (TEA)] on exogenous [U-14C]glucose incorporation into cellulose fraction of cell wall, and on the value of plasmalemma membrane potential. It has been shown that IAA and FC exert different influences on the intensity of [U-14C]glucose incorporation into cellulose fraction: IAA activates, while FC inhibits incorporation intensity. A conclusion is made that differences in affects of IAA and FC on the intensity of cellulose synthesis at the plasma membrane level may be due to the fact that the activating effect of IAA on plasma membrane proton pump involves activation of the inward direction potassium channels, whereas that of FC, on the contrary, is associated with their blocking. Under the action of TEA, the intensity of incorporation of radioactively labeled glucose was increased. Apparently, the role of plasma membrane in regulation of the intensity of cellulose synthesis may be associated with not only the activity of proton pump on plasma membrane, but also the functional condition of potassium channels of this membrane.

Cell Membrane↗
PubMed2001

[Actin-regulated water permeability of two transport channels of plasmodesmata in roots of winter wheat cultivars varying in drought resistance].

In roots of 5-6-day old seedlings of three cultivars of the winter wheat, varying in drought-resistance: Bezostaya 1 (low resistant), Mironovskaya 808 (resistant), and Albidum 114 (highly resistant) water permeability of two transport channels of plasmodesmata was studied at the action of cytochalasin B, which is known to inhibit polymerization of cytoskeleton actin filaments, by a pulse method of NMR, on the background of increasing water loss in the seedlings. It has been found that the registered coefficients of water self diffusion, two of which (D2 and D3) depend on the water permeability of different transport channels of plasmodesmata, differ in opposite directions. This may suggest that in roots of drought-resistant plants, after a moderate water loss, a diffusive water flow through the cytoplasmic symplast increases (demonstrated by an increase of D2), while that through the vacuolar symplast decreases (seen by an increase of D3). After a high water loss in seedlings, we noticed an even greater increase in water permeability of the cytoplasmic symplast, and a decrease in water permeability of the vacuolar symplast, however, in the roots of low resistant cultivars these changes were poorly expressed, if at all. Under stress-less conditions cytochalasin B would result in an increased water transport through the cytoplasmic channel of plasmodesmata due apparently to a destruction of their actin-myosin sphincters. Both weak and average degrees of water loss would strengthen the cytochalasin B exerted influence on plasmodesmal water conductance, that may testify to a synergetic action of these two factors. After a significant water loss this action was kept only partially, because the inhibitor, on blocking the cytoplasmic channel, did increase at the same time the effect of water stress, limiting water flows through the vacuolar symplast and, simultaneously, raising the water inflow to the apoplast.

Actins↗
PubMed2000

Influence of inhibitors of cytoskeleton proteins on water exchange of wheat roots under the after-action of water stress.

The dynamics of water molecular state and transport in winter wheat (Triticum aestivum L.) of roots different resistance cultivars was studied by a biophysical method, Nuclear Magnetic Resonance (NMR), and a physiological method, Water-Holding Capacity (WHC). The effective coefficient of water self-diffusion (D(eff)), spin-spin relaxation times (T(2)) and WHC were measured after structural modification of cytoskeleton by colchicine and cytochalasin B after the action of water stress. New information about molecular mechanisms of water state and water transport regulation determined by the influence of dynamic cytoskeleton structure has been obtained. This is very important for the development of a fundamental theory of water exchange in plants, and for the ways of its optimization under conditions of environmental stress.

Actin Cytoskeleton↗
PubMedDate not supplied

[Nonexponential diffusion extinction of spin echo from water protons in wheat root].

The method of NMR spin echo with the magnetic field pulse gradient was used for studying self-diffusion of water molecules in the radial root direction. It was shown on the basis of physiologopharmacological methods of modification of the object that the coefficients of water self-diffusion resulting from computer decomposition of nonexponential diffusion extinction of the relative echo amplitude in the root to components are related to the subcellular and supercellular organization (structure) of the root and reflect changes in water permeability of the two transport channels of plasmodesmas.

Diffusion↗
PubMedDate not supplied

[Diffusion of water through the narrow pores of biomembranes].

The pulsed-gradient, nuclear magnetic resonance method has been used to study diffusion of water through the cell membranes. An analytical expression is derived for relative amplitude of nuclear spin-echo, describing the diffusion of water in membrane pores. The latter are so narrow, that their diameter is only a little greater than the water molecule diameter. The experimental data for consumed yeast with normal content of water agree well with the theoretical dependence.

Cell Membrane Permeability↗