Activity Of Plasmalemma Research Articles

Exogenous salicylic acid-induced nitric oxide regulates leaf water condition through root osmoregulation of maize seedlings under drought stress

Under drought stress, the role of nitric oxide (NO) in the regulation of leaf water condition by salicylic acid (SA) through root osmoregulation of maize (Zea mays L.) seedlings was investigated. The results showed that drought stress markedly increased the contents of NO, soluble sugar, proline, soluble protein, Na+, K+ and Ca2+, as well as the activity of plasmalemma H+-ATPase in roots, compared with control. However, drought stress significantly decreased root hydraulic conductivity and leaf relative water content (RWC). Exogenous SA under drought stress significantly increased above indicators, compared with drought stress alone. Above effects of SA were significantly inhibited by the pretreatment with NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO). Overall, the findings indicated that SA-induced NO participated in the regulation of leaf water condition through root osmoregulation of maize seedlings under drought stress.

Exogenous IAA and ABA stimulate germination of petunia male gametophyte by activating Ca2+-dependent K+-channels and by modulating the activity of plasmalemma H+-ATPase and actin cytoskeleton

To date, the molecular mechanisms underlying the osmoregulation of pollen grains (PGs) related to the maintenance of their water status and allowing pollen tubes (PTs) to regulate concentrations in them of osmolytes and transmembrane water transport remain to be not so far characterized. In the present work, the data on the participation of IAA and ABA in the osmoregulation of germinating in vitro petunia male gametophyte were obtained. It has been established that the growth-stimulating effect of these phytohormones is due to their action on intracellular pH (pHc), the membrane potential of plasmalemma (PM), the activity of PM H(+)-ATPase, K(+)-channels in the same membrane and organization of actin cytoskeleton (AC). Two possible targets of the action of these compounds are revealed. These are represented by (1) PM H(+)-ATPase, electrogenic proton pump responsible for polarization of this membrane, and (2) Ca(2+)-dependent K+-channels. The findings of the present work suggest that the hormone-induced pHc shift is involved in cascade of the events including the functioning of pH-dependent K+-channels. It was shown that the hormoneinduced hyperpolarization of the PM is a result of stimulation of electrogenic activity of PM H(+)-ATPase and the hormonal effects are mediated by transient elevation in the level of free Ca(2+) in the cytosol and generation of reactive oxygen species (ROS). The results on the role of K(+) ions in the control of water-driving forces for transmembrane water transport allowed us to formulate the hypothesis that IAA and ABA stimulate germination of PGs and growth of PTs by activating K(+)-channels. In addition, the studies performed showed that the AC of male gametophyte is sensitive to the action of exogenous phytohormones, with to more extent to the action of IAA. As judged by the action of latrunculin B (LB) the AC may serve as the determinant of the level of endogenous phytohormones that most likely participate in the regulation of the polar growth of PTs impacting on the pool of F-actin in their apical and subapical zones.

Relationships between nitrate uptake and nitrate reductase activity in Cucumis sativus L.

Anti-NR IgG fragments obtained after papain digestion of polyclonal antibodies gave the positive immunological reaction with both, a soluble and plasma membrane-bound nitrate reductase. Anti-NR antibody as well as IgG fragments almost totally inhibited the nitrate reductase activity in cytosol proving a crossreaction of antibody with the catalytic site of a soluble NR. Anti-NR IgG fragments, but not undigested polyclonal antibodies affected the activity of the nitrate reductase associated with plasma membranes. Discrepancy in the action of intact antibodies and fragments obtained after they digestion were interpreted as a consequence of same differences in the ability of those molecules to the penetration through the membrane. Undigested anti-NR antibody have no effect on the nitrate uptake by intact plants, as well as by the right-side plasma membrane vesicles. On the other hand, IgG fragments of polyclonal antibodies abolished almost totally the nitrate uptake in the case of intact seedlings, but have only slight effect on the N03 uptake in plasma membranes. On the basis of above findings, some relations between nitrate uptake and its assimilation inside the cell are suggested. Since IgG fragments only slightly changed the N03 absorption in vesicles whereas the activity of plasmalemma associated nitrate reductase was strongly repressed, we concluded that the PM-NR is not structurally involved in the nitrate transport through the membrane.

Effect of salicylic acid on the proton translocation activity of plasmalemma of potato tuber cells

Action of salicylic acid (SA) on the activity of membrane bound H(+)-ATPase and passive proton permeability of plasmalemma membrane vesicles (PMV) from parenchyma cells of potato tubers was detected. A correlation between SA action and germination of tubers and activity of plasmalemma H(+)-ATPase was revealed: the application of growth-stimulating concentrations of SA (10(-10)-10(-8) M) in the system in vitro resulted in activation of plasmalemma H(+)-ATPase, while the utilization of growth-inhibiting concentrations (10(-4), 10(-5) M) provoked inhibition of the enzyme activity. Addition of jasmonic acid (JA) to the incubation mix resulted in increase of SA effect on the accumulation of H+ in PMV.

Role of cyclosis in asymmetric formation of alkaline zones at the boundaries of illuminated region in Chara cells

The role of cytoplasmic streaming in pattern formation at the plasma membrane and chloroplast layer was examined with Chara corallina Klein ex Willd. cells exposed to nonuniform illumination. Our hypothesis was that the exchange of ions and metabolites between the chloroplasts and the cytoplasm in the illuminated cell area alters the composition of the cytosol while the flow of modified cytoplasm induces asymmetrical changes in the plasmalemmal transport and fluorescence of chloroplasts in the adjacent shaded areas. The hypothesis was tested by measuring the H+-transporting activity of plasmalemma and non-photochemical quenching (NPQ) in shaded areas of Chara cells at distances of 1–5 mm on either side of the illuminated region (white light, 1000 μmol/(m2 s), beam width 2 mm). When measured at equal distances on opposite sides from the illuminated region, both pH and NPQ changes differed considerably depending on the direction of cytoplasmic movement at the light-shade boundary. In the region where the cytoplasm flowed out of irradiated area, the formation of alkaline zone (the plasma membrane domain with a high H+-conductance) and NPQ in chloroplasts was observed. In the vicinity of light-shade boundary where the flow was directed from the shade to the illuminated area, neither alkaline zone nor NPQ were formed. The results demonstrate the significance of cyclosis in the transfer of physiologically active intermediate that affects the membrane transport, the functional activity of chloroplasts, and the pattern formation in the plant cell.

Osmotic Water Permeability of Vacuolar and Plasma Membranes Isolated from Maize Roots

The method of stopped flow was used to follow the changes in light scattering by the vesicles of plasmalemma and tonoplast isolated from maize (Zea maysL.) roots and treated by osmotic pressure. In both membrane preparations, the rate of the process depended on the osmotic gradient and was described with the simple exponential function. The rate constants derived from these functions were the following: the coefficient of water permeability in the tonoplast (P= 165 ± 7 μm/s) exceeded by an order of magnitude the corresponding index for plasmalemma (11 ± 2 μm/s). The presence of HgCl2(1.6 nmol/μg membrane protein) decreased the tonoplast water permeability by 80%. Microviscosity studies of the hydrocarbon zone in the isolated membranes by using a fluorescent diphenylhexatriene probe demonstrated that the two membranes do not differ in the phase state of their lipid bilayer. The authors conclude that the observed difference in water permeability does not depend on the state of the lipid phase and probably reflects the dissimilar functional activity of plasmalemma and tonoplast aquaporins.

THE POSSIBLE ROLE OF MEMBRANE ELECTROPHORESIS IN THE POLAR TRANSPORT OF IAA AND OTHER SOLUTES IN PLANT TISSUES

SummaryPolar transport of IAA in young higher plant shoot tissue requires an asymmetric distribution of membrane‐transport sites in the plasmalemma of the cells. The ‘chemiosmotic’ hypothesis of IAA transport requires that IAA‐ uniporters be largely on the basal side of the cells. It is suggested that the longitudinal gradient of electrical potential difference (PD, base positive to apex) which may result from activation of plasmalemma H+ efflux in the basal cells by transported IAA, may serve to maintain and reinforce this asymmetric distribution of carriers by the process of membrane electrophoresis of the carriers. The origin of this asymmetric distribution (and hence of polar IAA transport) may lie in electrical potential differences in maternal tissue around the developing embryo. Maintenance of polarity through seed dormancy may be related to gradients in cell‐wall fixed charges (and hence of electrical potential difference) along the shoot axis related to the uronate content of cell walls at different stages of cell development. The possibility of testing this hypothesis, and its relevance to other polar transport phenomena in plants, are briefly discussed.