Role of Plasmalemma Microdomains (Rafts) in Protection of the Plant Cell Under Osmotic Stress.

Lipid-protein microdomains (presumably rafts) of the plasmalemma isolated from the beetroots subjected to hyperosmotic stress and hypoosmotic stress were studied. In these microdomains, the variations in the composition of total lipids, sterols, and fatty acids were observed. These variations differed under hypo- and hyperosmotic types of stress. We presumed that such variations were bound up with different strategies, which are probably related to protecting the cell from osmotic stress. One of the protection tendencies might be related, in our opinion, to credible growth of the content of such lipids as sterols and sterol esters, which are considered as raft-forming. Under osmotic stress, these lipids can contribute to the formation of both new raft structures and new membrane contacts of plasmalemma with intracellular organelles. Another protection tendency may be bound up with the redistribution of membrane phospholipids and phosphoglycerolipids possibly to stabilize the membrane's lamellar structure, which is ensured by credible growth of the content of such lipids as phosphatidylcholines, phosphatidylinositols, and digalactosyldiacylglycerol. The participation of lipid-protein microdomains in the adaptive mechanisms of plant cells may, in our opinion, also be bound up with the redistribution of membrane sterols, which (redistribution) in a number of variants may provoke credible growth in the content of cholesterol or "anti-stress" sterols (campesterol and stigmasterol). So, according to our results, the variations in the content of the plasmalemma lipid-protein microdomains take place under osmotic stress. These variations may influence the functioning of plasmalemma and take part in the adaptive mechanisms of plant cells.

Detection of lipid-protein microdomains (rafts) and investigation of their functional role in the chloroplast membranes of halophytes.

To study the characteristics of the structure and the functional role of chloroplast membranes of halophytes with different salt tolerance strategy, raft structures were isolated. Lipid analysis data provided evidence for the presence of rafts in the chloroplast membranes. The discovered significant differences in the content of raft-forming lipids in different halophytes suggest a relationship between the functions of rafts and the mechanisms of salt tolerance in plants.

[PECULIAR PROPERTIES OF SOME COMPONENTS OF MORPHOLOGICAL STRUCTURE IN A PLANT CELL VACUOLE REVEALED BY CONFOCAL MICROSCOPY].

Results of investigations of peculiar properties related to the structure of plant cell vacuolar membranes are discussed. The study was carried out using confocal microscopy, which allowed us in the process of scanning to identify membrane tubes and vesicules in the preparations of isolated vacuoles. Such membrane tubes were found both inside and outside the vacuoles, and, in the case of scanning intermittently at equal time intervals, transition of vesicles with the membrane tube was observed. Furthermore, scanning of isolated vacuoles was conducted at various distances from the glass substrate. Each time, in the upper area of the isolated vacuole lying on the substrate, we observed a large segment of vacuolar membrane and registered the effect of highly intensive fluorescing of some of membrane segments. The distributions of laurdan fluorescence generalized polarization (GP) values for the vacuolar membrane on the whole and for the intensively fluorescing membrane segments have been obtained. We have found that the microviscosity of the intensively fluorescing membrane segments essentially differs from that of the rest part of the membrane.

Effect of colchicine on physiological and biochemical properties of Rhodococcus qingshengii.

The genus Rhodococcus includes polymorphic non-spore-forming gram-positive bacteria belonging to the class Actinobacteria. Together with Mycobacterium and Corynebacterium, Rhodococcus belongs to the Mycolata group. Due to their relatively high growth rate and ability to form biof ilms, Rhodococcus are a convenient model for studying the effect of biologically active compounds on pathogenic Mycolata. Colchicine was previously found to reduce biof ilm formation by P. carotovorum VKM B-1247 and R. qingshengii VKM Ac-2784D. To understand the mechanism of action of this alkaloid on the bacterial cell, we have studied the change in the fatty acid composition and microviscosity of the R. qingshengii VKM Ac-2784D membrane. Nystatin, which is known to reduce membrane microviscosity, is used as a positive control. It has been found that colchicine at concentrations of 0.01 and 0.03 g/l and nystatin (0.03 g/l) have no signif icant effect on the survival of R. qingshengii VKM Ac-2784D cultivated in a buffered saline solution with 0.5 % glucose (GBSS). However, colchicine (0.03 g/l) signif icantly inhibits biof ilm formation. Rhodococcus cells cultivated for 24 hours in GBSS with colchicine acquire a rounded shape. Colchicine at 0.01 g/l concentration increases C16:1(n-7), C17:0, C20:1(n-9) and C21:0 fatty acids. The microviscosity of the membrane of individual cells was distributed from the lowest to the highest values of the generalized laurdan f luorescence polarization index (GP), which indicates a variety of adaptive responses to this alkaloid. At a higher concentration of colchicine (0.03 g/l) in the membranes of R. qingshengii VKM Ac-2784D cells, the content of saturated fatty acids increases and the content of branched fatty acids decreases. This contributes to an increase in membrane microviscosity, which is conf irmed by the data on the GP f luorescence of laurdan. All of the above indicates that colchicine induces a rearrangement of the Rhodococcus cell membrane, probably in the direction of increasing its microviscosity. This may be one of the reasons for the negative effect of colchicine on the formation of R. qingshengii VKM Ac-2784D biof ilms.

[Effect of dihydroquercetin on active and passive ion transport systems in plant vacuolar membranes].

The effect of dihydroquercetin (DHQ) on proton pumps of the vacuolar membrane (H(+)-ATPase and H(+)-pyrophosphatase), slow vacuolar (SV) channel, lipid peroxidation, and stability of isolated vacuoles was studied. The results of experiments showed that DHQ affected active and passive transport systems of the vacuolar membrane. The mechanism of action of DHQ may be based on its combined effect on the sulfhydryl groups of proteins and the lipid component of the membrane. The strong stabilizing effect of DHQ on the membranes of isolated vacuoles may be associated not only with its antioxidant properties but also with changes in the membrane permeability affecting the ion channels.

[The dynamics of hormonal status of developing red beet root (Beta vulgaris L.) in correlation with the dynamics of sugar accumulation].

We studied the dynamics of phytohormone levels (indole-3-acetic acid, abscisic acid, cytokinins, and gibberellin-like substances) in red beet (Beta vulgaris L.) roots at different developmental stages in comparison with the data on the dynamics of sugar accumulation in order to test possible hormonal regulation of sugar accumulation. The obtained data suggest the involvement of cytokinins and gibberellin-like substances in the control of sugar accumulation in the roots, while indole-3-acetic acid, abscisic acid, and gibberellin-like substances can control the outflow. The data on the dynamics of phytohormone levels shed light on their specific physiological role in red beet root development.

Relation between ionic and hormonal regulation of proton pumps in red beet tonoplast.

Effects of indoleacetic, abscisic, gibberellic acids and kinetin on the hydrolytic activity of the proton pumps H+-ATPase (EC 3.6.1.3) and H+-pyrophosphatase (EC 3.6.1.1) under non-optimal ionic conditions were studied in tonoplasts isolated from stored roots of red beet (Beta vulgaris L. cv. Bordo). We showed that ionic composition markedly affected the hormonal regulation. H+-pyrophosphatase was more sensitive to the ionic and hormonal regulation than H+-ATPase. Magnesium ions are essential for the maximal manifestation of hormonal stimulation.

The effect of low-intensity laser irradiation on the hydrolytic activity of vacuolar membrane proton pumps.

The effect of low-intensity irradiation by a helium-neon laser on the hydrolytic activity of the vacuolar membrane proton pumps has been studied. The maximum effect was found for the 3 min irradiation from a close distance (0.3 m); moreover, the PPase activity increased by 33%, whereas the ATPase activity was inhibited by 44%. The effect described is suggested to be due to different conformations of the enzymes in the membrane and their different physiological roles.