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.

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.

Growth-Stimulating Activity of Natural Polymer-Based Nanocomposites of Selenium during the Germination of Cultivated Plant Seeds.

The growth-stimulating activity of three selenium nanocomposites (NCs) in various matrices based on arabinogalactan (NC Se/AG, 6.4% Se), starch (NC Se/St, 2% Se), and carrageenan (NC Se/Car, 12% Se) with respect to plants of radish, soybean, and potato was investigated. It was shown that the treatment of plant seeds with NCs stimulated root growth during germination. It was found that the studied NCs affected both the level of lipid peroxidation and the activity of the antioxidant enzyme glutathione peroxidase (GPX). The treatment of radish seeds with NCs stimulated root growth during their germination and reduced the content of diene conjugates (DC) in root tissues. It was shown that soaking seeds in NC Se/AG solution increased the GPX activity in the tissues of the radish root by 40%. Stimulation of soybean root growth under the influence of NC Se/Car may also be associated with the activation of GPX. Furthermore, in potato plants, this NC led to the stimulation of germination; however, this was probably due to the activation of other antioxidant enzymes. The results obtained allow us to consider Se NCs as potential plant growth stimulants.