Influence Of Osmotic Stress Research Articles

Inheritance of signs of resistance to osmotic stresses in genetically modified wheat

Aim. To investigate the inheritance of transgenes and the preservation of increased resistance to drought in the seed generations of genetically modified wheat plants with a double-stranded RNA (dlRNA) suppressor of the proline dehydrogenase (pdh) gene. Methods. PCR, determination of free L-proline (Pro) content and yield structure indicators. Results. Under the influence of osmotic stress, T4 wheat plants were selected with elements that form dlRNA suppressor of the pdh gene of wheat, which retain the sign of increased resistance to water deficit. It was found that T4 plants had a higher content of Pro than their original forms under both normal cultivation conditions and water deficit. It is shown that during droughts, biotechnological plants were characterized by higher grain productivity compared to the original genotypes, while under conditions of sufficient moisture provision, the differences in the elements of the yield structure were insignificant. Conclusions. The analysis of seed generations of transgenic wheat showed variability in the manifestation of signs of increased resistance to osmotic stress, which is due to the instability of recombinant DNA in generations. Testing of T4 wheat under the effects of osmotic stress showed the fact of successful selection of plants with introduced elements that form dlRNA suppressor of the pdh gene and cause the sign of increased resistance to water deficit in seed generations.

Virus Mechanics under Molecular Crowding.

Viruses avoid exposure of the viral genome to harmful agents with the help of a protective protein shell known as the capsid. A secondary effect of this protective barrier is that macromolecules that may be in high concentration on the outside cannot freely diffuse across it. Therefore, inside the cell and possibly even outside, the intact virus is generally under a state of osmotic stress. Viruses deal with this type of stress in various ways. In some cases, they might harness it for infection. However, the magnitude and influence of osmotic stress on virus physical properties remains virtually unexplored for single-stranded RNA viruses-the most abundant class of viruses. Here, we report on how a model system for the positive-sense RNA icosahedral viruses, brome mosaic virus (BMV), responds to osmotic pressure. Specifically, we study the mechanical properties and structural stability of BMV under controlled molecular crowding conditions. We show that BMV is mechanically reinforced under a small external osmotic pressure but starts to yield after a threshold pressure is reached. We explain this mechanochemical behavior as an effect of the molecular crowding on the entropy of the "breathing" fluctuation modes of the virus shell. The experimental results are consistent with the viral RNA imposing a small negative internal osmotic pressure that prestresses the capsid. Our findings add a new line of inquiry to be considered when addressing the mechanisms of viral disassembly inside the crowded environment of the cell.

Efficient kefiran production by Lactobacillus kefiranofaciens ATCC 43761 in submerged cultivation: Influence of osmotic stress and nonionic surfactants, and potential bioactivities

Kefiran is a water soluble polysaccharide produced by Lactobacillus kefiranofaciens ATCC 43761. It has wide potential applications in food, pharmaceutical and nutraceutical industries. To the best of our knowledge, there have been no previous reports on the effect of osmotic stress and ionic surfactants on kefiran production by L. kefiranofaciens ATCC 43761. Accordingly, the current work aimed at optimizing kefiran production as affected by osmotic stress and nonionic surfactants in submerged cultivation system. Afterwards, the work was extended to investigate cytotoxic as well as antioxidant potentials of kefiran. Firstly, different osmolarities, different ionic surfactants (Triton X-100, Tween 20, Tween 80) as well as their concentrations and addition time were evaluated. The kinetics of cell growth and kefiran production were evaluated before and after the addition of surfactants. Results clearly demonstrated that osmotic stress and surfactant addition had a stimulatory effect on kefiran production. Using the optimal medium osmolality, 550 mOsmol.kg−1, kefiran production was enhanced from 1.29 to about 1.38 g.L−1. Furthermore, Triton X-100 was found to be the best surfactant stimulating kefiran production when added at a concentration of 1.0 g.L−1 at the onset of cultivation process (0 h). This increased kefiran production from 1.38 g.L−1 to 1.62 g.L−1. To summarize, the maximal kefiran production can be enhanced using 550 mOsmol.kg−1 and by adding 1.0 g.L−1 of Triton X-100 at 0 h. The new optimized medium showed an increase of about 25.6% in kefiran production (1.29 up to 1.62 g.L−1). After this step, the process was further optimized in 16-L stirred tank bioreactor. Maximal kefiran production reached 2.32 g.L−1 and 1.87 g.L−1 in bioreactor under control and un-controlled pH conditions, respectively, corresponding to 72.9 and 45.0% increase from the initial production titer, respectively. The produced kefiran exhibited promising anticancer activity against breast cancer (MCF-7) cells, with an IC50 value of 193.89 μg.mL−1. Also, kefiran showed 96.58% radical scavenging activity at 100 μg/mL, with an ED50 recorded of 12.29 ± 0.98 μg.mL−1.

The Influence of Osmotic Stress on Physiological and Biochemical Indices at Garlic (Allium sativum L.) Local Populations

Garlic is an asexually propagated crop with high morphological diversity and uses throughout the world. Although the salt tolerance among the cultivated species is low, there are some genotypes which present an acceptable level of adaptability to moderate saline conditions. In vegetables, these genotypes are represented especially by local varieties breeded by local farmers. It is therefore necessary to achieve a balance between productivity and salinity tolerance, for the obtaining of new genotypes with high productivity. Our experiments aimed to study the main physiological and biochemical indicators for the identification of salinity tolerant genotypes in a collection of local autumn and spring garlic populations from Timis County. The local populations studied show a wide genetic diversity based on synthesis of free proline, by selecting genotypes with good salinity tolerance for five autumn garlic varieties and five for spring garlic. There are major differences both morphologically and physiologically, between studied varieties of halophytes. Identification of these cultivars may represent a resource for breeding programs of cultivated vegetables on saline soils.

Reaction of Cells <i>Desmodesmus armatus</i> (Chod.) Hegew. on the Induction of Carotynogenesis

Various studies of the components of the antioxidant protection system of microalgae D. armatus under the influence of osmotic stress and active forms of oxygen will allow to develop methods for controlling carotenogenesis in a given culture and to obtain carotenoid enriched feed for zooplankton. These studies made it possible to evaluate the activity of catalase, peroxidase enzymes in cells that are cultured under the induction of carotenogenesis by free radical oxidation promoters and osmotic stress on the background of physiological changes. It is established that under these conditions, there is an increase in volumes and aggregation of vegetative cells. At the same time, the amount of biomass remains at the level of the first day of inductors application. Against the background of a decrease in growth activity, a decrease in the number of metabolically active cells in cytochrome oxidase was observed. It is also shown that, when iron sulfate is introduced with hydrogen peroxide and sodium chloride against the background of enhanced carotenogenesis, antioxidant systems are activated by increasing the activity of catalase and peroxidase. Under such conditions, it is possible to achieve increased production of carotenoids in Desmodesmus armatus culture.

Reaction of Cells <i>Desmodesmus armatus</i> (Chod.) Hegew. on the Induction of Carotynogenesis

Various studies of the components of the antioxidant protection system of microalgae D. armatus under the influence of osmotic stress and active forms of oxygen will allow to develop methods for controlling carotenogenesis in a given culture and to obtain carotenoid enriched feed for zooplankton. These studies made it possible to evaluate the activity of catalase, peroxidase enzymes in cells that are cultured under the induction of carotenogenesis by free radical oxidation promoters and osmotic stress on the background of physiological changes. It is established that under these conditions, there is an increase in volumes and aggregation of vegetative cells. At the same time, the amount of biomass remains at the level of the first day of inductors application. Against the background of a decrease in growth activity, a decrease in the number of metabolically active cells in cytochrome oxidase was observed. It is also shown that, when iron sulfate is introduced with hydrogen peroxide and sodium chloride against the background of enhanced carotenogenesis, antioxidant systems are activated by increasing the activity of catalase and peroxidase. Under such conditions, it is possible to achieve increased production of carotenoids in Desmodesmus armatus culture.

CHANGES OF CONTENT OF FREE AMINO ACIDS IN GRAINS OF FOREST GROWING EASTERS OF EASTER TRANSBAIKALIA IN PULLING IN OSMOSITIC STRESS

In the course of studying the content of free amino acids in dry and germinating grains of wild cereals, some biochemical features of their dynamics were revealed depending on the osmotic pressure. In most species, except Agropyron cristatum, a significant increase in the concentration of amino acids occurred in the control on the first day after the start of the experiment; in the subsequent period, their decrease was observed. For Agropyron cristatum, a decrease in the index and a smooth increase after the first day were observed. Under the influence of osmolyte, the tendency to mobilize amino acids has changed and in some species (Stipa krylovii, Melica virgata, Melica turczaninowiana) the maximum amounts were observed on the first day from the beginning of the experiment, in the others to the second day. The total amount of free amino acids in the control and in the test was not significantly different. There was also a rapid mobilization of proteinogenic amino acids with increasing osmotic stress for the widespread Stipa krylovii and Agropyron cristatum in the region. A similar trend was noted for the xerophyte Tripogon chinensis. For grasses with a narrow ecological niche, which are characterized by xeromesophilia, osmotic stress suppressed the rapid mobilization of free amino acids. The content of individual groups of amino acids under the influence of osmotic stress was characterized by significant differences for species of the Melica genus in the number of acidic amino acids, for Tripogon chinensis an increase in the content of basic amino acids, and for Agropyron cristatum by a decrease in their concentration.

Enhanced virulence of Fusarium species associated with spear rot of oil palm following recovery from osmotic stress

ABSTRACTFusarium spp., which are common inhabitants of oil palm leaves, are weak pathogens of common spear rot (CSR). We investigated the influence of osmotic stress on the growth, virulence, and activity of cell wall-degrading enzymes of CSR fungi, using potato dextrose agar (PDA) supplemented with KCl or sucrose (hyperosmotic medium). Hyperosmotic stress significantly inhibited mycelial growth, but growth rapidly recovered when mycelia were transferred to control medium. When inoculated into oil palm spear leaflets, Fusarium sp., and F. incarnatum precultured on 1.0 and 1.5 M KCl-hyperosmotic medium induced lesions that were two to four times larger than those in non-stressed cultures, suggesting enhanced virulence of the weak pathogens. Lesion size was not greatly affected in hyperosmotic cultures of moderately virulent F. sacchari. No activity of pectin lyase was detected in liquid cultures of the Fusarium isolates. All isolates except F. incarnatum BT48 secreted polygalacturonase (PG), which was active in both liquid cultures and inoculated leaves. Significantly increased PG activity (5–32-fold) was observed on leaves inoculated with hyperosmotic cultures of Fusarium sp. and F. sacchari. These findings suggest that Fusarium sp., F. incarnatum, and F. sacchari exhibit an adaptive physiological plasticity to hyperosmotic stress that results in enhanced virulence.

Influence of osmotic stress on desiccation and irradiation tolerance of (hyper)-thermophilic microorganisms.

This study examined the influence of prior salt adaptation on the survival rate of (hyper)-thermophilic bacteria and archaea after desiccation and UV or ionizing irradiation treatment. Survival rates after desiccation of Hydrogenothermus marinus and Archaeoglobus fulgidus increased considerably when the cells were cultivated at higher salt concentrations before drying. By doubling the concentration of NaCl, a 30 times higher survival rate of H. marinus after desiccation was observed. Under salt stress, the compatible solute diglycerol phosphate in A. fulgidus and glucosylglycerate in H. marinus accumulated in the cytoplasm. Several different compatible solutes were added as protectants to A. fulgidus and H. marinus before desiccation treatment. Some of these had similar effects as intracellularly produced compatible solutes. The survival rates of H. marinus and A. fulgidus after exposure to UV-C (254nm) or ionizing X-ray/gamma radiation were irrespective of the salt-induced synthesis or the addition of compatible solutes.

Influence of osmotic stress on the profile and gene expression of surface layer proteins in Lactobacillus acidophilus ATCC 4356

In this work, we studied the role of surface layer (S-layer) proteins in the adaptation of Lactobacillus acidophilus ATCC 4356 to the osmotic stress generated by high salt. The amounts of the predominant and the auxiliary S-layer proteins SlpA and SlpX were strongly influenced by the growth phase and high-salt conditions (0.6M NaCl). Changes in gene expression were also observed as the mRNAs of the slpA and slpX genes increased related to the growth phase and presence of high salt. A growth stage-dependent modification on the S-layer protein profile in response to NaCl was observed: while in control conditions, the auxiliary SlpX protein represented less than 10% of the total S-layer protein, in high-salt conditions, it increased to almost 40% in the stationary phase. The increase in S-layer protein synthesis in the stress condition could be a consequence of or a way to counteract the fragility of the cell wall, since a decrease in the cell wall thickness and envelope components (peptidoglycan layer and lipoteichoic acid content) was observed in L. acidophilus when compared to a non-S-layer-producing species such as Lactobacillus casei. Also, the stationary phase and growth in high-salt medium resulted in increased release of S-layer proteins to the supernatant medium. Overall, these findings suggest that pre-growth in high-salt conditions would result in an advantage for the probiotic nature of L. acidophilus ATCC 4356 as the increased amount and release of the S-layer might be appropriate for its antimicrobial capacity.

Influence of osmotic stress on thermal perception and thermoregulation in heat is different between sedentary and trained men

Hyperosmolality in extracellular fluid in humans attenuates autonomic thermoregulation in heat, such as sweating and blood flow in the skin. However, exercise training minimizes the attenuation. The aim of the present study was to clarify the influence of hyperosmolality on thermal perception and to assess the training effect of exercise. Ten sedentary (SED) and 10 endurance-trained (TR) healthy young men were infused with 0.9% (normal saline [NS]) or 3% NaCl (hypertonic saline [HS]) for 120min on two separate days. After infusion for 20min, heat stimulus to the skin of the whole body was produced by a gradual increase in hot water-perfused suit temperature (33°C, 36°C, and 39°C), which was first used in the normothermic condition and then in the mild hyperthermic condition (0.5–0.6°C increase in esophageal temperature) and controlled by immersion of the lower legs in a water bath at 34.5°C and 42°C, respectively. Thermal sensation and comfort were rated at the time of each thermal condition. Plasma osmolality increased by ~10mosmL/kg·H2O in the HS trial. In the mild hyperthermic condition, increases in sweat rate and cutaneous vascular conductance were lower in the HS than in the NS trial in both the SED and TR groups (p<0.05). In the SED group, thermal sensation in the mild hyperthermic condition was lower in the HS than in the NS trial (p<0.05); there was no significant difference between the trials in the TR group. These results might indicate that hyperosmolality attenuates thermal sensation with heat and that exercise training eliminates the attenuation.

Effect on β-galactosidase synthesis and burden on growth of osmotic stress in Escherichia coli.

Osmotic Shock is known to negatively affect growth rate along with an extended lag phase. The reduction in growth rate can be characterized as burden due to the osmotic stress. Studies have shown that production of unnecessary protein also burdens cellular growth. This has been demonstrated by growing Escherichia coli on glycerol in the presence of Isopropyl-β-D-1-thiogalactopyranoside (IPTG) to induce β-galactosidase synthesis which does not offer any benefit towards growth. The trade off between osmotic stress and burden on growth due to unnecessary gene expression has not been enumerated. The influence of osmotic stress on β-galactosidase synthesis and activity is not clearly understood. Here, we study the effect of salt concentration on β-galactosidase activity and burden on growth due to unnecessary gene expression in E.coli. We characterize the burden on growth in presence of varying concentrations of salt in the presence of IPTG using three strains, namely wild type, ∆lacI and ∆lacIlacZ mutant strains. We demonstrate that the salt concentrations, sensitively inhibits enzyme synthesis thereby influencing the burden on growth. In a wild type strain, addition of lactose into the medium demonstrated growth benefit at low salt concentration but not at higher concentrations. The extent of burden due to osmotic shock was higher in a lactose M9 medium than in a glycerol M9 medium. A linear relationship was observed between enzyme activity and burden on growth in various media types studied.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-3-748) contains supplementary material, which is available to authorized users.

Influence of osmotic stress, physicochemical factors and nitrogen supplements on embryogenesis and plantlet formation in Guizotia abyssinica Cass. (Niger)

An efficient protocol for somatic embryogenesis was developed for the edible oilseed crop Guizotia abyssinica Cass. (cv. IGP 76). Induction and proliferation of callus was achieved from cotyledonary explants on MS medium amended with 1.5 mg l−1 6-benzyladenine (BA) and 0.5 mg l−1 naphthalene acetic acid (NAA). Several auxin/cytokinin combinations, physical conditions, osmotic stresses and supplementary components, viz., amino acids and casein hydrolysate were tested for induction of embryogenic callus. Higher frequency of embryogenic calli (73.7 %) and somatic embryos per culture (22) were observed on MS + 1.5 mg l−1 BA + 0.5 mg l−1 NAA + 0.5 % NaCl. Histological analyses showed typical globular and other stages of embryo development. The MS medium lacking growth regulators was best for the maximum germination of embryos (53.4 %) and formation of plantlets (65.4 %). Regenerated plantlets were acclimatized and transferred to the field with 62 % survival rate.

Proton cycles through membranes in bacteria: Relationship between proton passive and active fluxes and their dependence on some external physico-chemical factors under fermentation

This paper represents H+ circles through the bacterial membranes, their peculiarities and relationship with ATP synthesis or hydrolysis, utilization or accumulation of energy are considered. Data on passive and active proton (H+) fluxes through the bacterial membranes are analyzed and their relationship with membrane H+ conductance (Gm(H+)) and permeability for H+ (P(H+)) is discussed. Methods for determination of bacterial membrane Gm(H+) are presented and some difficulties in obtaining and interpreting data are pointed out. Different ways and mechanisms of passive and active H+ fluxes, including a role of membrane lipids in H+ transfer, importance of phase transitions in lipid bilayers, operation of protonophores as well as H+ translocation via the F0 factor of the F0F1-ATPase, are discussed. Dependence of Gm(H+) for Escherichia coli, Enterococcus hirae, Streptococcus lactis and other bacteria on some external physico-chemical growth factors, particularly, on pH and oxidation reduction potential as well as influence of osmotic stress on Gm(H+) and H+ active fluxes through the bacterial membrane under fermentation have been shown. The relationship between Gm(H+), P(H+) and active H+ fluxes through a membrane is proposed, possible mechanisms of relationship between their alterations depending on pH and oxidation reduction potential are discussed. The results are important for understanding the structural and functional properties of bacterial membranes determining H+ cycles operation and mechanisms of H+ fluxes essential in adaptation of bacteria to altered environment conditions.

Novel Insights into E. coli’s Hexuronate Metabolism: KduI Facilitates the Conversion of Galacturonate and Glucuronate under Osmotic Stress Conditions

Using a gnotobiotic mouse model, we previously observed the upregulation of 2-deoxy-D-gluconate 3-dehydrogenase (KduD) in intestinal E. coli of mice fed a lactose-rich diet and the downregulation of this enzyme and of 5-keto 4-deoxyuronate isomerase (KduI) on a casein-rich diet. The present study aimed to define the role of the so far poorly characterized E. coli proteins KduD and KduI in vitro. Galacturonate and glucuronate induced kduD and kduI gene expression 3-fold and 7 to 11-fold, respectively, under aerobic conditions as well as 9 to 20-fold and 19 to 54-fold, respectively, under anaerobic conditions. KduI facilitated the breakdown of these hexuronates. In E. coli, galacturonate and glucuronate are normally degraded by UxaABC and UxuAB. However, osmotic stress represses the expression of the corresponding genes in an OxyR-dependent manner. When grown in the presence of galacturonate or glucuronate, kduID-deficient E. coli had a 30% to 80% lower maximal cell density and 1.5 to 2-fold longer doubling times under osmotic stress conditions than wild type E. coli. Growth on lactose promoted the intracellular formation of hexuronates, which possibly explain the induction of KduD on a lactose-rich diet. These results indicate a novel function of KduI and KduD in E. coli and demonstrate the crucial influence of osmotic stress on the gene expression of hexuronate degrading enzymes.

Influence of Osmotic Stress and Encapsulating Materials on the Stability of Autochthonous Lactobacillus plantarum after Spray Drying

With the aim of producing a functional fish food, autochthonous Lactobacillus plantarum LPS 47, isolated from healthy Chilean salmon, was stabilized using spray drying. In order to increase the resistance of microorganisms to high temperatures, osmotic stress during fermentation and different protective agents were evaluated (lactic solids: skim milk and whey, maltodextrin, pectin, and arabic gum). We found that bacteria that were not exposed to osmotic stress during culture, and that were spray-dried in the presence of cheese whey (20% w/w) as a protective material, gave the best results in terms of viability, humidity, and stability during storage. Dehydrated material reached a viability of approximately 109 CFU/g (colony-forming units per gram) and less than 5% humidity, values that were maintained over 10 weeks of storage at 4°C in a non-controlled atmosphere. Results show that it is possible to obtain a stable dehydrated probiotic product, with high concentration of microorganism, using spray drying and whey as a protective agent, without causing osmotic stress, by harvesting the biomass during the stationary phase.

The Effect of Created Local Hyperosmotic Microenvironment in Microcapsule for the Growth and Metabolism of Osmotolerant YeastCandida krusei

Candida krusei is osmotolerant yeast used for the production of glycerol. Addition of osmolyte such as NaCl into culture medium can increase the production of glycerol from glucose, but osmolytes may burden the glycerol separation. A coencapsulation method was suggested to create local extracellular hyperosmotic stress for glycerol accumulation. Firstly, the influence of osmotic stress induced by the addition of PEG4000 on growth and metabolism of free cell was studied in detail. Glycerol accumulation could be improved by employing PEG4000 as osmoregulator. Secondly, cells and PEG4000 were coentrapped in NaCS/PDMDAAC capsules to create local hyperosmotic stress. The effects of local hyperosmotic microenvironment on the cell growth and metabolism were studied. The coentrapment method increased the glycerol concentration by 25%, and the glycerol concentration attained 50 gL−1 with productivity of 18.8 gL−1Day−1 in shake flask. More importantly, the glycerol could be directly separated from the encapsulated cells. The entrapped cells containing PEG4000 were also cultivated for 15 days in an airlift reactor. The yield and productivity were ca. 35% and 21 gL−1Day−1, respectively.

Osmotic stress induced-capsaicin production in suspension cultures of Capsicum chinense Jacq.cv. Naga King Chili

The influence of osmotic stress on capsaicin production was investigated in cell suspension cultures of Capsicum chinense Jacq.cv. Naga King Chili, a chili species native to Northeastern India. The sterilized seeds were germinated in Murashige and Skoog medium. Two-week-old hypocotyls were excised from in vitro germinated seedlings and implanted in MS medium containing 2, 4-dichlorophenoxyacetic acid (2 mg/l), and Kinetin (0.5 mg/l) for callus induction. Capsaicin production in the suspension cultures was significantly affected using sucrose, mannitol, and NaCl in the medium. Stoichiometric analysis with different combinations of sucrose and non-sugar osmotic agent (NaCl) showed that osmotic stress was an important factor for enhancing capsaicin production in cell suspension cultures of C. chinense. The capsaicin content of 1,644.1 μg g−1 f.wt was recorded on day 15 in cultures grown in MS medium containing 87.64 mM sucrose in combination with 40 mM NaCl. However, osmotic stress treatment at 160 mM NaCl with sucrose resulted in lowering capsaicin accumulation and separation of cell wall from their cytoplasm, under microscopic observation.

Up-regulation of Human myo-Inositol Oxygenase by Hyperosmotic Stress in Renal Proximal Tubular Epithelial Cells

myo-Inositol oxygenase (MIOX) catalyzes the oxidative cleavage of myo-inositol (MI) to give d-glucuronic acid, a committed step in MI catabolism. d-Glucuronic acid is further metabolized to xylitol via the glucuronate-xylulose pathway. Although accumulation of polyols such as xylitol and sorbitol is associated with MI depletion in diabetic complications, no causal relationship has been established. Therefore we are examining the role of MIOX in diabetic nephropathy. Here we present evidence that the basis for the depletion of MI in diabetes is likely to be mediated by the increased expression of MIOX, which is induced by sorbitol, mannitol, and xylitol in a porcine renal proximal tubular epithelial cell line, LLC-PK1. To understand the molecular mechanism of regulation of MIOX expression by polyols, we have cloned the human MIOX gene locus of 10 kb containing 5.6 kb of the 5' upstream sequence. Analysis of the 5' upstream sequence led to the identification of an osmotic response element (ORE) in the promoter region, which is present approximately 2 kb upstream of the translation start site. Based on luciferase reporter and electrophoretic mobility shift assays, polyols increased the ORE-dependent expression of MIOX. In addition, we demonstrate that the activity of the promoter is dependent on the binding of the transcription factor, tonicity element-binding protein, or osmotic response element-binding protein, to the ORE site. These results suggest that the expression of MIOX is up-regulated by a positive feedback mechanism where xylitol, one of the products of MI catabolism via the glucuronate-xylulose pathway, induces an overexpression of MIOX.

Effect of osmotic stress on the activity of H +-ATPase and the levels of covalently and noncovalently conjugated polyamines in plasma membrane preparation from wheat seedling roots

The influence of osmotic stress on the H +-ATPase (EC 3.6.1.35) activity and the contents of covalently and noncovalently conjugated polyamines were investigated using plasma membrane (PM) vesicles isolated from the roots of wheat ( Triticum aestivum L.) seedlings with different drought-tolerance by the sucrose gradient centrifugation method. Results showed that after polyethylene glycol (PEG) 6000 (−0.55 MPa) treatment for 7 days, leaf relative water content (LRWC), relative dry weight increase rate (RDWIR) of seedlings of drought-sensitive Yangmai No. 9 cv. decreased more markedly than that of drought-tolerant Yumai No. 18 cv., while plasma membrane (PM) H +-ATPase activity, the content ratio of noncovalently conjugated polyamine (NCC-PAs) NCC-Spd + NCC-Spm to NCC-Put and the sum contents of covalently conjugated polyamines (CC-PAs) CC-Put + CC-Spd of PM of Yumai No. 18 cv. increased more markedly than that of Yangmai No. 9 cv. Exogenous Spd treatment alleviated osmotic stress injury to Yangmai No.9 seedlings, coupled with marked increases of NCC-Spd and NCC-Spm levels and H +-ATPase activity in the root PM vesicle. Under PEG osmotic stress, the concomitant treatment of drought-tolerant cv. Yumai No. 18 seedlings with methylglyoxyl-bis (guanylhydrazone) (MGBG), an inhibitor of S-adenosylmethionine decarboxylase (SAMDC), and phenanthrolin (o-Phen), an inhibitor of transglutaminase (TGase), caused a decrease of the NCC-Spd + NCC-Spm: NCC-Put ratio and a reduction of sum contents of CC-Put + CC-Spd, respectively. This was associated with decreased PM-H +-ATPase activity and tolerance of seedlings to osmotic stress. Together, these results suggest that tolerance of the wheat seedlings to osmotic stress is associated with the activity of H +-ATPase and the contents of NCC-Spd and NCC-Spm together with CC-Put and CC-Spd in the plasma membrane of roots.