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Adaptations to salt stress were studied in embryogenic cultures from two ecotypes of reed (Phragmites communisT.). In the 600 mM NaCl treatment, relative cell viability of dune reed embryogenic cultures from a desert region was 56% greater than the control, 198% greater than swamp reed embryogenic cultures. After treatment with different NaCl concentrations, their relative growth rates (RGRs), pyridine nucleotides, activities of antioxidant enzymes and plasma membrane H⁺-ATPase (EC 3.6.1.35) were determined. The results showed that NADPH content, NADPH/NADP⁺ ratio and the activity of plasma membrane H⁺-ATPase in dune reed embryogenic cultures were higher than those of the control in the present of 600 mM NaCl. The activities of peroxidase (POD, EC 1.11.1.7) and catalase (CAT, EC 1.11.1.6) increased more in dune reed embryogenic cultures than in swamp reed embryogenic cultures. Dune reed embryogenic cultures tolerated higher concentration of NaCl than swamp reed embryogenic cultures. Under high concentration of NaCl, the survival of dune reed embryogenic cultures might be due to reductive status maintenance and ions absorption regulation in the plant cells. This phenomenon would be a result of cross-adaptation in nature.     

Regulation of the structure and catalytic properties of plasma membrane H<Superscript>+</Superscript>-ATPase involved in adaptation of two reed ecotypes to their different habitats

The properties and kinetics of ATP and p-nitrophenyl phosphate (PNPP) hydrolysis activities of plasma membrane H⁺-ATPase from the two reed ecot ypes, swamp reed (SR) and dune reed (DR), were investigated. The pH optimum of the plasma membrane H⁺-ATPase in both reed ecotypes was similar but the sensitivity of the enzyme to the reaction medium pH seemed to be higher in DR than that in SR. Compared to SR, the DR exhibited a higher V_max value for ATP hydrolysis whereas the K_m value was almost similar in both reed ecotypes. The PNPP hydrolysis of the plasma membrane H⁺-ATPase was also studied in both reed ecotypes at increasing PNPP concentrations. K_m and V_max for PNPP hydrolysis showed great differences in the two reed ecotypes and in DR the K_m and V_max values were 2- and 10-fold, respectively, higher than those in SR. The ATP hydrolysis activity of the plasma membrane was markedly inhibited by hydroxylamine in both reed ecotypes, and the percentage inhibition of ATP hydrolysis rate seemed higher in DR than that in SR. In addition, the structure or property of the C-terminal end of the plasma membrane H⁺-ATPase were also different in the two reed ecotypes. These data suggest that different isoforms of the plasma membrane H⁺-ATPase might be developed and involved in the adaptation of the plant to the long-term drought-prone habitat.This research was supported by Natural Science Foundation of China (No. 30270238 & No. 30470274) and the National Key Basic Research Special Funds of China (G1999011705).     

The Regulation of the Plasma Membrane Redox System and H+-transport in Adaptation of Reed Ecotypes to Their Habitats

The redox system and H⁺-transport activities in the plasma membranes from two ecotypes of reed (Phragmites communis Trin.), named swamp reed (SR) and dune reed (DR) according to their habitats, were investigated. Compared to the SR, the DR possessed the very high rates of NADH oxidation and Fe(CN)₆ ^3– and EDTA-Fe³⁺ reduction when NADH was taken as the electron donor. As NADPH was an electron donor, the rate of NADPH oxidation was also significantly higher in the DR than that in the SR. In addition, the H⁺-transport activity in the plasma membranes was also significantly higher in the DR than in the SR.     

Effects of salt-adaptation and salt-stress on extracellular acidification and microsome phosphohydrolase activities in tomato cell suspensions

The effects of NaCl-adaptation and NaCl-stress on in vivo H⁺ extrusion and microsomal vanadate- and bafilomycin-sensitive ATPase and PPase activities were studied in tomato cell suspensions. Acidification of the external medium by 50 mM NaCl-adapted and non-adapted (control) tomato cells was similar. Extracellular acidification by both types of cells during the first hour of incubation with 2 μM fusicoccin (FC) in the presence of 100 mM NaCl was lightly increased while in the presence of 100 mM KCl it was increased by 3 (control)- and 6.5 (adapted)-fold. Extracellular alkalinization after 2 h of cell incubation in 100 mM NaCl indicated the possibility that a Na⁺/H⁺ exchange activity could be operating in both types of cells. Moreover, acidification induced by adding 100 mM NaCl + FC to non-adapted cells was relatively less affected by vanadate than that induced by 5 mM KCl + FC, which suggested that salt stress could induce some component other than H⁺ extrusion by H⁺-ATPase. In addition, no differences were observed in microsomal vanadate-sensitive ATPase activity among control, NaCl-adapted and NaCl-stressed cells, while K⁺-stimulated H⁺-PPase and bafilomycin-sensitive H⁺-ATPase activities were higher in microsomes from NaCl-adapted than in those from control cells. Likewise, the stimulation of in vivo H⁺ extrusion in NaCl adapted cells under NaCl or KCl stress in the presence of FC occurred with an inhibition of H⁺-PPase and bafilomycin-sensitive H⁺-ATPase activities and without changes in the vanadate-sensitive H⁺-ATPase activity. These results suggest that the stimulation of tonoplast proton pumps in NaCl-adapted cells, without changes in plasmalemma H⁺-ATPase, could serve to energize Na⁺ efflux across the plasmalemma and Na⁺ fluxes into vacuoles catalyzed by the Na⁺/H⁺ antiports. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ethylene and nitric oxide are involved in maintaining ion homeostasis in <Emphasis Type="Italic">Arabidopsis</Emphasis> callus under salt stress

In the present study, the role of ethylene in nitric oxide (NO)-mediated protection by modulating ion homeostasis in Arabidopsis callus under salt stress was investigated. Results showed that the ethylene-insensitive mutant etr1-3 was more sensitive to salt stress than the wild type (WT). Under 100 mM NaCl, etr1-3 callus displayed a greater electrolyte leakage and Na⁺/K⁺ ratio but a lower plasma membrane (PM) H⁺-ATPase activity compared to WT callus. Application of exogenous 1-aminocyclopropane-1-carboxylic acid (ACC, an ethylene precursor) or sodium nitroprusside (SNP, a NO donor) alleviated NaCl-induced injury by maintaining a lower Na⁺/K⁺ ratio and an increased PM H⁺-ATPase activity in WT callus but not in etr1-3 callus. The SNP actions in NaCl stress were attenuated by a specific NO scavenger or an ethylene biosynthesis inhibitor in WT callus. Under 100 mM NaCl, the NO accumulation and ethylene emission appeared at early time, and NO production greatly stimulated ethylene emission in WT callus. In addition, ethylene induced the expression of PM H⁺-ATPase genes under salt stress. The recovery experiment showed that NaCl-induced injury was reversible, as signaled by the similar recovery of Na⁺/K⁺ ratio and PM H⁺-ATPase activity in WT callus. Taken together, the results indicate that ethylene and NO cooperate in stimulating PM H⁺-ATPase activity to modulate ion homeostasis for salt tolerance, and ethylene may be a part of the downstream signal molecular in NO action.     

Properties of plasma membrane H<Superscript>+</Superscript>-ATPase in salt-treated <Emphasis Type="Italic">Populus euphratica</Emphasis> callus

The plasma membrane (PM) vesicles from Populus euphratica (P. euphratica) callus were isolated to investigate the properties of the PM H⁺-ATPase. An enrichment of sealed and oriented right-side-out PM vesicles was demonstrated by measurement of the purity and orientation of membrane vesicles in the upper phase fraction. Analysis of pH optimum, temperature effects and kinetic properties showed that the properties of the PM H⁺-ATPase from woody plant P. euphratica callus were consistent with those from herbaceous species. Application of various thiol reagents to the reaction revealed that reduced thiol groups were essential to maintain the PM H⁺-ATPase activity. In addition, there was increased H⁺-ATPase activity in the PM vesicles when callus was exposed to NaCl. Western blotting analysis demonstrated an enhancement of H⁺-ATPase content in NaCl-treated P. euphratica callus compared with the control.     

Nitric oxide enhances salt tolerance in maize seedlings through increasing activities of proton-pump and Na+/H+ antiport in the tonoplast

Nitric oxide (NO), an endogenous signaling molecule in animals and plants, mediates responses to abiotic and biotic stresses. Our previous work demonstrated that 100 μM sodium nitroprusside (SNP, an NO donor) treatment of maize seedlings increased K⁺ accumulation in roots, leaves and sheathes, while decreasing Na⁺ accumulation (Zhang et al. in J Plant Physiol Mol Biol 30:455–459, 2004b). Here we investigate how NO regulates Na⁺, K⁺ ion homeostasis in maize. Pre-treatment with 100 μM SNP for 2 days improved later growth of maize plants under 100 mM NaCl stress, as indicated by increased dry matter accumulation, increased chlorophyll content, and decreased membrane leakage from leaf cells. An NO scavenger, methylene blue (MB-1), blocked the effect of SNP. These results indicated that SNP-derived NO enhanced maize tolerance to salt stress. Further analysis showed that NaCl induced a transient increase in the NO level in maize leaves. Both NO and NaCl treatment stimulated vacuolar H⁺-ATPase and H⁺-PPase activities, resulting in increased H⁺-translocation and Na⁺/H⁺ exchange. NaCl-induced H⁺-ATPase and H⁺-PPase activities were diminished by MB-1. 1-Butanol, an inhibitor of phosphatidic acid (PA) production by phospholipase D (PLD), reduced NaCl- and NO-induced H⁺-ATPase activation. In contrast, applied PA stimulated H⁺-ATPase activity. These results suggest that NO acts as a signal molecule in the NaCl response by increasing the activities of vacuolar H⁺-ATPase and H⁺-PPase, which provide the driving force for Na⁺/H⁺ exchange. PLD and PA play an important role in this process.     

Changes in plasma membrane lipids, aquaporins and proton pump of broccoli roots, as an adaptation mechanism to salinity

Salinity stress is known to modify the plasma membrane lipid and protein composition of plant cells. In this work, we determined the effects of salt stress on the lipid composition of broccoli root plasma membrane vesicles and investigated how these changes could affect water transport via aquaporins. Brassica oleracea L. var. Italica plants treated with different levels of NaCl (0, 40 or 80 mM) showed significant differences in sterol and fatty acid levels. Salinity increased linoleic (18:2) and linolenic (18:3) acids and stigmasterol, but decreased palmitoleic (16:1) and oleic (18:1) acids and sitosterol. Also, the unsaturation index increased with salinity. Salinity increased the expression of aquaporins of the PIP1 and PIP2 subfamilies and the activity of the plasma membrane H⁺-ATPase. However, there was no effect of NaCl on water permeability (P_f) values of root plasma membrane vesicles, as determined by stopped-flow light scattering. The counteracting changes in lipid composition and aquaporin expression observed in NaCl-treated plants could allow to maintain the membrane permeability to water and a higher H⁺-ATPase activity, thereby helping to reduce partially the Na⁺ concentration in the cytoplasm of the cell while maintaining water uptake via cell-to-cell pathways. We propose that the modification of lipid composition could affect membrane stability and the abundance or activity of plasma membrane proteins such as aquaporins or H⁺-ATPase. This would provide a mechanism for controlling water permeability and for acclimation to salinity stress.     

Reinvestigation of auxin and fusicoccin stimulation of the plasma-membrane H+-ATPase activity

In vivo treatment of maize (Zea mays L.) coleoptile segments with auxin (indole-3-acetic acid; IAA) and fusicoccin (FC) followed by plasma-membrane isolation was used to characterize the effects of these treatments on the plasma-membrane H⁺-ATPase. Both IAA and FC increased H⁺ extrusion and elongation rate of the coleoptile segments, FC more strongly than IAA. Plasma membranes isolated after in-vivo treatment with FC showed a twofold stimulation of ATP hydrolysis and a several-fold stimulation of H⁺ pumping, whereas no effect was observed after IAA treatment, irrespective of whether the plasma membranes were prepared by two-phase partitioning or sucrose-gradient centrifugation. A more detailed investigation of the kinetic properties and pH dependence of the enzyme showed that FC treatment led to a twofold increase in V _max, a decrease in K _m for ATP from 1.5 mM to 0.24 mM, and a change in pH dependence resulting in increased activity at physiological pH levels. Again, IAA treatment showed no effects. Quantitation of the H⁺-ATPase by immunostaining using four different antibodies revealed no difference between IAA-and FC-treated material, and controls. From these data we conclude that (i) neither IAA nor FC gives rise to an increase in the amount of H⁺ -ATPase molecules in the plasma membrane that can be detected after membrane isolation, and (ii) if the H⁺-ATPase is activated by IAA, this activation is, in contrast to FC activation, not detectable after membrane isolation.Abbreviations BTP 1,3-bis(tris[hydroxymethyl]methylamino)-propane - FC fusicoccin - lyso-PC lysophosphatidylcholine - Mes 2-(N-morpholino)ethanesulfonic acid This paper is dedicated to Prof. Dieter Klämbt on the occasion of his 65th birthdayWe thank Ann-Christine Holmström and Adine Karlsson for excellent technical assistance, Professor Ramón Serrano (Instituto de Biologia Molecular y Celular de Plantas, UPV-CSIC, Universidad Politecnica, Valencia, Spain) for a generous gift of antisera to the H⁺-ATPase and Professor Wolfgang Michalke (Institut für Biologie III, Albert-Ludwigs-Universität, Freiburg, Germany) for kindly providing the monoclonal antibody to the H⁺-ATPase. This work was supported by the Swedish Natural Science Research Council, the Deutsche Agentur für Raumfahrtangelegenheiten (DARA, Bonn) via AGRAVIS (Bonn) and by the Ministerium für Wissenschaft und Forschung (MWF, Düsseldorf). Thomas Jahn received scholarships from the Deutsche Graduiertenförderung des Landes Nordrhein-Westfalen and the Deutscher Akademischer Austauschdienst (DAAD, Bonn).     

NaCl increases the activity of the plasma membrane H+-ATPase in C3 halophyte Suaeda salsa callus

Suaeda salsa calli treated with different concentrations of NaCl were used to examine the response of the plasma membrane (PM) H⁺-ATPase to NaCl and its role in salt tolerance. The optimum concentration of NaCl for growth of the calli was 50 mM, while growth was significantly inhibited at 250 mM NaCl. The ion and organic solute contents of calli increased with increasing NaCl. Activity of the PM H⁺-ATPase increased when the calli were treated with NaCl over a certain concentration range (0–150 mM NaCl). However, the activity reached its maximum with 150 mM NaCl. Immunoblotting analysis of the PM H⁺-ATPase protein from calli cultures with anti-Zea mays H⁺-ATPase serum (monoclonal 46E5B11D5) identified a single polypeptide of ~90 kDa. The peptide levels increased in the calli treated with NaCl at 150 mM NaCl compared to control, but the increase at 50 mM NaCl was less pronounced. Northern blot analysis showed that the expression of the PM H⁺-ATPase also increased after the calli were treated with NaCl. These results suggest that the increase in PM H⁺-ATPase activity is due to both an increase in the amount of PM H⁺-ATPase protein and an up-regulation of the PM H⁺-ATPase gene, which is involved in the salt tolerance of S. salsa calli.     

Plant regeneration from callus cultures in two ecotypes of reed (Phragmites communis Trinius)

Summary Different ecotypes of reed (Phragmites communis Trinius) provide an ideal resource for studies on plant environmental adaptations and presence of genes relating to stress resistance. Dune reed is a drought-tolerant reed ecotype growing in the desert regions of north-west China. In this work, in vitro culture systems of dune reed and local swamp reed (as control) were established by optimizing the culture conditions for each of them. Bright yellow calluses were induced on a Murashige and Skoog medium containing 4.5 μM 2,4-dichlorophenoxyacetic acid (2,4-D), 5.4 μM naphthaleneacetic acid and 2.2μM benzyladenine. Benzyladenine promoted callus induction, but was not required for callus maintenance. Four types of callus have been identified from each of the reed ecotypes. Two types of callus, i.e. type A (formed normal green shoots) and type C (formed albino plants), were both found as embryogenic calluses. The optimal concentrations of 2,4-D to maintain embryogenic callus were 2.3–4.5 μM for dune reed and 9.0–13.5 μM for swap reed. Plant regeneration was achieved from types A and C callus in a hormone-free medium. The embryogenic calluses of swamp reed have been maintained for over 2 yr and still retain their strong embryogenic potential; however, those of dune reed gradually lost their embryogenic potential after only 7 mo. of culture. Regenerated plants from the two reed ecotypes showed, after a growth season, similar morphology and the same chromosome number (2n=8x=96, octoploid) as the wild plants.     

Nitrogen deprivation induces cross-tolerance of Poa annua callus to salt stress

Alternative respiration pathway (AP) is an important pathway which can be induced by environment stresses in plants. In the present study, we show a new mechanism involving the AP in nitrogen deprivation-induced tolerance of Poa annua callus to salt stress. The AP capacity markedly increased under a 600 mM NaCl treatment or nitrogen deprivation pretreatment and reached a maximum under the nitrogen deprivation pretreatment combined with the NaCl treatment (–N+NaCl). Malondialdehyde (MDA) and H₂O₂ content and Na⁺/K⁺ ratio significantly increased under the 600 mM NaCl treatment but less under the–N+NaCl treatment. Moreover, both the nitrogen deprivation and the NaCl stress stimulated the plasma membrane (PM) H⁺-ATPase activity and increased pyruvate content. The maximal stimulating effect was found under the–N+NaCl treatment. When the AP capacity was reduced by salicylhydroxamic acid (SHAM, an inhibitor of AP), content of MDA and H₂O₂ and Na⁺/K⁺ ratio dramatically increased, whereas PM H⁺-ATPase activity decreased. Moreover, exogenous application of pyruvate produced a similar effect as the nitrogen deprivation pretreatment. The effects of SHAM on the Poa annua callus were counteracted by catalase (a H₂O₂ scavenger) and diphenylene iodonium (a plasma membrane NADPH oxidase inhibitor). Taken together, our results suggest that the nitrogen deprivation enhanced the capacity of AP by increasing pyruvate content, which in turn prevented the Poa annua callus from salt-induced oxidative damages and Na⁺ over-uptake.     

Salinity adaptation of plasma membrane H+-ATPase in the salt marsh plant Spartina patens: ATP hydrolysis and enzyme kinetics

Spartina patens, an intertidal C4 grass, grows in the upper salt marsh and tolerates coastal seawater salinity. The regulation of ion movement across the plasma membrane (PM) for plant salt tolerance is thought to be achieved by an electrochemical gradient generated by plasma membrane H⁺-ATPase. In this study, the change of PM H⁺-ATPase in response to NaCl was characterized for S. patens callus. Callus was cultured for 10 weeks under salinity levels of 0 mM, 170 mM, 340 mM, and 510 mM NaCl. Plasma membrane was isolated from a Dextran/PEG aqueous polymer two-phase system and the purity was demonstrated with membrane enzyme markers. There was a significant increase (up to 2-3 fold) of PM H⁺-ATPase activity when callus was grown on media containing NaCl. The incremental activation of PM H⁺-ATPase activity would enable the cell to tolerate higher cytoplasmic NaCl concentrations. PM H⁺-ATPase appeared to have a higher Vmax and a lower substrate concentration (Km to reach Vmax. When growth medium salinity increased from 0 mM to 170 and 340 mM, the Vmax of H⁺-ATPase increased from 0.64 to 1.00 and 1.73, respectively, while the Km decreased from 3.58 to 2.07 and 2.44 mM, respectively. In vitro NaCl inhibition kinetic data revealed a pattern of non-competitive inhibition by NaCl on PM H⁺-ATPase. The response of PM H⁺-ATPase in S. patens callus suggests that this species has evolved mechanisms that can regulate this important enzyme when cells are exposed to NaCl.     

Localization of plasma membrane H+-ATPase in nodules of Phaseolus vulgaris L.

Legume nodules have specialized transport functions for the exchange of carbon and nitrogen compounds between bacteroids and root cells. Plasma membrane-type (vanadate-sensitive) H⁺-ATPase energizes secondary active transporters in plant cells and it could drive exchanges across peribacteroidal and plasmatic membranes. A nodule cDNA corresponding to a major isoform of Phaseolus vulgaris H⁺-ATPase (designated BHA1) has been cloned. BHA1 is a functional proton pump because after removal of its inhibitory domain and can complement a yeast mutant unable to synthesize a H⁺-ATPase. BHA1 is not nodule-specific, since it is also expressed in roots of uninfected plants. It belongs to the subfamily of plasma membrane H⁺-ATPases defined by the Arabidopsis AHA1, AHA2 and AHA3 genes and the tobacco PMA4 and corn MHA2 genes. In situ hybridization in nodule sections indicates high expression of BHA1 limited to uninfected cells. These results were confirmed by immunocytochemistry. The relatively low expression of plasma membrane-type H⁺-ATPase in Rhizobium-infected cells put a note of caution on the origin of the vanadate-sensitive ATPase described in preparations of peribacteroidal membranes. Also, our results indicate that active transport in symbiotic nodules is most intense at the plasma membrane of uninfected cells and support a specialized role of uninfected tissue for nitrogen transport.     

Relationship between expression of the PM H<Superscript>+</Superscript>-ATPase,growth and ion partitioning in the leaves of salt-treated <Emphasis Type="Italic">Medicago</Emphasis> species

The role of the plasma membrane (PM) H⁺-ATPase (E.C. 3.6.1.3) in the plants response to salt stress was studied in the perennial leguminosae forage Medicago arborea L. and its close relative Medicago citrina (Font-Quer) Greuter, a species exposed to saline conditions in its original habitat. Plants were solution cultured for 8 days in 1 or 100 mM NaCl. Leaf growth and CO₂ assimilation were more inhibited by salt in M. arborea than in M. citrina. Both species were able to osmoregulate, and salt-treated plants maintained turgor potentials, with no differences between species. Contrasting ion distribution patterns showed that M. citrina was able to exclude Na⁺ from the leaves more selectively, while M. arborea had a greater buildup of leaf blade Na⁺. Isolation of purified PM and quantification of H⁺-ATPase protein by Western blot analysis against the 46E5B11D5 or AHA3 antibodies showed an increase in response to salt stress in the expanding (92%) and expanded leaves (87%) of M. citrina, while no differences were found in the corresponding leaves of M. arborea. The assay of H⁺-ATPase specific activity of the two leaf types in salinized M. citrina confirmed this increase, as activities increased with 55% and 104% for the expanded and expanding leaves, respectively, while no significant differences were found for either leaf type of salinized M. arborea. A possible role of the increased expression of the PM H⁺-ATPase for leaf expansion and ion exclusion in salt-stressed plants is discussed.     

Reversible changes of extracellular pH during action potential generation in a higher plant Cucurbita pepo

A pH-sensitive electrode was applied to measure activity of H⁺ ions in the medium surrounding excitable cells of pumpkin (Cucurbita pepo L.) seedlings during cooling-induced generation of action potential (AP). Reversible alkalization shifts were found to occur synchronously with AP, which could be due to the influx of H⁺ ions from external medium into excitable cells. Ethacrynic acid (an anion channel blocker) reduced the AP amplitude but had no effect on the transient alkalization of the medium. An inhibitor of plasma membrane H⁺-ATPase, N,N’-dicyclohexylcarbodiimide suppressed both the AP amplitude and the extent of alkalization. In experiments with plasma membrane vesicles, the hydrolytic H⁺-ATPase activity was subjected to inhibition by Ca²⁺ concentrations in the range characteristic of cytosolic changes during AP generation. The addition of a calcium channel blocker verapamil and a chelating agent EGTA to inhibit Ca²⁺ influx from the medium eliminated the AP spike and diminished reversible alkalization of the external solution. An inhibitor of protein kinase, H-7 alleviated the inhibitory effect of Ca²⁺ on hydrolytic H⁺-ATPase activity in plasma membrane vesicles and suppressed the reversible alkalization of the medium during AP generation. The results provide evidence that the depolarization phase of AP is associated not only with activation of chloride channels and Cl^? efflux but also with temporary suppression of plasma membrane H⁺-ATPase manifested as H⁺ influx. The Ca²⁺-induced inhibition of the plasma membrane H⁺-ATPase is supposedly mediated by protein kinases.     

Dimorphism-associated changes in plasma membrane H+-ATPase activity of Candida albicans

In situ plasma membrane H⁺-ATPase activity was monitored during pH-regulated dimorphism of Candida albicans using permeabilized cells. ATPase activity was found to increase in both the bud and germ tube forming populations at 135 min which coincides with the time of evagination. Upon reaching the terminal phenotype the mycelial form exhibited higher H⁺-ATPase activity as compared to the yeast form. At the time of evagination H⁺-efflux exhibited an increase. K⁺ depletion resulted in attenuated ATPase activity and glucose induced H⁺-efflux. The results demonstrate that ATPase may play a regulatory role in dimorphism of C. albicans and K⁺ acts as a modulator.Abbreviations PM Plasma membrane - pHi intracellular pH - Pi inorganic phosphorus - TET Toluene: Ethanol: Triton X-100     

Protective effect of exogenous polyamines on root tonoplast function against salt stress in barley seedlings

Salinity stress is one of the most serious factors limiting the productivity of agricultural crops. A possible survival strategy of plants under saline conditions is to sequester excess Na⁺ in the vacuole by vacuolar Na⁺/H⁺ antiport using a pH gradient generated by H⁺-ATPasc (EC 3.6.1.35) and H⁺-Pyrophosphatase (H⁺-PPase; EC 3.6.1.1) to maintain a higher K⁺/Na⁺ ratio in cytoplasm. The effect of exogenously applied polyamines (PAs) in stabilizing root tonoplast integrity and function against salt stress in the barley (Hordeum vulgare L.) seedlings was investigated. The NaCl-induced reductions in the contents of phospholipids and PAs in tonoplast vesicles isolated from barely seedling roots, as well as the activities of H⁺-ATPase, H⁺-PPase and vacuolar Na⁺/H⁺ antiport were all partially restored by the application of 0.5 mM putrescine and 0.5 mM spermidine, especially the former. The above results indicated that one of the mechanisms involved in attenuating salt injury in barley seedlings by exogenous PAs application was to maintain tonoplast integrity and function under saline conditions. Moreover, the possible mechanism involved in counteracting detrimental effects of salt on the barley seedlings by the application of exogenous PAs was discussed.