Effects of silicon on enzyme activity and sodium,potassium and calcium concentration in barley under salt stress

Two contrasting barley (Hordeum vulgare L.) cultivars: Kepin No.7 (salt sensitive), and Jian 4 (salt tolerant) were grown in a hydroponics system containing 120 mol m^-3 NaCl only and 120 mol m^-3 NaCl with 1.0 mol m^-3 Si (as potassium silicate). Compared with the plants treated with salt alone, superoxide dismutase (SOD) activity in plant leaves and H⁺-ATPase activity in plant roots increased, and malondialdehyde (MDA) concentration in plant leaves decreased significantly for both cultivars when treated with salt and Si. The addition of Si was also found to reduce sodium but increase potassium concentrations in shoots and roots of salt-stressed barley. Sodium uptake and transport into shoots from roots was greatly inhibited by added Si under salt stress conditions. However, Si addition exhibited little effect on calcium concentrations in shoots of salt-stressed barley. Thus, Si-enhanced salt tolerance is attributed to selective uptake and transport of potassium and sodium by plants. The results of the present study suggest that Si is involved in the metabolic or physiological changes in plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

The effects of salt stress on polypeptides in membrane fractions from barley roots

Cell fractions enriched in endoplasmic reticulum, tonoplast, plasma membrane, and cell walls were isolated from roots of barley (Hordeum vulgare L. cv CM 72) and the effect of NaCl on polypeptide levels was examined by two-dimensional (2D) polyacrylamide gel electrophoresis. The distribution of membranes on continuous sucrose gradients was not significantly affected by growing seedlings in the presence of NaCl; step gradients were used to isolate comparable membrane fractions from roots of control and salt-grown plants. The membrane and cell wall fractions each had distinctive polypeptide patterns on 2D gels. Silver-stained gels showed that salt stress caused increases or decreases in a number of polypeptides, but no unique polypeptides were induced by salt. The most striking change was an increase in protease resistant polypeptides with isoelectric points of 6.3 and 6.5 and molecular mass of 26 and 27 kilodaltons in the endoplasmic reticulum and tonoplast fractions. Fluorographs of 2D gels of the tonoplast, plasma membrane, and cell wall fractions isolated from roots of intact plants labeled with [³⁵S]methionine in vivo also showed that salt induced changes in the synthesis of a number of polypeptides. There was no obvious candidate for an integral membrane polypeptide that might correspond to a salt-induced sodium-proton anti-porter in the tonoplast membrane.     

Photosynthesis and ion content of leaves and isolated chloroplasts of salt-stressed spinach

Spinach (Spinacia oleracea) plants were subjected to salt stress by adding NaCl to the nutrient solution in increments of 25 millimolar per day to a final concentration of 200 millimolar. Plants were harvested 3 weeks after starting NaCl treatment. Fresh and dry weight of both shoots and roots was decreased more than 50% compared to control plants but the salt-stressed plants appeared healthy and were still actively growing. The salt-stressed plants had much thicker leaves. The salt-treated plants osmotically adjusted to maintain leaf turgor. Leaf K⁺ was decreased but Na⁺ and Cl⁻ were greatly increased.

The potential photosynthetic capacity of the leaves was measured at saturating CO₂ to overcome any stomatal limitation. Photosynthesis of salt-stressed plants varied only by about 10% from the controls when expressed on a leaf area or chlorophyll basis. The yield of variable chlorophyll a fluorescence from leaves was not affected by salt stress. Stomatal conductance decreased 70% in response to salt treatment.

Uncoupled rates of electron transport by isolated intact chloroplasts and by thylakoids were only 10 to 20% below those for control plants. CO₂-dependent O₂ evolution was decreased by 20% in chloroplasts isolated from salt-stressed plants. The concentration of K⁺ in the chloroplast decreased by 50% in the salt-stressed plants, Na⁺ increased by 70%, and Cl⁻ increased by less than 20% despite large increases in leaf Na⁺ and Cl⁻.

It is concluded that, for spinach, salt stress does not result in any major decrease in the photosynthetic potential of the leaf. Actual photosynthesis by the plant may be reduced by other factors such as decreased stomatal conductance and decreased leaf area. Effective compartmentation of ions within the cell may prevent the accumulation of inhibitory levels of Na⁺ and Cl⁻ in the chloroplast.

     

Exogenous silicon (Si) increases antioxidant enzyme activity and reduces lipid peroxidation in roots of salt-stressed barley (Hordeum vulgare L.)

Two contrasting barley (Hordeum vulgare L.) cultivars, i.e. Kepin No.7 (salt sensitive) and Jian 4 (salt tolerant), were grown hydroponically to study the effect of exogenous silicon (Si) on time dependent changes of the activities of major antioxidant enzymes and of lipid peroxidation in roots under salt stress. Enzymes included: superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and glutathione reductase (GR). Three treatments with three replicates were investigated consisting of a control (basal nutrients with neither NaCl nor Si added), 120 mmol/L-1 NaCl, and 120 mmol/L-1 NaCl +1.0 mmol/L-1 Si. Plant roots were harvested 2, 4 and 6 days after treatment and assayed for activities of the antioxidant enzymes and the concentrations of reduced glutathione (GSH) and malondialdehyde (MDA), and electrolytic leakage percentage (ELP). The activities of SOD, POD and CAT in roots of salt-stressed plants were significantly stimulated at Day 2 compared to control plants, but considerably decreased at Day 4 and onward. GR activity in roots of salt-stressed plants remained unchanged at Day 2, but significantly decreased at Day 4 and onward. However, exogenous Si significantly enhanced these enzyme activities in roots of salt-stressed plants compared to Si-deprived salt treatments. This Si effect was time-dependent and became stronger as the experiments continued. The tendency of change in the activities of antioxidant enzymes and the concentration of GSH coincided with the concentration of MDA, the end product of lipid peroxidation, and the ELP. Higher activities of antioxidant enzymes, and higher concentration of GSH, but lower concentration of MDA and lower ELP were noted in cultivar Jian 4 compared to Kepin No. 7, implying genotypic differences with Jian 4 being less susceptible to stress-dependent membrane lipid peroxidation. The effects of Si-enhanced salt tolerance are discussed with respect to cell membrane integrity, stability and function in barley.     

Effect of ABA on the contents of proline, polyamines, and cytokinins in the common ice plants under salt stress

The effects of ABA treatment on the contents of proline, polyamines (PA), and cytokinins (CK) in the facultative halophyte the common ice plant (Mesembryanthemum crystallinum L.) subjected to salt stress were studied. Plants grown in the phytotron chamber on Jonson nutrient medium for 6 weeks were subjected to 6-day-long salinity by a single NaCl adding to medium. During first three days of salinity, half plants of each treatment were placed for 30 min on nutrient medium containing 0, 100, or 300 mM NaCl plus ABA in the final concentration of 1 μM. Salinity reduced biomass accumulation and water and chlorophyll contents in plants. This was accompanied by the increase in the levels of MDA, proline, and sodium ions. ABA treatment of salt-stressed plants favored biomass accumulation and photosynthetic pigment protection, reduced the intensity of oxidative stress and the level of NaCl-induced proline accumulation. ABA treatment increased the contents of putrescine (Put) and spermidine (Spd) in the leaves and roots of control plants (not subjected to salt stress), reduced the losses of Put in the leaves and roots and Spd in the roots in the presence of 100 mM NaCl, and suppressed cadaverine (Cad) accumulation in the roots in the presence of 300 mM NaCl. In the presence of NaCl, ABA reduced the contents of zeatin and zeatin riboside and increased the level of zeatin-O-glucoside in the roots and isopentenyladenosine and isopentenyladenine in the leaves. Thus, ABA protective action under salinity can be realized through the weakening of oxidative stress (a decrease in MDA content) and the regulation of PA, proline, and CK metabolism, which has a great significance in plant adaptation to injurious factors.     

In vitro and in vivo phosphorylation of polypeptides in plasma membrane and tonoplast-enriched fractions from barley roots

Phosphorylation of polypeptides in membrane fractions from barley (Hordeum vulgare L. cv CM 72) roots was compared in in vitro and in vivo assays to assess the potential role of protein kinases in modification of membrane transport. Membrane fractions enriched in endoplasmic reticulum, tonoplast, and plasma membrane were isolated using sucrose gradients and the membrane polypeptides separated using sodium dodecyl sulfate polyacrylamide gel electrophoresis. When the membrane fractions were incubated with γ-[³²P]ATP, phosphorylation occurred almost exclusively in the plasma membrane fraction. Phosphorylation of a band at 38 kilodaltons increased as the concentration of Mg²⁺ was decreased from millimolar to micromolar levels. Phosphorylation of bands at 125, 86, 58, 46, and 28 kilodaltons required millimolar Mg²⁺ concentrations and was greatly enhanced by Ca²⁺. When roots of intact plants were labeled with [³²P]orthophosphate, polypeptides at approximately 135, 116, 90, 46 to 53, 32, 28, and 19 kilodaltons were labeled in the plasma membrane fraction and polypeptides at approximately 73, 66, and 48 kilodaltons were labeled in the tonoplast fraction. Treatment of the roots of intact plants with 150 millimolar NaCl resulted in increased phosphorylation of some polypeptides while treatment with 100 mm NaCl had no effect.     

Genetic and epigenetic effects of salinity on in vitro growth of barley

Morphological, physiological and molecular changes were investigated in in vitro salt-stressed barley (Hordeum vulgare L. cv. Tokak). Mature embryos were cultured in Murashige and Skoog medium containing 0 (control), 50 and 100 mM NaCl for 20 days. Both concentrations inhibited shoot growth, decreased fresh weight and protein content, and increased SOD (EC 1.15.1.1) activity in a dose-dependent manner. The lower concentration increased root growth. Salinity caused nucleotide variations in roots, but did not affect shoot DNAs. The higher concentration caused methylation changes, mainly hypermethylation in shoots. This is the first study on genetic and epigenetic effects of salinity in barley.     

A Comparison of the Effect of Salt on Polypeptides and Translatable mRNAs in Roots of a Salt-Tolerant and a Salt-Sensitive Cultivar of Barley

The effect of salt stress on polypeptide and mRNA levels in roots of two barley (Hordeum vulgare L.) cultivars differing in salt tolerance (cv CM 72, tolerant; cv Prato, sensitive) was analyzed using two-dimensional polyacrylamide gel electrophoresis. Preliminary experiments indicated that germination of Prato was inhibited significantly in the presence of NaCl, but growth of the surviving Prato seedlings was not substantially different from that of CM 72. Fluorographs of two-dimensional gels containing in vivo labeled polypeptides or in vitro translation products were computer analyzed to identify and quantitate changes that resulted when plants were grown in the presence of 200 millimolar NaCl for 6 days. The patterns of in vivo labeled polypeptides and in vitro products of CM 72 and Prato were qualitatively the same. Salt caused quantitative changes in numerous polypeptides and translatable mRNAs, but, overall, the changes were relatively small. Salt did not induce the synthesis of unique polypeptides or translatable mRNAs and did not cause any to disappear. Because of the similarities of the two cultivars with respect to growth and polypeptide patterns and the slight changes in polypeptide and translation product levels caused by salt, specific polypeptides or translatable mRNAs that are related to salt tolerance in barley could not be identified.     

Nitrogenase Inhibition in Nodules from Pea Plants Grown Under Salt Stress Occurs at the Physiological Level and can be Alleviated by B and Ca

In order to shed new light on the mechanisms of salt-mediated symbiotic N₂-fixation inhibition, the effect of salt stress (75 mM) on N₂-fixation in pea root nodules induced by R. leguminosarum was studied at the gene expression, protein production and enzymatic activity levels. Acetylene reduction assays for nitrogenase activity showed no activity in salt-stressed plants. To know whether salt inhibits N₂-fixing activity at a molecular or at a physiological level, expression of the nifH gene, encoding the nitrogenase reductase component of the nitrogenase enzyme was analyzed by RT-PCR analysis of total RNA extracted from nodulated roots. The nifH messenger RNA was present both in plants grown in the presence and absence of salt, although a reduction was observed in salt-stressed plants. Similar results were obtained for the immunodetection of the nitrogenase reductase protein in Western-blot assays, indicating that nitrogen fixation failed mainly at physiological level. Given that nutrient imbalance is a typical effect of salt stress in plants and that Fe is a prosthetic component of nitrogenase reductase and other proteins required by symbiotic N₂-fixation, as leghemoglobin, plants were analyzed for Fe contents by atomic absorption and the results confirmed that Fe levels were severely reduced in nodules developed in salt-stressed plants. In a previous papers (El-Hamdaoui et al., 2003b), we have shown that supplementing inoculated legumes with boron (B) and calcium (Ca) prevents nitrogen fixation decline under saline conditions stress. Analysis of salt-stressed nodules fed with extra B and Ca indicated that Fe content and nitrogenase activity was similar to that of non-stressed plants. These results indicate a linkage between Fe deprivation and salt-mediated failure of nitrogen fixation, which is prevented by B and Ca leading to increase of salt tolerance.     

Effects of silicon on H+-ATPase and H+-PPase activity,fatty acid composition and fluidity of tonoplast vesicles from roots of salt-stressed barley (Hordeum vulgare L.)

We investigated the effects of silicon (Si) on time-dependent changes in root tonoplast H⁺-ATPase and H⁺-PPase activities, membrane fatty acid compositions and tonoplast fluidity in two barley (Hordeum vulgare L.) cultivars differing in salt tolerance. Plants were grown in NaCl-free (control) and NaCl-supplied (60 and 120 mM, respectively) nutrient solutions with or without 1.0 mM Si. Plant roots were harvested to isolate tonoplast vesicles for assay of H⁺-ATPase and H⁺-PPase activities at days 2, 4, and 6 after treatment in the first experiment and for analysis of membrane fatty acid composition and fluidity at day 4 after treatment in the second experiment. The results showed that tonoplast H⁺-ATPase and H⁺-PPase activities in roots of salt-treated plants increased at day 2, which was more obvious at 60 mM NaCl in the salt-tolerant cultivar than in the salt-sensitive cultivar, and then decreased at day 4 and onward. These enzyme activities decreased consistently from days 2 to 6 for treatment with 120 mM NaCl. However, inclusion of 1.0 mM Si significantly enhanced both H⁺-ATPase and H⁺-PPase activities in roots of salt stressed barley, which was irrespective of NaCl level or cultivar used. The ratio of unsaturated to saturated fatty acids (U/S) increased under salt stress for both cultivars. Addition of Si to salt treatment increased the ratio of U/S in salt-tolerant cultivar but it did not in salt-sensitive cultivar compared to non-Si-amended salt treatment. Salt treatment decreased tonoplast fluidity of roots of barley significantly compared with control treatment. However, root tonoplast fluidity was significantly lower in the Si-amended salt treatment than in the non-Si-amended salt treatment. These results were in line with the previous findings that Si could help increase antioxidative defense and reduce membrane lipid oxidative damage in barley under salt stress. The possible mechanisms involved in Si-enhanced salt tolerance were discussed with respect to cell membrane integrity, stability and function in barley.     

Growth, Phosphate Pools, and Phosphate Mobilization of Salt-stressed Sesame and Pepper

The growth and phosphate mobilization of control and salt-stressed sesame (Sesamum indicum L.) and pepper (Capsicum annuum L.) plants were examined to ascertain whether or not translocation limits growth of salt-stressed plants. Plants were grown in a complete nutrient solution with and without excess salt. One-half of the control and salt-stressed plants were later transferred to phosphate-free culture solution (“−P” plants). Measurements of growth and phosphate pools in leaves indicated that with or without salinity “−P” plants utilized their phosphate reserves to support growth for a time at rates equaling those of plants supplied with phosphate. The results indicate that mobilization was not limiting for growth of salt-stressed plants.

Defoliation experiments were performed at a developmental stage when the import of assimilates by the youngest expanding leaves could be changed by removing certain source or sink leaves. These experiments also indicated that phloem transport was not limiting for leaf growth on salt-stressed plants.

     

Influence of silicon on microdistribution of mineral ions in roots of salt-stressed barley as associated with salt tolerance in plants

Two contrasting barley (Hordeum vulgare L.) cultivars: Kepin No.7 (salt sensitive), and Jian 4 (salt tolerant) were grown hydroponically to investigate the microdistribution of mineral ions in roots as affected by silicon (Si) with respect to salt tolerance. The experiment was undertaken consisting of two treatments with 3 replicates: (i) 120 mmol · L⁻¹ NaCl alone (referred to as Si-NaCl+), (ii) 120 mmol · L⁻¹ NaCl + 1.0 mmol · L⁻¹ Si (as potassium silicate) (referred to as Si+NaCl+). Plant root tips were harvested for microanalysis using an energy dispersive X-ray microanalyzer (EDX) 30 d after transplanting. Higher Cl and Na X-ray peaks were recorded in the root epidermal, cortical and stelar cells of roots for the treatment Si-NaCl+ with the majorities of Na and Cl being accumulated in epidermal and cortical cells, while relatively low K peaks were observed regardless of the barley cultivars used. By contrast, considerably higher K peaks were detected in the epidermal, cortical and stelar cells of the roots for the treatment Si+NaCl+, but lower Cl and Na peaks were also observed for this treatment with both Na and Cl ions being evenly distributed in the epidermal, cortical and stelar cells. These findings directly support our previous finding, which showed that Si depressed the uptake of sodium but enhanced the uptake of potassium by salt-stressed barley. We believe that one of the possible mechanisms involved in Si-enhancement of salt tolerance in barley is attributed to the Si-induced changes in the uptake and microdistribution of mineral ions in plants.     

The effect of salt stress on polyamine biosynthesis and content in mung bean plants and in halophytes

The activity of L-arginine decarboxylase (EC 4.1.1.19) and L-ornithine decarboxylase (EC 4.1.1.17), polyamine content, and incorporation of arginine and ornithine into polyamines, were determined in mung bean [Vigna radiata (L.) Wilczek] plants subjected to salt (hypertonic) stress (NaCl at 0.51–2.27 MPa). Changes in enzyme activity in response to hypotonic stress were determined as well in several halophytes [Pulicaria undulata (L.), Kostei, Salsola rosmarinus (Ehr.) Solms-Laub, Mesembryanthemum forskahlei Hochst, and Atriplex halimus L.]. NaCl stress, possibly combined with other types of stress that accompanied the experimental conditions, resulted in organ-specific changes in polyamine biosynthesis and content in mung bean plants. The activity of both enzymes was inhibited in salt-stressed leaves. In roots, however, NaCl induced a 2 to 8-fold increase in ornithine decarboxylase activity. Promotion of ornithine decarboxylase in roots could be detected already 2 h after exposure of excised roots to NaCl, and iso-osmotic concentrations of NaCl and KCl resulted in similar changes in the activity of both enzymes. Putrescine level in shoots of salt-stressed mung bean plants increased considerably, but its level in roots decreased. The effect of NaCl stress on spermidine content was similar, but generally more moderate, resulting in an increased putrescine/spermidine ratio in salt-stressed plants. Exposure of plants to NaCl resulted also in organ-specific changes in the incorporation of both arginine and ornithine into putrescine: incorporation was inhibited in leaf discs but promoted in excised roots of salt-stressed mung bean plants. In contrast to mung bean (and several other glycophytes), ornithine and arginine decarboxylase activity in roots of halophytes increased when plants were exposed to tap water or grown in a pre-washed soil—i.e. a hypotonic stress with respect to their natural habitat. NaCl, when present in the enzymatic assay mixture, inhibited arginine and ornithine decarboxylase in curde extracts of mung bean roots, but did not affect the activity of enzymes extracted from roots of the halophyte Pulicaria. Although no distinct separation between NaCl stress and osmotic stress could be made in the present study, the data suggest that changes in polyamines in response to NaCl stress in mung bean plants are coordinated at the organ level: activation of biosynthetic enzymes concomitant with increased putrescine biosynthesis from its precursors in the root system, and accumulation of putrescine in leaves of salt-stressed plants. In addition, hypertonic stress applied to glycophytes and hypotonic stress applied to halophytes both resulted in an increase in the activity of polyamine biosynthetic enzymes in roots.     

Plant growth promoting rhizobacteria alleviate salinity induced negative effects on growth, oil content and physiological status in Mentha arvensis

This study was aimed to investigate the effect of inoculation on three salt-tolerant, plant-growth-promoting rhizobacteria (PGPR) STR2 (Bacillus pumilus), STR8 (Halomonas desiderata) and STR36 (Exiguobacterium oxidotolerans), for their growth-promoting potential and efficacy in augmenting salt tolerance in Mentha arvensis, an essential oil-bearing crop and natural source of l-menthol, under varying levels of NaCl stress (0, 100, 300 and 500 mM) imposed through irrigating water. Increase in the levels of salt concentration led to a decrease in the growth, fresh weight, leaf–stem ratio, oil content and yield. However, the negative effects of salinity were observed to be convalesced in the PGPR inoculated plants. At salinity levels of 100 and 300 mM NaCl, H. desiderata inoculated plants recorded the highest herb yield, whereas at 500 mM NaCl, the plants inoculated with E. oxidotolerans yielded maximum herb. The oil content in non-inoculated, salt-stressed plants was observed to be 0.46, 0.42 and 0.35 % at 100, 300 and 500 mM NaCl, respectively, whereas the plants inoculated with H. desiderata recorded the oil content of 0.71 and 0.60 and 0.48 % at similar levels of NaCl stress, respectively. The halotolerant PGPR minimized the deleterious effects of salt toxicity producing at par or higher yields at lower and medium salinity levels (100, 300 mM NaCl) than the un-inoculated non-salt-stressed plants through improved foliar nutrient uptake and enhanced antioxidant machinery. Based on the results of the experiments reported herein, the use of salt-tolerant, plant-growth-promoting bacteria may provide an effective means of facilitating M. arvensis growth in salt-stressed environments.     

Effects of 5-aminolevulinic acid on nitrogen metabolism and ion distribution of watermelon seedlings under salt stress

The effects of foliar spray application of 5-aminolevulinic acid (ALA) on the growth, nitrogen metabolism, and ion distribution of salt-stressed watermelon (Citrullus lanatus (Thunb.) Matsum. and Nakai) seedlings were investigated. Supplementation of the nutrient solution with 100 mM NaCl significantly reduced leaf and root biomass of watermelon plants. Foliar application of 1.25 mM ALA significantly alleviated the inhibition of plant growth under salt stress. Salinity induced significant accumulation of nitrate, ammonium, and soluble protein and a significant decrease in the activities of nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH) in watermelon plants. However, ALA significantly increased the activities of NR, GS, GOGAT, and GDH, but decreased the ammonium content and NiR activity. In addition, salt stress resulted in significant accumulation of Na⁺ and Cl^? in plants, but decreased the contents of K⁺ and Mg²⁺. Application of ALA alleviated the salt stress-induced ion toxicity, and increased the contents of K⁺ and Mg²⁺. ALA also increased soluble protein and proline contents in salt-stressed watermelon plants. These results indicated that application of ALA alleviated the accumulation of Na⁺ and Cl^? in salt-stressed watermelon plants, especially through regulating nitrogen metabolism and ion distribution, which were associated with an improvement in plant growth.     

Short-term leaf elongation kinetics of maize in response to salinity are independent of the root

The essentiality of roots to the short-term responses of leaf elongation to salinity was tested by removing the roots of maize (Zea mays L.) from the shoots and comparing the initial short-term response of leaf elongation to that with intact plants. Eightday-old seedlings growing in solution culture were treated with 80 millimolar NaCl and their leaf elongation rate (LER) was monitored with a linear variable differential transformer connected to a computerized data aquisition system. Initially, LER of intact plants was sharply reduced by salinity, then rose rapidly to reach a new steady-state rate about 1.5 hours after salinization. The new steady-state rate of salinized intact plants was about 80% of the control rate. When the roots of nonsalinized plants were excised under the surface of the nutrient solution, excision did not disturb the steady-state LER. When these shoots were salinized, they responded in a manner nearly identical to that of intact plants, indicating that roots are not essential for the modulation of short-term LER of salt-stressed plants.     

Levels of Betaine and Betaine Aldehyde Dehydrogenase Activity in the Green Leaves, and Etiolated Leaves and Roots of Barley

The accumulation of betaine and the induction of betaine aldehydedehydrogenase, which catalyzes the last step in the synthesisof betaine, were analyzed in salt-stressed barley leaves. Whenhydroponically grown barley plants were transferred to a mediumthat contained 200 mM NaCl, the levels of both betaine and thetotal extractable betaine aldehyde dehydrogenase activity inthe leaves increased approximately 7-fold and 3-fold when calculatedon the basis of total leaf protein, respectively, over the courseof 7 days. Betaine aldehyde dehydrogenase activity was alsodetected in either etiolated leaves or roots of barley plantsgrown under aseptic conditions. Betaine was detected in bothetiolated leaves and roots at levels that were about 20% ofthat in green leaves when calculated on a fresh weight basis. ¹ This research was supported financially by a research grantfrom the Ministry of Education, Science and Culture (63560080) (Received March 9, 1990; Accepted May 29, 1990)     

Lipid Composition of Plasma Membranes and Endomembranes Prepared from Roots of Barley (Hordeum vulgare L.) : Effects of Salt

Membrane fractions enriched in endoplasmic reticulum (ER), tonoplast and Golgi membranes (TG) and plasma membranes (PM) were prepared from barley (Hordeum vulgare L. cv CM 72) roots and the lipid compositions of the three fractions were analyzed and compared. Plants were grown in an aerated nutrient solution with or without 100 millimolar NaCl. Each membrane fraction had a characteristic lipid composition. The mole per cent of the individual phospholipids, glycolipids, and sterols in each fraction was not altered when roots were grown in 100 millimolar NaCl. The ER had the highest percentages of phosphatidylinositol and phosphatidylcholine of the three fractions (7 and 45 mole per cent, respectively, of the total lipid). The TG contained the highest percentage of glycosylceramide (13 mole per cent). The PM had the highest percentage of phosphatidylserine (3 mole per cent) and nearly equal percentages of phosphatidylethanolamine (15 mole per cent and phosphatidylcholine (18 mole per cent). The most abundant sterols in membranes prepared from barley roots were stigmasterol (10 mole per cent), sitosterol (50 mole per cent), and 24ζ-methylcholesterol (40 mole per cent of the total sterol). Salt-treated plants contained a slightly higher percentage of stigmasterol than controls. The percentage of stigmasterol increased with age and a simple cause and effect relationship between salt treatment and sterol composition was not observed.