Changes in water relation parameters under osmotic and salt stresses in maize and sorghum

A relatively drought tolerant cultivar of maize ( Zea mays L. cv. Pioneer 3950) and a drought tolerant line of sorghum ( Sorghum bicolor [L.] Moench cv. ICSV 112) were grown hydroponically for 11 days. Treatments for non-ionic osmotic and salt stresses were started at the 8th day by addition of polyethylene glycol 6000 and NaCl, respectively, at 200 mOsm equivalent concentrations in the presence or absence of 0. 1 μ M abscisic acid. Relative growth rate was depressed by both stress factors, more severely for maize than sorghum. Abscisic acid increased the growth rate and reverted the negative effect of NaCl in maize, while sorghum was only slightly affected. In general, sorghum had higher levels of K⁺ and lower levels of Na⁺ and the K⁺/Na⁺ ratio was further increased by abscisic acid treatment. From the pressure-volume curves, osmotic potential, the water potential at turgor loss point, bulk elastic modulus and the water saturation deficit at initial turgor loss were estimated. Most significantly, sorghum had a higher elastic modulus than maize and it decreased under osmotic treatment, while in maize it increased under NaCl stress. The results suggest that bulk tissue turgor was not limiting growth under these conditions and underscores the possible implications of changes in the elastic condition of the cell walls in stress responses.     

Salt tolerance of the reed plant Phragmites communis

Reed plants ( Phragmites communis Trinius) were grown at NaCl concentrations up to 500 m M and their growth, mineral contents and leaf blade osmotic potential were determined. Addition of NaCl up to 300 m M did not affect growth significantly. Sucrose, Cl^-and Na⁺ concentrations in the shoots increased with the salinity of the medium and the shoot water content decreased. K⁺ always contributed most to the leaf osmotic potential. Even in the presence of 250 m M NaCl in the rooting medium, the leaf blade contained only 50 mM Na⁺, suggesting that the plants have an efficient mechanism for Na⁺ exclusion. ²²Na⁺ uptake experiments suggested that the retranslo-cation of absorbed Na⁺ from shoots to the rooting medium lowered the uptake of Na⁺.     

Na+/H+ antiport activity in tonoplast vesicles from roots of the salt-tolerant Plantago maritima and the salt-sensitive Plantago media

Plantago species differ in their strategy towards salt stress, a major difference being the uptake and distribution of Na⁺ ions. A salt-sensitive ( Plantago media L.) and a salt-tolerant ( P. maritima L.) species were compared with respect to Na⁺/H⁺ antiport activities at the tonoplast. After exposure of the plants to 50 m M NaCl for 6 days isolated tonoplast vesicles of P. maritima showed Na⁺/H⁺ antiport activity with saturation kinetics and a K_m of 2.4 m M Na⁺, NaCl-grown P. media and the control plants of both species showed no antiport activity. Selectivity of the antiport system for Na⁺ was high and was determined by adding different chloride salts after formation of a Δ pH in the vesicles. Specific tonoplast ATPase activities were similar in the two species and did not alter after exposure to NaCl stress.     

The HAL1 function on Na+ homeostasis is maintained over time in salt-treated transgenic tomato plants, but the high reduction of Na+ in leaf is not associated with salt tolerance

To achieve a deeper knowledge on the function of HAL1 gene in tomato ( Solanum lycopersicum ) plants submitted to salt stress, in this study, we studied the growth and physiological responses to high salt stress of T3 transgenic plants (an azygous line without transgene and both homozygous and hemizygous lines for HAL1 ) proceeding from a primary transformant with a very high expression level of HAL1 gene. The homozygous plants for HAL1 gene did not increase their salt tolerance in spite of an earlier and higher reduction of the Na⁺ accumulation in leaves, being moreover the Na⁺ homeostasis maintained throughout the growth cycle. The greater ability of the homozygous line to regulate the Na⁺ transport to the shoot to long term was even shown in low accumulation of Na⁺ in fruits. By comparing the homozygous and hemizygous lines, a higher salt tolerance in the hemizygous line, with respect to the homozygous line, was observed on the basis of fruit yield. The Na⁺ homeostasis and osmotic homeostasis were also different in homozygous and hemizygous lines. Indeed, the Na⁺ accumulation rate in leaves was greater in hemizygous than in homozygous line after 35 days of 100 m M NaCl treatment and only at the end of growth cycle did the hemizygous line show leaf Na⁺ levels similar to those found in the homozygous line. With respect to the osmotic homeostasis, the main difference between lines was the different contribution of inorganic and organic solutes to the leaf osmotic balance. Taken together, these results suggest that the greater Na⁺ exclusion ability of the homozygous line overexpressing HAL1 induces a greater use of organic solutes for osmotic balance, which seems to have an energy cost and hence a growth penalty that reverts negatively on fruit yield.     

Changes in sodium and potassium in Nitellopsis cells treated with transient salt stress

Abstract. Nitellopsis cells grown in fresh water have a relatively low cytoplasmic Na⁺ (11 mol m⁻³) and high cytoplasmic K⁺ (90 mol m⁻³) content. A 30-min treatment with 100 mol m⁻³ external NaCl resulted in a high [Na⁺]_c (90 mol m⁻³) and a low [K⁺]_c (33 mol m⁻³), Subsequent addition of external Ca²⁺ (10 mol m⁻³) prevented Na⁺ influx and then [Na⁺]_c decreased slowly. Changes in [K⁺]_c were opposite to [Na⁺]_c. During the recovery time vacuolar Na⁺ increased, while vacuolar K⁺ decreased. Since all these processes proceeded also under ice-cold conditions, the restoration of original cytoplasmic ion compositions is suggested to be a passive nature. The notion that the passive movement of ions across the tonoplast can act as an effective and economic mechanism of salt tolerance under transient or under mild salt stress conditions is discussed.     

Reactive oxygen species mediate Na+-induced SOS1 mRNA stability in Arabidopsis

Salt Overly Sensitive 1 (SOS1), a plasma membrane Na⁺/H⁺ antiporter in Arabidopsis, is a salt tolerance determinant crucial for the maintenance of ion homeostasis in saline stress conditions. SOS1 mRNA is unstable at normal growth conditions, but its stability is substantially increased under salt stress and other ionic and dehydration stresses. In addition, H₂O₂ treatment increases the stability of SOS1 mRNA. SOS1 mRNA is inherently unstable and rapidly degraded with a half-life of approximately 10 min. Rapid decay of SOS1 mRNA requires new protein synthesis. Stress-induced SOS1 mRNA stability is mediated by reactive oxygen species (ROS). NADPH oxidase is also involved in the upregulation of SOS1 mRNA stability, presumably through the control of extracellular ROS production. The cis -element required for SOS1 mRNA instability resides in the 500-bp region within the 2.2 kb at the 3' end of the SOS1 mRNA. Furthermore, mutations in the SOS1 gene render sos1 mutants more tolerant to paraquat, a non-selective herbicide causing oxidative stress, indicating that SOS1 plays negative roles in tolerance of oxidative stress. A hypothetical model for the signaling pathway involving SOS1-mediated pH changes, NADPH oxidase activation, apoplastic ROS production and downstream signaling transduction is proposed, and the biological significance of ROS-mediated induction of SOS1 mRNA stability is discussed.     

Genetic analysis of involvement of ETR1 in plant response to salt and osmotic stress

The involvement of ethylene and ethylene receptor Ethylene Response 1 (ETR1) in plant stress responses has been highlighted. However, the physiological processes involved remain unclear. In this study, we have investigated the physiological response of two alleles etr1-1 and etr1-7 mutants during germination and post-germination seedling development in response to salt and osmotic stress. The etr1-1 mutants showed increased sensitivity to osmotic (200 mM or higher mannitol) and salt stress (50 mM NaCl or higher) during germination and seedling development, whereas the etr1-7 mutants displayed enhanced tolerance to the severe stresses (500 mM mannitol or 200 mM NaCl). These results provide physiological and genetic evidence that ethylene receptor ETR1 modulates plant response to abiotic stress. Furthermore, the etr1-1 and etr1-7 mutants showed different responses to exogenous abscisic acid (ABA) inhibition. The etr1-1 mutants were more sensitive to ABA than the wild type during germination, and young seedling development. In sharp contrast, the etr1-7 mutants showed enhanced insensitivity to ABA treatment (>1 μM ABA) in post-germination development including root elongation and greening of cotyledons of the treated seedlings, although the germination was not greatly altered at the tested doses of ABA. The results suggest that ETR1-modulated stress response may mediate ABA. Youning Wang and Tao Wang contributed equally to this report.     

Salinity response of a freshwater charophyte, Chara vulgaris

Abstract. Chara vulgaris L. growing in an oligohaline lake was adapted to laboratory conditions and subjected to long-term salinity treatments ranging from 0 to 350 mol m ³ NaCl added to the lake water (40–680 mosmol kg ¹). Osmotic potential and concentration of the main osmotically active solutes (K⁺, Na⁺, Mg²⁺, Cl and sucrose) in the vacuolar sap of the central internodal cells were estimated. C. vulgaris did regulate turgor but incompletely. Turgor decreased from 335 mosmol kg ¹ under control conditions to 52–111 mosmol kg ¹ at 350 mol m ³ NaCl. The enhancement of πⁱ was achieved by increase in both ions and sucrose. Sterile and fertile plants differed in their response to osmotic stress. In sterile plants, the ions accounted for about 87% of the vacuolar osmotic potential. The increase of πⁱ under osmotic stress was exclusively due to an accumulation of Na⁺ and Cl^-. In fertile plants, sucrose accounted for about 35% of πⁱ and ions for about 51% Under osmotic stress, sucrose content increased together with the ionic content of Na⁺ and Cl^-.     

Salt stress in cultured rice cells: effects of proline and abscisic acid

Abstract. The presence of 1 and 10 mol m⁻³ proline in media containing 100 and 200 mol m⁻³ of NaCl, had little effect on the growth of salt-adapted callus of rice. However, in such callus proline accumulation was stimulated by 10 mol m⁻³ proline in the presence of 100 mol m⁻³ NaCl. On the other hand, with 100 mol m⁻³ NaCl, both 1 and 10 mol m⁻³ proline significantly increased both the growth and proline content of salt-unadapted callus. On replacing NaCl with KCl (100 and 200 mol m⁻³), growth of saltadapted as well as unadapted callus was inhibited, but the presence of 10 mol m⁻³ proline had an ameliorating effect. Abscisic acid (ABA) supressed the growth of both salt-adapted and unadapted callus of rice in the absence of salt stress. ABA inhibited the growth of callus adapted to and grown in 100 and 200 mol m⁻³ of NaCl or when it was replaced by equimolar concentrations of KCl. Growth of 100 mol m⁻³ NaCl adapted cells was inhibited when they were transferred to a medium containing 200 mol m⁻³ of NaCl, but in the presence of ABA it was stimulated. ABA increased the growth of unadapted cells when subjected to different salts. Also, ABA accelerated the adaptation of cells exposed to salt but not to water deficits imposed by nonionic solutes.     

Isolation and characterisation of mutants from the halotolerant yeast Pichia sorbitophila defective in H+/glycerol symport activity

Abstract Pichia sorbitophila , a yeast species that is highly resistant to osmotic stress in general and to salt stress in particular, was subjected to a mutagenesis strategy in order to obtain mutants deficient in the glycerol active uptake previously described. Density centrifugation was used for enrichment of NaCl sensitive mutants in either glucose or glycerol media. Several phenotypic classes of mutants were identified, to which physiological tests were applied concerning the activity of the symporter, its accumulation capacity and the detection of the activity of glycerol pathway specific enzymes. From these, two mutant strains were selected, presenting a clearly deficient phenotype on H⁺/glycerol symport activity.     

NaCl胁迫对4种豆科树种幼苗生长和K+、Na+含量的影响

以合欢、刺槐、国槐和皂荚4种豆科树种盆栽实生幼苗为试验材料,研究了NaCl胁迫下4个树种幼苗的生长、耐盐临界浓度和Na⁺、K⁺含量的变化,并对其耐盐性进行了比较.结果表明：NaCl胁迫抑制了4个树种幼苗的生长,苗木的干物质积累量减小、根冠比增大,尤其对合欢和皂荚的影响较大;以相对干质量降至对照组50%时的NaCl浓度作为生长临界NaCl浓度(C₅₀)指标,4个树种的耐盐强弱顺序为：刺槐(5.0‰)＞国槐(4.5‰)＞皂荚(3.9‰)＞合欢(3.0‰);随NaCl浓度的增加,各树种幼苗根、茎、叶中Na⁺含量逐渐增加,K⁺含量先增加后减小（合欢根除外）,而K⁺/Na⁺差异较大.相同浓度NaCl胁迫下,幼苗器官的Na⁺分布为根＞茎＞叶,K⁺因树种和NaCl浓度不同而各异,以叶片中较多,K⁺/Na⁺为叶＞茎＞根.NaCl胁迫下,刺槐的K⁺含量和K⁺/Na⁺较高,地上部分Na⁺含量较低,幼苗干物质量大,耐盐性较强;而合欢的K⁺/Na⁺较小,高浓度NaCl胁迫下地上部分的Na⁺含量较高,幼苗干物质量小,耐盐性较差.苗木地上部分对K⁺的积累和根部对Na⁺的滞留是影响豆科树种耐盐性能的主要因素.     

Effects of salt stress on H+- ATPase and H+-PPase activities of tonoplast-enriched vesicles isolated from sunflower roots

The control of ion concentration in the cytosol and the accumulation of ions in vacuoles are thought to be key factors in salt tolerance. These processes depend on the establishment in vacuolar membranes of an electrochemical H⁺ gradient generated by two distinct H⁺-translocating enzymes: a H⁺-PPase and a H⁺-ATPase. H⁺-lrans locating activities were characterized in tonoplast-enriched membrane fractions isolated by sucrose gradient centrifugation from sunflower ( Helianthus annuus L.) roots exposed for 3 days to different NaCl regimes. The 15/32% sucrose interface was enriched in membrane vesicles possessing a vacuolar-type H⁺-ATPase and a H⁺-PPase, as indicated by inhibitor sensitivity, pH optimum, substrate specificity, ion effects kinetic data and immunolabelling with specific antibodies. Mild and severe stress did not alter the pH profile, ion dependence, apparent K_m nor the amount of antigenic protein of either enzyme. Saline treatments slightly increased K⁺-stimulaied PPase activity with no change in ATPase activity, while both PP_i-dependent and NO₃-sensitive ATP-dependent H⁺ transport activities were strongly stimulated. These results are discussed in terms of an adaptative mechanism of the moderately tolerant sunflower plants to salt stress.     

Mechanism of calcium-dependent salt tolerance in cells of Nitellopsis obtusa: role of intracellular adenine nucleotides

Abstract. The tonoplasts of internodal cells of Nitellopsis were removed by perfusing the vacuoles with media containing a Ca² chelator, EGTA. Treatment of tonoplast-free cells with 100 mol m³ NaCl induces a large membrane depolarization, a drastic decrease in the membrane resistance and an increase in Na⁺ influx. These events are identical to those that occur in intact cells subjected to high NaCl. These responses to NaCl are prevented if 10 mol m³ Ca²⁺ is supplied together with 100 mol m³ NaCl. The protective effect of Ca²⁺ is evident only when the intracellular ATP concentration exceeds 0.1 mol m³ and does not occur full when the intracellular ATP is removed. AMP at concentrations greater than 0.5 mol m³ or 0.25 mol m³ AMPPNP can replace ATP. It is concluded that ATP does not act as an energy source nor as a substrate for protein phosphorylation. ATP seems to exert its effects as a coeffector with Ca²⁺ in regulating the Na⁺ permeability of the plasma membrane.     

Fluxes of Na+, K+ and Cl-, and osmotic adjustment in Lycopersicon pimpinellifolium and L. esculentum during short- and long-term exposures to NaCl

NaCl (140 m M ) was applied to 14-day-old plants of salt-sensitive Lycopersicon esculentum Mill. cv. Volgogradskij and its wild relative L. pimpinellifolium Mill. accession PE-2. Changes in the relative growth rate of whole plant, and in the levels of inorganic and organic solutes in leaves, stems and roots were followed for 15 days after the application. Short-term salt exposure (4–6 days of salinization) resulted in enhanced relative growth rates for L. pimpinellifolium , but did not affect growth of L. esculentum , After 6 days of salinization, the relative growth rates of both species decreased significantly; leading to practically comparable growth rates for them by day 15. In all parts of both species, the contribution of organic solutes to the osmotic potential (Ψ_s) gradually decreased from 30% on day 0 to a value lower than 5% on day 4. In L. pimpinellifolium , compared to L. esculentum , short-term salt exposure resulted in (1) a higher percentage of adjustment of Ψ_s; and (2) increases in Na⁺ and K⁺ uptake rates, and in the levels of organic acids and proline (the level of which reached that of sugars, i.e., 10 μmol g^-1 dry weight. Conversely, in L. esculentum , drastic reductions of K⁺ uptake rates and organic acid levels occurred already on day 1. During long-term salt exposure, both species were able to adjust osmotically and both exhibited decreases in organic acid levels as well as in K⁺ uptake and accumulation rates in all parts. The results are discussed in an attempt to explain the adaptive responses during short-term salt exposure and the metabolic dysfunctions that lead to growth decrease after long-term exposure to salt.     

Physiological effects of Na2SO4 and NaCl on callus cultures of Brassica campestris (Chinese cabbage)

Hypocotyl-derived callus cultures of Brassica campestris L. ssp. pekinensis cv. Kim-jung (Chinese cabbage) were grown on Murashige and Skoog medium containing no additional salt, NaCl or Na₂SO₄. Na₂SO₄ was more than twice as inhibitory in comparison to the same concentration of NaCl when growth and fresh:dry weight ratios of established callus were measured. Levels of protein, starch, sucrose and α-amino nitrogen were not significantly altered in salt-grown callus. Concentrations of reducing sugars and chlorophyll were 2–3 times greater in callus grown on either salt. Proline concentration increased 15–20 fold on the highest levels of salt. Final concentrations (reached in 20–24 days) were closely correlated to the initial Na⁺ concentration of the medium, regardless of salt type. The osmotic potential in callus transferred to NaCl or Na₂SO₄ reached a maximum negative value after 16 days. For both salts, subsequent increases were correlated to increases in fresh:dry weight and growth. On both salts, turgor remained relatively constant (0. 6–0.75 MPa). Changes in Na⁺, K⁺, Mg²⁺ and Ca²⁺ content were correlated to initial Na⁺ concentration in the medium, not salt type. Accumulation of Na⁺ was accompanied by loss of K⁺ and Mg²⁺. Six to seven times less sulfate was measured in callus grown on Na₂SO₄ than chloride in callus grown on similar concentrations of NaCl.     

水杨酸调控盐胁迫下羽衣甘蓝种子萌发的机理

盐胁迫是植物种子萌发与植株生长的重要限制因子。以羽衣甘蓝(Brassica oleracea var.acephala)名古屋为材料,研究不同盐分对其种子萌发的影响,探索水杨酸(SA)及其合成抑制剂氨基茚磷酸(AIP)处理对羽衣甘蓝种子萌发的调控效应。实验结果表明,150与200 mmol·L^–1 NaCl处理后的羽衣甘蓝种子活力显著降低。盐胁迫显著降低种子的吸水速率、种子活力与幼苗质量,降低苯丙氨酸裂解酶活性与内源SA含量,提高过氧化氢(H2O2)与超氧阴离子(O2^–.)含量。SA可以缓解盐胁迫对羽衣甘蓝种子活力的抑制作用,通过促进内源SA合成,从而提高种子吸水率与种子活力,促进种子对K^+、Mg^2+的吸收,降低Na+含量。此外,外源施加SA能够显著增强超氧化物歧化酶和过氧化物酶活性,降低H2O2与O2^–.的积累。相反,氨基茚磷酸(AIP)处理能够增强盐胁迫对种子萌发的抑制作用,推测这与AIP处理能够显著降低种子内源SA含量密切相关。研究表明外源SA主要通过提高保护酶活性、降低活性氧积累和维持体内离子平衡来增强羽衣甘蓝的耐盐性。     

Does calcium ameliorate the negative effect of NaCl on melon root water transport by regulating aquaporin activity?

The hydraulic conductance ( L ₀) of detached, exuding root systems from melon ( Cucumis melo cv. Amarillo oro) was measured. All plants received a half-strength Hoagland nutrient solution, and plants stressed either solely with NaCl (50 mM) or with NaCl (50 mM) following treatment (2 d) with CaCl₂ (10 mM) were compared with controls and CaCl₂-treated (10 mM) plants. The L ₀ of NaCl-treated plants was markedly decreased when compared to control and CaCl₂-treated plants, but the decrease was smaller when NaCl was added to plants previously treated with CaCl₂. A similar effect was observed when the flux of Ca²⁺ into the xylem and the Ca²⁺ concentration in the plasma membrane of the root cells were determined. In control, CaCl₂- and NaCl + CaCl₂-treated plants, HgCl₂ treatment (50 μM) caused a sharp decline in L ₀ to values similar to those of NaCl-stressed roots, but L ₀ was restored by treatment with 5 mM DTT. However, in NaCl roots only a slight effect of Hg²⁺ and DTT were observed. The effect of all treatments on L ₀ was similar to that on osmotic water permeability ( P _f) of individual protoplasts isolated from roots. The results suggest that NaCl decreased the passage of water through the membrane and roots by reducing the activity of Hg-sensitive water channels. The ameliorative effect of Ca²⁺ on NaCl stress could be related to water-channel function.     

野皂荚对NaCl胁迫的生理响应及耐盐性

以盆栽野皂荚2年生实生苗为材料,设置土壤NaCl含量分别为0.053%（CK）、0.15%、0.3%、0.45%和0.6%的盐胁迫处理,研究不同浓度盐处理对苗木生长、细胞膜透性、细胞保护酶活性以及Na⁺和K⁺分布格局的影响,探讨了其耐盐阈值和机理.结果表明：随着NaCl浓度增加,苗木生长量逐渐降低,盐害指数逐渐升高;野皂荚可忍耐的土壤含盐量为0.42%.随着NaCl浓度增加,叶片相对电导率、氧自由基产生速率和丙二醛(MDA)含量均逐渐增大;超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性呈先上升后下降的变化趋势,在土壤含盐量0.3%或0.45%时达到峰值;高盐胁迫下,SOD、POD和CAT活性的增强可及时清除盐胁迫产生的氧自由基,进而缓解或避免膜脂过氧化作用对组织细胞的伤害.盐胁迫下根、茎、叶的Na⁺含量均逐渐增大,且呈现根>叶>茎的分布格局;K⁺含量和K⁺/Na⁺呈下降趋势,呈现叶>根>茎的分布格局;K⁺-Na⁺选择性运输系数(S_K⁺·Na⁺)随着土壤含盐量的增加逐渐升高,且叶S_K⁺·Na⁺高于茎S_K⁺·Na⁺.野皂荚耐盐机制是根系拒盐和叶片耐盐;盐胁迫下,根系Na⁺累积能力增强可控制Na⁺向地上运输以避免盐害发生,叶片K⁺选择性吸收和累积能力的显著提高可忍耐和补偿Na⁺对组织的伤害.