Identification of quantitative trait loci for ion homeostasis and salt tolerance in barley (Hordeum vulgare L.)

Ion homeostasis is considered to be one of the most important mechanisms underlying salt stress tolerance. We used the Steptoe × Morex barley doubled haploid population to screen for genetic variation in response to salinity stress at an early development stage in a hydroponics system, focusing on ion homeostasis. Salinity induced a strong adverse effect on growth of the parents and their derived population, with Steptoe as the more tolerant parent. Steptoe maintained higher concentrations of K⁺, Na⁺ and Cl^? in the roots and a similar shoot/root ion ratio (<1) under stress conditions compared to control conditions. In contrast, Morex had higher concentrations of these ions in the shoots under stress and a doubled shoot/root ion ratio relative to control conditions, indicating that salt exclusion might contribute to the higher tolerance of Steptoe. Correlation and path analysis demonstrated that shoot Cl^? contents most strongly affected salt tolerance and suggest that both Na⁺ and Cl^? contents are important for salinity stress tolerance in barley. We identified 11 chromosomal regions involved in the control of the variation observed for salt tolerance and various salt stress response traits, including Na⁺, Cl^? and K⁺ contents in shoots. Two specific regions on chromosomes 2H and 3H were found controlling ion contents and salt tolerance, pointing to genes involved in ion homeostasis that contribute to salt tolerance.     

Evidence that arbuscular mycorrhizal and phosphate-solubilizing fungi alleviate NaCl stress in the halophyte Kosteletzkya virginica: nutrient uptake and ion distribution within root tissues

The effects of an arbuscular mycorrhizal (AM) fungus, Glomus mosseae, and a phosphate-solubilizing microorganism (PSM), Mortierella sp., and their interactions, on nutrient (N, P and K) uptake and the ionic composition of different root tissues of the halophyte Kosteletzkya virginica (L.), cultured with or without NaCl, were evaluated. Plant biomass, AM colonization and PSM populations were also assessed. Salt stress adversely affected plant nutrient acquisition, especially root P and K, resulting in an important reduction in shoot dry biomass. Inoculation of the AM fungus or/and PSM strongly promoted AM colonization, PSM populations, plant dry biomass, root/shoot dry weight ratio and nutrient uptake by K. virginica, regardless of salinity level. Ion accumulation in root tissues was inhibited by salt stress. However, dual inoculation of the AM fungus and PSM significantly enhanced ion (e.g., Na⁺, Cl^?, K⁺, Ca²⁺, Mg²⁺) accumulation in different root tissues, and maintained lower Na⁺/K⁺ and Ca²⁺/Mg²⁺ ratios and a higher Na⁺/Ca²⁺ ratio, compared to non-inoculated plants under 100 mM NaCl conditions. Correlation coefficient analysis demonstrated that plant (shoot or root) dry biomass correlated positively with plant nutrient uptake and ion (e.g., Na⁺, K⁺, Mg²⁺ and Cl^?) concentrations of different root tissues, and correlated negatively with Na⁺/K⁺ ratios in the epidermis and cortex. Simultaneously, root/shoot dry weight ratio correlated positively with Na⁺/Ca²⁺ ratios in most root tissues. These findings suggest that combined AM fungus and PSM inoculation alleviates the deleterious effects of salt on plant growth by enabling greater nutrient (e.g., P, N and K) absorption, higher accumulation of Na⁺, K⁺, Mg²⁺ and Cl^? in different root tissues, and maintenance of lower root Na⁺/K⁺ and higher Na⁺/Ca²⁺ ratios when salinity is within acceptable limits.     

Different mechanisms of ion homeostasis are dominant in the recretohalophyte <Emphasis Type="Italic">Tamarix ramosissima</Emphasis> under different soil salinity

Total ion (Na⁺, K⁺, Ca²⁺, SO₄ ^2? and Cl^?) accumulation by plants, ion contents in plant tissues and ion secretion by salt glands on the surface of shoots of Tamarix ramosissima adapted to different soil salinity, namely low (0.06 mmol Na⁺/g soil), moderate (3.14–4.85 mmol Na⁺/g soil) and strong (7.56 mmol Na⁺/g soil) were analyzed. There are two stages of interrelated and complementary regulation of ion homeostasis in whole T. ramosissima plants: (1) regulation of ion influx into the plant from the soil and (2) changing the secretion efficiency of salt glands on shoots. The secretion efficiency of salt glands was appraised by the ratio of ion secretion to tissue ion content. Independent of soil salinity, the accumulation of K⁺ and Ca²⁺ was higher than the contents of these ions in the soil. Furthermore, the accumulation of K⁺, Ca²⁺ and SO₄ ^2? ions by plants was maintained within a narrow range of values. Under low soil salinity, Na⁺ was accumulated, whereas under moderate and strong salinity, the influxes of Na⁺ were limited. However, under strong salinity, the accumulation of Na⁺ was threefold higher than that under low soil salinity. This led to a change in the Na⁺/K⁺ ratio (tenfold), an increase in the activity of salt glands (tenfold) and a reduction in plant growth (fivefold). An apparently high Na⁺/K⁺ ratio was the main factor determining over-active functioning of salt glands under strong salinity. Principal component analysis showed that K⁺ ions played a key role in ion homeostasis at all levels of salinity. Ca²⁺ played a significant role at low salinity, whereas Cl^? and interrelated regulatory components (K⁺ and proline) played a role under strong salinity. Proline, despite its low concentration under strong salinity, was involved in the regulation of secretion by salt glands. Different stages and mechanisms of ion homeostasis were dominant in T. ramosissima plants adapted to different levels of salinity. These mechanisms facilitated the accumulation of Na⁺ in plants under low soil salinity, the limitation of Na⁺ under moderate salinity and the over-activation of Na⁺ secretion by salt glands under strong salinity, which are all necessary for maintaining ion homeostasis and water potential in the whole plant.     

Salt-Induced Hypodermal Transfer Cells in Roots of Prosopis farcta and Ion Distribution within Young Plants

Prosopis farcta was grown on hydroculture with additions of 0.5, 10, 50, and 100 mM NaCl and without salt treatment. In plants from a 0.5 mM NaCl treatment, Cl^? was taken up into stems and leaves, but Na⁺ was withheld from the shoot. At 10 mM NaCl, shoot K⁺ concentration was below that of the control; Na⁺ and Cl^? were taken up to stems and cotyledons in nearly equimolar amounts. However, in the leaves, Na⁺ concentrations were only half of those of Cl^?. With increasing salt stress, Na⁺ and Cl^? were transported to the shoot, but kept at relatively low levels in the roots. Na⁺/ K⁺ ratios in roots did not increase proportionally to those in the solution. At an external Na⁺/K⁺ of > 5 and a root Na⁺/K⁺ of >1 (10 mM NaCl treatment), K⁺ selectivity was induced which rose exponentially with increasing salt stress; and cell wall protuberances were discovered in the hypodermis at the zone of side root formation. These transfer cells were found neither in roots from the 0.5 mM NaCl treatment nor in the controls. Their possible role in the Na⁺/K⁺ selectivity of the roots of Prosopis farcta is discussed.     

Differential growth and yield responses of salt-tolerant and susceptible rice cultivars to individual (Na<Superscript>+</Superscript> and Cl<Superscript>−</Superscript>) and additive stress effects of NaCl

Negative impacts exerted by sodium (Na⁺) and chloride (Cl^?) ions individually as well their possible additive effects (under NaCl) were evaluated on growth and yield reductions in rice, besides investigating whether salt-tolerant genotypes respond differentially than their sensitive counterparts. Though both Na⁺ and Cl^? ions get accumulated in plant tissues under NaCl stress, most research has historically been aimed to decipher harmful effects induced by Na⁺ ions. Accordingly, physiological and molecular mechanisms involved in Cl^? toxicity are not clearly understood in crop plants. To address these issues, 65-day-old plants of two rice cultivars, Panvel-3 (tolerant) and Sahyadri-3 (sensitive) were subjected to Cl^?, Na⁺ and NaCl (each with 100 mM concentration and electrical conductivity of ≈10 dS m^?1) stress using soil-based systems. Stress conditions were maintained till harvesting of mature (128-day-old) plants. All three treatments induced substantial antagonistic effects on growth, dry mass, yield components (number of grains per panicle, length, width, thickness and weight of grain, along with the percentage of grains filled) and overall crop yield, with greater impacts under NaCl than its constituent ions. Salinity treatments caused an imbalance in reducing sugars, protein, starch and proline contents, with the greatest magnitude under NaCl. A negative correlation between Cl^?/Na⁺ accumulation and crop yield was witnessed, with higher severity on the sensitive cultivar. The overall magnitude of toxicity was observed highest in NaCl followed by Na⁺ and Cl^?, respectively, suggesting additive effects of constituent ions under NaCl. Both cultivars responded similarly; however, the tolerant cultivar, unlike the sensitive one, kept Na⁺:K⁺ ratio <1.0 and accumulated proline in response to salinity treatments used in this study.     

Effect of salt stress on cucumber: Na+–K+ ratio, osmolyte concentration, phenols and chlorophyll content

A pot experiment with 17 diverse genotypes of cucumber with four levels of salt stress viz., 0, 2, 4 and 6 dS m^?1 was carried out during 2006. ANOVA revealed significant differences amongst genotypes and genotype × salt stress interaction indicating the genetic variability and differential response of the genotypes to different salt stress levels. The salt stress adversely affected the biochemical parameters; effects were severe under 4 dS m^?1. No genotype could survive at 6 dS m^?1. Sodium content, Na⁺–K⁺ ratio, proline, reducing sugars, phenol and yield reduction (%) increased significantly as the salt stress increased. Potassium, chlorophyll, membrane stability index and fruit yield decreased significantly under salt stress in all genotypes. However, the genotypes CRC-8, CHC-2 and G-338 showed lower accumulation of sodium, lesser depletion of potassium, lower Na⁺–K⁺ ratio and higher accumulation of proline, reducing sugars, phenols, better membrane stability and lower yield reduction (%) under salt stress, while CH-20 and DC-1 were sensitive to salt stress. Thus, a combination of traits such as higher membrane stability, lower Na⁺–K⁺ ratio, higher osmotic concentration and selective uptake of useful ions and prevention of over accumulation of toxic ions contribute to salt stress tolerance in cucumber. These traits would be useful selection criteria during salt stress breeding in cucumber.     

外源SA和NO对NaCl胁迫下番茄幼苗生长、光合及离子分布的影响

以番茄(Lycopersicon esculentum Mill.)品种‘秦丰保冠’为试材,采用营养液培养法,研究单独和复配施用外源水杨酸(SA)、一氧化氮(NO)供体硝普钠(SNP)对100mmol/L NaCl胁迫下番茄幼苗生长、光合及离子分布的影响。结果表明:(1)单独和复配外施SA、SNP均能有效抑制NaCl胁迫下番茄幼苗叶片光合色素(Chla、Chlb、Chla+b和Car)含量、Chla/b值、净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)、瞬时水分利用效率(WUEt)、表观光能利用效率(LUEapp)和表观CO2利用效率(CUEapp)的下降及Car/Chla+b值和胞间CO2浓度(Ci)的升高,并以SA和SNP复配处理效果最明显。(2)NaCl胁迫下,外源SA、SNP单独和复配处理的番茄幼苗各器官(叶、茎和根)中Cl-、Na+含量和Na+/K+、Na+/Ca2+、Na+/Mg2+值显著降低,而K+、Ca2+和Mg2+的含量却不同程度提高,其中以SA和SNP复配处理效果最好。(3)单独和复配外施SA、SNP均能有效减轻NaCl胁迫对番茄幼苗生长的抑制作用,并促进各器官生物量的积累和壮苗的形成,且以SA和SNP复配处理效果更佳。研究表明,复配外施SA和SNP在诱导番茄幼苗提高抗(耐)盐能力方面具有协同增效作用。     

Brief pre- and post-irrigation sprinkling with fresh water reduces foliar salt uptake in maize and barley sprinkler irrigated with saline water

Brief pre- and post-irrigation sprinkling treatments using freshwater were tested to determine if these practices could reduce the uptake of salts through leaves when saline water is used to sprinkler irrigate crops. Maize and barley were sprinkler irrigated 2 to 3 times per week for 30 min with saline water (4.2 dS m^–1, 30 mmol L^–1 NaCl and 2.8 mmoles L^–1 CaCl₂ for maize and 9.6 dS m^–1, 47 mmoles L^–1 NaCl and 23.5 mmoles L^–1 CaCl₂ for barley) in separate experiments with plants grown in pots outdoors. The soil surface of all pots was covered to prevent salinization of the soil by the sprinkling water. One half of the sprinkled plants was grown in nonsaline soil to study the effects of pre-wetting and post-washing when ion uptake was primarily through leaves. The other half of the sprinkled plants was grown in soil salinized by drip irrigation, in order to evaluate the effects of pre-wetting and post-washing when Na⁺ and Cl^- uptake was through both leaves and roots.Post-washing with freshwater (5 min) reduced the leaf sap concentrations of Cl^- in saline-sprinkled plants from 56 to 43 mmol L^–1 in maize and from 358 to 225 mmol L^–1 in barley (averages for plants grown in nonsaline and saline soil). Na⁺ concentrations in leaf sap were reduced from 93 to 65 mmoles L^–1 (maize) and from 177 to 97 mmoles L^–1 (barley) by the post-washing. Pre-wetting had a small effect on ion uptake through leaves, the only significant reduction in seasonal means being in leaf Na⁺ concentrations for plants grown in nonsaline soil. Pre-wetting and post-washing, when combined, reduced leaf Cl^- concentrations to levels similar to those of nonsprinkled plants grown in saline soil; however, Na⁺ concentrations in leaves remained 3.5 times (maize) and 1.5 times (barley) higher than those of nonsprinkled plants. When pre-wetting and post-washing were not applied, sprinkled barley plants grown in saline soil had grain yields which were 58% lower than nonsprinkled plants grown in saline soil, but the reduction in grain yield was only 17% when the freshwater treatments were given. We conclude that a brief period of post-washing with freshwater is essential when saline water is employed in sprinkler irrigation. By comparison, the benefits from pre-wetting were small in these experiments. ei]T J Flowers     

盐分胁迫对啤酒大麦幼苗生长、离子平衡和根际pH变化的影响

盐分胁迫不仅影响植物的生长,而且会影响植物根际微域环境。根际pH的改变对土壤养分的有效性和微生物群落组成的变化有重要影响。为了探究啤酒大麦幼苗对不同类型盐分胁迫的生理生态响应机制和根际pH变化影响的生理机制,采用水培法,通过不同类型盐分(对照、混合Na盐、混合Cl盐和NaCl)胁迫处理啤酒大麦幼苗,对其生长、离子平衡和根际pH变化进行了研究。结果表明,1)在3种不同类型盐分胁迫下,啤酒大麦幼苗地上部干重、含水量均有所降低,而根冠比增加,尤其在NaCl胁迫下啤酒大麦幼苗地上部干重较对照显著降低了17.88%,而根干重和根冠比则分别增加了19.12%和43.86%。不同类型盐分胁迫抑制了啤酒大麦幼苗根长的生长,尤其在混合Na盐胁迫下根长降低明显(P0.05),但促进了根表面积和根体积的增加,尤其在混合Cl盐胁迫下,根表面积和根体积分别增加了41.76%和84.38%。2)不同类型盐分胁迫下啤酒大麦幼苗地上部离子平衡发生改变,在混合Na盐和NaCl胁迫下啤酒大麦幼苗主要吸收Na~+,地上部K~+/Na~+、Ca~(2+)/Na~+和Mg~(2+)/Na~+显著降低;混合Cl盐和NaCl胁迫下则过量吸收Cl~-,抑制了H_2PO_4~-、NO_3~-和SO_4~(2-)的吸收。3)在混合Na盐、混合Cl盐和NaCl盐分胁迫下,啤酒大麦幼苗对阴离子的吸收总量高于对阳离子的吸收总量,离子平衡计算结果表明根际呈碱化现象,与原位显色结果一致,且在混合Cl盐胁迫下根际碱化程度最大。     

Morpho-anatomical and physiological attributes for salt tolerance in sewan grass (Lasiurus scindicus Henr.) from Cholistan Desert,Pakistan

Three differently adapted populations of sewan grass (Lasiurus scindicus Henr.) were evaluated for structural and functional adaptations to high salinity. The habitats were Derawar Fort (DF, least saline, ECe 15.21), Bailahwala Dahar (BD, moderately saline, ECe 27.56 dS m^?1) and Ladam Sir (LS, highly saline, ECe 39.18 dS m^?1) from within the Cholistan Desert. The adaptive components of salt tolerance in sewan grass were assessed by determining various morpho–anatomical and physiological attributes. The degree of salt tolerance of all three ecotypes of L. scindicus from the saline habitats was compared in a controlled hydroponic system to evaluate the adaptive components that are expected to be genetically fixed during a long evolutionary process. Salinity tolerance in the most tolerant LS population relied on increased root length and total leaf area, restricted uptake of toxic Cl^?, increased uptake of Ca²⁺, high excretion of Na⁺, accumulation of organic osmolytes, high water use efficiency, increased root, thicker leaf and cortical region, intensive sclerification, large metaxylem vessels, and dense pubescence on abaxial leaf surface. The BD population (from moderately saline soil) relied on high Ca²⁺ uptake, Na⁺ excretion, epidermal thickness, large cortical cells, thick endodermis and large vascular tissue. The DF population (from less saline soil) showed a significant decrease in all morphological characteristics; however, it accumulated organic osmolytes for its survival under high salinities. Structural modifications in all three populations were crucial for checking undue water loss under physiological stress that is caused by high amounts of soluble salts in the soil.     

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.     

Foliar and root absorption of Na+ and Cl− in maize and barley: Implications for salt tolerance screening and the use of saline sprinkler irrigation

Above-canopy sprinkler irrigation with saline water favours the absorption of salts by wetted leaves and this can cause a yield reduction additional to that which occurs in salt-affected soils. Outdoor pot experiments with both sprinkler and drip irrigation systems were conducted to determine foliar ion accumulation and performance of maize and barley plants exposed to four treatments: nonsaline control (C), salt applied only to the soil (S), salt applied only to the foliage (F) and salt applied to both the soil and to the foliage (F+S). The EC of the saline solution employed for maize in 1993 was 4.2 dS m^–1 (30 mM NaCl and 2.8 mM CaCl₂) and for barley in 1994, 9.6 dS m^–1 (47 mM NaCl and 23.5 mM CaCl₂). The soil surface of all pots was covered so that in the F treatment the soil was not salinized by the saline sprinkling and drip irrigation supplied nutrients in either fresh (treatments C and F) or saline water (treatments S and F+S).Saline sprinkling increased leaf sap Na⁺ concentrations much more than did soil salinity, especially in maize, even though the saline sprinkling was given only two or three times per week for 30 min, whereas the roots of plants grown in saline soil were continuously exposed to salinity. By contrast, leaf sap Cl^– concentrations were increased similarly by saline sprinkling and soil salinity in maize, and more by saline sprinkling than saline soil in barley. It is concluded that barley leaves, and to a greater extent maize leaves, lack the ability to selectively exclude Na⁺ when sprinkler irrigated with saline water. Moreover, maize leaves selectively absorbed Na⁺ over Cl^– whereas barley leaves showed no selectivity. When foliar and root absorption processes were operating together (F+S treatment) maize and barley leaves accumulated 11–14% less Na⁺ and Cl^– than the sum of individual absorption processes (treatment F plus treatment S) indicating a slight interaction between the absorption processes. Vegetative biomass at maturity and cumulative plant water use were significantly reduced by saline sprinkling. In maize, reductions in biomass and plant water use relative to the control were of similar magnitude for plants exposed only to saline sprinkling, or only to soil salinity; whereas in barley, saline sprinkling was more detrimental than was soil salinity. We suggest that crops that are salt tolerant because they possess root systems which efficiently restrict Na⁺ and Cl^– transport to the shoot, may not exhibit the same tolerance in sprinkler systems which wet the foliage with saline water. ei]T J Flowers     

Effects of 24‐epibrassinolide on plant growth,osmotic regulation and ion homeostasis of salt‐stressed canola

This study evaluated effects of foliar spraying 24‐epibrassinoide (24‐EBL) on the growth of salt‐stressed canola. Seedlings at the four‐leaf stage were treated with 150 mm NaCl and different concentrations of 24‐EBL (10^?6, 10^?8, 10^?10, 10^?12 m ) for 15 days. A concentration of 10^?10 m 24‐EBL was chosen as optimal and used in a subsequent experiment on plant biomass and leaf water potential parameters. The results showed that 24‐EBL mainly promoted shoot growth of salt‐stressed plants and also ameliorated leaf water status. Foliar spraying of salt‐stressed canola with 24‐EBL increased osmotic adjustment ability in all organs, especially in younger leaves and roots. This was mainly due to an increase of free amino acid content in upper leaves, soluble sugars in middle leaves, organic acids and proline in lower leaves, all of these compounds in roots, as well as essential inorganic ions. Na⁺ and Cl^? sharply increased in different organs under salt stress, and 24‐EBL reduced their accumulation. 24‐EBL improved the uptake of K⁺, Ca²⁺, Mg²⁺ and NO₃^? in roots, which were mainly transported to upper leaves, while NO₃^? was mainly transported to middle leaves. Thus, 24‐EBL improvements in ion homeostasis of K⁺/Na⁺, Ca²⁺/Na⁺, Mg²⁺/Na⁺ and NO₃^?/Cl^?, especially in younger leaves and roots, could be explained. As most important parts, younger leaves and roots were the main organs protected by 24‐EBL via improvement in osmotic adjustment ability and ion homeostasis. Further, physiological status of growth of salt‐stressed canola was ameliorated after 24‐EBL treatment.     

渗透胁迫和离子毒害对转Bt基因棉幼苗生长及离子分布的影响

研究了渗透和盐胁迫处理对转Bt基因抗虫棉(Gossypium hirsutum) 99B种子的萌发和幼苗生长的影响,以及幼苗不同器官离子吸收和分配的差异。结果表明:渗透和盐胁迫均对转Bt基因抗虫棉幼苗的生长有抑制作用,其中PEG的抑制作用最强,而3种盐的抑制程度以CaCl₂>NaCl>Na₂SO₄,且在Na⁺含量相同时,Cl^-的毒害大于SO₄^2-。渗透胁迫下使根、茎和叶中的Na⁺和Cl^-含量提高,K⁺、Ca²⁺、SO₄^2-含量和K⁺/Na⁺、Ca²⁺/Na⁺和SO₄^2-/Cl^-比值降低,且地上部的变化幅度大于地下部的,其中以PEG的影响最为显著,其次是CaCl₂,Na₂SO₄处理最弱。这些说明,转Bt基因抗虫棉99B的耐盐性较弱。     

The ionic relations of Porphyra purpurea(Roth) C.Ag. (Rhodophyta, Bangiales)

Abstract Radioisotope equilibration techniques have been used to determine the intracellular concentration of K⁺, Na⁺ and Cl_?, together with the unidirectional ion fluxes across the plasmalemma of Porphyra purpurea. Influx and efflux of ⁴²K⁺, ²⁴Na⁺ and ³⁶C1^? are biphasic, the rapid, initial uptake and loss of tracer from individual thalli being attributable to desorption from extracellular regions. Cellular fluxes are slower and monophasic, cells discriminating in favour of K⁺ and Cl^? and against Na⁺. A comparison between the equilibrium potential of individual ion species and the measured membrane potential demonstrates that there is an active component of K⁺ and Cl^? influx and Na⁺ efflux. ‘Active’ uptake and ‘passive’ loss of K⁺ and Cl^? are reduced when plants are kept in darkness, suggesting that a fraction of the transport of K⁺ and Cl^? may be due to ‘exchange diffusion’ (K⁺/K⁺ and Cl^?/Cl^?antiport).     

Association mapping of salt tolerance in barley (Hordeum vulgare L.)

A spring barley collection of 192 genotypes from a wide geographical range was used to identify quantitative trait loci (QTLs) for salt tolerance traits by means of an association mapping approach using a thousand SNP marker set. Linkage disequilibrium (LD) decay was found with marker distances spanning 2–8 cM depending on the methods used to account for population structure and genetic relatedness between genotypes. The association panel showed large variation for traits that were highly heritable under salt stress, including biomass production, chlorophyll content, plant height, tiller number, leaf senescence and shoot Na⁺, shoot Cl^? and shoot, root Na⁺/K⁺ contents. The significant correlations between these traits and salt tolerance (defined as the biomass produced under salt stress relative to the biomass produced under control conditions) indicate that these traits contribute to (components of) salt tolerance. Association mapping was performed using several methods to account for population structure and minimize false-positive associations. This resulted in the identification of a number of genomic regions that strongly influenced salt tolerance and ion homeostasis, with a major QTL controlling salt tolerance on chromosome 6H, and a strong QTL for ion contents on chromosome 4H.     

Biochemical characterization of maize (Zea mays L.) for salt tolerance

The inherent differences for salt tolerance in two maize cultivars (Agatti-2002 and Sahiwal-2002) were evaluated in pot experiments. Plants were grown in half-strength of Hoagland nutrient solution added with 0, 80, 100, 120, 140 and 160 mM of NaCl. Salt stress markedly reduced the shoot and root lengths and fresh and dry masses. Reduction in growth attributes was more pronounced in cv. Agatti-2002 than cv. Sahiwal-2002. Both maize cultivars exhibited significant perturbations in important biochemical attributes being employed for screening the crops for salt tolerance. Cultivar Sahiwal-2002 was found salt tolerant as compared to cv. Agatti-2002 because it exhibited lower levels of H₂O₂, malondialdehyde (MDA) and higher activities of antioxidant enzymes. In addition, cultivar Sahiwal-2002 exhibited less salt-induced degradation of photosynthetic pigments, lower levels of toxic Na⁺ and Cl^?  and higher endogenous levels of K⁺ and K⁺/Na⁺ ratio. The results indicate that salt stress induced a marked increase in MDA, H₂O₂, relative membrane permeability, total soluble proteins and activities of antioxidant enzymes (superoxide dismutase, peroxidase, catalase andascorbate peroxidase). Moreover, increase in endogenous levels of Na⁺ and Cl^?  and decrease in K⁺ and K⁺/Na⁺ ratio and photosynthetic pigments were recorded in plants grown under salinity regimes.     

Long‐term effect of salinity on plant quality,water relations,photosynthetic parameters and ion distribution in Callistemon citrinus

The effect of saline stress on physiological and morphological parameters in Callistemon citrinus plants was studied to evaluate their adaptability to irrigation with saline water. C. citrinus plants, grown under greenhouse conditions, were subjected to two irrigation treatments lasting 56 weeks: control (0.8 dS·m^?1) and saline (4 dS·m^?1). The use of saline water in C. citrinus plants decreased aerial growth, increased the root/shoot ratio and improved the root system (increased root diameter and root density), but flowering and leaf colour were not affected. Salinity caused a decrease in stomatal conductance and evapotranspiration, which may prevent toxic levels being reached in the shoot. Net photosynthesis was reduced in plants subjected to salinity, although this response was evident much later than the decrease in stomatal conductance. Stem water potential was a good indicator of salt stress in C. citrinus. The relative salt tolerance of Callistemon was related to storage of higher levels of Na⁺ and Cl^? in the roots compared with the leaves, especially in the case of Na⁺, which could have helped to maintain the quality of plants. The results show that saline water (around 4 dS·m^?1) could be used for growing C. citrinus commercially. However, the cumulative effect of irrigating with saline water for 11 months was a decrease in photosynthesis and intrinsic water use efficiency, meaning that the interaction of the salinity level and the time of exposure to the salt stress should be considered important in this species.     

盐胁迫对3种平欧杂种榛幼苗叶片解剖结构及离子吸收、运输与分配的影响

研究盐胁迫下3个品种平欧杂种榛幼苗叶片解剖结构和离子代谢特征,以揭示盐胁迫响应与适应机制及不同品种的耐盐性差异。以‘达维’、‘辽榛7号’、‘玉坠’2年生压条苗为材料,在盆栽条件下经轻度、中度、重度(分别为50、100、200 mmol/L NaCl)盐胁迫处理,设对照为0,研究幼苗叶片显微解剖结构参数和Na~+、K~+、Cl~-、Ca²⁺含量的变化及其在根、茎、叶中的吸收、运输和分配特征。不同品种平欧杂种榛叶片厚度、上表皮厚度、下表皮厚度、栅栏组织和海绵组织厚度随着盐胁迫程度的增强呈现出先增加后降低的特点,轻度和中度胁迫下各参数显著高于对照。中度盐胁迫显著提高了各品种叶片结构紧密度。盐胁迫导致平欧杂种榛根、茎、叶Na~+和Cl~-含量明显高于对照。盐胁迫下,Na~+和Cl~-在叶中的绝对含量明显高于茎和根,但二者的增幅以根中最大,叶中最小,表明平欧杂种榛根系首先会吸收并截留一定数量的Na~+和Cl~-,然后将其运输至茎和叶中。与对照相比,轻度和中度盐胁迫下根、茎对K~+和Ca²⁺的吸收保持稳定或减少,叶对K~+和Ca²⁺...     

Relation between Ion Accumulation of Salt-Sensitive and Isolated Stable Salt-Tolerant Cell Lines of Citrus aurantium

Four selected NaCl-tolerant cell lines of Sour orange (Citrus aurantium) were compared with the nonselected cell line in their growth and internal ion content of Na⁺, K⁺, and Cl⁻ when exposed to increasing NaCl concentrations. No difference was found among the various NaCl-tolerant cell lines in Na⁺ and Cl⁻ uptake, and all these cell lines took up similar or even larger amounts of Na⁺ and Cl⁻ than the NaCl-sensitive cell line. Exposure of cells of NaCl-sensitive and NaCl-tolerant lines to equal external concentrations of NaCl, resulted in a greater loss of K⁺ from the NaCl-sensitive cell line. This observation leads to the conclusion that growth and ability to retain high levels of internal K⁺ are correlated. Exposure of the NaCl-tolerant cell lines to salts other than NaCl resulted in even greater tolerance to Na₂SO₄, but rather poor tolerance to K⁺ introduced as either K₂SO₄ or KCl; the latter has a stronger inhibitory effect. The NaCl-sensitive cell line proved to be more sensitive to replacement of Na⁺ by K⁺. Analyses of internal Na⁺, K⁺, and Cl⁻ concentrations failed to identify any particular internal ion concentration which could serve as a reliable marker for salt tolerance.