Functional characterization of a wheat plasma membrane Na+/H+ antiporter in yeast

The functional analysis of the sodium exchanger SOS1 from wheat, TaSOS1, was undertaken using Saccharomyces cerevisiae as a heterologous expression system. The TaSOS1 protein, with significant sequence homology to SOS1 sodium exchangers from Arabidopsis and rice, is abundant in roots and leaves, and is induced by salt treatment. TaSOS1 suppressed the salt sensitivity of a yeast strain lacking the major Na⁺ efflux systems by decreasing the cellular Na⁺ content while increasing K⁺ content. Na⁺/H⁺ exchange activity of purified plasma membrane from yeast cells expressing TaSOS1 was higher than controls transformed with empty vector. These results demonstrate that TaSOS1 contributes to plasma membrane Na⁺/H⁺ exchange.     

Osmotic adjustment,water relations and growth attributes of the xero-halophyte <Emphasis Type="Italic">Reaumuria vermiculata</Emphasis> L. (Tamaricaceae) in response to salt stress

Reaumuria vermiculata (L.), a perennial dwarf shrub in the family of Tamaricaceae, is a salt-secreting xero-halophyte found widely in arid areas of Tunisia. In the present study, physiological attributes of R. vermiculata were investigated under salt stress. Four-month-old plants were subjected to various salinity levels (0, 100, 200, 300, 400 or 600 mM NaCl) for 30 days under greenhouse conditions. Results showed that plants grew optimally when treated with standard nutrient solution without NaCl supply. However, increasing osmolality of nutrient solutions caused a significant reduction in biomass production and relative growth rate. This reduction was more pronounced in roots than in shoots. In addition, this species was able to maintain its shoot water content at 30% of the control even when subjected to the highest salt level, whereas root water content seemed to be unaffected by salt. Shoot water potential declined significantly as osmotic potential of watering solutions was lowered and the more negative values were reached at 600 mM NaCl (−3.4 MPa). Concentrations of Na⁺ and Cl⁻ in the shoots of R. vermiculata were markedly increased with increasing osmolality of nutrient solutions, whereas concentration of K⁺ was not affected by NaCl supply. Salt excretion is an efficient mechanism of Na⁺ exclusion from the shoots of this species exhibiting high K⁺/Na⁺ selectivity ratio over a wide range of NaCl salinity. Proline accumulation in shoots was significantly increased with increase in salt level and may play a role in osmoregulation.     

短期NaCl胁迫对不同小麦品种幼苗K+吸收和Na+、K+积累的影响

为研究盐胁迫下小麦幼苗生长及Na⁺、K⁺的吸收和积累规律,以中国春、洲元9369和长武134等3种耐盐性不同小麦品种为材料,采用非损伤微测技术检测盐胁迫2 d后的根系K⁺离子流变化,并对植株体内的Na⁺、K⁺含量进行测定。结果表明:短期(2d)盐胁迫对小麦生长有抑制作用,且对根系的抑制大于地上部,耐盐品种下降幅度小于盐敏感品种。盐胁迫下,小麦根际的 K⁺大量外流,盐敏感品种中国春K⁺流速显著高于耐盐品种长武134,最高可达15倍。小麦幼苗地上部分和根系均表现为Na⁺积累增加,K⁺积累减少,Na⁺/K⁺比随盐浓度增加而上升。中国春限Na⁺能力显著低于长武134,Na⁺/K⁺则显著高于长武134。综上所述,盐胁迫下造成小麦组织器官中Na⁺/K⁺比上升的主要原因是根系K⁺大量外流和Na⁺的过量积累,耐盐性不同的小麦品种间差异显著,并认为根系对K⁺的保有能力可能是作物耐盐性评价的一个重要指标。     

Salt,Na+,K+-ATPase and hypertension

Chronic hypertension is characterized by a persistent increase in vascular tone. Sodium-rich diets promote hypertension; however, the underlying molecular mechanisms are not fully understood. Variations in the sodium content of the diet, through hormonal mediators such as dopamine and angiotensin II, modulate renal tubule Na⁺,K⁺-ATPase activity. Stimulation of Na⁺,K⁺-ATPase activity increases sodium transport across the renal proximal tubule epithelia, promoting Na⁺ retention, whereas inhibited Na⁺,K⁺-ATPase activity decreases sodium transport, and thereby natriuresis. Diets rich in sodium also enhance the release of adrenal endogenous ouabain-like compounds (OLC), which inhibit Na⁺,K⁺-ATPase activity, resulting in increased intracellular Na⁺ and Ca²⁺ concentrations in vascular smooth muscle cells, thus increasing the vascular tone, with a corresponding increase in blood pressure. The mechanisms by which these homeostatic processes are integrated in response to salt intake are complex and not completely elucidated. However, recent scientific findings provide new insights that may offer additional avenues to further explore molecular mechanisms related to normal physiology and pathophysiology of various forms of hypertension (i.e. salt-induced). Consequently, new strategies for the development of improved therapeutics and medical management of hypertension are anticipated.     

Effect of nitric oxide signaling in bacterial-treated soybean plant under salt stress

To understand protective roles of nitric oxide against salt stress, the effects of exogenous sodium nitroprusside on activities of lipoxygenase, peroxidase, phenylalanine ammonialyase, catalase, superoxide dismutase enzymes, proline accumulation, and distribution of sodium in soybean plants under salt were determined. Application of sodium nitroprusside + bacterium enhanced plant growth-promotion characteristics, activities of different enzymes, and proline accumulation in the presence of sodium nitroprusside under salt stress. Treatment with NaCl at 200 mM and sodium nitroprusside (0.1 mM) reduced Na⁺ levels but increased K⁺ levels in leaves in comparison with the NaCl-treated plants. Correspondingly, the plants treated with exogenous sodium nitroprusside and NaCl maintained a lower ratio of [Na⁺]/[K⁺] in NaCl-stressed plants.     

NaCl胁迫对滨梅扦插苗生物量和水分积累的影响

以1年生滨梅(Prunus maritima Marshall)扦插苗为实验材料,在盆栽条件下用质量浓度为0.15%、0.29%、0.58%、0.88%、1.17%、1.46%的NaCl溶液进行盐胁迫处理,测定胁迫后根、茎、叶Na+、K+含量以及全叶、一年生茎、二年生茎和根系生物量、含水率、根系活力变化,探讨滨梅的抗盐胁迫机制。结果显示:(1)盐胁迫80d后,随着盐胁迫强度提高,滨梅植株根、茎、叶Na+含量显著提高,而其根、茎K+含量显著降低,根、茎、叶K+/Na+值显著降低;根Na+含量在低于0.58%NaCl胁迫下显著高于茎、叶,而在高于0.58%NaCl胁迫下却表现为叶Na+含量显著高于根、茎。(2)滨梅根、茎、叶生物量均随盐胁迫强度的提高呈先增加后减少的趋势;随着盐胁迫时间的延长,茎、叶生物量在低于0.58%NaCl胁迫下均呈积累趋势,且茎生物量在0.58%NaCl胁迫下显著提高,而根、一年生茎、叶生物量在高于0.58%NaCl胁迫下均显著下降。(3)滨梅茎、叶含水率均随盐胁迫强度的增加呈先增加后减少的趋势,而随着胁迫时间的延长呈逐渐减少趋势;根系活力及根含水率均随盐胁迫强度的提高而增加,但根含水率随着胁迫时间的延长变化不明显。由此可见,滨梅能通过根系稀释并蓄积Na+,保护地上部分正常生长,当进入根系的Na+量超过吸收阈值时,Na+迅速在叶中积累储存,且叶中较高含量的K+对Na+形成了有效的缓冲。     

Cation fluxes in excised and intact roots in relation to specific and varietal differences

Summary In this short survey differences between species and varieties in the four major mechanisms that affect selective uptake of potassium and sodium to the plant within the root are considered. These include influx selectivity, K⁺/Na⁺ exchange at the plasmalemma, and selectivity at the tonoplast as well as at the symplasm-xylem boundary. The affinity of various plants for potassium influx in system 1 is rather uniform although varietal differences in barley have been observed. Differences are much more pronounced for sodium influx, for which Helianthus showed rather high and Fagopyrum rather low affinity. There is substantial variation between species in the efficiency of K⁺/Na⁺ exchange at the plasmalemma of cortical root cells; the three cereals Hordeum, Triticum, and Secale were highly efficient while K⁺/Na⁺ exchange in Atriplex, Helianthus and Allium was poor, even if the cytoplasmic sodium content was accounted for. Apparently there was no direct relation between salt tolerance and K⁺/Na⁺ exchange. The observed differences in the efficiency of K⁺-dependent sodium extrusion or K⁺/Na⁺ exchange were not due to the use of excised roots, they were observed also when roots of whole seedlings were investigated. At the tonoplast a 11 exchange of vacuolar potassium for sodium has been observed in roots of Hordeum. By this exchange sodium ions are removed from the symplasm and potassium ions are recovered from vacuoles and thus made available for transport to the shoot. Indications for specific differences in this exchange have been observed; the exchange appears to be more efficient in Helianthus than in Hordeum roots. More comparative studies are needed here. At the boundary between symplasm and xylem vessels selectivity can be set up during xylem release of cations and there are reports that suggest a preference for sodium (Lycopersicum cheesemanii, Solanum pennellii, and Suaeda) and for varietal differences amongst tomatoes. Selectivity at this boundary, the plasmalemma of the xylem parenchyma cells was described in this paper by the selectivity ratio of transport that relates the rates of xylem transport to the cytoplasmic sodium and potassium concentrations. Based on this ratioAtriplex hortensis was shown to discriminate for sodium during xylem release while there was little selectivity in Hordeum and possibly some discrimination in favour of K⁺ in Allium roots. The data are shortly discussed in relation to salt tolerance and to the breeding of salt-tolerant crop varieties.     

Physiological adaptation and gene expression analysis of <Emphasis Type="Italic">Casuarina equisetifolia</Emphasis> under salt stress

Casuarina equisetifolia is widely planted in coastal areas of tropical and subtropical regions as windbreaks or to stabilize dunes against wind erosion due to its high salt tolerance and nitrogen-fixing ability. To investigate the mechanisms responsible for its salt tolerance, we examined growth, mineral composition, expression of genes for sodium (Na⁺) and potassium (K⁺) transport proteins, and antioxidant responses under NaCl treatments. Increasing NaCl concentrations inhibited lateral root elongation and decreased plant height, length of internodes, and numbers of branches and twigs. The Na⁺ content significantly increased whereas the K⁺ content significantly decreased in both shoots and roots with increasing external NaCl concentration, resulting in a significant increase in Na⁺/K⁺ ratio. Most of the Na⁺/H⁺ antiporter genes (NHXs) were obviously upregulated in roots after 24 and 168 h of salt stress, and NHX7 was especially induced after 168 h. Almost all salt overly sensitive (SOS) genes were induced after 168-h treatment. Additionally, activities of superoxide dismutase, glutathione peroxidase, and catalase were significantly changed in shoots and roots under salt stress. Hence, we conclude that salinity tolerance of C. equisetifolia mainly relied on sequestering excess Na⁺ into vacuoles and on induced expression of NHX and SOS genes in roots and thus the maintenance of sufficient K⁺ content in shoots.     

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.     

披针叶黄华试管苗适应盐胁迫的渗透调节机制

以披针叶黄华(Thermopsis lanceolata)试管苗为材料,通过组培方法研究其在0、0.2%、0.4%、0.6%、0.8%和1.0%NaCl和Na2SO4胁迫30d后的生长、有机渗透调节物质和无机渗透调节物质(Na+、K+和Ca2+)含量的变化,以探讨其耐盐性机制。结果显示:(1)随NaCl和Na2SO4胁迫浓度的增加,披针叶黄华试管苗叶片脯氨酸和可溶性糖含量均显著持续增加,且NaCl胁迫下脯氨酸上升的幅度均大于相同浓度Na2SO4胁迫下的增幅,而可溶性糖上升的幅度却小于相同浓度Na2SO4胁迫下的幅度;可溶性蛋白含量随NaCl浓度的增大呈先升高后降低的趋势,但随Na2SO4浓度的增加呈持续上升的趋势。(2)随NaCl和Na2SO4浓度的增加,披针叶黄华试管苗Na+含量呈增加趋势且各处理均显著高于对照,Ca2+含量和叶片K+含量却呈逐渐减少趋势且各处理均显著低于对照,而根系K+含量呈先降后升的趋势;Na2SO4胁迫下披针叶黄华试管苗叶片Na+含量上升幅度以及K+和Ca2+含量下降幅度均明显低于相同浓度NaCl胁迫组;而Na+/K+和Na+/Ca2+比值随NaCl和Na2SO4浓度增加而升高;NaCl胁迫下,叶片Na+/K+和Na+/Ca2+高于相同浓度Na2SO4胁迫下的比值,而根系Na+/K+和Na+/Ca2+却低于相同浓度Na2SO4胁迫下的比值。研究表明,盐胁迫下,披针叶黄华试管苗通过抑制叶片中Na+积累并增加可溶性糖和可溶性蛋白含量,在根系中维持较高K+和Ca2+含量以及较低水平Na+/K+和Na+/Ca2+比,以降低披针叶黄华细胞渗透势来适应盐渍环境;披针叶黄华对NaCl胁迫的调节能力弱于Na2SO4。     

Salt sensitivity and low discrimination between potassium and sodium in bean plants

Bean plants (Phaseolus vulgaris) were very sensitive to moderate concentrations of NaCl, showing a dramatic decrease in their K⁺ content in the presence of this salt. Increasing the KCl content of the nutrient medium released the inhibitory effect of NaCl by increasing the K⁺ content of the plants. Likewise moderate concentrations of KCl were toxic for bean plants because they produced a large K⁺ loading. NaCl partially released this toxicity by inhibiting the K⁺ loading. When compared to the moderately salt tolerant sunflower plants (Helianthus annuus), bean plants showed a lower capacity to discriminate between K⁺ and Na⁺, at high Na⁺ levels, and an uncontrolled K⁺ uptake at moderate concentrations of K⁺. It is concluded that this low capacity of discrimination of the K⁺ uptake system of bean plants in presence of Na⁺ can account for by the NaCl sensitivity of bean plants.     

Mesurement of longitudinal ion profiles in single roots of Hordeum and Atriplex by use of flameless atomic absorption spectroscopy

Summary A method is described by which the Na⁺ and K⁺ content in 0.5 mm sections of single roots of Hordeum distichon L. and Atriplex hortensis L. can be determined by use of flameless atomic absorption spectroscopy. By this method the longitudinal profiles of K⁺ and Na⁺ along low salt roots and roots which had been equilibrated with or grown in K⁺-free 1 mM Na⁺-solution were determined. The profiles reveal that high K⁺/Na⁺ ratios in the cytoplasm are maintained also in K⁺-free solutions. In solutions containing 1 mM Na⁺ a high K⁺/Na⁺ selectivity was found to be dependent on sufficient aeration. From the ion profiles the cytoplasmic (110 mM) and vacuolar (20 mM) K⁺ concentration in low salt barley roots—values which are unobtainable by compartmental analysis—could be estimated.     

NaCl胁迫对不同耐盐性玉米自交系萌动种子和幼苗离子稳态的影响

盐胁迫影响植物组织的离子分布,不同品种间存在差异。以玉米耐盐自交系81162和8723及盐敏感自交系P138为材料,研究了不同浓度(0、60、140、220 mmol/L)Na Cl胁迫下萌动期种子和幼苗的不同部位中Na+、K+、Ca2+含量以及K+/Na+和Ca2+/Na+比值的变化,旨在探讨不同自交系耐盐性差异的原因。结果表明,在萌动种子中,3个玉米自交系中的Na+积累量表现为种皮胚胚乳,K+累积表现为胚种皮胚乳;幼苗中,Na+积累表现为根茎叶。随着Na Cl浓度的增加,3个玉米自交系萌动种子和幼苗中的Na+含量逐渐升高,但是萌动种子中耐盐自交系81162和8723的Na+增加幅度小于盐敏感自交系P138,Na+含量小于盐敏感自交系P138;幼苗中耐盐自交系81162和8723的Na+增加幅度大于盐敏感自交系P138,幼苗根中Na+含量大于盐敏感自交系P138;茎叶中的Na+含量小于盐敏感自交系P138。随着Na Cl浓度的增加,萌动种子和幼苗中的K+和Ca2+含量逐渐降低。K+离子在耐盐自交系81162和8723萌动种子和幼苗中的降低幅度小于盐敏感自交系P138;Ca2+离子在耐盐自交系81162和8723幼苗中的降低幅度小于盐敏感自交系P138;而在萌动种子中3个自交系Ca2+的流失差异不大。耐盐自交系81162和8723萌动种子和幼苗中K+含量都大于盐敏感自交系P138。耐盐自交系81162和8723的萌动种子和幼苗根中Ca2+含量都大于盐敏感自交系P138;幼苗叶片中则小于盐敏感自交系P138。萌动种子和幼苗中K+/Na+和Ca2+/Na+均随着Na Cl浓度的升高而降低,K+/Na+比值表现为耐盐自交系81162和8723大于盐敏感自交系P138。耐盐自交系81162和8723通过调节离子平衡维持萌动种子和幼苗中较高的K+/Na+比值从而提高耐盐性。     

Transport,signaling, and homeostasis of potassium and sodium in plants

Potassium （K＋） is an essential macronutrient in plants and a lack of K＋ significantly reduces the potential for plant growth and development. By contrast, sodium （Na＋）, while beneficial to some extent, at high concentrations it disturbs and inhibits various physiological processes and plant growth. Due to their chemical similarities, some functions of K＋ can be undertaken by Na＋ but K＋ homeostasis is severely affected by salt stress, on the other hand. Recent advances have highlighted the fascinating regulatory mechanisms of K＋ and Na＋ transport and signaling in plants. This review summarizes three major topics： （i） the transport mechanisms of K＋ and Na＋ from the soil to the shoot and to the cellular - compartments; （ii） the mechanisms through which plants sense and respond to K＋ and Na＋ availability; and （iii） the components involved in maintenance of K＋/Na＋ homeostasis in plants under salt stress.     

Sulfatide content and (Na++K+)-ATPase activity of skin and gill during larval development of the chilean frog,Calyptocephalella caudiverbera

Summary The sulfatide content, phospholipid concentration, and (Na⁺+K⁺)-ATPase activity from skin and gills of different stages of larval development ofCalyptocephalella caudiverbera (a Chilean frog) were analyzed. Additionally, the short-circuit current in skin was studied. When skin and gills, depending on the stage of larval development, present (Na⁺+K⁺)-ATPase activity, they have a high ratio of sulfatide to amount of membrane and the phosphatidylserine concentration remains unchanged. Sulfatide content and (Na⁺+K⁺)-ATPase activity in skin are in direct relationship with the level of sodium flux present during development. The specific enzymatic hydrolysis of sulfatide with partially purified arylsulfatase of pig kidney inhibits 100% of the ouabain-sensitive (Na⁺+K⁺)-ATPase. The ouabain-insensitive ATPase remains virtually unchanged with the treatment, even with a high concentration of arylsulfatase or with ouabain present in the medium. These experiments strongly suggest a role of sulfatides in the (Na⁺+K⁺)-ATPase activity and, as a consequence, in sodium ion transport.     

Nitric Oxide Mediates Root K+/Na+ Balance in a Mangrove Plant,Kandelia obovata,by Enhancing the Expression of AKT1-Type K+ Channel and Na+/H+ Antiporter under High Salinity

It is well known that nitric oxide (NO) enhances salt tolerance of glycophytes. However, the effect of NO on modulating ionic balance in halophytes is not very clear. This study focuses on the role of NO in mediating K⁺/Na⁺ balance in a mangrove species, Kandelia obovata Sheue, Liu and Yong. We first analyzed the effects of sodium nitroprusside (SNP), an NO donor, on ion content and ion flux in the roots of K. obovata under high salinity. The results showed that 100 μM SNP significantly increased K⁺ content and Na⁺ efflux, but decreased Na⁺ content and K⁺ efflux. These effects of NO were reversed by specific NO synthesis inhibitor and scavenger, which confirmed the role of NO in retaining K⁺ and reducing Na⁺ in K. obovata roots. Using western-blot analysis, we found that NO increased the protein expression of plasma membrane (PM) H⁺-ATPase and vacuolar Na⁺/H⁺ antiporter, which were crucial proteins for ionic balance. To further clarify the molecular mechanism of NO-modulated K⁺/Na⁺ balance, partial cDNA fragments of inward-rectifying K⁺ channel, PM Na⁺/H⁺ antiporter, PM H⁺-ATPase, vacuolar Na⁺/H⁺ antiporter and vacuolar H⁺-ATPase subunit c were isolated. Results of quantitative real-time PCR showed that NO increased the relative expression levels of these genes, while this increase was blocked by NO synthesis inhibitors and scavenger. Above results indicate that NO greatly contribute to K⁺/Na⁺ balance in high salinity-treated K. obovata roots, by activating AKT1-type K⁺ channel and Na⁺/H⁺ antiporter, which are the critical components in K⁺/Na⁺ transport system.     

Functional Characterization of a Wheat NHX Antiporter Gene TaNHX2 That Encodes a K+/H+ Exchanger

The subcellular localization of a wheat NHX antiporter, TaNHX2, was studied in Arabidopsis protoplasts, and its function was evaluated using Saccharomyces cerevisiae as a heterologous expression system. Fluorescence patterns of TaNHX2-GFP fusion protein in Arabidopsis cells indicated that TaNHX2 localized at endomembranes. TaNHX2 has significant sequence homology to NHX sodium exchangers from Arabidopsis, is abundant in roots and leaves and is induced by salt or dehydration treatments. Western blot analysis showed that TaNHX2 could be expressed in transgenic yeast cells. Expressed TaNHX2 protein suppressed the salt sensitivity of a yeast mutant strain by increasing its K⁺ content when exposed to salt stress. TaNHX2 also increased the tolerance of the strain to potassium stress. However, the expression of TaNHX2 did not affect the sodium concentration in transgenic cells. Western blot analysis for tonoplast proteins indicated that the TaNHX2 protein localized at the tonoplast of transgenic yeast cells. The tonoplast vesicles from transgenic yeast cells displayed enhanced K⁺/H⁺ exchange activity but very little Na^+/H⁺ exchange compared with controls transformed with the empty vector; Na⁺/H⁺ exchange was not detected with concentrations of less than 37.5 mM Na⁺ in the reaction medium. Our data suggest that TaNHX2 is a endomembrane-bound protein and may primarily function as a K⁺/H⁺ antiporter, which is involved in cellular pH regulation and potassium nutrition under normal conditions. Under saline conditions, the protein mediates resistance to salt stress through the intracellular compartmentalization of potassium to regulate cellular pH and K⁺ homeostasis.     

盐胁迫对二穗短柄草幼苗生长及不同器官中盐离子稳态的影响

采用4种浓度的NaCl溶液(50、100、150、200 mmol/L)处理二穗短柄草和拟南芥(对照)幼苗,测定不同浓度盐胁迫下2种植物幼苗的生长指标和离子分布,以探讨二穗短柄草在盐胁迫下主要阳离子平衡机制.结果表明:(1)盐胁迫显著抑制二穗短柄草根叶的生物量积累.(2)根冠比数据显示,在盐胁迫条件下二穗短柄草能够更好地维系地下部分的生物量积累.(3)在4种浓度盐胁迫下,二穗短柄草叶中Na+含量低于根系,而且K+、Cl-含量和K+/Na+比值始终高于根系,说明在二穗短柄草中Na+从地下到地上的转运受到抑制,但对Cl-的转运缺乏有效的调控.(4)回归分析发现,盐胁迫下二穗短柄草和拟南芥根部Na+与K+含量变化呈正相关关系,而在叶部则不相关,说明二穗短柄草和拟南芥Na+与K+在根部具有相同的离子通道,而在叶部却具有各自独立的转运途径.     

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.     

Adenosine Triphosphatase Activities in Leaves of the Mangrove Avicennia nitida Jacq: Influence of Sodium to Potassium Ratios and Salt Concentrations

Homogenates from the salt-excreting leaves of the mangrove Avicennia nitida were subjected to differential centrifugation and investigated for adenosine triphosphatase activities. At pH 6.75 a salt stimulation with peaks at three different sodium to potassium ratios could be demonstrated above the activity due to Mg²⁺ ions. The stimulation by sodium and potassium depends on the ionic strength of the test medium, higher salt concentrations being inhibitory. The plant system seems thus more complicated than the animal activities. Technically, this means that a search for (Na⁺ + K⁺)-activated ATPases in plants should be performed with a close spacing of Na:K ratios at several constant levels of salt. Literature data on the transport of Na⁺ and K⁺ indicate that the physiological situation is rather complex in plants.