Assessment of the preventive effect of vermicompost on salinity resistance in tomato (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis> cv. Ailsa Craig)

To determine the effects of vermicompost leachate (VCL) on resistance to salt stress in plants, young tomato seedlings (Solanum lycopersicum, cv. Ailsa Craig) were exposed to salinity (150 mM NaCl addition to nutrient solution) for 7 days after or during 6 mL L^??1 VCL application. Salt stress significantly decreased leaf fresh and dry weights, reduced leaf water content, significantly increased root and leaf Na⁺ concentrations, and decreased K⁺ concentrations. Salt stress decreased stomatal conductance (g_s), net photosynthesis (A), instantaneous transpiration (E), maximal efficiency of PSII photochemistry in the dark-adapted state (F_v/F_m), photochemical quenching (qP), and actual PSII photochemical efficiency (ΦPSII). VCL applied during salt stress increased leaf fresh weight and g_s, but did not reduce leaf osmotic potential, despite increased proline content in salt-treated plants. VCL reduced Na⁺ concentrations in leaves (by 21.4%), but increased them in roots (by 16.9%). VCL pre-treatment followed by salt stress was more efficient than VCL concomitant to salt stress, since VCL pre-treatment provided the greatest osmotic adjustment recorded, with maintenance of net photosynthesis and K⁺/Na⁺ ratios following salt stress. VCL pre-treatment also led to the highest proline content in leaves (50 µmol g^??1 FW) and the highest sugar content in roots (9.2 µmol g^??1 FW). Fluorescence-related parameters confirmed that VCL pre-treatment of salt-stressed plants showed higher PSII stability and efficiency compared to plants under concomitant VCL and salt stress. Therefore, VCL represents an efficient protective agent for improvement of salt-stress resistance in tomato.     

Coordination of AtHKT1;1 and AtSOS1 facilitates Na+ and K+ homeostasis in Arabidopsis thaliana under salt stress

Reducing Na⁺ accumulation and maintaining K⁺ stability in plant is one of the key strategies for improving salt tolerance. AtHKT1;1 and AtSOS1 are not only the salt tolerance determinants themselves, but also mediate K⁺ uptake and transport indirectly. To assess the contribution of AtHKT1;1 and AtSOS1 to Na⁺ homeostasis and K⁺ nutrition in plant, net Na⁺ and K⁺ uptake rate, Na⁺ and K⁺ distributions in Arabidopsis thaliana wild type (WT), hkt1;1 mutant (athkt1;1) and sos1 mutant (atsos1) were investigated. Results showed that under 2.5 mM K⁺ plus 25 or 100 mM NaCl, athkt1;1 shoot concurrently accumulated more Na⁺ and less K⁺ than did WT shoot, suggesting that AtHKT1;1 was critical for controlling Na⁺ and K⁺ distribution in plant; while atsos1 root accumulated more Na⁺ and absorbed lower K⁺ than did WT root, implying that AtSOS1 was determiner of Na⁺ excretion and K⁺ acquisition. Under 0.01 mM K⁺, athkt1;1 absorbed lower Na⁺ than did WT with 100 mM NaCl, suggesting that AtHKT1;1 is involved in Na⁺ uptake in roots; while atsos1 shoot accumulated less Na⁺ than did WT shoot no matter with 25 or 100 mM NaCl, implying that AtSOS1 played a key role in controlling long-distance Na⁺ transport from root to shoot. We present a model in which coordination of AtHKT1;1 and AtSOS1 facilitates Na⁺ and K⁺ homeostasis in A. thaliana under salt stress: under the normal K⁺, the major function of AtHKT1;1 is Na⁺ unloading and AtSOS1 is mainly involved in Na⁺ exclusion, whereas under the low K⁺, AtHKT1;1 may play a dominant role in Na+ uptake and AtSOS1 may be mainly involved in Na⁺ loading into the xylem.     

Biochemical characterization of α- and β-glucosidases in alimentary canal, salivary glands and haemolymph of the rice green caterpillar, Naranga aenescens M. (Lepidoptera: Noctuidae)

The biochemical properties of ??- and ??-glucosidase in salivary glands, alimentary canal and haemolymph of Naranga aenescens larvae, one of the most damaging pests of the rice crop in Iran, were investigated. The specific activity of ??-glucosidases were 3.88, 2.74 and 1.58 ??mol/min per mg protein in the alimentary canal, salivary glands and haemolymph of last instar larvae, respectively. The specific activity of ??-glucosidases were 1.27, 0.077 and 0.414 ??mol/min per mg protein in the alimentary canal, salivary glands and haemolymph of last instar larvae, respectively. The optimal pH for ??-glucosidases were 6.0, 6.0?C8.0 and 6.0 and the maximum activity for ??-glucosidases were obtained at pH 6.0, 5.0?C7.0 and 5.0 in alimentary canal, salivary glands and haemolymph, respectively. The optimum temperatures for ??-glucosidases were determined at 55°C in alimentary canal, 35?C45°C in salivary glands and 55°C in haemolymph, whereas the ??-glucosidases reached their optimum at 45°C in all three tissues. Effect of metal ions on the activity of ??- and ??-glucosidases showed that K⁺ (20 mM) and Mg²⁺ (10 and 20 mM) increased N. aenescens ??- and ??-glucosidases activities from salivary glands, while Ca²⁺ increased ??- and ??-glucosidases activities in haemolymph. In the presence of Fe²⁺, Mn²⁺, Hg⁺ and Zn²⁺ (10, 20 mM) and Hg²⁺ (20 mM), these enzymes from all tissues were completely inactivated. K _m values were estimated for the ??-glucosidases as 3.96, 0.547 and 3.084 mM and for ??-glucosidases as 1.93, 1.014 and 1.93 mM in the alimentary canal, salivary gland and haemolymph, respectively. The zymogram analyses of N. aenescens crude extracts indicated the presence of at least two isoforms for ??-glucosidase and one isoform for ??-glucosidase.     

Influence of inorganic nitrogen sources on K+/Na+ homeostasis and salt tolerance in sorghum plants

This work aimed to study the regulation of K⁺/Na⁺ homeostasis and the physiological responses of salt-treated sorghum plants [Sorghum bicolor (L.) Moench] grown with different inorganic nitrogen (N) sources. Four days after sowing (DAS), the plants were transferred to complete nutrient solutions containing 0.75 mM K⁺ and 5 mM N, supplied as either NO₃ ^? or NH₄ ⁺. Twelve DAS, the plants were subjected to salt stress with 75 mM NaCl, which was applied in two doses of 37.5 mM. The plants were harvested on the third and seventh days after the exposure to NaCl. Under the salt stress conditions, the reduction of K⁺ concentrations in the shoot and roots was higher in the culture with NO₃ ^? than with NH₄ ⁺. However, the more conspicuous effect of N was on the Na⁺ accumulation, which was severely limited in the presence of NH₄ ⁺. This ionic regulation had a positive influence on the K⁺/Na⁺ ratio and the selective absorption and transport of K⁺ in the plants grown with NH₄ ⁺. Under control and salt stress conditions, higher accumulation of free amino acids and soluble proteins was promoted in NH₄ ⁺ grown roots than NO₃ ^? grown roots at both harvesting time, whereas higher accumulation of soluble sugars was observed only at 7 days of salt stress exposure. Unlike the NH₄ ⁺ grown plants, the gas exchanges of the NO₃ ^? grown plants were reduced after 7 days of salt stress. These results suggest that external NH₄ ⁺ may limit Na⁺ accumulation in sorghum, which could contribute to improving its physiological and metabolic responses to salt stress.     

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.     

Ecosystem changes in Galápagos highlands by the invasive tree Cinchona pubescens

Background and aims

Salinity is an increasing problem for agricultural production worldwide. Understanding how Na⁺ enters plants is important if reducing Na⁺ influx, a key component of the regulation of Na⁺ accumulation in plants and improving salt tolerance of crop plants, is to be achieved. Our previous work indicated that two distinct low-affinity Na⁺ uptake pathways exist in the halophyte Suaeda maritima. Here, we report the external NaCl concentration at which uptake switches from pathway 1 to pathway 2 and the kinetics of the interaction between external K⁺ concentration and Na⁺ uptake and accumulation in S. maritima in order to determine the roles of K⁺ transporters or channels in low-affinity Na⁺ uptake.

Methods

Na⁺ influx, Na⁺ and K⁺ accumulations in S. maritima exposed to various concentrations of NaCl (0–200 mM) were analyzed in the absence and presence of the inhibitors TEA and Ba⁺ (5 mM TEA or 3 mM Ba²⁺) or KCl (0, 10 or 50 mM).

Results

Our earlier proposal was confirmed and extended that there are two distinct low-affinity Na⁺ uptake pathways in S. maritima: pathway 1 might be mediated by a HKT-type transporter under low salinity conditions and pathway 2 by an AKT1-type channel or a KUP/HAK/KT type transporter under high salinity conditions. The external NaCl concentration at which two distinct low-affinity Na⁺ uptake switches from pathway 1 to pathway 2, the ‘turning point’, is between 90 and 95 mM. Over a short period (12 h) of Na⁺ and K⁺ treatments, a low concentration of K⁺ (10 mM) facilitated Na⁺ uptake by S. maritima under high salinity (100–200 mM NaCl), whether or not the plants had been subjected to a longer (3 d) period of K⁺ starvation. The kinetics suggests that low concentration of K⁺ (10 mM) might activate AKT1-type channels or KUP/HAK/KT-type transporters under high salinity (100–200 mM NaCl).

Conclusions

The turning-point of external NaCl concentrations for the two low-affinity Na⁺ uptake pathways in Suaeda maritima is between 90 and 95 mM. A low concentration of K⁺ (10 mM) might activate AKT1 or KUP/HAK/KT and facilitate Na⁺ uptake under high salinity (100–200 mM NaCl). The kinetics of K⁺ on Na⁺ uptake and accumulation in S maritima are also consistent with there being two low-affinity Na⁺ uptake pathways.     

NaCl胁迫下沙枣幼苗生长和阳离子吸收、运输与分配特性

沙枣(Elaeagnus angustifolia L.)耐盐性强,是我国北方生态脆弱地区造林绿化的一个先锋树种。为探讨沙枣的盐适应机制,研究了不同浓度NaCl(0、100和200 mmol/L)胁迫30d对其水培幼苗生物量累积以及不同组织(根、茎、叶)K+、Na+、Ca2+和Mg2+吸收、运输与分配的影响。结果表明:盐胁迫不同程度地促进了沙枣苗根系生长;100 mmol/L NaCl胁迫对幼苗生物量累积无明显影响,而200 mmol/L则显著抑制了生物量累积;盐胁迫幼苗根、茎、叶中Na+含量以及K+-Na+选择性运输系数(S K,Na)和Ca2+-Na+选择性运输系数(S Ca,Na)显著或大幅度增加,而K+、Ca2+、Mg2+含量以及K+/Na+、Ca2+/Na+和Mg2+/Na+比值则显著或大幅度下降;200 mmol/L NaCl胁迫沙枣根Na+含量和根Na+净累积量分别为22.15 mg/g干重和1.87 mg/株(是对照的16.20倍和20.06倍),根成为Na+净累积量增加幅度最大的组织和Na+含量最高的组织;200 mmol/L NaCl胁迫沙枣茎、叶中的Na+含量以及冠组织Na+净累积量分别高达5.15、7.71 mg/g干重和3.29 mg/株(是对照的7.22倍、9.58倍和5.45倍),但幼苗仍能正常生长。综合分析认为,沙枣的盐适应机制是根系拒盐和冠组织耐盐,主要通过根系的补偿生长效应、根系对Na+的聚积与限制作用以及冠组织对Na+的忍耐来实现的,同时也与根、茎和叶对K+、Ca2+选择性运输能力显著增强有关。     

Hydrolysis of adenylyl imidodiphosphate in the presence of Na+ + Mg+ by (Na+ + K+)-activated ATPase

(1) Contrary to what has usually been assumed, (Na⁺ + K⁺)-ATPase slowly hydrolyses AdoPP[NH]P in the presence of Na⁺ + Mg²⁺ to ADP-NH₂ and P_i. The activity is ouabain-sensitive and is not detected in the absence of either Mg²⁺ or Na²⁺. The specific activity of the Na⁺ + Mg²⁺ dependent AdoPP[NH]P hydrolysis at 37°C and pH 7.0 is 4% of that for ATP under identical conditions and only 0.07% of that for ATP in the presence of K⁺. The activity is not stimulated by K⁺, nor can K⁺ replace Na⁺ in its stimulatory action. This suggests that phosphorylation is rate-limiting. Stimulation by Na⁺ is positively cooperative with a Hill coefficient of 2.4; half-maximal stimulation occurs at 5–9 mM. The K_m value for AdoPP[NH]P is 17 μM. At 0°C and 21°C the specific activity is 2 and 14%, respectively, of that at 37°C. AMP, ADP and AdoPP[CH₂]P are not detectably hydrolysed by (Na⁺ + K⁺)-ATPase in the presence of Na⁺ + Mg²⁺. (2) In addition, AdoPP[NH]P undergoes spontaneous, non-enzymatic hydrolysis at pH 7.0 with rate constants at 0, 21 and 37°C of 0.0006, 0.006 and 0.07 h^?1, respectively. This effect is small compared to the effect of enzymatic hydrolysis under comparable conditions. Mg²⁺ present in excess of AdoPP[NH]P reduces the rate constant of the spontaneous hydrolysis to 0.005 h^?1 at 37°C, indicating that the MgAdoPP[NH]P complex is virtually stable to spontaneous hydrolysis, as is also the case for its enzymatic hydrolysis. (3) A practical consequence of these findings is that AdoPP[NH]P binding studies in the presence of Na⁺ + Mg²⁺ with enzyme concentrations in the mg/ml range are not possible at temperatures above 0°C. On the other hand, determination of affinity in the (Na⁺ + K⁺)-ATPase reaction by competition with ATP at low protein concentrations (μg/ml range) remains possible without significant hydrolysis of AdoPP[NH]P even at 37°C.     

Na+ uptake and extrusion in the cyanobacterium SynechocystisPCC6714 in response to hypersaline treatment. Evidence for transient changes in plasmalemma Na+ permeability

The kinetics of uptake and loss of Na⁺ have been studied using radioisotopic tracer techniques in cells of the cyanobacterium Synechocystis PCC6714 exposed to hyperosmotic stress. Cells transferred from a fresh-water-based medium to NaCl at 300–1000 mmol·dm⁻³ showed net Na⁺ uptake during the first 2 min following transfer, with the intracellular Na⁺ level at 2 min increasing as a direct function of the external NaCl concentration. Further incubation of cells in low-level hypersaline media (350–500 mmol · dm⁻³ NaCl) led to a marked reduction in cell Na⁺ within 20 min, indicating an efficient active Na⁺ extrusion system. In contrast, cells maintained in more extreme hypersaline media showed little (750 mmol · dm⁻³ NaCl) or no (1000 mmol · dm⁻³ NaCl) net Na⁺ extrusion following upshock. Cells grown in a saline medium (with NaCl at 500 mmol · dm⁻³ showed a greatly reduced net Na⁺ uptake after 2 min in media containing higher levels of NaCl. However, net Na⁺ uptake was also observed when these cells were downshocked to media containing 50–200 mmol · dm⁻³ NaCl. This is the first demonstration of downshock-induced Na⁺ accumulation in a microbial cell. Time-courses for Na⁺ extrusion in cells downshocked from 500 mmol · dm⁻³ to 100 mmol · dm⁻³ NaCl were similar to those for cells upshocked from freshwater to 500 mmol · dm⁻³ NaCl, requiring approximately 30 min to reach their lowest values. Net Na⁺ extrusion in upshocked cells was found to be markedly sensitive to the external K⁺ concentration, with limited net Na⁺ extrusion in the absence of external K⁺ and maximal reductions in cell Na⁺ in media containing K⁺ at 1–10 mmol · dm⁻³. Temperature was also shown to affect uptake and loss of cell Na⁺ during upshock: cells maintained at 5°C showed no capacity for net Na⁺ extrusion, while higher temperatures (up to 35°C) led to a progressive reduction in the amount of cell Na⁺ at 2 min following upshock and also in the rate of net Na⁺ extrusion after this time.     

Interactive effects of cadmium and carbon nanotubes on the growth and metal accumulation in a halophyte Spartina alterniflora (Poaceae)

A study quantifying the interactive effects of cadmium (Cd) and carbon nanotubes (CNTs) on plant growth and Cd accumulation of pot-cultured Spartina alterniflora was conducted. The experiment consisted of two Cd levels (50, 200 mg kg^?1) as well as two CNTs levels (800, 2,400 mg kg^?1). As expected, CNTs alleviated higher Cd stress (200 mg kg^?1) due to restored shoot growth reduction, retrieved water content and resumed plant height. Furthermore, CNTs mitigated the deleterious effects of Cd stress through improving K⁺ and Ca²⁺ contents, while reducing Na⁺/K⁺ and Na⁺/Ca²⁺ ratios, regardless of the level of Cd stress. The proline contents in combined Cd and CNTs treatments were lower than Cd alone, suggesting that CNTs could reduce production of organic solutes under Cd stress. The results also showed higher Cd accumulation in roots than shoots, and both were improved by CNTs, except inhibition in roots under higher Cd stress (200 mg kg^?1). It appears that CNTs may not significantly affect negative Cd effects on growth of S. alterniflora, but improve total Cd accumulation under lower Cd stress (50 mg kg^?1). However, under higher Cd stress (200 mg kg^?1), CNTs restored the reduced plant growth, improved and reduced Cd accumulation in shoots and roots, respectively. Therefore, the effects of CNTs on plant growth and Cd accumulation are different, and levels of Cd stress should be considered when evaluating the combined application of CNTs and S. alterniflora on phytoremediation of Cd pollution.     

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.     

Overexpression of a poplar two-pore K+ channel enhances salinity tolerance in tobacco cells

Populus euphratica is a plant model intensively studied for elucidating physiological and molecular mechanisms of salt tolerance in woody species. Several studies have shown that vacuolar potassium (K⁺) ion channels of the two-pore K⁺ (TPK) family play an important role in maintaining K⁺ homeostasis. Here, we cloned a putative TPK channel gene from P. euphratica, termed PeTPK. Sequence analysis of PeTPK1 identified the universal K-channel-specific pore signature, TXGYGD. Over-expression of PeTPK1 in tobacco BY-2 cells improved salt tolerance, but did not enhance tolerance to hyperosmotic stress caused by mannitol (200?C600?mM). After 3?weeks of NaCl stress (100 and 150?mM), PeTPK1-transgenic cells had higher fresh and dry weights than wild-type cells. Salt treatment caused significantly higher Na⁺ accumulation and K⁺ loss in wild-type cells compared to transgenic cells. During short-term salt stress (100?mM NaCl, 24-h), PeTPK1-transgenic cells showed higher cell viability and reduced membrane permeabilization compared to wild-type cells. Scanning ion-selective electrode data revealed that salt-shock elicited a significantly higher transient K⁺ efflux from PeTPK1-transgenic callus cells and protoplasts compared to that observed in wild-type cells and protoplasts. We concluded that salt tolerance in P. euphratica is most likely mediated through PeTPK1. We propose that, under salt stress, PeTPK1 functions as an outward-rectifying, K⁺ efflux channel in the vacuole that transfers K⁺ to the cytosol to maintain K⁺ homeostasis.     

Water and electrolyte balance in protoscoleces of Echinococcus granulosus incubated in vitro: general procedures for the determination of water,sodium, potassium and chloride in protoscoleces

Reisin I.L. and Rotunno C.A. 1981. Water and electrolyte balance in protoscoleces of Echimcoccus granulosus incubated in vitro: General procedures for the determination of water, sodium, potassium and chloride in protoscoleces. International Journal for Parasitology11: 399–404. Protoscoleces of E. granulosus (sheep strain) were incubated in vitro at 37°C in Ringer Krebs solution (RKS) for up to 3 h. When they were briefly washed in sucrose 0.3 M at 4°C, the water and electrolyte contents were: 1.768 ± 0.034 mlg^?1 d.w. for water content and 123 ± 2, 209 ± 2 and 78 ± 2 μmolg^?1 d.w. for Na⁺, K⁺ and Cl^? respectively. When protoscoleces were not washed in sucrose solution but were spun down from RKS, the K⁺ content suffered a very small change but larger values for Na⁺ and Cl⁺ contents were obtained. These higher Na⁺ and Cl^? contents are attributed to the RKS ions retained in the trapping space. The steady state distribution of Na⁺ and K⁺ in the protoscoleces incubated at 37°C indicates the activity of an active transport mechanism.     

Univalent ions in phospholipid model membranes: Thermodynamic and hydration aspects

By means of differential scanning calorimetry, effects of systematic series of Group I and VII ions on the phase state of model multibilayer dimyristoylphosphatidylcholine (di(14:0)PC) membranes have been studied at a lipid/ion molar ratio of 3/1. The sign-changing correlations between the ionic radii of cations and temperature shifts of di(14:0)PC phase transition were obtained. For cosmotropic Li⁺ and Na⁺, the observed shifts were positive (LiCl: ΔT _m = 0.6°C; ΔT _p = 1.9°C), whereas chaotropic K⁺ and Rb⁺ presence resulted in negative shifts (RbCl: ΔT _m = ?0.3°C; ΔT _p = ?2.5°C). The anions (Cl^?, Br^?, I^?) showed a similar effect increasing with the ion chaotropicity. An essentially weaker effect of Cs⁺ as compared to other alkali metal ions (CsCl: ΔT _m ≈ 0°C; ΔT _p = ?0.1°C) can be one of the reasons of its accumulation in living organisms. Generalization of all available data allowed us to specify some important factors of lipid-ion interactions that should be taken into account in further investigations in this field.     

Accumulation of potassium and sodium by barley roots in a k-na replacement series

Excised roots of barley (Hordeum vulgare, var. Campana) were incubated for 24 hr in solutions containing constant total concentrations of KCl and NaCl but in which the mole fractions of K and Na were varied in replacement series. In solutions containing 1, 10, or 50 mm concentrations of K⁺ plus Na⁺, total cation accumulation was dependent upon the total salt concentration but was relatively independent of the mole fractions of K⁺ and Na⁺. These results imply that accumulation of K⁺ and Na⁺ was limited by a common factor. In solutions containing 0.01 mm K⁺ plus Na⁺ there was a strong preference for K⁺ over Na⁺ and the sum of K⁺ and Na⁺ accumulation increased with increasing K⁺ concentration.     

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。     

A strategy of Ca2+ alleviating Na+ toxicity in salt-treated Cyclocarya paliurus seedlings: photosynthetic and nutritional responses

Cyclocarya paliurus seedlings were subjected to 85?mM NaCl and 0, 6, 12 or 18?mM Ca(NO₃)₂ treatments to study changes in plant growth, photosynthetic parameters and distribution and/or accumulation of organic and inorganic solutes. Na⁺ toxicity symptoms were observed in plants non-treated with Ca(NO₃)₂, while 12?mM Ca(NO₃)₂ supplementation produced a significant promotion of shoot growth; meanwhile chlorophyll content, photosynthetic rate and optimum quantum yield of photosystem II (PSII), represented by the F_v/F_m ratio and pigments content as well as proline and soluble sugars, significantly increased. Ca(NO₃)₂ supply increased K⁺ and Ca²⁺ concentration, whereas the Na⁺ transport to the shoot was inhibited. There was a strong increase in the K⁺/Na⁺ ratio in shoot of Ca(NO₃)₂-treated plants. X-Ray microanalysis of roots showed that K⁺, Ca²⁺ and Na⁺ accumulated mainly in the epidermal cells and cortical cells of roots with 12?mM Ca(NO₃)₂ supply, and low accumulation was observed in stelar parenchyma, indicating exogenous Ca²⁺ possibly induced or strengthened effects of Casparian bands on ion transport. These results suggest that Ca(NO₃)₂ supplement increased inorganic and organic solutes accumulation in shoot and leaf, and restricted Na⁺ transport to the shoot by reinforcing barrier effects for attenuating salt injuries in plants, which could be a strategy of Ca²⁺ alleviating Na⁺ toxicity in C. paliurus seedlings subjected to salt stress.     

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.     

The K<Superscript>+</Superscript>/H<Superscript>+</Superscript> antiporter <Emphasis Type="Italic">AhNHX1</Emphasis> improved tobacco tolerance to NaCl stress by enhancing K<Superscript>+</Superscript> retention

High salinity is the one of important factors limiting plant growth and crop production. Many NHX-type antiporters have been reported to catalyze K⁺/H⁺ exchange to mediate salt stress. This study shows that an NHX gene from Arachis hypogaea L. has an important role in K⁺ uptake and transport, which affects K⁺ accumulation and plant salt tolerance. When overexpressing AhNHX1, the growth of tobacco seedlings is improved with longer roots and a higher fresh weight than the wild type (WT) under NaCl treatment. Meanwhile, when exposed to NaCl stress, the transgenic seedlings had higher K⁺/H⁺ antiporter activity and their roots got more K⁺ uptake. NaCl stress could induce higher K⁺ accumulation in the roots, stems, and leaves of transgenic tobacco seedlings but not Na⁺ accumulation, thus, leading to a higher K⁺/Na⁺ ratio in the transgenic seedlings. Additionally, the AKT1, HAK1, SKOR, and KEA genes, which are involved in K⁺ uptake or transport, were induced by NaCl stress and kept higher expression levels in transgenic seedlings than in WT seedlings. The H⁺-ATPase and H⁺-PPase activities were also higher in transgenic seedlings than in the WT seedlings under NaCl stress. Simultaneously, overexpression of AhNHX1 increased the relative distribution of K⁺ in the aerial parts of the seedlings under NaCl stress. These results showed that AhNHX1 catalyzed the K⁺/H⁺ antiporter and enhanced tobacco tolerance to salt stress by increasing K⁺ uptake and transport.