Shoot Ion Research Articles

Prediction of Salt Tolerance in Rice (Oryza Sativa) Based on Shoot Ion Content under Non-Stressed Conditions

Prediction of Salt Tolerance in Rice (Oryza Sativa) Based on Shoot Ion Content under Non-Stressed Conditions

A rice mutant defective in antioxidant-defense system and sodium homeostasis possesses increased sensitivity to salt stress

Screening salt-sensitive mutants is a powerful method to identify genes associated with salt tolerance. We used forward genetic screening with sodium azide-mutated rice (Oryza sativa L. cv. Tainung 67) to identify mutants showing hypersensitivity to salt stress. A new mutant line, named salt hypersensitive 1 (shs1) and exhibiting a severe salt-sensitivity when grown under a high NaCl concentration, was identified; the salt hypersensitivity was caused by duplicate recessive epistasis with mutations likely in two different loci. The shs1 salt sensitive phenotypes included a decreased seed germination rate, reduced shoot height and root length, severe and quick wilting, and overaccumulation of sodium ions in shoots as compared with wild-type plants. In addition, shs1 showed a decreased photosynthetic efficiency and enhanced hydrogen peroxide (H2O2) production under the salt stress. An increased superoxide dismutase activity and decreased catalase activity were responsible for the hyperaccumulation of H2O2 in shs1. The hypersensitivity of shs1 to the salt stress might be caused by an impaired antioxidant machinery and cellular Na+ homeostasis.

Enhanced Heavy Metal Tolerance and Accumulation by Transgenic Sugar Beets Expressing Streptococcus thermophilus StGCS-GS in the Presence of Cd, Zn and Cu Alone or in Combination.

Phytoremediation is a promising means of ameliorating heavy metal pollution through the use of transgenic plants as artificial hyperaccumulators. A novel Streptococcus thermophilus γ-glutamylcysteine synthetase-glutathione synthetase (StGCS-GS) that synthesizes glutathione (GSH) with limited feedback inhibition was overexpressed in sugar beet (Beta vulgaris L.), yielding three transgenic lines (s2, s4 and s5) with enhanced tolerance to different concentrations of cadmium, zinc and copper, as indicated by their increased biomass, root length and relative growth compared with wild-type plants. Transgenic sugar beets accumulated more Cd, Zn and Cu ions in shoots than wild-type, as well as higher GSH and phytochelatin (PC) levels under different heavy metal stresses. This enhanced heavy metal tolerance and increased accumulation were likely due to the increased expression of StGCS-GS and consequent overproduction of both GSH and PC. Furthermore, when multiple heavy metal ions were present at the same time, transgenic sugar beets overexpressing StGCS-GS resisted two or three of the metal combinations (50 μM Cd-Zn, Cd-Cu, Zn-Cu and Cd-Zn-Cu), with greater absorption in shoots. Additionally, there was no obvious competition between metals. Overall, the results demonstrate the explicit role of StGCS-GS in enhancing Cd, Zn and Cu tolerance and accumulation in transgenic sugar beet, which may represent a highly promising new tool for phytoremediation.

PDH45 overexpressing transgenic tobacco and rice plants provide salinity stress tolerance via less sodium accumulation

Salinity stress negatively affects the crop productivity worldwide, including that of rice. Coping with these losses is a major concern for all countries. The pea DNA helicase, PDH45 is a unique member of helicase family involved in the salinity stress tolerance. However, the exact mechanism of the PDH45 in salinity stress tolerance is yet to be established. Therefore, the present study was conducted to investigate the mechanism of PDH45-mediated salinity stress tolerance in transgenic tobacco and rice lines along with wild type (WT) plants using CoroNa Green dye based sodium localization in root and shoot sections. The results showed that under salinity stress root and shoot of PDH45 overexpressing transgenic tobacco and rice accumulated less sodium (Na+) as compared to their respective WT. The present study also reports salinity tolerant (FL478) and salinity susceptible (Pusa-44) varieties of rice accumulated lowest and highest Na+ level, respectively. All the varieties and transgenic lines of rice accumulate differential Na+ ions in root and shoot. However, roots accumulate high Na+ as compared to the shoots in both tobacco and rice transgenic lines suggesting that the Na+ transport in shoot is somehow inhibited. It is proposed that the PDH45 is probably involved in the deposition of apoplastic hydrophobic barriers and consequently inhibit Na+ transport to shoot and therefore confers salinity stress tolerance to PDH45 overexpressing transgenic lines. This study concludes that tobacco (dicot) and rice (monocot) transgenic plants probably share common salinity tolerance mechanism mediated by PDH45 gene.

Emergence, Forage Production, and Ion Relations of Alfalfa in Response to Saline Waters

ABSTRACTAlfalfa (Medicago sativa L.) is an important crop utilized in irrigated regions that are commonly impacted by salinity. We evaluated the effect of salinity continually from emergence to mature plant growth in successive harvests. We studied emergence, biomass production, salt tolerance, and shoot ion composition as potential physiological mechanisms in four nondormant salt‐tolerant cultivars: Salado, SW 8421S, SW 9720, and SW 9215. Irrigation water salinity dominated by sodium sulfate ranging from 3.1 to 30 dS m−1 of electrical conductivity (ECiw) was imposed at planting date. Plants were grown in outdoor sand tanks in Riverside, CA for 300 d. Relative emergence (%) decreased above ECiw 12.7 dS m−1 and was reduced to 53 and 13.4% at 18.4 and 24 dS m−1, respectively. At ECiw 30 dS m−1 there were no survivor plants. Absolute and relative accumulated biomass from 6 harvests significantly decreased for ECiw above 12.7 dS m−1 (6.0 dS m−1 in the saturation extract [ECe]). Plants grown at 18.4 and 24 dS m−1 produced 68% and 30% respectively of the biomass produced at 3.1 dS m−1. Salado showed the least reduction in biomass at elevated salinity and, as with all the cultivars, exhibited yield increases in successive harvests from first through seventh. Increasing salinity increased shoot Na+, total‐S, Cl−, Mg2+, and P and decreased K+ and Ca2+. The ability of Salado to maintain low shoot Na was the mechanism most associated with salt tolerance. Saline waters with resultant ECe values of up to 6 dS m−1 did not significantly reduce total forage production of the second through the seventh harvests. This suggests that irrigation with saline waters resulting in ECe values less than 6 dS m‐1 can be used throughout the production cycle (planting to multiple harvests) without significant yield loss for the cultivars examined.

Salinity tolerance in soybean is modulated by natural variation in GmSALT3.

The identification of genes that improve the salt tolerance of crops is essential for the effective utilization of saline soils for agriculture. Here, we use fine mapping in a soybean (Glycine max (L.) Merr.) population derived from the commercial cultivars Tiefeng 8 and 85-140 to identify GmSALT3 (salt tolerance-associated gene on chromosome 3), a dominant gene associated with limiting the accumulation of sodium ions (Na+) in shoots and a substantial enhancement in salt tolerance in soybean. GmSALT3 encodes a protein from the cation/H+ exchanger family that we localized to the endoplasmic reticulum and which is preferentially expressed in the salt-tolerant parent Tiefeng 8 within root cells associated with phloem and xylem. We identified in the salt-sensitive parent, 85-140, a 3.78-kb copia retrotransposon insertion in exon 3 of Gmsalt3 that truncates the transcript. By sequencing 31 soybean landraces and 22 wild soybean (Glycine soja) a total of nine haplotypes including two salt-tolerant haplotypes and seven salt-sensitive haplotypes were identified. By analysing the distribution of haplotypes among 172 Chinese soybean landraces and 57 wild soybean we found that haplotype 1 (H1, found in Tiefeng 8) was strongly associated with salt tolerance and is likely to be the ancestral allele. Alleles H2-H6, H8 and H9, which do not confer salinity tolerance, were acquired more recently. H1, unlike other alleles, has a wide geographical range including saline areas, which indicates it is maintained when required but its potent stress tolerance can be lost during natural selection and domestication. GmSALT3 is a gene associated with salt tolerance with great potential for soybean improvement.

Salinity Effects on Germination, Growth, Photosynthesis, and Ion Accumulation in Wild Miscanthus sinensis Anderss. Populations

ABSTRACTThe lignocellulosic crop Miscanthus spp. has been identified as a good candidate for biomass production. To satisfy the need for high yield and to avoid competition with food production by growing the crop in marginal areas, we studied the responses of M. sinensis to salinity. Effects of salt concentrations (0−360 mM NaCl) on seed germination, growth, photosynthesis, and shoot ion accumulation were examined. In the germination test of 17 accessions, high salt concentration inhibited seed germination in all accessions, while germination percentage varied significantly among the accessions. Two accessions showing variable salt tolerance, JM0119 (salt‐tolerant) and JM0099 (salt‐sensitive), were selected for a greenhouse study on plant dry weight, leaf chlorophyll content, total leaf area, tiller number, photosynthetic rate (A), stomatal conductance (gs), photosystem‐II (PSII) operating efficiency (∆F/F´m), and shoot ion concentration during various lengths of time. The experiment was performed twice, but for most parameters, no significant differences between runs were observed. Salinity resulted in a reduction of plant growth. Photosynthetic rate and gs were adversely affected by all salt treatment levels, while ∆F/F´m was not reduced until salt concentrations reached 120 mM NaCl. In contrast to the increases of shoot Na+ and Cl− concentrations, shoot K+ concentration declined in the presence of salt. Overall, this study revealed a great variability for salt tolerance in M. sinensis germplasm. The relative advantage of JM0119 over JM0099 under saline conditions was primarily associated with larger leaf area, a greater number of tillers, greater photosynthetic capacity, and restricted Na+ accumulation in shoots.

Growth responses of Melilotus siculus accessions to combined salinity and root-zone hypoxia are correlated with differences in tissue ion concentrations and not differences in root aeration

Soil salinity and root-zone hypoxia often occur together in saline landscapes. For many plants, this combination of stresses causes greater increases in Na+ and Cl− in shoots, and decreases in K+, than from salinity alone. These changes in ion concentrations from combined salinity and hypoxia can have more adverse consequences for growth than from salinity alone. The herbaceous forage legume Melilotus siculus naturally occurs in saline soils prone to waterlogging; however, accessions differ in their tolerances, although all form high levels of aerenchyma. We hypothesised that tolerance to combined salinity and hypoxia would be associated with either greater aerenchyma formation in roots or the innate ability of the accessions to regulate tissue ion concentrations. Fifteen accessions of M. siculus were grown in nutrient solution with two salinities (0 or 200mM NaCl) and two aeration treatments (aerated or hypoxic) for 21 days. Dry mass (shoot and root), root porosity and ion concentrations (Cl−, Na+, K+) in shoots and roots were assessed. In the M. siculus accessions variation in the shoot dry mass under saline–hypoxic conditions was negatively correlated with shoot Cl− and Na+, and positively correlated with the shoot K+. Shoot ion concentrations under saline–hypoxic conditions were related to concentrations under saline–aerated conditions, but not to the porosity of the main root, which was relatively high (∼18 to 25%). Differences in the tolerance of M. siculus accessions to combined salinity and root-zone hypoxia were mediated by variation in the plants’ ability to regulate ions, and were not related to variation in root porosity, which was relatively high in all accessions. The interaction between salinity and hypoxia was not detrimental to M. siculus, a waterlogging tolerant species.

Image-based phenotyping for non-destructive screening of different salinity tolerance traits in rice.

BackgroundSoil salinity is an abiotic stress wide spread in rice producing areas, limiting both plant growth and yield. The development of salt-tolerant rice requires efficient and high-throughput screening techniques to identify promising lines for salt affected areas. Advances made in image-based phenotyping techniques provide an opportunity to use non-destructive imaging to screen for salinity tolerance traits in a wide range of germplasm in a reliable, quantitative and efficient way. However, the application of image-based phenotyping in the development of salt-tolerant rice remains limited.ResultsA non-destructive image-based phenotyping protocol to assess salinity tolerance traits of two rice cultivars (IR64 and Fatmawati) has been established in this study. The response of rice to different levels of salt stress was quantified over time based on total shoot area and senescent shoot area, calculated from visible red-green-blue (RGB) and fluorescence images. The response of rice to salt stress (50, 75 and 100 mM NaCl) could be clearly distinguished from the control as indicated by the reduced increase of shoot area. The salt concentrations used had only a small effect on the growth of rice during the initial phase of stress, the shoot Na+ accumulation independent phase termed the ‘osmotic stress’ phase. However, after 20 d of treatment, the shoot area of salt stressed plants was reduced compared with non-stressed plants. This was accompanied by a significant increase in the concentration of Na+ in the shoot. Variation in the senescent area of the cultivars IR64 and Fatmawati in response to a high concentration of Na+ in the shoot indicates variation in tissue tolerance mechanisms between the cultivars.ConclusionsImage analysis has the potential to be used for high-throughput screening procedures in the development of salt-tolerant rice. The ability of image analysis to discriminate between the different aspects of salt stress (shoot ion-independent stress and shoot ion dependent stress) makes it a useful tool for genetic and physiological studies to elucidate processes that contribute to salinity tolerance in rice. The technique has the potential for identifying the genetic basis of these mechanisms and assisting in pyramiding different tolerance mechanisms into breeding lines.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-014-0016-3) contains supplementary material, which is available to authorized users.

Effect of Salinity Stress on Yield, Component Characters and Nutrient Compositions in Rapeseed (Brassica napus L.) Genotypes

Abstract Crops growing in salt-affected soils may suffer from physiological drought stress, ion toxicity, and mineral deficiency which then lead to reduced growth and productivity. Eight rapeseed genotypes were evaluated at control and two salinity levels of irrigation, i.e. ECe=0 dS m-1 (control), 6 and 12 dS m-1. A factorial experiment based on completely randomized design with 4 replications was considered for evaluation of 24 treatments. Significant mean square of the salinity levels and genotypes were exhibited for 1000-seed weight, pod length, seed yield, Mg, K and Cl, indicating significant differences of genotypes for the traits at three salinity levels. Pods per plant and Mg had lowest variations among the genotypes at the high salinity levels. Hyola401, LRT1 and KRN1 with seed yield of 3.09, 2.78 and 2.30 g/plot, respectively were considered as salt tolerant genotypes. Stress (12dsm-1 ) to control ratio (S/C) which is indicating of salinity tolerance was high for seed yield of DSM12 and Hyola401.Significant positive correlation of seed yield with K and Cl, indicated that these shoot ions can be considered as good indicators for seed yield improving at saline environment.

Genetic variation in the root growth response of barley genotypes to salinity stress.

We aimed to identify genetic variation in root growth in the cereal crop barley (Hordeum vulgare L.) in response to the early phase of salinity stress. Seminal root elongation was examined at various concentrations of salinity in seedlings of eight barley genotypes consisting of a landrace, wild barley and cultivars. Salinity inhibited seminal root elongation in all genotypes, with considerable variation observed between genotypes. Relative root elongation rates were 60-90% and 30-70% of the control rates at 100 and 150mM NaCl, respectively. The screen identified the wild barley genotype CPI71284-48 as the most tolerant, maintaining root elongation and biomass in response to salinity. Root elongation was most significantly inhibited in the landrace Sahara. Root and shoot Na+ concentrations increased and K+ concentrations decreased in all genotypes in response to salinity. However, the root and shoot ion concentrations did not correlate with root elongation rates, suggesting that the Na+ and K+ concentrations were not directly influencing root growth, at least during the early phase of salt stress. The identification of genetic diversity in root growth responses to salt stress in barley provides important information for future genetic, physiological and biochemical characterisation of mechanisms of salinity tolerance.

Study of silicon and nitrogen effects on yield components and shoot ions nutrient composition in rice

Rice (Oryza sativa L.) is an important crop in Iran and other parts of the word and it is also a staple food of nearly one-half of world‘s population contributing high calorie intake. Silicon is considered as a beneficial and nitrogen as an essential element for rice production. In order to study the effects of silicon and nitrogen on some yield components and shoot nutrition ion compositions in rice, a hydroponic culture experiment was conducted under the greenhouse condition. Two factors, including silicon and nitrogen, each one with three levels (0, 50, and 100 ppm) were studied in a completely randomized design in factorial arrangement with 3 replications. The traits including panicle length, unfilled grains, 1000- grain weight and shoot ions including silicon, potassium, and nitrogen were significantly affected by applied silicon levels. All the traits were affected by nitrogen levels except unfilled grains and shoot potassium concentration. The highest grain yield was detected at 100 ppm of silicon application. Shoot silicon ranged from 5.01 to 6.92 ppm in 0 and 100 ppm silicon application. Shoot potassium was increased in high levels of silicon treatment. Significant negative correlation of unfilled grain with shoot silicon and potassium indicated that increasing these shoot ions had reduction effects on unfilled grains. Significant positive correlation was determined between shoot potassium and 1000-grain weight, implied that this trait was affected by indirect effect of silicon via shoot potassium increasing.

Relationship Between Seed Yield and Shoot Ions at Vegetative and Reproductive Stages of Rapeseed Genotypes under Saline Environment

Soil salinity is a major constraint to crop production in many areas of the world. To investigate the effects of salinity stress on seed yield and shoot ions at vegetative and reproductive stages, a factorial experiment was applied for evaluating the seven rapeseed genotypes under four salinity levels including 0, 4, 8 and 12 dsm-1. The salt solution was prepared by taking NaCl:CaCl2 in the ratio of 1:1. Significant mean square of salinity levels were exhibited for seed yield and all shoot ions at two growth stages except Ca at reproductive stage. Due to increasing salinity levels Ca at vegetative stage was increased in L14 and Zarfam but in other genotypes it was not affected by increasing salinity levels. Significant negative correlation of K with Na and Cl indicating the ameliorating effect of K on toxic effects of Na and Cl. Due to adverse effect of Cl on seed yield, the correlation of this ion with seed yield was significant and negative at vegetative and reproductive stages. Significant positive correlation of K content at vegetative stage with seed yield implied that K at this stage can be used as selection criterion for detecting high seed yield genotypes in saline environment.

Ions uptake, yield and yield attributes of rapeseed exposed to salinity stress

Soil salinity is a serious constrain to crop production in many areas of the world. A pot experiment was carried out with rapeseed genotypes in order to investigate the effects of salinity stress on yield associated traits and shoot ions composition. Eight rapeseed genotypes were evaluated in three salinity levels of irrigation water including 0, 6 and 12 dsm -1 . A factorial experiment based on completely randomized design with 4 replications was considered for evaluation of 24 treatments. Significant mean square of the salinity levels, genotypes and salinity ×genotypes interaction effects were exhibited for seeds per pod, pods per plant, seed yield, Ca, K and Na, indicating significant differences of salinity levels and genetic differences for these traits. Due to significant correlation of seed yield with seeds per pod and pods per plant these traits can be considered as indirect selection criteria for seed yield improving. Among shoot ions compositions, K had significant positive correlation with seed yield, therefore this ion can be considered as good indicator for seed yield improving at saline environment. The genotypes including Hyola401, LRT1 and DSM12 had high amounts of seed yield at 12 dsm -1 of salinity level and were con

Salinity Stress Indices of Seed Yield and Nutrient Compositions in Rapeseed (Brassica napus L.)

Soil salinity is a serious constrain to crop production in many areas of the world. Seven rapeseed genotypes were evaluated at two salinity levels of irrigation water including 0 and 12 ds/m in green house condition based on completely randomized design with three replications. The results showed that the most of the genotypes with the high seed yield in the non saline condition had high amount of seed yield in saline condition. Amount of sodium (Na) and calcium (Ca) were more correlated than potassium (K) with seed yield. Stress tolerance index related to potassium (STI) was significant positive correlated to Yp and Ys which indicating the importance of this stress index for improving seed yield in saline condition.L18 with high efficiency of Ca absorption in saline condition had the highest amount of seed yield in stress condition. STI was more efficient selection than SSI for improving seed yield and the other ions composition. On the basis of factor analysis the shoot ions compositions including Ca and Na are more suitable than K for discriminate the saline tolerant genotypes.

Chloride and sodium excluding capacities of citrus rootstock germplasm introduced to Australia from the People's Republic of China

The responses to root zone salinity (0, 25 and 50 mM NaCl) by 40 citrus rootstock genotypes introduced from the People's Republic of China, measured as shoot chloride (Cl −) and sodium (Na +) ion accumulation, growth and dry matter accumulation, were investigated under glasshouse conditions. Two experiments, one using aerated nutrient solutions and the other irrigated sand cultures, were conducted with plants grown from rooted cuttings taken from representative trees of different mandarin ( Citrus reticulata Blanco and C. erythrosa Hort. ex Tan.), yuzu ( C. junos Sieb. ex Tan.), Ichang papeda ( C. ichangensis Swing.), sour orange ( C. aurantium L.) and trifoliate orange ( Poncirus trifoliata (L.) Raf.) genotypes. Two standard genotypes, viz. Rangpur lime ( Citrus x limonia Osbeck.) and William's trifoliate orange were included in the experiments as reference controls. After 56 days, plant growth and shoot Cl − and Na + concentrations varied significantly between genotypes within salt treatments in both experiments. There were significant differences between genotypes for relative tolerance indices, expressed as ratios of growth at 25 and 50 mM NaCl to growth at 0 mM, but the relative rankings did not change between root zone salt concentrations. Although there were some correlations between plant growth and tolerance indices with shoot ion concentrations, these were generally poor. As the plant material was clonal, estimates of broad sense heritability from intra-class correlation coefficients indicated that the genotypes investigated could prove to be valuable parents in breeding for new salt excluding rootstocks. Of particular interest were strains of trifoliate orange that accumulated low concentrations of Cl − and Na + in shoot tissues. Since P. trifoliata is normally a poor Cl − excluder, but a major source of disease resistance, these results suggested that progeny testing should be conducted to investigate the value of these strains for future rootstock breeding.

Subcellular distribution and chemical forms of chromium in rice plants suffering from different levels of chromium toxicity

AbstractThe subcellular distribution and chemical forms of different heavy metals in rice are correlated with their bio‐toxicity. An experiment was conducted to investigate the subcellular distribution and chemical forms of chromium (Cr) in two rice genotypes (Oryza sativa L. cv. Xiushui 113 and cv. Dan K5) differing in Cr accumulation, to understand the mechanisms of Cr toxicity and resistance in rice plants. The results show that Cr in the roots of rice plants exposed to Cr stress was mainly localized in cell walls, whereas Cr in leaves and stems was mainly present in both cell walls and vacuoles, suggesting that both compartments act as important protective barriers against Cr toxicity in rice plants. Although Cr ions in all plant tissues exist predominantly in the forms extracted by 80% ethanol and distilled water, the amount of Cr in the chemical forms extracted by 2% HAc, 0.6 M HCl, and in residues was significantly increased under the highest Cr level (100 μM Cr) compared to the plants grown under lower Cr levels. These results indicate that excess Cr accumulated in rice plants under Cr stress is bound to undissolved or low‐bioavailable compounds, such as undissolved phosphate and oxalate, being beneficial for rice plants to alleviate Cr toxicity. In addition, under the highest Cr level (100 μM), Dan K5 had a higher percentage of Cr in the chemical forms extracted by 2% HAc, 0.6 M HCl, and in residues compared to Xiushui 113 in both stems and leaves, indicating that more Cr ions in shoots of Dan K5 were bound to undissolved or low‐bioavailable compounds, in comparison with those of Xiushui 113. It is evident that the low bioavailability of Cr in the shoots of Dan K5 is related to a high Cr accumulation.

Variation in salinity tolerance, early shoot mass and shoot ion concentrations within Lotus tenuis: towards a perennial pasture legume for saline land

Perennial legumes are needed for productive pastures in saline areas. We evaluated 40 lines of Lotus tenuis for tolerance to salinity at both germination and vegetative growth stages. Salt tolerance during the early vegetative stage was assessed in a sand-tank experiment with NaCl concentrations of 0–450 mm NaCl for 5 weeks. Most L. tenuis lines were more salt tolerant and had at least 50% lower shoot Na+ plus Cl– (% dry mass (DM)) compared with some other common pasture legumes, Medicago sativa, M. polymorpha and Trifolium subterraneum. Within L. tenuis significant variation in salt tolerance was found, with C50 values (concentrations of NaCl that decreased shoot dry matter to 50% of control) ranging from ~100 to 320 mm. Shoot concentrations of Cl–, Na+ and K+ did not always correlate with salt tolerance; some tolerant lines had low shoot Na+ and Cl– (and thus better nutritive value), while others tolerated high shoot Na+ and Cl–. We also found variation within L. tenuis for salt tolerance of seeds, with lines ranging from 0 to 70% germination after recovery from a prior exposure to 800 mm NaCl for 15 days. There was no relationship between salinity tolerance of scarified seeds and subsequent growth of seedlings; therefore, testing of seeds alone would not be an appropriate screening method for salt tolerance in L. tenuis. This study of 40 L. tenuis lines has shown significant genetic variation for salt tolerance within this species, and we have identified key lines with potential to be productive in saltland pasture systems.

Insights into the salt tolerance mechanism in barley (Hordeum vulgare) from comparisons of cultivars that differ in salt sensitivity

Although barley (Hordeum vulgare L.) is a salt-tolerant crop, the underlying physiological and molecular mechanisms of salt tolerance remain to be elucidated. Therefore, we investigated the response of salt-tolerant (K305) and salt-sensitive (I743) cultivars to salt stress at both physiological and molecular levels. Salt treatment increased xylem sap osmolarity, which was attributed primarily to a rise in Na(+) and Cl(-) concentration; enhanced accumulation of the ions in shoots; and reduced plant growth more severely in I743 than K305. The concentration of K(+) in roots and shoots decreased during 8 h of salt treatment in both cultivars but with no marked difference between cultivars. Hence, the severe growth reduction in I743 is attributed to the elevated levels of (mainly) Na(+) in shoots. Analysis of gene expression using quantitative RT-PCR showed that transcripts of K(+)-transporters (HvHAK1 and HvAKT1), vacuolar H(+)-ATPase and inorganic pyrophosphatase (HvHVA/68 and HvHVP1) were more abundant in shoots of K305 than in shoots of I743. Expression of HvHAK1 and Na(+)/H(+) antiporters (HvNHX1, HvNHX3 and HvNHX4) was higher in roots of K305 than in I743 with prolonged exposure to salt. Taken together, these results suggest that the better performance of K305 compared to I743 during salt stress may be related to its greater ability to sequester Na(+) into sub-cellular compartments and/or maintain K(+) homeostasis.

Response of alfalfa (Medicago sativa L.) to diurnal and nocturnal saline sprinkler irrigations. II: shoot ion content and yield relationships

When using saline waters, sprinkling irrigation at night is a recommended practice to reduce evaporation, salt absorption by the wetted leaves and its negative effects on crops. We measured shoot ion concentrations (Cl−, Na+ and K+) and total dry matter (TDM) in alfalfa subject to diurnal and nocturnal saline sprinkler irrigations and established potential relationships among them. The work was carried out along the 2004–2006 growing seasons using EC waters from 0.5 to 5.6 dS m−1. Saline sprinkling irrigations linearly increased shoot Cl− and Na+ and decreased shoot K+. Even though daytime evaporation was much higher than nigh-time, shoot ion accumulation and TDM were similar in the diurnal and nocturnal irrigations. The salinity tolerance of alfalfa decreased in year 2006 due to increases in shoot Cl− and, particularly, shoot Na+. The lower threshold for shoot Na+ (276 meq kg−1) than for shoot Cl− (726 meq kg−1) shows that alfalfa is more sensitive to Na+ than to Cl−, and that Na+ accumulation is the preponderant cause of alfalfa yield decline after 3 years of sprinkling with saline waters.