Shoot Cl Research Articles

Expression of the grapevine anion transporter ALMT2 in Arabidopsis root decreases shoot Cl-/NO3- ratio under salt stress.

Grapevines (Vitis vinifera, Vvi) are economically important crop plants which, when challenged with salt (NaCl) in soil and/or irrigation water, tend to accumulate Na+ and Cl- in aerial tissues impacting yield, and berry acceptability for winemaking. Grapevine (Vitis spp.) rootstocks vary in their capacity for shoot Cl- exclusion. Here, we characterise two putative anion transporter genes - Aluminium-activated Malate Transporter VviALMT2 and VviALMT8 - that were differentially expressed in the roots of efficient (140 Ruggeri) and inefficient (K51-40) Cl- excluding rootstocks, to explore their potential for impacting shoot Cl- exclusion. Using the Xenopus laevis oocyte expression system, VviALMT2 and VviALMT8 formed conductive channels that were highly permeable to NO3-, slightly-to-moderately permeable to other substrates including Cl- and malate, but impermeable to SO42-. RT-qPCR analyses revealed that VviALMT2 was more highly expressed in the root vasculature and up-regulated by high [NO3-] re-supply post starvation, while fluorescently tagged translational fusion VviALMT2 localised to the plasma membrane. As VviALMT8 showed no such features, we selected VviALMT2 as our salt exclusion candidate and assessed its function in planta. Expression of VviALMT2 in Arabidopsis thaliana root vasculature reduced shoot [Cl-]/[NO3-] after NaCl treatment, which suggests that VviALMT2 can be beneficial to plants under salt stress.

A Whole Plant Analysis of Chloride and Sodium Exclusion Using a Range of Grapevine Rootstock Genotypes

Background and Aims. Salt exclusion is an important attribute for wine grapes since many countries have limits to the concentration of sodium (Na+) and/or chloride (Cl−) tolerated in wine. The aim was to investigate whole plant capacity for Na+ and Cl‾ exclusion and the within-plant partitioning of accumulated ions to better understand these important salt tolerance traits. Methods and Results. Rooted cuttings of 140 Ruggeri and K51-40 (good and poor shoot Cl− excluders, respectively) and five hybrids from a cross between the two genotypes were used. When challenged with salinity, 140 Ruggeri limited the accumulation of Cl− and Na+ in the stem, petioles, and laminae and had a significantly lower whole plant concentration of Cl− and Na+ when compared to K51-40. The latter indicates that 140 Ruggeri accumulates less Cl− and Na+ than K51-40 by a lower uptake or a potentially greater efflux by roots, or both. While K51-40 accumulated significantly more Na+, it was able to retrieve it from the xylem; store it in the roots, stem, and petiole; and keep the lamina concentration comparable to that of 140 Ruggeri. Petioles of all genotypes appeared to play a role in limiting Cl− accumulation in laminae and particularly for K51-40, to limit Na+ accumulation in laminae. Conclusions. The grapevine capacity for Cl− and Na+ exclusion can be defined primarily as the lower net accumulation on a whole plant basis, reflecting the difference between the uptake and any efflux that may occur. Lower root to shoot transport is a key factor in shoot Cl− and Na+ exclusion. Petiole accumulation assists in limiting the Cl− and Na+ accumulation in the laminae. Significance of the Study. The study addressed the knowledge gap by examining Cl− and Na+ exclusion on a whole plant basis, highlighting a range of within-plant mechanisms that act in limiting the accumulation of both ions in the laminae.

Potential Use of Biochar as a Mitigation Strategy for Salinity-Related Issues in Tomato Plants (Solanum lycopersicum L.)

The continuous growth of the population, along with climate change and the resulting surge in food demand, requires the development of alternative crop cultivation strategies that reduce the excessive use of freshwater for agricultural purposes. Biochar, which is a carbon-rich material made from organic waste through pyrolysis, has been recommended as a potential soil amendment to mitigate the negative effects of salinity. Biochar has unique properties such as high porosity, an ion exchange capacity, and the ability to retain water and nutrients. The purpose of this study was to evaluate the feasibility and effectiveness of using saline water for the cultivation of tomato plants (Solanum lycopersicum L.) and to investigate the potential use of biochar as a mitigation strategy for salinity-related issues in tomato cultivation. The concentration of NaCl during the experiment was 100 mM. We examined the impact of salt stress on plant growth, protein and chlorophyll content, the activation of the antioxidant response, and nutritional status. Our results indicated that salt treatments led to a significant accumulation of Na and Cl in shoots (regardless of the biochar addition) but did not result in a corresponding reduction in plant growth. However, the degree of oxidative damage caused by NaCl treatment, measured as malondialdehyde (MDA) accumulation, was reduced by biochar addition to the growth medium, most likely because of an increased guaiacol peroxidase (GPX) activity, which led to lower MDA accumulation. The strong positive effect of biochar on GPX activity could be reasonably attributed to increased Mo accumulation. In conclusion, the findings of this study represent a valuable starting point for developing crop management strategies based on biochar application to enhance plant performance under unfavorable conditions and reduce freshwater dependence in agriculture.

Root-Specific Expression of Vitis vinifera VviNPF2.2 Modulates Shoot Anion Concentration in Transgenic Arabidopsis.

Grapevines (Vitis vinifera L., Vvi) on their roots are generally sensitive to salt-forming ions, particularly chloride (Cl–) when grown in saline environments. Grafting V. vinifera scions to Cl–-excluding hybrid rootstocks reduces the impact of salinity. Molecular components underlying Cl–-exclusion in Vitis species remain largely unknown, however, various anion channels and transporters represent good candidates for controlling this trait. Here, two nitrate/peptide transporter family (NPF) members VviNPF2.1 and VviNPF2.2 were isolated. Both highly homologous proteins localized to the plasma membrane of Arabidopsis (Arabidopsis thaliana) protoplasts. Both were expressed primarily in grapevine roots and leaves and were more abundant in a Cl–-excluding rootstock compared to a Cl–-includer. Quantitative PCR of grapevine roots revealed that VviNPF2.1 and 2.2 expression was downregulated by high [NO3–] resupply post-starvation, but not affected by 25 mM Cl–. VviNPF2.2 was functionally characterized using an Arabidopsis enhancer trap line as a heterologous host which enabled cell-type-specific expression. Constitutive expression of VviNPF2.2 exclusively in the root epidermis and cortex reduced shoot [Cl–] after a 75 mM NaCl treatment. Higher expression levels of VviNPF2.2 correlated with reduced Arabidopsis xylem sap [NO3–] when not salt stressed. We propose that when expressed in the root epidermis and cortex, VviNPF2.2 could function in passive anion efflux from root cells, which reduces the symplasmic Cl– available for root-to-shoot translocation. VviNPF2.2, through its role in the root epidermis and cortex, could, therefore, be beneficial to plants under salt stress by reducing net shoot Cl– accumulation.

Silicon application and plant growth promoting rhizobacteria consisting of six pure Bacillus species alleviate salinity stress in cucumber (Cucumis sativus L)

As water quality and availability decreases in many parts of the world, salinity is becoming a major challenge that reduces crop yield, even in soilless cultivation systems. Therefore, novel strategies are needed to promote plant salt tolerance in these systems. We hypothesized that the non-essential element silicon (Si) and plant-growth promoting Bacillus spp. can alleviate salt stress of cucumber (Cucumis sativus L.) grown in hydroponics. We tested this hypothesis by growing cucumber seedlings with and without salt stress (75 mM NaCl) and with and without 1.5 mM Si and an inoculum of six rhizosphere Bacillus species in a full-factorial design. Seedlings were grown in a climate room for two weeks in independent deep-water culture containers. The applied salt stress strongly reduced plant biomass, whereas Si application under salt stress resulted in a substantial increase in cucumber shoot and root biomass. This beneficial impact of Si was also observed in increased plant height, leaf area, specific leaf area, root length, specific root length, root surface area and root volume. The Bacillus species increased root dry weight, specific leaf area as well as specific root length. In seedlings grown under salt stress, Si application increased shoot and root Si concentration, whereas Cl− concentration was reduced in the plant shoots. A reduction in Cl− concentration of the shoots was also apparent in the Bacillus treatment. Under non-stress conditions, neither Si nor Bacillus species affected plant growth parameters. However, shoot mineral content was affected as Si application reduced shoot Cl−and Ca2+ concentrations, and inoculation with Bacillus species decreased K concentration. We conclude that Si does promote salt stress alleviation during the early growth stage of cucumber grown in deep water culture and this has implications for soilless crop production. Seed inoculation with Bacillus species showed a beneficial trend for some plant growth characteristics and nutrient status under high salinity, although not as pronounced as for Si.

Soybean CHX-type ion transport protein GmSALT3 confers leaf Na+ exclusion via a root derived mechanism, and Cl- exclusion via a shoot derived process.

Soybean (Glycine max) yields are threatened by multiple stresses including soil salinity. GmSALT3 (a cation-proton exchanger protein) confers net shoot exclusion for both Na+ and Cl- and improves salt tolerance of soybean; however, how the ER-localized GmSALT3 achieves this is unknown. Here, GmSALT3's function was investigated in heterologous systems and near isogenic lines that contained the full-length GmSALT3 (NIL-T; salt-tolerant) or a truncated transcript Gmsalt3 (NIL-S; salt-sensitive). GmSALT3 restored growth of K+ -uptake-defective Escherichia coli and contributed towards net influx and accumulation of Na+ , K+ and Cl- in Xenopus laevis oocytes, while Gmsalt3 was non-functional. Time-course analysis of NILs confirmed shoot Cl- exclusion occurs distinctly from Na+ exclusion. Grafting showed that shoot Na+ exclusion occurs via a root xylem-based mechanism; in contrast, NIL-T plants exhibited significantly greater Cl- content in both the stem xylem and phloem sap compared to NIL-S, indicating that shoot Cl- exclusion likely depends upon novel phloem-based Cl- recirculation. NIL-T shoots grafted on NIL-S roots contained low shoot Cl- , which confirmed that Cl- recirculation is dependent on the presence of GmSALT3 in shoots. Overall, these findings provide new insights on GmSALT3's impact on salinity tolerance and reveal a novel mechanism for shoot Cl- exclusion in plants.

The root as a sink for chloride under chloride-salinity

Maize has to avoid excess tissue accumulation of Cl− to withstand conditions of Cl−-salinity. Restriction of loading of Cl− into the root xylem is one mechanism to keep shoot Cl−-concentrations low. The proportion of Cl− that reaches the shoot has to be stored away from the primary site of photosynthesis and growth. We tested whether or not maize is able to re-translocate significant amounts of Cl− from shoot back to root and out into the rooting media. Ion analysis revealed that maize cannot re-translocate Cl−; however, it is stored in sheaths of the old leaves and, surprisingly, in roots. Sequestration of Cl− in the roots might be a strategy to keep concentrations low in young growing shoot tissues and in leaf blades where photosynthesis is running.

RNAseq Analysis Reveals Altered Expression of Key Ion Transporters Causing Differential Uptake of Selective Ions in Canola (Brassica napus L.) Grown under NaCl Stress.

Salinity is one of the major abiotic stresses prevailing throughout the world that severely limits crop establishment and production. Every crop has an intra-specific genetic variation that enables it to cope with variable environmental conditions. Hence, this genetic variability is a good tool to exploit germplasms in salt-affected areas. Further, the selected cultivars can be effectively used by plant breeders and molecular biologists for the improvement of salinity tolerance. In the present study, it was planned to identify differential expression of genes associated with selective uptake of different ions under salt stress in selected salt-tolerant canola (Brassica napus L.) cultivar. For the purpose, an experiment was carried out to evaluate the growth response of different salt-sensitive and salt-tolerant canola cultivars. Plants were subjected to 200 mM NaCl stress. Canola cultivars—Faisal Canola, DGL, Dunkled, and CON-II—had higher growth than in cvs Cyclone, Ac-EXcel, Legend, and Oscar. Salt-tolerant cultivars were better able to maintain plant water status probably through osmotic adjustment as compared to salt-sensitive cultivars. Although salt stress increased shoot Na+ and shoot Cl− contents in all canola cultivars, salt-tolerant cultivars had a lower accumulation of these toxic nutrients. Similarly, salt stress reduced shoot K+ and Ca2+ contents in all canola cultivars, while salt-tolerant cultivars had a higher accumulation of K+ and Ca2+ in leaves, thereby having greater shoot K+/Na+ and Ca2+/Na+ ratios. Nutrient utilization efficiency decreased significantly in all canola cultivars due to the imposition of salt stress; however, it was greater in salt-tolerant cultivars—Faisal Canola, DGL, and Dunkled. Among four salt-tolerant canola cultivars, cv Dunkled was maximal in physiological attributes, and thus differentially expressed genes (DEGs) were assessed in it by RNA-seq analysis using next-generation sequencing (NGS) techniques. The differentially expressed genes (DEG) in cv Dunkled under salt stress were found to be involved in the regulation of ionic concentration, photosynthesis, antioxidants, and hormonal metabolism. However, the most prominent upregulated DEGs included Na/K transporter, HKT1, potassium transporter, potassium channel, chloride channel, cation exchanger, Ca channel. The RNA-seq data were validated through qRT-PCR. It was thus concluded that genes related to the regulation of ionic concentrate are significantly upregulated and expressed under salt stress, in the cultivar Dunkled.

Positive effects of co-inoculation with Rhizophagus irregularis and Serendipita indica on tomato growth under saline conditions, and their individual colonization estimated by signature lipids.

Tomato roots can be colonized by both mycorrhizal fungi and the endophytic fungus Serendipita indica. This study was aimed at assessment of the impact of single or dual inoculation with R. irregularis and S. indica on tomato growth under saline conditions. We used signature compounds to estimate the abundance of each of these two fungi (fatty acid 16:1ω5 for R. irregularis and ergosterol for S. indica) in roots. A randomized block design was applied with four types of inoculation (no fungus, R. irregularis, S. indica or S. indica + R. irregularis) at different levels of salinity (1.2, 5, and 10 dS/m) with four replications per treatment. The plant dry weight was slightly higher in R. irregularis- than S. indica-inoculated plants, and the highest plant biomass was achieved with dual inoculation. R. irregularis increased the content of the neutral lipid fatty acid 16:1ω5 from 97 to 5300 nmol/g and phospholipid fatty acid 16:1ω5 from 8 to 141 nmol/g in roots (at a salinity level of 1.2 dS m-1), but the increases were lower at higher levels of salinity. Moreover, both these arbuscular mycorrhizal fungal markers were slightly decreased in the presence of S. indica. Root ergosterol increased from 7 to 114 μg g-1 with S. indica inoculation. With increasing salinity, the concentration of ergosterol in roots decreased. Inoculation with R. irregularis caused a decrease in root ergosterol. Increasing salinity resulted in an increase of Cl and Na in tomato shoots, but the increase was significantly lower in single- or dual-inoculated plants in contrast to the control plants.

The Importance of Cl- Exclusion and Vacuolar Cl- Sequestration: Revisiting the Role of Cl- Transport in Plant Salt Tolerance.

Salinity threatens agricultural production systems across the globe. While the major focus of plant researchers working in the field of salinity stress tolerance has always been on sodium and potassium, the transport patterns and physiological roles of Cl− in plant salt stress responses are studied much less. In recent years, the role of Cl− in plant salinity stress tolerance has been revisited and has received more attention. This review attempts to address the gap in knowledge of the role of Cl− transport in plant salinity stress tolerance. Cl− transport, Cl− exclusion, vacuolar Cl− sequestration, the specificity of mechanisms employed in different plant species to control shoot Cl− accumulation, and the identity of channels and transporters involved in Cl− transport in salt stressed plants are discussed. The importance of the electrochemical gradient across the tonoplast, for vacuolar Cl− sequestration, is highlighted. The toxicity of Cl− from CaCl2 is briefly reviewed separately to that of Cl− from NaCl.

Micronutrient Status and Selected Physiological Parameters of Roots in Nickel-Exposed Sinapis alba L. Affected by Different Sulphur Levels.

An efficient method of improving the micronutrient status of Ni-treated white mustard (Sinapis alba L.) using intensive S-SO4 nutrition was developed. Twelve variants of Hoagland’s nutrient solution differing in the concentration of S-SO4 (standard: 2 mM S, and elevated level: 6 or 9 mM S) and Ni (0, 0.0004, 0.04, or 0.08 mM Ni) were tested. The beneficial effect of intensive S nutrition on Ni-stressed plants was manifested by a significant rise in the content of Fe, Mn, and Zn, especially in the shoots. An increase was also found in the shoot B, Cu, and Mo content, whilst there were no changes in their root concentrations. Simultaneously, the shoot Cl concentrations dropped. The elevated level of S in the nutrient solution in general enhanced the translocation of Fe, Cu, Mo, and B in Ni-exposed plants. The beneficial effect of intensive S nutrition on the growth and micronutrient balance of Ni-exposed plants can be at least partially related to the positive changes in root surface properties, especially in cation exchange capacity (CEC). Meanwhile both reduced glutathione (GSH) and phytochelatins (PCs) probably do not significantly contribute to Ni resistance of white mustard under intensive S nutrition.

Shoot chloride translocation as a determinant for NaCl tolerance in Vicia faba L.

Faba bean (Vicia faba L.) is sensitive to salinity. While toxic effects of sodium (Na+) are well studied, toxicity aspects of chloride (Cl−) and the underlying tolerance mechanisms to Cl− are not well understood. For this reason, shoot Cl− translocation and its effect as potential determinant for tolerance was tested. Diverse V. faba varieties were grown hydroponically and stressed with 100 mM NaCl until necrotic leaf spots appeared. At this point, biomass formation, oxidative damage of membranes as well as Na+, Cl− and potassium concentrations were measured. The V. faba varieties contrasted in the length of the period they could withstand the NaCl stress treatment. More tolerant varieties survived longer without evolving necrosis and were less affected by inhibitory effects on photosynthesis. The concentration of Cl− at the time point of developing leaf necrosis was in the same range irrespective of the variety, while that of Na+ varied. This indicates that Cl− concentrations, and not Na+ concentrations are critical for the formation of salt necrosis in faba bean. Tolerant varieties profited from lower Cl− translocation to leaves. Therefore, photosynthesis was less affected in those varieties with lower Cl−. This mechanism is a new trait of interest for salt tolerance in V. faba.

Sulfur nutrition level modifies the growth, micronutrient status, and cadmium distribution in cadmium-exposed spring wheat.

The effect of S nutrition level (standard-2 and intensive-6 or 9mmolSL-1) on the growth, micronutrient status, and Cd concentration of Cd-exposed (0, 0.0002, 0.02, and 0.04mmol Cd L-1) Triticum aestivum L. 'Zebra' was examined. The hypothesis that Cd-induced micronutrient imbalance in this species is alleviated by enhanced S-sulfate (S-SO4) nutrition was tested. The intensive S nutrition, especially the dose of 6mmolL-1, to some extent alleviated Cd-induced stress by improving the adverse changes in micronutrient status and increase of the biomass. The root and shoot Fe, Cu, Mn, and Zn concentrations of Cd-exposed wheat rose at 6 and remained unaltered at 9mmolSL-1. Particularly noteworthy is the substantial increase of Fe bioconcentration found in Cd-stressed plants at 6mmolSL-1. The root Cu concentration increased at 6 and decreased at 9mmolSL-1, but did not change in shoots. Simultaneously, both the high S levels elevated the shoot Cl concentration but had no effect on the root Cl concentration. There were no substantial changes in the Mo concentration. The intensive S nutrition of the Cd-treated wheat did not affect the translocation factor (TF) of Fe and B. In turn, root-to-shoot translocation of Mo and Zn was enhanced at 6 and remained unchanged at 9mmolSL-1. The changes in TF of Cl, Cu, and Mn varied greatly, depending on the S and Cd concentrations. Intensive S nutrition of Cd-stressed wheat, as a rule, dropped the root and increased the shoot Cd concentration as well as reduced Cd bioconcentration/bioaccumulation factor enhancing root-to-shoot Cd translocation.

Friend or Foe? Chloride Patterning in Halophytes.

In this opinion article, we challenge the traditional view that breeding for reduced Cl- uptake would benefit plant salinity tolerance. A negative correlation between shoot Cl- concentration and plant biomass does not hold for halophytes - naturally salt tolerant species. We argue that, under physiologically relevant conditions, Cl- uptake requires plants to invest metabolic energy, and that the poor selectivity of Cl--transporting proteins may explain the reported negative correlation between Cl- accumulation and crop salinity tolerance. We propose a new paradigm: salinity tolerance could be achieved by improving the selectivity of some of the broadly selective anion-transporting proteins (e.g., for NO3->Cl-), alongside tight control of Cl- uptake, rather than targeting traits mediating its efflux from the root.

Spinach (Spinacea oleracea L.) Response to Salinity: Nutritional Value, Physiological Parameters, Antioxidant Capacity, and Gene Expression

Scarcity of good-quality irrigation water is a major impediment to meet food demand for a growing world population. Recycled waters may be available locally more affordably, but their higher salinity is a concern. Salinity effects on spinach mineral composition, antioxidant capacity, photosynthesis, and gene expression have not been established. Spinach cv. Raccoon was greenhouse-grown and irrigated with four levels of water salinity of electrical conductivities (ECiw) of 1.4 (control) or ranging from 3.6 to 9.4 dS m−1, combined with three levels of K (3, 5, and 7 meq L−1). Irrigation waters had 2, 20, 40, and 80 meq L−1 of NaCl. After 23 treatment days, plants significantly accumulated Na and Cl in shoots and roots with increasing salinity, regardless of the K concentration in the irrigation water. Plants exhibited no visual symptoms of salt toxicity and there were no differences in shoot growth. Plants maintained their overall concentrations of mineral nutrients, physiological parameters, and oxalic acid across salinity treatments. Leaves retained all their antioxidant capacity at 20 meq L−1 NaCl, and 74% to 66% at 40 and 80 meq L−1 NaCl, respectively. Expression analyses of ten genes, that play important role in salt tolerance, indicated that although some genes were upregulated in plants under salinity, compared to the control, there was no association between Na or K tissue concentrations and gene expression. Results clearly show that spinach maintains its growth, mineral composition, and antioxidant capacity up to ECiw = 9.4 dS m−1. As this salinity is equivalent to a soil salinity of 4.5 dS m−1, spinach can tolerate over two-fold its previously-considered salinity threshold. Thus, growers can cultivate spinach using recycled, saline, waters without detriment to shoot biomass accumulation, and nutritional value.

Pomegranate Growth Affected by Arbuscular Mycorrhizae, Phosphorus Fertilizer, and Irrigation Water Salinity

ABSTRACTPomegranate (Punica granatum L.) symbiosis with arbuscular mycorrhizae fungi (AMF) is a strategy in saline soils. In this study, two AMF (+AMF and –AMF), two phosphorus (P) fertilizer (+ P and –P), and three irrigation salinity (1, 4, and 8 dS m−1) treatments were studied. The highest salinity level decreased the root colonization by hyphae. Plant growth parameters including shoot dry weight, leaf surface area, and plant height were negatively affected by salinity. However, the growth parameters improved in AMF treatments. Salinity decreased the shoot P concentration and increased the shoot chlorine (Cl). The root and shoot sodium (Na) concentrations were the greatest in unfertilized and P-fertilized treatments, respectively. AMF treatment improved the root and shoot P concentration and reduced the negative effect of salinity on shoot Cl concentrations. In conclusion, the effects of AMF symbiosis on growth and tissue elements concentration depend on irrigation water salinity and P fertilization.

Molecular characterization and functional analysis of a cation-chloride cotransporter gene from trifoliate orange (Poncirus trifoliata L.)

A cation-chloride cotransporter gene PtrCCC from trifoliate orange was identified, its ectopic expression confers salt tolerance in transgenic tobacco. Salinity is one of the most serious environmental stresses that limit crop growth. Cation-chloride cotransporters (CCCs) are membrane proteins that are involved in plant development and salt tolerance. Here we provide an insight into the molecular characterization and functional analysis of CCC-encoding gene (PtrCCC) from trifoliate orange (Poncirus trifoliata L.). The open-reading frame of PtrCCC is 2943 bp in length, which encodes a protein of 980 amino acids. Phylogenetic analysis revealed that PtrCCC is closely related to CCCs from its allied genera as well as woody perennials. Quantitative real-time PCR (qRT-PCR) analysis demonstrated that PtrCCC was expressed in all tested tissues, with higher expression level in root tip and leaf tip. Its expression was up-regulated in the leaves of trifoliate orange under the presence of KCl conditions. Ectopic expression of PtrCCC gene in tobacco exhibited an improvement in salt tolerance. The transgenic plants had higher dry biomass in the roots and shoots than that in wild type plants. Moreover, under KCl and NaCl + KCl stress conditions, the accumulation of shoot Cl− was remarkably decreased in the transgenic lines as compared with the wild type plants. Collectively, these results suggest that PtrCCC plays an important role in salt tolerance, which is partially attributed to its role in ions homeostasis.

AtNPF2.5 Modulates Chloride (Cl-) Efflux from Roots of Arabidopsis thaliana.

The accumulation of high concentrations of chloride (Cl−) in leaves can adversely affect plant growth. When comparing different varieties of the same Cl− sensitive plant species those that exclude relatively more Cl− from their shoots tend to perform better under saline conditions; however, the molecular mechanisms involved in maintaining low shoot Cl− remain largely undefined. Recently, it was shown that the NRT1/PTR Family 2.4 protein (NPF2.4) loads Cl− into the root xylem, which affects the accumulation of Cl− in Arabidopsis shoots. Here we characterize NPF2.5, which is the closest homolog to NPF2.4 sharing 83.2% identity at the amino acid level. NPF2.5 is predominantly expressed in root cortical cells and its transcription is induced by salt. Functional characterisation of NPF2.5 via its heterologous expression in yeast (Saccharomyces cerevisiae) and Xenopus laevis oocytes indicated that NPF2.5 is likely to encode a Cl− permeable transporter. Arabidopsis npf2.5 T-DNA knockout mutant plants exhibited a significantly lower Cl− efflux from roots, and a greater Cl− accumulation in shoots compared to salt-treated Col-0 wild-type plants. At the same time, content in the shoot remained unaffected. Accumulation of Cl− in the shoot increased following (1) amiRNA-induced knockdown of NPF2.5 transcript abundance in the root, and (2) constitutive over-expression of NPF2.5. We suggest that both these findings are consistent with a role for NPF2.5 in modulating Cl− transport. Based on these results, we propose that NPF2.5 functions as a pathway for Cl− efflux from the root, contributing to exclusion of Cl− from the shoot of Arabidopsis.

Evaluation of Alfalfa (Medicago sativa L.) Populations’ Response to Salinity Stress

Alfalfa (Medicago sativa L.) is a moderately salt‐tolerant crop with high economic return and is therefore more suitable for production with lower quality water than most high‐value crops. This study was conducted to examine the effect of water composition types (Cl− or SO42−) of irrigation water and five salinity levels (electrical conductivity of irrigation water [ECiw] = 0.85, 8, 13, 18.3, and 24.5 dS m−1) on biomass production, salt tolerance, and ion concentration of 15 alfalfa populations. The plants were grown in a greenhouse in 60 sand tanks for 347 d under salt treatment. There was no significant effect of water composition type on shoot and root biomass production. Water composition type × EC and water composition type x population interactions were also not significant. Salinity impact was population dependent (EC × population: P < 0.05), except at ECiw 18.3 dS m−1. Across all populations, shoot biomass was significantly reduced with increasing salinity to 77, 50, and 27% of the control at 13, 18.3, and 24.5 dS m−1, respectively. The ‘SISA14’ and ‘SW 8421S’ populations were the most productive under saline conditions with the highest degree of salt tolerance. The results showed that alfalfa biomass response to salinity did not depend on the type of salts (Cl− or SO42−). Shoot Cl− also did not correlate with relative biomass response. Thus, Cl− ion toxicity does not appear to be a factor in alfalfa salt tolerance for these populations. Although there was a correlation between salt tolerance and shoot Na+, the shoot ion concentration provides only a partial explanation of the relative salt tolerance of the alfalfa populations.

Response of snapdragon (Antirrhinum majus L.) to blended water irrigation and arbuscular mycorrhizal fungi inoculation: uptake of minerals and leaf water relations

A greenhouse study was performed in order to investigate the effects of three arbuscular mycorrhizal fungi (AMF) species on vegetative growth, water relations, and mineral composition parameters of snapdragon (Antirrhinum majus cv. Bells white) under irrigation from different water sources. Five irrigation treatments included using purely desalinized (fresh) water (DW), as a control, three different blends of DW with saline ground water from a well with increasing salinity, and one with 100% of saline well water. Inoculation with AMF enhanced growth rates and a relative water content of snapdragon plants grown under well-water irrigation. AMF also improved the leaf water potential and increased water-use efficiency of the plants. Shoot and root dry masses were higher in the AMF-treated plants than those in AMF-free plants. In both shoots and roots, concentrations of total P, Ca2+, N, Mg2+, and K+ were higher in the AMF-treated plants compared with AMF-free plants under salt-stress conditions. Shoot Cl- and Na+ concentrations were lower in the AMF-treated plants than those in the AMF-free plants grown under well-water irrigation. Snapdragon plants exhibited a high degree of dependency on AMF; it improved plant growth rates and leaf water relations, particularly, with increasing salinity of irrigation water.