Knock-out of Arabidopsis AtNHX4 gene enhances tolerance to salt stress

AtNHX4 belongs to the monovalent cation:proton antiporter-1 (CPA1) family in Arabidopsis. Several members of this family have been shown to be critical for plant responses to abiotic stress, but little is known on the biological functions of AtNHX4. Here, we provide the evidence that AtNHX4 plays important roles in Arabidopsis responses to salt stress. Expression of AtNHX4 was responsive to salt stress and abscisic acid. Experiments with CFP-AtNHX4 fusion protein indicated that AtNHX4 is vacuolar localized. The nhx4 mutant showed enhanced tolerance to salt stress, and lower Na⁺ content under high NaCl stress compared with wild-type plants. Furthermore, heterologous expression of AtNHX4 in Escherichia coli BL21 rendered the transformants hypersensitive to NaCl. Deletion of the hydrophilic C-terminus of AtNHX4 dramatically increased the hypersensitivity of transformants, indicating that AtNHX4 may function in Na⁺ homeostasis in plant cell, and its C-terminus plays a role in regulating the AtNHX4 activity.     

Arabidopsis sos1 mutant in a salt-tolerant accession revealed an importance of salt acclimation ability in plant salt tolerance

An analysis of the salinity tolerance of 354 Arabidopsis thaliana accessions showed that some accessions were more tolerant to salt shock than the reference accession, Col-0, when transferred from 0 to 225 mM NaCl. In addition, several accessions, including Zu-0, showed marked acquired salt tolerance after exposure to moderate salt stress. It is likely therefore that Arabidopsis plants have at least two types of tolerance, salt shock tolerance and acquired salt tolerance. To evaluate a role of well-known salt shock tolerant gene SOS1 in acquired salt tolerance, we isolated a sos1 mutant from ion-beam-mutagenized Zu-0 seedlings. The mutant showed severe growth inhibition under salt shock stress owing to a single base deletion in the SOS1 gene and was even more salt sensitive than Col-0. Nevertheless, it was able to survive after acclimation on 100 mM NaCl for 7 d followed by 750 mM sorbitol for 20 d, whereas Col-0 became chlorotic under the same conditions. We propose that genes for salt acclimation ability are different from genes for salt shock tolerance and play an important role in the acquisition of salt or osmotic tolerance.     

Overexpression of wheat dehydrin DHN-5 enhances tolerance to salt and osmotic stress in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Late Embryogenesis Abundant (LEA) proteins are associated with tolerance to water-related stress. A wheat (Triticum durum) group 2 LEA proteins, known also as dehydrin (DHN-5), has been previously shown to be induced by salt and abscisic acid (ABA). In this report, we analyze the effect of ectopic expression of Dhn-5 cDNA in Arabidopsis thaliana plants and their response to salt and osmotic stress. When compared to wild type plants, the Dhn-5 transgenic plants exhibited stronger growth under high concentrations of NaCl or under water deprivation, and showed a faster recovery from mannitol treatment. Leaf area and seed germination rate decreased much more in wild type than in transgenic plants subjected to salt stress. Moreover, the water potential was more negative in transgenic than in wild type plants. In addition, the transgenic plants have higher proline contents and lower water loss rate under water stress. Also, Na⁺ and K⁺ accumulate to higher contents in the leaves of the transgenic plants. Our data strongly support the hypothesis that Dhn-5, by its protective role, contributes to an improved tolerance to salt and drought stress through osmotic adjustment.     

The CCCH zinc finger protein gene AtZFP1 improves salt resistance in Arabidopsis thaliana

The CCCH type zinc finger proteins are a super family involved in many aspects of plant growth and development. In this study, we investigated the response of one CCCH type zinc finger protein AtZFP1 (At2g25900) to salt stress in Arabidopsis. The expression of AtZFP1 was upregulated by salt stress. Compared to transgenic strains, the germination rate, emerging rate of cotyledons and root length of wild plants were significantly lower under NaCl treatments, while the inhibitory effect was significantly severe in T-DNA insertion mutant strains. At germination stage, it was mainly osmotic stress when treated with NaCl. Relative to wild plants, overexpression strains maintained a higher K⁺, K⁺/Na⁺, chlorophyll and proline content, and lower Na⁺ and MDA content. Quantitative real-time PCR analysis revealed that the expression of stress related marker genes KIN1, RD29B and RD22 increased more significantly in transgenic strains by salt stress. Overexpression of AtZFP1 also enhanced oxidative and osmotic stress tolerance which was determined by measuring the expression of a set of antioxidant genes, osmotic stress genes and ion transport protein genes such as SOS1, AtP5CS1 and AtGSTU5. Overall, our results suggest that overexpression of AtZFP1 enhanced salt tolerance by maintaining ionic balance and limiting oxidative and osmotic stress.     

盐胁迫对2种栎树苗期生长和根系生长发育的影响

以低浓度(50 mmol/L)和高浓度(150 mmol/L)NaCl处理弗吉尼亚栎(Quercus virginiana)和麻栎(Quercus acutissima)1年生幼苗,研究了2种栎树在盐胁迫下的生长、对盐分的敏感性和耐受性及其根系形态学参数变化以及根系对盐离子的吸收与积累。结果表明,高浓度盐胁迫明显抑制了2种栎树地上部生物量的积累(P0.05),而低浓度盐胁迫对弗吉尼亚栎地上部干重的影响不明显,但显著抑制了麻栎地上部干重(P0.05);2种栎树的根冠比在盐胁迫下呈增加趋势,特别是在高浓度盐胁迫下,2种栎树的根冠比明显增加(P0.05),盐胁迫下增加生物量在根部的分配是植物应对盐胁迫的方式之一。2种栎树根部生物量积累在盐胁迫下变化不明显,但2种栎树根系形态学参数在盐胁迫下的响应不同,弗吉尼亚栎根系总长度、总表面积和总体积在盐胁迫下均有不同程度增加,特别是在低浓度盐胁迫下,根系形态学参数明显增加(P0.05),但麻栎根系形态学参数有下降趋势,但与对照相比变化不明显;通过对不同径级根系总长的分析发现,弗吉尼亚栎根系总长度的增加主要是由于直径小于2 mm的细根总长的增加,细根长度的增加对于植物吸收水分和营养物质具有重要意义;通过对Na+和Cl-在根系的含量分析表明,盐胁迫下2种栎树根系盐离子的积累均有明显增加,但弗吉尼亚栎根系盐离子的含量在低浓度和高浓度盐胁迫下的差异不明显,而麻栎在高浓度盐胁迫下根系盐离子的含量明显高于弗吉尼亚栎。综合2种栎树盐胁迫下的生物量分配策略和根系形态学响应以及盐离子的积累规律,证明2种栎树尽管在生物量分配策略方面具有相同的特点,但根系的响应策略截然不同,弗吉尼亚栎在盐胁迫下能够扩大根系吸收范围,维持较高的K+/Na+比值,而麻栎在盐胁迫下根系由于吸收过多的盐离子,导致根系的生长发育受到抑制,影响了根系在逆境中的分布范围,从而在一定程度上避免了进一步的盐害。     

Effect of NaCl on photosynthesis,salt accumulation and ion compartmentation in two mangrove species, Kandelia candel and Bruguiera gymnorhiza

In a 4-week study, we investigated the effects of increasing soil NaCl (100–400 mM) on photosynthesis, salt uptake and transport, and intracellular compartmentation of Na⁺ and Cl⁻ in 1-year-old seedlings of Kandelia candel (L.) Druce and Bruguiera gymnorhiza (L.) Savigny. Increasing NaCl stress significantly elevated Na⁺ and Cl⁻ in root and shoot tissues (stem + leaf) of both species, but B. gymnorhiza showed a rapid Na⁺ accumulation upon the initiation of salt stress and leaves contained 90% more Na⁺ and 40% more Cl⁻ than K. candel at the end of experiment. Net photosynthetic rate (Pn) declined with increasing salinity, and the most marked reduction occurred after exposure of mangrove seedlings to a severe salinity, 400 mM NaCl. However, the inhibitory effects of severe stress varied with species: Pn decreased by 80% in K. candel whereas in B. gymnorhiza the decline was 60%. The quantum yield (AQY) and carboxylation efficiency (CE) response to severe salinity showed a trend similar to Pn, in which a lesser reduction of AQY and CE was observed in B. gymnorhiza (33–35%), as compared to K. candel (43–52%). X-ray microanalysis of leaf mesophyll cells showed evidence of distinct vacuolar compartmentation of Na⁺ in K. candel but Cl⁻ in B. gymnorhiza after seedlings were subjected to 100 mM NaCl for 7 d. Moreover, Na⁺ within cell wall, cytoplasm, vacuole and chloroplast remained 23–72% lower in stressed B. gymnorhiza as compared to K. candel. In conclusion, B. gymnorhiza exhibited effective salt exclusion from chloroplasts although increasing salt stress caused a rapid and higher build up of Na⁺ and Cl⁻ in the leaves. We suggest that the salt-induced Pn reduction in the two mangrove species is correlated with the ability to exclude Na⁺ and Cl⁻ from the chloroplast, rather than with the bulk leaf salt concentration.     

Salt tolerance strategies of Lygeum spartum L.: A new fodder crop for Algerian saline steppes

Lygeum spartum L. is a native species in Algerian salt steppes. The plant is of interest because of its tolerance to environmental stresses and its use as a fodder grass for livestock in low-rainfall Mediterranean areas. Nevertheless, plant responses of this plant to salt stress are still not investigated in detail. Therefore, L. spartum L. was grown in hydroponic conditions to investigate the effect of salinity (0, 30, 60 and 90 mM NaCl) on growth, water relations, gas exchange, leaf chlorophyll concentration, glycine betaine and mineral uptake. Plant growth was reduced at 60 and 90 mM NaCl, but was not significantly lower than in the controls at 30 mM NaCl. Sodium (Na⁺), chloride (Cl⁻) and glycine betaine contents in plants increased, whereas calcium (Ca²⁺), potassium (K⁺), relative water content (RWC), root hydraulic conductivity (L₀) and chlorophyll content decreased with an increase in salinity. Water potential (Ψ_ω) and osmotic potential (Ψ_π) of plants decreased with an increase in salinity. No change was observed in the turgor potential (Ψ_τ). Photosynthesis parameters (CO₂ assimilation rate, stomatal conductance and transpiration rate) did not change significantly at 30 mM NaCl, as compared to the control. Higher salt levels impaired photosynthetic capacity of L. spartum mainly via a stomatal limitation leading to a low CO₂ assimilation rate. This might be a consequence of the reduced whole-plant hydraulic conductivity under salt stress. The results demonstrated that L. spartum L. can be characterised as a moderately salt-tolerant species. Salt tolerance in this species is achieved by appropriate osmotic adjustment involving accumulation of ions and glycine betaine. At high salinities, growth reduction probably occurs as a result of high concentrations of Na⁺ and Cl⁻ and their interference with other ions such as Ca²⁺ and K⁺. This plant can be used locally as a fodder for livestock and to stabilise sand dunes and rehabilitate salt soils.     

盐胁迫对槲树(Quercus dentata)幼苗离子平衡及其生理生化特性的影响

检测NaCl胁迫对槲树（Quercus dentata）幼苗离子平衡和生理生化特性的影响,为揭示槲树的耐盐机理,其在园林中的推广应用提供参考。以一年生槲树实生苗作为实验材料,经100、200、300 mmol/L的NaCl溶液浇灌处理30 d,测定不同时间的离子含量和生理生化指标变化。结果表明,随NaCl浓度的增加和处理的时间延长,槲树各指标表现出以下规律：（1）根茎叶积累大量Na⁺,引起离子毒害,导致叶片受损,根系Na⁺含量显著高于地上部分,这种补偿作用有助于减轻地上部分受到的损害;（2）各部分K⁺含量降低,根部较茎叶更为显著,导致Na⁺/K⁺明显升高;（3）Ca²⁺由根部向地上部分转运,在叶片中浓度显著增加,有助于建立新的离子稳态;（4）Mg²⁺含量总体上呈降低趋势;（5）叶片含水量逐渐降低,丙二醛含量和相对电导率逐步升高,且在重度胁迫下的变化更显著;（6）轻度盐胁迫下,叶片过氧化物酶（POD）活性无显著变化,而过氧化氢酶（CAT）和超氧化物歧化酶（SOD）活性逐渐升高,在重度胁迫下3种酶活性出现降低;（7）脯氨酸和可溶性糖少量积累,辅助调节渗透平衡。总之,槲树幼苗能够通过调控离子平衡,提升抗氧化酶活性,积累渗透调节物,从而提高耐盐性,抵御200 mmol/L以下的NaCl胁迫。     

MdVHP1 encodes an apple vacuolar H(+)-PPase and enhances stress tolerance in transgenic apple callus and tomato

Vacuolar H⁺-translocating inorganic pyrophosphatase (VHP, EC 3.6.1.1) is an electrogenic proton pump, which is related to growth as well as abiotic stress tolerance in plants. In this study, a VHP gene MdVHP1 was isolated from apple. The alignment of nucleotide and amino acid sequences showed that it encoded a type I VHP protein. It expressed in vegetative and reproductive organs, and its expression was induced by salt, PEG-mediated osmotic stress, cold and heat in apple in vitro shoot cultures. MdVHP1 expression showed a similar pattern in different apple tissues, but different change dynamics in response to abiotic stresses, compared with MdVHP2 (another MdVHP gene in apple). MdVHP1 overexpression enhanced tolerance to salt, PEG-mimic drought, cold and heat in transgenic apple calluses, which was related to an increased accumulation of proline and decreased MDA content compared with control calluses. In addition, MdVHP1 overexpression confers improved tolerance to salt and drought in transgenic tomato, along with an increased ion accumulation, high RWC and low solute potential compared with wild type. These results indicate that MdVHP1 is an important regulator for plant tolerance to abiotic stresses by modulating internal stores of ions and solutes.     

Soil salinity as a selection pressure is a key determinant for the evolution of salt tolerance in Blue Panicgrass (Panicum antidotale Retz.)

To assess the role of selection pressure in plant adaptation to saline environment, a hydroponic experiment was conducted on six Panicum antidotale Retz. populations collected from a wide range of habitats with varying selection pressure in the form of soil salinity. The soil electrical conductivity of six different habitats ranged from 3.39 to 19.23 dS m⁻¹ and pH from 5.86 to 7.65. Plants of all populations collected from varying habitats were established in pots containing normal soil and allowed to grow for 6 months. Newly grown tillers from each plant were separated and 10 of them each formed a composite sample for a particular population. They were then transplanted in plastic containers each containing 10 l of half strength Hoagland's nutrient solution alone or with 150 mol m⁻³ NaCl. After 42 days growth in salt treatment, the populations collected form highly saline habitats proved to be more salt-tolerant compared with those from mild or non-saline habitats in terms of growth performance. The populations adapted to high salinity showed less decrease in leaf K⁺/Na⁺ and Ca²⁺/Na⁺ ratios under salinity stress. Moreover, under stress the salt-tolerant populations showed less reduction in photosynthetic capacity than the salt-sensitive populations. In addition, hyper-accumulation of organic solutes such as glycinebetaine and proline and thereby higher osmotic adjustment seemed to be associated with the higher degree of adaptability of the salt-tolerant populations to salt stress. From the data presented, it is plausible to conclude that selection pressure (soil salinity) must have been one of the important determinants bringing about the evolution of salt-tolerance trait in Blue Panic grass.     

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。     

盐胁迫下不同基因型冬小麦渗透及离子的毒害效应

以4种不同基因型冬小麦为试验材料,利用分根法研究了盐胁迫对小麦的渗透胁迫和离子毒害的效应。结果表明,在盐胁迫下,小麦既受渗透胁迫,也受盐离子胁迫。渗透胁迫效应比较快,大约在处理后1-2d内发生;离子毒害效应比较缓慢,大约需3-4d时间。在一半盐胁迫(200mmol/L NaCl)和一半非盐胁迫的分根条件下,小麦没有明显的渗透胁迫效应,小麦植株地上部Na⁺ 累积到毒性水平之前盐处理对小麦生长无抑制效应。小麦具有将Na⁺ 从盐胁迫一侧转移非盐一侧的能力,说明小麦吸收的Na⁺ 有一部分可以从地上部回流到根系中,回流率可达76%-89%。无水分胁迫(不加入PEG)的回流率大于水分胁迫(加入PEG)的回流率。不同基因型小麦在盐分吸收累积和回流,及渗透和离子胁迫的速度和程度等方面具有明显差异。NR 9405和小偃6号的Na⁺ 累积速度要少于陕229和RB 6;NR 9405根系排Na⁺ 能力强于陕229和RB 6。因此,NR 9405和小偃6号的耐盐性高于陕229和RB 6。     

渗透胁迫和离子毒害对转Bt基因棉幼苗生长及离子分布的影响

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

Ecophysiological response of Crambe maritima to airborne and soil-borne salinity

Background and Aims

There is a need to evaluate the salt tolerance of plant species that can be cultivated as crops under saline conditions. Crambe maritima is a coastal plant, usually occurring on the driftline, with potential use as a vegetable crop. The aim of this experiment was to determine the growth response of Crambe maritima to various levels of airborne and soil-borne salinity and the ecophysiological mechanisms underlying these responses.

Methods

In the greenhouse, plants were exposed to salt spray (400 mm NaCl) as well as to various levels of root-zone salinity (RZS) of 0, 50, 100, 200 and 300 mm NaCl during 40 d. The salt tolerance of Crambe maritima was assessed by the relative growth rate (RGR) and its components. To study possible salinity effects on the tissue and cellular level, the leaf succulence, tissue Na⁺ concentrations, Na⁺ : K⁺ ratio, net K⁺/Na⁺ selectivity, N, P, K⁺, Ca²⁺, Mg²⁺, proline, soluble sugar concentrations, osmotic potential, total phenolics and antioxidant capacity were measured.

Key Results

Salt spray did not affect the RGR of Crambe maritima. However, leaf thickness and leaf succulence increased with salt spray. Root zone salinities up to 100 mm NaCl did not affect growth. However, at 200 mm NaCl RZS the RGR was reduced by 41 % compared with the control and by 56 % at 300 mm NaCl RZS. The reduced RGR with increasing RZS was largely due to the reduced specific leaf area, which was caused by increased leaf succulence as well as by increased leaf dry matter content. No changes in unit leaf rate were observed but increased RZS resulted in increased Na⁺ and proline concentrations, reduced K⁺, Ca²⁺ and Mg²⁺ concentrations, lower osmotic potential and increased antioxidant capacity. Proline concentrations of the leaves correlated strongly (r = 0·95) with RZS concentrations and not with plant growth.

Conclusions

Based on its growth response, Crambe maritima can be classified as a salt spray tolerant plant that is sensitive to root zone salinities exceeding 100 mm NaCl.     

Effect of salinity on tomato (Lycopersicon esculentum Mill.) during seed germination stage

A study was conducted using ten genetically diverse genotypes along with their 45F₁ (generated by diallel mating) under normal and salt stress conditions. Although, tomato (Lycopersicon esculentum Mill.) is moderately sensitive to salinity but more attention to salinity is yet to be required in the production of tomato. In present study, germination rate, speed of germination, dry weight ratio and Na⁺/K⁺ ratio in root and shoot, were the parameters assayed on three salinity levels; control, 1.0 % NaCl and 3.0 % NaCl with Hoagland’s solution. Increasing salt stress negatively affected growth and development of tomato. When salt concentration increased, germination of tomato seed was reduced and the time needed to complete germination lengthened, root/shoot dry weight ratio was higher and Na⁺ content increased but K⁺ content decreased. Among the varieties, Sel-7 followed by Arka Vikas and crosses involving them as a parent were found to be the more tolerant genotypes in the present study on the basis of studied parameters.     

Overexpression of SeNHX1 improves both salt tolerance and disease resistance in tobacco

Recently, we found NHX1, the gene encoding a Na⁺/H⁺ exchanger, participated in plant disease defense. Although NHX1 has been confirmed to be involved in plant salt tolerance, whether the NHX1 transgenic plants exhibit both salt tolerance and disease resistance has not been investigated. The T1 progenies of Nicotiana tabacum L. lines expressing SeNHX1 (from Salicornia europaea) were generated for the present study. Compared with PBI-type control plants, SeNHX1 transgenic tobaccos exhibited more biomass, longer root length, and higher K⁺/Na⁺ ratio at post germination or seedling stage under NaCl treatment, indicating enhanced salt tolerance. The vacuolar H⁺ efflux in SeNHX1 transgenic tobacco was increased after treatment of NaCl with different concentration. Meanwhile, the SeNHX1 transgenic tobaccos showed smaller wilted spot area, less H₂O₂ accumulation in leaves after infection of Phytophthora parasitica var. nicotianae. Further investigation demonstrated a larger NAD(P)(H) pool in SeNHX1 transgenic tobacco. These evidences revealed that overexpression of SeNHX1 intensified the compartmentation of Na⁺ into vacuole under salt stress and improved the ability of eliminating ROS after pathogen attack, which then enhanced salt tolerance and disease resistance simultaneously in tobacco. Our findings indicate NHX1 has potential value in creating crops with both improved salt tolerance and disease resistance.     

Understanding Saline and Osmotic Tolerance of Populus euphratica Suspended Cells

Tolerance of Populus euphratica suspended cells to ionic and osmotic stresses implemented respectively by NaCl and PEG (6000) was characterized by monitoring cell growth, morphological features, ion compartmentation and polypeptide patterns. The cells grew and proliferated when submitted to stresses of 137 mM NaCl or 250 g l⁻¹ PEG, and survived at 308 mM of NaCl, showing tolerance to saline and particularly osmotic stress. They were resistant to plasmolysis and had dense cytoplasms, large nuclei and nucleoli, and evident cytoplasmic strands under high saline and osmotic stress. The sequestration of Cl⁻ into the vacuoles was observed in the cells stressed with 137 and 223 mM NaCl. The cellular protein profile was modified by high salt and osmotic stress and showed 28 kDa polypeptides up-regulated by both NaCl and PEG, and 66 and 25 kDa polypeptides up-regulated only by high NaCl stress. The salt tolerance of P. euphratica cells might be related to their capacity of adapting to higher osmotic stress by maintaining cell integrity, sequestrating Cl⁻ into vacuoles and modulating polypeptides that reflect cellular metabolic adaptations.     

A role for GIGANTEA: Keeping the balance between flowering and salinity stress tolerance

The initiation of flowering in Arabidopsis is retarded or abolished by environmental stresses. Focusing on salt stress, we provide a molecular explanation for this well-known fact. A protein complex consisting of GI, a clock component important for flowering and SOS2, a kinase activating the [Na⁺] antiporter SOS1, exists under no stress conditions. GI prevents SOS2 from activating SOS1. In the presence of NaCl, the SOS2/GI complex disintegrates and GI is degraded. SO2, together with the Ca²⁺-activated sensor of sodium ions, SOS3, activates SOS1. In gi mutants, SOS1 is constitutively activated and gi plants are more highly salt tolerant than wild type Arabidopsis. The model shows GI as a transitory regulator of SOS pathway activity whose presence or amount connects flowering to environmental conditions.