Variability in response to salinity stress in natural Tunisian populations of Hordeum marinum subsp. marinum

• Soil salinity is one of the most serious environmental factors affecting crop productivity around the world.
• In this study, we analysed morpho‐physiological variation in responses to salt stress in Tunisian populations of Hordeum marinum subsp. marinum. The plants were grown under two treatments (0 and 200 mm NaCl) until maturity. A total of 19 quantitative traits were measured before and during the harvest.
• It was observed that most studied traits are influenced by the increasing salinity. High to moderate broad‐sense heritability (H²) were noted for most of parameters under control and salt treatment, implying that salt tolerance is moderately heritable and environmental variation plays an equally important role. The majority of correlations between measured traits under the two treatments are positive, where the strongest correlations were between spike number (SN) and weight (SW). Based on the salt response index (SRI) values, SN and SW are the most affected by salinity. The 150 studied lines formed three groups according to the SRI values of the 19 quantitative parameters, of which 101 were moderately sensitive, 27 tolerant and 22 highly tolerant.
• Overall genetic variation of H. marinum in response to salt stress may provide novel insight to identify genes responsible for salt tolerance.

     

Changes in the levels of jasmonates and free polyamines induced by Na<Subscript>2</Subscript>SO<Subscript>4</Subscript> and NaCl in roots and leaves of the halophyte <Emphasis Type="Italic">Prosopis strombulifera</Emphasis>

Prosopis strombulifera, a common legume in high-salinity soils of Argentina, is a useful model for elucidation of salt tolerance mechanisms and specific biochemical pathways in halophytes, since its NaCl tolerance exceeds the limit described for most halophytic plants. We analyzed the effects of the increasing concentration of two main soil salts, Na₂SO₄ and NaCl, on growth parameters of P. strombulifera, chlorophyll levels, and content of jasmonates (JAs) and polyamines (PAs), which are key molecules involved in stress responses. P. strombulifera showed a halophytic response (growth promotion) to NaCl, but strong growth inhibition by iso-osmotic solutions of Na₂SO₄. Chlorophyll levels, number of leaves and leaf area were also differentially affected. An important finding was the partial alleviation of SO₄²⁻ toxicity by treatment with two-salt mixture. JAs are not directly involved in salt tolerance in this species since its levels decrease under all salt treatments. Beneficial effects of Putrescine (Put) accumulation in NaCl treated plants maybe inferred probably associated with the antioxidative defense system. Another novel finding is the accumulation of the uncommon PA cadaverine in roots under high Na₂SO₄, which may be related to SO₄²⁻ toxicity.     

QTLs mapping of morphological traits related to salt tolerance in <Emphasis Type="Italic">Medicago truncatula</Emphasis>

To understand the complex inheritance of tolerance to salt stress in Medicago truncatula, quantitative trait loci (QTLs) analysis was performed using a set of recombinant inbred lines (RILs) derived from a cross between the tolerant line Jemalong A17 and susceptible line F83005.5. The RILs and parental lines were grown in individual pots filled with sterilized sand in a greenhouse under 0 and 50 mM NaCl. Plants were harvested after a period of 60 days. Fourteen quantitative traits related to aerial and root growths were measured. Broad-sense heritability of measured traits ranged from 0.21 to 0.83 and from 0.05 to 0.62 in control and in salt-stressed conditions, respectively. Established correlations between measured traits are dependent on treatment effect. We identified and mapped 10 QTLs in control conditions and 19 in salt stress. No major QTL was identified indicating that tolerance to salt stress is governed by several genes with low effects. The QTLs detected under control and under salt-stressed conditions almost did not share the same map locations suggesting that the loci that are not stable across treatments reflect adaptation to this constraint. The maximum of QTLs was observed on the chromosome 8. The usefulness of these QTLs, identified in greenhouse conditions, for marker-assisted selection should therefore be evaluated under field conditions, and validated in other genetic backgrounds.     

Variability in the response of six genotypes of N<Subscript>2</Subscript>-fixing <Emphasis Type="Italic">Medicago ciliaris</Emphasis> to NaCl

Genotypic variability was assessed within six Medicago ciliaris genotypes growing symbiotically with Sinorhizobium medicae in order to identify physiological criteria (growth, ion content, and plant health) associated with salt tolerance. Response to salt stress depended on the line and the level of salt. Two lines with lower dry biomass under non-saline conditions (TNC 1.8 from a semi-arid area and TNC 10.8 from a sub-humid area), were more tolerant to NaCl, whereas the most productive lines (TNC 11.5 and TNC 11.9 from a humid bioclime) were more sensitive in terms of growth and nitrogen fixation. Susceptibility of symbiotic nitrogen fixation to saline stress was not associated with a higher accumulation of Na⁺ in nodules, since the most tolerant lines TNC 1.8 and TNC 10.8 accumulated the highest Na⁺ amount in nodules. Leaf area and net photosynthate assimilation rate were conserved in line TNC 1.8 and to a lesser extent in line TNC 10.8 potentially owing to a greater ability to protect aerial organs and nodules from Na⁺ damage and to insure a better supply of leaves with nitrogen. Our results suggest that nodule growth and number and nodule Na⁺ content should not be used as selection tools for tolerance or susceptibility, since two of the tested lines maintained consistent growth in spite of reduced nodule and high Na⁺ content. Instead, the most reliable physiological indicators for tolerance appear to be consistent growth (i.e., no growth changes) and reduced leaf Na⁺ accumulation with increasing concentrations of NaCl.     

Photosynthetic limitations of a halophyte sea aster (<Emphasis Type="Italic">Aster tripolium</Emphasis> L) under water stress and NaCl stress

To understand the mechanisms of salt tolerance in a halophyte, sea aster (Aster tripolium L.), we studied the changes of water relation and the factors of photosynthetic limitation under water stress and 300 mM NaCl stress. The contents of Na⁺ and Cl^- were highest in NaCl-stressed leaves. Leaf osmotic potentials (Ψ _s) were decreased by both stress treatments, whereas leaf turgor pressure (Ψ _t) was maintained under NaCl stress. Decrease inΨ _s without any loss ofΨ _t accounted for osmotic adjustment using Na⁺ and Cl^- accumulated under NaCl stress. Stress treatments affected photosynthesis, and stomatal limitation was higher under water stress than under NaCl stress. Additionally, maximum CO₂ fixation rate and O₂ evolution rate decreased only under water stress, indicating irreversible damage to photosynthetic systems, mainly by dehydration. Water stress severely affected the water relation and photosynthetic capacity. On the other hand, turgid leaves under NaCl stress have dehydration tolerance due to maintenance of Ψ _t and photosynthetic activity. These results show that sea aster might not suffer from tissue dehydration in highly salinized environments. We conclude that the adaptation of sea aster to salinity may be accomplished by osmotic adjustment using accumulated Na⁺ and Cl^-, and that this plant has typical halophyte characteristics, but not drought tolerance. Electronic Publication     

Responses of antioxidant defense system of <Emphasis Type="Italic">Catharanthus roseus</Emphasis> (L.) G. Don. to paclobutrazol treatment under salinity

The effect of paclobutrazol, a plant growth regulator, on antioxidant defense system was investigated in Catharanthus roseus (L.) G. Don. plants subjected to NaCl stress. The growth parameters were significantly reduced under 80 mM NaCl treatment; however, this growth inhibition was less in paclobutrazol-treated (15 mg l⁻¹ plant⁻¹) plants. The non-enzymatic antioxidants ascorbic acid and reduced glutathione were affected under NaCl stress and they increased significantly under paclobutrazol treatment when compared to NaCl treated as well as control plants (P ≤ 0.05). The activity of antioxidant enzyme ascorbate peroxidase showed a significant enhancement under salinity stress. The catalase activity decreased in roots of NaCl-treated plants, but recovered with paclobutrazol treatment. The results suggested that paclobutrazol have significant role in contributing salt stress tolerance of C. roseus by improving the components of antioxidant defense system.     

Salt stress effects on growth,pigments, proteins and lipid peroxidation in <Emphasis Type="Italic">Salicornia persica</Emphasis> and <Emphasis Type="Italic">S. europaea</Emphasis>

The effects of NaCl stress on growth, water status, contents of protein, proline, malondialdehyde (MDA), various sugars and photosynthetic pigments were investigated in seedlings of Salicornia persica and S. europaea grown in vitro. Seeds were germinated under NaCl (0, 100, 200, 300, 400, 500 and 600 mM) on Murashige and Skoog medium for 45 d. The shoot growth of both species increased under low NaCl concentration (100 mM) and then decreased with increasing NaCl concentrations. In contrast to S. persica, root length in S. europaea reduced steadily with an increase in salinity. Proline content in S. persica was higher than in S. europaea at most NaCl concentrations. Proline, reducing saccharide, oligosaccharide and soluble saccharide contents increased under salinity in both species. In contrast, contents of proteins and polysaccharides reduced in both species under salt stress. MDA content remained close to control at moderate NaCl concentrations (100 and 200 mM) and increased at higher salinities. MDA content in S. europaea was significantly higher than S. persica at higher salinities. Salt treatments decreased K⁺ and P contents in seedlings of both species. Significant reduction in contents of chlorophylls and carotenoids due to NaCl stress was also observed in seedlings of both species. Some differences appeared between S. persica and S. europaea concerning proteins profile. On the basis of the data obtained, S. persica is more salt-tolerant than S. europaea.     

NaCl tolerance in <Emphasis Type="Italic">Lycopersicon pennellii</Emphasis> introgression lines: QTL related to physiological responses

The growth and ion content of salt sensitive Lycopersicon esculentum Mill. cv. M82 and salt tolerant L. pennellii Correll accession LA716 were examined under both control and stress conditions (150 mM NaCl). L. esculentum grew more vigorously than L. pennellii under optimal conditions, however, L. pennellii was able to maintain its growth better than cultivated tomato when the plants were exposed to salinity. Sodium content of both L. esculentum and L. pennellii increased as a result of NaCl stress. In addition, both species showed reduced potassium and calcium content due to salinity. The physiological traits were also measured in a population of 52 L. pennellii introgression lines grown under both normal and stress conditions. A total of 311 quantitative trait loci (QTL) were identified for the studied traits: plant height, stem diameter, leaf number, leaf and root fresh and dry mass, and sodium, potassium and calcium contents. Some of the loci (124) were identified under both control and stress conditions while 86 QTL were identified only under non-stress conditions and 101 loci were identified only under NaCl stress.     

Akaline,saline and mixed saline–alkaline stresses induce physiological and morpho‐anatomical changes in Lotus tenuis shoots

Saline, alkaline and mixed saline–alkaline conditions frequently co‐occur in soil. In this work, we compared these plant stress sources on the legume Lotus tenuis, regarding their effects on shoot growth and leaf and stem anatomy. In addition, we aimed to gain insight on the plant physiological status of stressed plants. We performed pot experiments with four treatments: control without salt (pH = 5.8; EC = 1.2 dS·m^?1) and three stress conditions, saline (100 mm NaCl, pH = 5.8; EC = 11.0 dS·m^?1), alkaline (10 mm NaHCO₃, pH = 8.0, EC = 1.9 dS·m^?1) and mixed salt–alkaline (10 mm NaHCO₃ + 100 mm NaCl, pH = 8.0, EC = 11.0 dS·m^?1). Neutral and alkaline salts produced a similar level of growth inhibition on L. tenuis shoots, whereas their mixture exacerbated their detrimental effects. Our results showed that none of the analysed morpho‐anatomical parameters categorically differentiated one stress from the other. However, NaCl‐ and NaHCO₃‐derived stress could be discriminated to different extents and/or directions of changes in some of the anatomical traits. For example, alkalinity led to increased stomatal opening, unlike NaCl‐treated plants, where a reduction in stomatal aperture was observed. Similarly, plants from the mixed saline–alkaline treatment characteristically lacked palisade mesophyll in their leaves. The stem cross‐section and vessel areas, as well as the number of vascular bundles in the sectioned stem were reduced in all treatments. A rise in the number of vessel elements in the xylem was recorded in NaCl‐treated plants, but not in those treated exclusively with NaHCO_3.     

Responses of two lines of <Emphasis Type="Italic">Medicago ciliaris</Emphasis> to Fe deficiency under saline conditions

The aim of this research was to study the responses of two lines of Medicago ciliaris: TN11.11 and TN8.7 to iron deficiency under saline conditions. However; the paper showed also the results of a preliminary study which report the contrastive responses of the two lines to salinity. We found that plant growth and chlorophyll content of TN11.11 line were more affected by salinity than TN8.7. The severity of symptoms was linked to the sodium accumulation in shoots as well as a limitation of potassium uptake. Our data allowed us to note that TN8.7 line is less sensitive and can better cope with the salinity. Concerning the effect of salinity on iron deficiency responses, we noted that root PM H⁺-ATPase and FCR activities were reduced when iron deficiency was associated with salinity. This probably explained the decrease of Fe uptake. On the contrary, PEPC activity was not affected.     

Identification of two phenotypes of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> under <Emphasis Type="Italic">in vitro</Emphasis> salt stress conditions

This study describes two phenotypes of Arabidopsis thaliana (ecotype Columbia) developed in vitro under salt stress (75 mM NaCl). The phenotypes 01 and 02 appeared visibly distinguishable by rosette morphology and competence to produce flowers. Phenotype 01, sensible to salt stress, accumulated high quantities of Na⁺, showed a slight reduction in dry mass, and high protein and chlorophyll contents. Moreover, its anatomy exhibited some xeromorphic traits. Phenotype 02, clearly salt tolerant, showed a morphology similar to control plants, displaying typical phyllotactic rosette and flowering stalk production. Accumulation of Na⁺, protein and chlorophyll contents were close to control plants. Reversion experiments on NaCl free MS medium, showed a partially recovered phenotype 01. A threshold salt stress concentration that permits the simultaneous development of two phenotypes, was found.     

Effects of sodium chloride and polyethylene glycol on root-hair infection and nodulation of Vicia faba L. plants by Rhizobium leguminosarum

The effects of sodium chloride and polyethylene glycol (PEG) on the interaction between Rhizobium leguminosarum strain 29d and root hairs of field bean (Vicia faba L. cv. Maris Bead) plants were investigated. Two levels each of NaCl (50 and 100 mol·m^–3) and PEG (100 and 200 mol·m^–3) were given at the time of root-hair formation. Scanning electron microscopy showed rhizobial attachment and colonization on root-hair tips. Adhesion of rhizobia in both lateral and polar orientation, sometimes associated with microfibrils, occurred mainly in crooks at the root-hair tips; most of the infections also occurred here. Bacterial colonization and root-hair curling were both reduced by stress treatments. Polyethylene glycol but not NaCl significantly reduced root-hair diameter. The proportion of root hairs containing infection threads was reduced by 30% under NaCl and by 52% under PEG. The structure of some of the root hairs, epidermal and hypodermal cells, as seen by light microscopy in ultrasections, was distorted as a result of NaCl and PEG treatments; cells showed plasmolysis and folded membranes. After three weeks of treatment, both NaCl and PEG inhibited nodule number by about 50% and nodule weight by more than 60%. It is concluded that the root-hair infection process in Vicia faba is impaired by NaCl and PEG treatments and this in turn results in fewer nodules being produced.Abbreviation PEG polyethylene glycol     

外源5-氨基乙酰丙酸对NaCl胁迫下酸枣光合特性的影响

以2年生酸枣幼苗为试验材料,探讨不同浓度NaCl(0、4、8、12g·kg-1)胁迫下喷施5-氨基乙酰丙酸(ALA,75、150mg·L~(-1))对酸枣光合特性的影响。结果显示:(1)不同浓度NaCl胁迫下,外源ALA对酸枣叶片的净光合速率(Pn)、胞间二氧化碳浓度(Ci)、气孔导度(Gs)、蒸腾速率(Tr)及叶绿素含量等具有明显促进作用。(2)在不同浓度NaCl胁迫下,喷施75mg·L~(-1)的ALA仅在NaCl浓度为4和8g·kg-1处理下对酸枣Tr值具有显著提高作用,而喷施150mg·L~(-1) ALA在各NaCl浓度胁迫下对其Pn、Ci和Tr均具有显著促进作用。(3)在重度NaCl胁迫(12g·kg-1)下,喷施150mg·L~(-1) ALA对酸枣叶片叶绿素含量具有显著提高作用,而喷施75mg·L~(-1)浓度ALA却无明显提高。研究表明,在NaCl胁迫条件下,外源ALA能有效改善酸枣叶片光合气体交换参数,提高叶绿素含量,从而缓解NaCl胁迫的伤害,提高其光合能力,并以喷施150mg·L~(-1) ALA的缓解效果更好。     

Effect of salt stress on photosynthesis and chlorophyll fluorescence in Medicago truncatula

In the present study, photosynthetic parameters including gas exchanges, pigment contents, and chlorophyll fluorescence, were compared in two contrasting local Medicago truncatula lines TN6.18 and TN8.20, in response to salt added to the nutrient solution. Plants were cultivated under symbiotic nitrogen fixation (SNF) after inoculation with a reference strain Sinorhizobium meliloti 2011, a very tolerant strain to salinity (700 mM NaCl), and grown in a controlled glasshouse. On one month old plants (with active SNF), salt treatment (75 mM NaCl) was gradually applied. Photosynthesis, assimilating pigments and chlorophyll fluorescence were monitored throughout the experiment during both short and long terms, compared to control (non-saline) conditions. A genotypic variation in salt tolerance was found; TN6.18 was the more sensitive to salinity. The relative tolerance of TN8.20 was concomitant with the highest photochemical quenching coefficient (q_P) affecting the maximum quantum yield of PSII (Y); the real quantum yield (?_exc) was the most affected in the sensitive line. Moreover, stomatal and PSII reaction centers activities differed clearly between the studied lines. We found that the effect of salinity on photosynthesis of M. truncatula was related to PSII activity reduction rather than to stomatal conductance limitation. Photosynthesis was reduced by the inhibition of CO₂ assimilation caused by PSII damage. This was clearly estimated by the Y, ?_exc and especially by the quantum yield of electron transport of PSII (Φ_PSII). Thus, on the basis of our results on the two local M. truncatula lines, we recommend the use of chlorophyll fluorescence as non-destructive screening method to discriminate susceptible and resistant legumes to salt stress.     

Combined effect of salinity and hypoxia in wheat (Triticum aestivum L.) and wheat-Thinopyrum amphiploids

The effects of sodium chloride salinity and hypoxia were studied in eight wheat lines and three wheat-Thinopyrum amphiploids in vermiculite-gravel culture. The lines were treated with either 100 or 150 mol m^–3 NaCl with and without hypoxia. Saline hypoxic conditions significantly reduced the vegetative growth, water use, grain and straw yields for all wheat varieties except the amphiploids, whereas NaCl or hypoxia alone had less pronounced effects. In addition, saline hypoxic stress reduced K⁺ concentration and increased significantly the Na⁺ and Cl^– concentrations in cell sap expressed from leaves. There was more Na⁺ and Cl^– accumulation in wheats than the amphiploids in hypoxic conditions at 150 mol m^–3 NaCl. Of the wheats, Pato was the most sensitive at all stress levels while aTriticum aestivum cv. Chinese Spring ×Thinopyrum elongatum amphiploid was the most tolerant of the three amphiploids.     

Growth, nitrogen fixation and ion distribution in Medicago truncatula subjected to salt stress

This study compared the growth, nodulation, N₂ fixation, and ion distribution in three Medicago truncatula lines, in response to salt in nutrient solution. Two local lines (TN8.20 and TN6.18) and a reference line (Jemalong 6) were inoculated with a reference strain Sinorhizobium meliloti 2011, a very tolerant strain to salinity (700 mM NaCl) and grown in a controlled glasshouse with or without 75 mM NaCl. A genotypic variation in tolerance to salt was found: TN6.18 was the most sensitive line whereas TN8.20 was the most tolerant. The relative tolerance of TN8.20 was concomitant with the lowest leaf Na⁺ concentration and the highest nodule biomass production. However, nodule efficiency (amount of nitrogen fixed per g dry weight nodule) decreased in all lines. Results suggest that the tolerance to salt seems to depend on the host plant ability to protect its leaves against an excessive Na⁺ (and Cl^?) accumulation, and its ability to maintain the development of an abundant nodular system, which in turn determines an important rate of nitrogen fixation and allows the plants to conserve their growth potentialities. The loss of the nodular efficiency under salt stress seems to be compensated by a large nodule biomass.     

Effect of salinity on osmotic adjustment characteristics of <Emphasis Type="Italic">Kandelia candel</Emphasis>

To elucidate the osmotic adjustment characteristics of mangrove plants, inorganic ion and organic solute contents of intermediate leaves were investigated in 3-month-old Kandelia candel (L.) Druce seedlings during 45 days of NaCl treatments (0, 200, and 500 mM NaCl). The contents of Na⁺, Cl⁻, total free amino acids, proline, total soluble sugars, pinitol and mannitol increased to different degree by salinity, whereas, K⁺ content decreased by salinity compared with control. NaCl treatment induced an increase of inorganic ion contribution while a decrease of organic solute contribution. It was concluded that accumulating a large amount of inorganic ions was used as the main osmotic adjustment mechanism under salinity treatment. However, accumulation of organic osmolytes might be considered to play much more important role in osmoregulation under severe salinity (500 mM NaCl) than under moderate salinity (200 mM NaCl), thus the damage caused by high toxic ions (Na⁺ and Cl⁻) concentration in K. candel leaves could be avoided.     

Effects of NaCl or Na<Subscript>2</Subscript>SO<Subscript>4</Subscript> salinity on plant growth,ion content and photosynthetic activity in <Emphasis Type="Italic">Ocimum basilicum</Emphasis> L.

Basil (Ocimum basilicum L., cultivar Genovese) plants were grown in Hoagland solution with or without 50 mM NaCl or 25 mM Na₂SO₄. After 15 days of treatment, Na₂SO₄ slowed growth of plants as indicated by root, stem and leaf dry weight, root length, shoot height and leaf area, and the effects were major of those induced by NaCl. Photosynthetic response was decreased more by chloride salinity than by sulphate. No effects in both treatments on leaf chlorophyll content, maximal efficiency of PSII photochemistry (F _v/F _m) and electron transport rate (ETR) were recorded. Therefore, an excess of energy following the limitation to CO₂ photoassimilation and a down regulation of PSII photochemistry was monitored under NaCl, which displays mechanisms that play a role in avoiding PSII photodamage able to dissipate this excess energy. Ionic composition (Na⁺, K⁺, Ca²⁺, and Mg²⁺) was affected to the same extent under both types of salinity, thus together with an increase in leaves Cl⁻, and roots SO₄ ²⁻ in NaCl and Na₂SO₄-treated plants, respectively, may have resulted in the observed growth retardation (for Na₂SO₄ treatment) and photosynthesis activity inhibition (for NaCl treatment), suggesting that those effects seem to have been due to the anionic component of the salts.