沙地云杉和青海云杉种子萌发和幼苗生长对干旱盐碱胁迫的响应

利用控制实验研究了水分、盐分生态因子对沙地云杉和青海云杉种子萌发和幼苗生长的影响,以探索沙地云杉和青海云杉种子对水分、盐分生态因子的适应性。结果表明:(1)水分胁迫和盐分胁迫对沙地云杉和青海云杉种子萌发具有明显的抑制作用,可显著的降低种子的发芽率,两种云杉种子对水分胁迫的临界值和极限值分别是-0.03、-0.15 MPa和-0.5、-0.58 MPa;对盐分胁迫的临界值和极限值分别是78、148 mmol/L和284、345mmol/L;其幼苗长度随着渗透势和NaCl浓度的增加而显著减小。(2)沙地云杉和青海云杉种子恢复发芽率及恢复后的幼苗长度随着渗透势和NaCl浓度的增加先增加后减少。(3)在相同的水势条件下,PEG溶液比等渗的NaCl溶液对沙地云杉和青海云杉种子萌发具有更大的抑制作用,种子萌发过程中渗透胁迫比离子毒害的抑制作用更大。研究发现,沙地云杉和青海云杉种子对水分和盐分胁迫表现出不同程度的耐受性,两者对盐分胁迫的忍耐能力超过对水分胁迫;而且青海云杉种子比沙地云杉更耐旱、耐盐;早期的低盐和充分的水分条件是沙地云杉和青海云杉存活的关键。     

Relationship between cation accumulation and water content of salt-tolerant grasses and a sedge

Abstract Salt-tolerant grasses and a sedge were grown at three salinities in a controlled-environment greenhouse. They were measured for growth rate, ash content, water content and cations. Fourteen species from the genera Sporobolus, Aeluropus, Leptochloa, Paspalum, Puccinellia, Hordeum, Elymus, Distichlis and Spartina survived up to the highest salt treatment (540 mol m^?3 NaCl). These were designated halophytes. Eleven species from the genera Triticum, Phragmites, Dactylotenium, Cynodon, Polypogon, Panicum, Jovea and Heleocharis only survived up to 180 mol m^?3 NaCl and were designated salt-tolerant glycophytes. All species except Distichlis palmeri grew fastest on the non-saline control treatment. All species tended to have higher Na⁺ contents and lower K⁺ and water contents on saline treatments compared to control plants. Halophytes differed from glycophytes in having statistically significant lower water contents on the non-saline treatment, and lower ash contents and Na:K ratios on 180 mol m^?3. However, the range of values among species was greater than the differences between halophytes and glycophytes. All species appeared to use Na⁺ accumulation and loss of water as the main means of osmotic adjustment. Three halophytic species were grown for a longer period of time to check the above results. The osmolality of the cell sap was measured directly by the vapour pressure method and compared to calculated values based on Na⁺, K⁺ and water contents (and assuming a balancing anion such as Cl^?). Na⁺ and K⁺ alone could account for greater than 75% of the osmotic potential at all salinities. Hence, the accumulation of organic solutes did not appear to be an important factor in the osmotic adjustment of these species. The results support the conclusion that grasses coordinate Na⁺ uptake and water loss to maintain a constant osmotic potential gradient between the shoot tissues and the external solution. The results were compared to a previous study with dicotyledonous halophytes at the same location.     

Structural,physiological, and biochemical aspects of salinity tolerance of halophytes

Modern concepts on structural, physiological, and biochemical aspects of salt tolerance of higher plants were considered. Integral physiological processes, such as growth and photosynthesis of glycophytes and halophytes in the context of their ecological plasticity, variety of their adaptive strategies developed in the course of their evolution, and natural selection, were discussed. Analysis of the known anatomical and morphological adaptations of halophytes (succulence, special salt-excreting structures, features associated with special tissues growth, leaf kranz-anatomy and mesostructure) providing their salt tolerance was conducted. The most important physiological and biochemical adaptations of such plants to salinity related to uptake, accumulation and excretion of Na⁺ and Cl^–, peculiarities of membrane composition and the pigment system, and protection against osmotic and oxidative stresses were described. The association of physiological and biochemical peculiarities of halophytes with ecological salt tolerance strategy was discussed.     

Salinity tolerant Trichoderma harzianum reinforces NaCl tolerance and reduces population dynamics of Fusarium oxysporum f.sp. ciceri in chickpea (Cicer arietinum L.) under salt stress conditions

The antagonistic potential of salinity tolerant (ST) Trichoderma (Th) isolates against Fusarium oxysporum f.sp. ciceri (foc) was tested, along with their capability to induce relative salt stress tolerance in chickpea with the aim to exploit their use as biological agents in reducing deleterious effects of salinity and controlling Fusarium wilt of chickpea under saline soil conditions. Under laboratory conditions, salt stress was created by supplementing nutrient medium with different concentrations of NaCl viz. 0, 70, 150 and 240?mM NaCl and a pot experiment was conducted using natural saline soil (EC – 6.6 dS?m^?1). Out of 45 Th isolates studied, only five isolates viz. Th-13, Th-14, Th-19, Th-33 and Th-50 were selected to be ST as these were able to grow and sporulate in growth medium containing up to 240?mM NaCl. In saline medium, ST isolates greatly surpassed salinity sensitive (SS) isolate with respect to growth rate, mycelial dry weight, sporulation and biological proficiency against foc. Out of five ST isolates that retained their tolerance to different salt stress levels, Th-14 and Th-19 showed maximum antagonism against foc. Under greenhouse conditions, chickpea plants obtained from seeds bioprimed with Th-14 and Th-19 performed well both at germination and seedling stage in comparison to control in saline soil. As compared to untreated plants, characterisation of Th treated plants confirmed that they had reinforced contents of proline along with relatively higher levels of total phenols, membrane stability index and superoxide dismutase activity while lower accumulation of hydrogen peroxide and malondealdehyde contents. ST isolates, Th-14 and Th-19 significantly reduced foc-induced wilt disease incidence in chickpea plants. The population density of both the Th isolates in rhizosphere far exceeded that of foc under both saline and non-saline soils. However, Th-14 was found more efficient in increasing relative salt stress tolerance in chickpea and reducing the foc growth in rhizosphere under present materials and conditions. These findings provide a novel paradigm for developing alternative, environmentally safe strategy to alleviate salt stress and manage fungal diseases such as foc that aggravates under saline soils.     

Osmotic adjustment in Lycopersicon esculentum and L. Pennellii under NaCl and polyethylene glycol 6000 iso–osmotic stresses

Changes in leaf solute contents in response to saline (NaCl) and osmotic (polyethylene glycol, PEG, 6000) stresses were measured in three different salt tolerant cultivars of Lycopersicon esculentum (L.) Mill. (Pera, P-73 and Volgogradskij), and its wild relative L. pennellii (Correll) D'Arcy accession PE-47. Iso-osmotic stresses (–0. 5 MPa) of NaCl (140 mM) and PEG 6000 (150 g l^-1) were applied to one-month old plants for 3 weeks. Decreasing leaf dry weight was similar in L. pennellii or L. esculentum cv. P-73 and Volgogradskij under both stresses, while leaf dry weight of L. esculentum cv. Pera decreased more under PEG stress than under NaCl stress. Water contents decreased in all the PEG treated populations, while their calculated solute potential (Ψ_s increased. Under osmotic stress, the total ion contents decreased in relation to control, whereas organic solutes (sugars, amino acids and organic acids) markedly increased in both tomato species, specially in the tomato cultivars, where these solutes represented 50% of the Ψ₅ calculated. Soluble sugar increase was three times higher in leaves of L. esculentum than in the leaves of L. pennellii. Free proline increased under both stresses and its content was highest in L. esculentum and in L. pennellii, respectively, under NaCl and PEG stresses. Nevertheless, the contribution of this metabolite to Ψ_s did not exceed 5%, irrespective of treatment and species. The greater organic solute accumulation in L. esculentum than in L. pennellii– which was not reflected in their Ψ₅ values – was not correlated with the tolerances of the two species to osmotic stress. Therefore, osmotic adjustment may not be the only process influencing salt and drought tolerances in tomato; the ability of plants to regulate their metabolic and physiological functions could also play an important role under these harmful conditions. The possible roles of inorganic solutes and metabolites in osmotic adjustment, energetic metabolism and redox regulation are discussed     

The effect of salt stress on polyamine biosynthesis and content in mung bean plants and in halophytes

The activity of L-arginine decarboxylase (EC 4.1.1.19) and L-ornithine decarboxylase (EC 4.1.1.17), polyamine content, and incorporation of arginine and ornithine into polyamines, were determined in mung bean [Vigna radiata (L.) Wilczek] plants subjected to salt (hypertonic) stress (NaCl at 0.51–2.27 MPa). Changes in enzyme activity in response to hypotonic stress were determined as well in several halophytes [Pulicaria undulata (L.), Kostei, Salsola rosmarinus (Ehr.) Solms-Laub, Mesembryanthemum forskahlei Hochst, and Atriplex halimus L.]. NaCl stress, possibly combined with other types of stress that accompanied the experimental conditions, resulted in organ-specific changes in polyamine biosynthesis and content in mung bean plants. The activity of both enzymes was inhibited in salt-stressed leaves. In roots, however, NaCl induced a 2 to 8-fold increase in ornithine decarboxylase activity. Promotion of ornithine decarboxylase in roots could be detected already 2 h after exposure of excised roots to NaCl, and iso-osmotic concentrations of NaCl and KCl resulted in similar changes in the activity of both enzymes. Putrescine level in shoots of salt-stressed mung bean plants increased considerably, but its level in roots decreased. The effect of NaCl stress on spermidine content was similar, but generally more moderate, resulting in an increased putrescine/spermidine ratio in salt-stressed plants. Exposure of plants to NaCl resulted also in organ-specific changes in the incorporation of both arginine and ornithine into putrescine: incorporation was inhibited in leaf discs but promoted in excised roots of salt-stressed mung bean plants. In contrast to mung bean (and several other glycophytes), ornithine and arginine decarboxylase activity in roots of halophytes increased when plants were exposed to tap water or grown in a pre-washed soil—i.e. a hypotonic stress with respect to their natural habitat. NaCl, when present in the enzymatic assay mixture, inhibited arginine and ornithine decarboxylase in curde extracts of mung bean roots, but did not affect the activity of enzymes extracted from roots of the halophyte Pulicaria. Although no distinct separation between NaCl stress and osmotic stress could be made in the present study, the data suggest that changes in polyamines in response to NaCl stress in mung bean plants are coordinated at the organ level: activation of biosynthetic enzymes concomitant with increased putrescine biosynthesis from its precursors in the root system, and accumulation of putrescine in leaves of salt-stressed plants. In addition, hypertonic stress applied to glycophytes and hypotonic stress applied to halophytes both resulted in an increase in the activity of polyamine biosynthetic enzymes in roots.     

Assessing the role of endophytic bacteria in the halophyte Arthrocnemum macrostachyum salt tolerance

• There is an increasing interest to use halophytes for revegetation of salt affected ecosystems, as well as in understanding their mechanisms of salt tolerance. We hypothesized that bacteria from the phyllosphere of these plants might play a key role in its high tolerance to excessive salinity.
• Eight endophytic bacteria belonging to Bacillus and closely related genera were isolated from phyllosphere of the halophyte Arthrocnemum macrostachyum growing in salty agricultural soils. The presence of plant‐growth promoting (PGP) properties, enzymatic activities and tolerance towards NaCl was determined. Effects of inoculation on seeds germination and adult plant growth under experimental NaCl treatments (0, 510 and 1030 mM NaCl) were studied.
• Inoculation with a consortium including the best performing bacteria improved considerably the kinetics of germination and the final germination percentage of A. macrostachyum seeds. At high NaCl concentrations (1030 mM), inoculation of plants mitigated the effects of high salinity on plant growth and physiological performance and, in addition, this consortium appears to have increased the potential of A. macrostachyum to accumulate Na⁺ in its shoots, thus improving sodium phytoextraction capacity.
• Bacteria isolated from A. macrostachyum phyllosphere seem to play an important role in plant salt tolerance under stressing salt concentrations. The combined use of A. macrostachyum and its microbiome can be an adequate tool to enhance plant adaptation and sodium phytoextraction during restoration of salt degraded soils.

     

Quaternary ammonium compounds in plants in relation to salt resistance

Fourteen plant species exhibiting a wide range of salt resistance as halophytes, semi-resistant glycophytes and sensitive glycophytes, have been grown in nutrient solution culture under low and high salt conditions. Inorganic analyses and shoot sap osmotic pressure values of these plants confirm that osmotic compensation at high salt levels is largely achieved by the accumulation of Na salts. Choline was found in shoots and roots in the range 1.0-0.2 μmol g fr. wt^?1 and varied little following salt stress. Trigonelline was found in some of the sensitive glycophytes and did not increase significantly in stressed plants. Betaine levels were high (10 μmol g fr. wt^?1) in the shoot of the halophytes at low salt conditions, lower values (1–10 μmol g fr. wt^?1) were found in the semi-resistant glycophytes and none detected in the sensitive glycophytes. In the two resistant groups betaine accumulated to higher levels following NaCl stress. Shoot betaine levels always exceeded root levels. Proline occurred in all plants and in all cases was accumulated following NaCl stress.     

蒭雷草对盐胁迫的生理响应

该文选择从西沙东岛采集蒭雷草,通过分株繁殖挑选健壮植株作为材料,模拟热带珊瑚岛生境设置不同浓度NaCl处理,研究不同程度的盐胁迫对其植株叶片丙二醛(MDA)、抗氧化酶以及渗透调节物质的影响.结果表明:(1)短期(28 d)盐胁迫下,NaCl浓度的增加并未加速蒭雷草叶片细胞发生膜脂过氧化作用,MDA含量增加幅度较小;随着...     

Plant salt tolerance: adaptations in halophytes

Background Most of the water on Earth is seawater, each kilogram of which contains about 35 g of salts, and yet most plants cannot grow in this solution; less than 0·2 % of species can develop and reproduce with repeated exposure to seawater. These ‘extremophiles’ are called halophytes.Scope Improved knowledge of halophytes is of importance to understanding our natural world and to enable the use of some of these fascinating plants in land re-vegetation, as forages for livestock, and to develop salt-tolerant crops. In this Preface to a Special Issue on halophytes and saline adaptations, the evolution of salt tolerance in halophytes, their life-history traits and progress in understanding the molecular, biochemical and physiological mechanisms contributing to salt tolerance are summarized. In particular, cellular processes that underpin the ability of halophytes to tolerate high tissue concentrations of Na⁺ and Cl⁻, including regulation of membrane transport, their ability to synthesize compatible solutes and to deal with reactive oxygen species, are highlighted. Interacting stress factors in addition to salinity, such as heavy metals and flooding, are also topics gaining increased attention in the search to understand the biology of halophytes.Conclusions Halophytes will play increasingly important roles as models for understanding plant salt tolerance, as genetic resources contributing towards the goal of improvement of salt tolerance in some crops, for re-vegetation of saline lands, and as ‘niche crops’ in their own right for landscapes with saline soils.     

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.     

Overaccumulation of glycine betaine alleviates the negative effects of salt stress in wheat

To investigate the physiological mechanisms of glycinebetaine (GB) involved in the improvement of salt tolerance of wheat, three transgenic wheat (Triticum aestivum L.) lines-T1, T4, and T6-and the wild-type (WT) line Shi4185 were used. The transgenic lines were generated by introducing the BADH gene encoding betaine aldehyde dehydrogenase, which was cloned from Atriplex hortensis L. The BADH gene induced overexpression of GB in transgenic lines. Salt stress was induced by adding 200 mM NaCl, and the osmotic adjustment (OA), ion homeostasis, and antioxidant characteristics of wheat plants were observed. Under salt stress, the OA in the transgenic wheat lines was significantly higher than that in WT; this may be attributed to GB itself and/or the GB-induced overaccumulation of other osmolytes, such as free proline, soluble protein, and soluble sugar. Moreover, the transgenic lines could maintain the lower Na⁺ and Cl⁻ concentrations in their leaves by accumulating these ions in the sheaths in order to protect the leaves from ion toxicity; however, these lines maintained a higher K⁺ concentration in the leaves since K⁺ functions as an osmolyte and maintains ion homeostasis in the leaf cells. Furthermore, the in vivo overaccumulated GB could enhance or stabilize the activity of antioxidant enzymes that can scavenge reactive oxygen species (ROS) and mitigate oxidative damage of biomembranes. The experimental results suggest that GB overexpression can enhance the salt tolerance of transgenic plants by regulating ion homeostasis, enhancing OA, and scavenging ROS. Published in Russian in Fiziologiya Rastenii, 2009, vol. 56, No. 3, pp. 410–417. This text was submitted by the authors in English.     

Soil salt and nutrient concentration in the rhizosphere of desert halophytes

North-West China is an arid region where halophyte plants are rich. Very little is known on the rhizospheric soil of the halophytes in this arid desert region. We conducted a rhizobag experiment on the desert Solonchak soil to investigate the salt and nutrient content in the rhizospheric soil of the desert halophytes. The total salt and the concentrations of 8 major kinds of salt ions increased in the rhizosphere of both succulent halophytes and salt secreting halophytes, but this increase was insignificant for salt-resisting halophytes. Accumulation of Cl^– and Na⁺ is the most significant among the 8 major kinds of salt ions. Accumulation of Cl^– was more significant than that of SO₄^2– in succulent halophytes and salt secreting halophytes. The Na⁺/K⁺, Na⁺/Ca²⁺ and Na⁺/Mg²⁺ ratios in the rhizosphere of all 7 kinds of halophytes were higher than those in the bulk soil. Total N increased significantly in the rhizosphere, but total P and total K decreased. However, the available N, P and K in the rhizosphere of the 7 kinds of halophytes except Phragmites communis Trin. behaved in such an opposite way that available N decreased but available P and available K increased. The ionic contents in the aboveground parts were higher than those in the underground parts of the 7 kinds of halophytes, in particular of both the succulent halophytes and the salt secreting halophytes. Accumulation of Cl^– and Na⁺ in the aboveground parts of the plants was the most significant among that of the 8 major kinds of salt ions.     

Physiological and biochemical traits involved in the genotypic variability to salt tolerance of Tunisian Cakile maritima

Cakile maritima (family: Brassicaceae) was collected from three provenances belonging to different bioclimatic stages (humid, semi arid and arid) in Tunisia to study their eco‐physiological and biochemical responses to salinity. Seedlings were cultivated on inert sand for 20 days under NaCl treatments (0, 100, 200, 400 mm NaCl). Plant response to salinity was provenance‐ and salt‐dependent. At 100 mm NaCl, growth parameters (leaf biomass, area, number per plant and relative growth rate) were improved in plants from Jerba (originating from arid bioclimatic stage) compared with the control, while growth was reduced in those from Tabarka (from humid area). High salt levels (400 mm NaCl) decreased the plant growth in the three provenances, but plants in Tabarka were the most salt sensitive. The relative salt tolerance of plants from Jerba and Bekalta provenances was associated with low levels of malondialdehyde as well as of electrolyte leakage and endoproteolytic activity. Salt reduced leaf hydration, the decrease in water content being dose‐dependent and more pronounced in Tabarka. Increase in salinity led to significant increase in leaf succulence and decrease in leaf water potential, especially in Jerba plants. The plants from the latter displayed the highest leaf levels of Na⁺ and Cl^?, proline, soluble carbohydrates, soluble proteins, and polyphenols. Overall, the higher salt tolerance of plants from Jerba provenance, and to a lower extent of those from Bekalta, may be partly related to their better capacity for osmotic adjustment and to limit oxidative damage when salt‐challenged.     

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.     

Salt tolerance of Beta macrocarpa is associated with efficient osmotic adjustment and increased apoplastic water content

The chenopod Beta macrocarpa Guss (wild Swiss chard) is known for its salt tolerance, but the mechanisms involved are still debated. In order to elucidate the processes involved, we grew wild Swiss chard exposed to three salinity levels (0, 100 and 200 mm NaCl) for 45 days, and determined several physiological parameters at the end of this time. All plants survived despite reductions in growth, photosynthesis and stomatal conductance in plants exposed to salinity (100 and 200 mm NaCl). As expected, the negative effects of salinity were more pronounced at 200 mm than at 100 mm NaCl: (i) leaf apoplastic water content was maintained or increased despite a significant reduction in leaf water potential, revealing the halophytic character of B. macrocarpa; (ii) osmotic adjustment occurred, which presumably enhanced the driving force for water extraction from soil, and avoided toxic build up of Na⁺ and Cl^– in the mesophyll apoplast of leaves. Osmotic adjustment mainly occurred through accumulation of inorganic ions and to a lesser extent soluble sugars; proline was not implicated in osmotic adjustment. Overall, two important mechanisms of salt tolerance in B. macrocarpa were identified: osmotic and apoplastic water adjustment.     

Salt Tolerance in Aquatic Macrophytes: Ionic Relation and Interaction

Effects of seawater salinity (SWS) and pure NaCl on the intracellular contents of Na⁺, K⁺, Mg²⁺, Ca²⁺, chlorophylls (Chl) and carotenoids (Car) were studied in three submerged aquatic macrophytes, Hydrilla verticillata, Najas indica and Najas gramenia, which differed in their tolerance to salinity. NaCl resulted in significant increase in Chl/Car ratio in the salt-sensitive H. verticillata and moderately salt-tolerant N. indica, but not in the salt-tolerant N. gramenia. SWS treatment did not result in any significant change in the ratio. The intracellular content of Na⁺ increased significantly in all the test plants upon exposure to both NaCl and SWS. The content of K⁺ decreased significantly in these plants upon salinity treatment, except in N. gramenia. The contents of Ca²⁺ and Mg²⁺ decreased significantly upon NaCl treatment and remained unchanged or increased upon SWS treatment. No relationship between salt tolerance and K⁺/Na⁺ ratio was observed. The maintenance of a minimal level of K⁺ was observed to be the most probable requirement of salt tolerance in aquatic macrophytes.