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.     

Influence of NaCl-salinity on growth,photosynthesis, water relations and solute accumulation in <Emphasis Type="Italic">Phragmites australis</Emphasis>

The aim of this study was to investigate the effects of NaCl-salinity on the physiological attributes in common reed, Phragmites australis (Cav.) Trin. ex Steudel. Plants grew optimally under salinity treatment with standard nutrient solution without added salt and at NaCl concentrations up to 100 mM. Applied for 21 days, NaCl-salinity (300 and 500 mM) caused a significant reduction in growth allocation of all different tissues of P. australis. Shoot growth of reed plants displayed a highly significant correlation with plant–water relations and photosynthetic parameters. The net photosynthetic rate and stomatal conductance of reed plants treated with NaCl-salinity at varying osmotic potential (ψ_π) of nutrient solutions were positively correlated, and the former variable also had a strong positive relationship with transpiration rate. Leaf water potential and ψ_π followed similar trends and declined significantly as ψ_π of watering solutions was lowered. The increase in total inorganic nutrients resulting from increased Na⁺ and Cl⁻ in all tissues and K⁺, Ca²⁺ and Mg²⁺ concentrations were maintained even at the most extreme salt concentration. Common reed exhibited high K⁺/Na⁺ and Ca²⁺/Na⁺ selectivity ratios over a wide range of salinities under NaCl-salinity. These findings suggest that reed plants were able to adapt well to high salinities by lowering their leaf ψ_π and the adjustment of osmotically active solutes in the leaves.     

Osmotic and ionic effects of NaCl and Na2SO4 salinity on Phragmites australis

Osmotic and ion-specific effects of NaCl and Na₂SO₄ on Phragmites australis (Cav.) Trin ex. Steud. were investigated in a laboratory experiment by examining effects of iso-osmotic solutions of NaCl and Na₂SO₄ on growth, osmolality of cell sap, proline content, elemental composition and gas exchange. Plants were supplied with a control standard nutrient solution (Ψ = −0.09 MPa) or solutions of NaCl or Na₂SO₄ at water potentials of −0.50, −1.09 or −1.74 MPa. Salt treatments increased root concentrations of Na and S or Cl, whereas P. australis had efficient mechanisms for exclusion of Na and S and partly Cl ions from the leaves. Incomplete exclusion of Cl from the leaves may affect aboveground biomass production, which was significantly more reduced by NaCl than Na₂SO₄. Stomatal conductance was negatively influenced by decreasing water potentials caused by NaCl or Na₂SO₄, implying that a non-significant photosynthetic depression observed in plants grown at −1.74 MPa was mainly due to osmotically induced stomatal closure. This was supported by decreasing internal CO₂ concentrations. Saline conditions increased the intrinsic water use efficiency and did not alter photosynthetic parameters derived from light response curves, supporting the assumption of a well-functioning CO₂ utilization in salt stressed plants. The leaf proline concentration increased equally in NaCl and Na₂SO₄-treated plants, and may play an important role as a compatible organic solute. P. australis possesses a range of mechanisms conferring tolerance to both NaCl and Na₂SO₄ stress and except in terms of growth the phytotoxicity of NaCl and Na₂SO₄ are comparable.     

Effect of high salinity on Atriplex portulacoides: Growth,leaf water relations and solute accumulation in relation with osmotic adjustment

Atriplex (Halimione) portulacoides is a halophyte with potential interest for saline soil reclamation and phytoremediation. Here, we assess the impact of salinity reaching up to two-fold seawater concentration (0–1000 mM NaCl) on the plant growth, leaf water status and ion uptake and we evaluate the contribution of inorganic and organic solutes to the osmotic adjustment process. A. portulacoides growth was optimal at 200 mM NaCl but higher salinities (especially 800 and 1000 mM NaCl) significantly reduced plant growth. Na⁺ and Cl⁻ contents increased upon salt exposure especially in the leaves compared to the roots. Interestingly, no salt-induced toxicity symptoms were observed and leaf water content was maintained even at the highest salinity level. Furthermore, leaf succulence and high instantaneous water use efficiency (WUE_i) under high salinity significantly contributed to maintain leaf water status of this species. Leaf pressure–volume curves showed that salt-challenged plants adjusted osmotically by lowering osmotic potential at full turgor (Ψ_π¹⁰⁰) along with a decrease in leaf cell elasticity (values of volumetric modulus elasticity (ε) increased). As a whole, our findings indicate that A. portulacoides is characterized by a high plasticity in terms of salt-response. Preserving leaf hydration and efficiently using Na⁺ for the osmotic adjustment especially at high salinities (800–1000 mM NaCl), likely through its compartmentalization in leaf vacuoles, are key determinants of such a performance. The selective absorption of K⁺ over Na⁺ in concomitance with an increase in the K⁺ use efficiency also accounted for the overall plant salt tolerance.     

Cloning and functional analysis of the K+ transporter, PhaHAK2, from salt-sensitive and salt-tolerant reed plants

We isolated PhaHAK2 cDNAs from salt-tolerant and salt-sensitive reed plants. PhaHAK2 belongs to group II by phylogenetic analysis, and was predicted to be a high-affinity plasma membrane K⁺ transporter. Yeast transformed with the PhaHAK2-u from salt-sensitive reed plants (Phragmites australis) had a decreased ability to take up K⁺ in the presence of NaCl and showed a higher Na⁺ permeability than yeast transformed with PhaHAK2-n or PhaHAK2-e from two salt-tolerant reed plants. These results suggest a possibility that the continuous K⁺ uptake by PhaHAK2 and maintenance of high K⁺/Na⁺ ratio under salt stress condition is one of the causes of the salt-tolerance in reed plants.     

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.     

Intrinsic water use efficiency controls the adaptation to high salinity in a semi-arid adapted plant,henna (Lawsonia inermis L.)

Adaptation to salinity of a semi-arid inhabitant plant, henna, is studied. The salt tolerance mechanisms are evaluated in the belief that gas exchange (water vapor and CO₂) should play a key role on its adaptation to salt stress because of the strong evaporation conditions and soil water deficit in its natural area of distribution. We grow henna plants hydroponically under controlled climate conditions and expose them to control (0 mM NaCl), and two levels of salinity; medium (75 mM NaCl) and high (150 mM NaCl). Relative growth rate (RGR), biomass production, whole plant and leaf structure and ultrastructure adaptation, gas exchange, chlorophyll fluorescence, nutrients location in leaf tissue and its balance in the plant are studied. RGR and total biomass decreased as NaCl concentration increased in the nutrient solution. At 75 mM NaCl root biomass was not affected by salinity and RGR reached similar values to control plants at the end of the experiment. At this salinity level henna plant responded to salinity decreasing shoot to root ratio, increasing leaf specific mass (LSM) and intrinsic water use efficiency (iWUE), and accumulating high concentrations of Na⁺ and Cl⁻ in leaves and root. At 150 mM NaCl growth was severely reduced but plants reached the reproductive phase. At this salinity level, no further decrease in shoot to root ratio or increase in LSM was observed, but plants increased iWUE, maintaining water status and leaf and root Na⁺ and Cl⁻ concentrations were lower than expected. Moreover, plants at 150 mM NaCl reallocated carbon to the root at the expense of the shoot. The effective PSII quantum yield [Y(II)] and the quantum yield of non-regulated energy dissipation [Y(NO)] were recovered over time of exposure to salinity. Overall, iWUE seems to be determinant in the adaptation of henna plant to high salinity level, when morphological adaptation fails.     

Melilotus indicus (L.) All., a salt-tolerant wild leguminous herb with high potential for use as a forage crop in salt-affected soils

Previously unexploited legume species may offer utilization potential where environmental stresses constrain the use of more conventional forage crops. Melilotus indicus (L.) All., Yellow sweet clover, occurs as a weed in different habitats in Egypt. It grows in moderately saline areas, where traditional forage legumes cannot be cultivated. Our extensive field studies have recorded the species in many different habitats ranging from healthy agricultural lands to abandoned saline areas. The studied plants maintained high nodulation capacity (68 – 95%) and nitrogenase activities (about 1.81 μmol C₂H₄ plant⁻¹ h⁻¹) in different habitats. Greenhouse experiments demonstrated that seed germination was maintained at 80% when growing on substrats containing 200 mM NaCl and that 25% of the germination capability was preserved when 300 mM NaCl was added to the growth medium. The growth rate of seedlings was not significantly affected by 200 mM NaCl but was reduced by 30% under 300 mM NaCl. It is supposed that M. indicus uses a salt inclusion mechanism for maintaining growth under saline conditions, as it accumulated high amounts of Na⁺ and Cl⁻ ions. Leaf succulence and indices of leaf water status did not differ among the salt treatments, whereas relative water content was reduced by only 3% and water content at saturation increased by about 14% at high salt concentrations in the growing medium. Our results suggest recommending the cultivation of M. indicus in salt-affected soils, which are widespread and pose a problem for the farmers of Egypt and other countries in the world's arid belt.     

Abscisic acid root and leaf concentration in relation to biomass partitioning in salinized tomato plants

Salinization is one of the most important causes of crop productivity reduction in many areas of the world. Mechanisms that control leaf growth and shoot development under the osmotic phase of salinity are still obscure, and opinions differ regarding the Abscisic acid (ABA) role in regulation of biomass allocation under salt stress. ABA concentration in roots and leaves was analyzed in a genotype of processing tomato under two increasing levels of salinity stress for five weeks: 100 mM NaCl (S10) and 150 mM NaCl (S15), to study the effect of ABA changes on leaf gas exchange and dry matter partitioning of this crop under salinity conditions. In S15, salinization decreased dry matter by 78% and induced significant increases of Na⁺ and Cl⁻ in both leaves and roots. Dry matter allocated in different parts of plant was significantly different in salt-stressed treatments, as salinization increased root/shoot ratio 2-fold in S15 and 3-fold in S15 compared to the control. Total leaf water potential (Ψ_w) decreased from an average value of approximately −1.0 MPa, measured on control plants and S10, to −1.17 MPa in S15. In S15, photosynthesis was reduced by 23% and stomatal conductance decreased by 61%. Moreover, salinity induced ABA accumulation both in tomato leaves and roots of the more stressed treatment (S15), where ABA level was higher in roots than in leaves (550 and 312 ng g⁻¹ fresh weight, respectively). Our results suggest that the dynamics of ABA and ion accumulation in tomato leaves significantly affected both growth and gas exchange-related parameters in tomato. In particular, ABA appeared to be involved in the tomato salinity response and could play an important role in dry matter partitioning between roots and shoots of tomato plants subjected to salt stress.     

Effectiveness of potassium sulfate in mitigating salt-induced adverse effects on different physio-biochemical attributes in sunflower (Helianthus annuus L.)

To assess whether foliar application of K+S as potassium sulfate (K₂SO₄) could alleviate the adverse effects of salt on sunflower (Helianthus annuus L. cv. SF-187) plants, a greenhouse experiment was conducted. There were two NaCl levels (0 and 150 mM) applied to the growth medium and six levels of K+S as K₂SO₄ (NS (no spray), WS (spray of water+0.1% Tween 20 solution), 0.5% K+0.21% S, 1.0% K+0.41% S, 1.5% K+0.62% S, and 2.0% K+0.82% S in 0.1% Tween-20 solution) applied two times foliarly to non-stressed and salt-stressed sunflower plants. Salt stress markedly repressed the growth, yield, photosynthetic pigments, water relations and photosynthetic attributes, quantum yield (F_v/F_m), leaf and root K⁺, Mg²⁺, P, Ca²⁺, N as well as K⁺/Na⁺ ratios, while it enhanced the cell membrane permeability, and leaf and root Na⁺ and Cl⁻ concentrations. Foliar application of potassium sulfate significantly improved growth, achene yield, photosynthetic and transpiration rates, stomatal conductance, water use efficiency, leaf turgor and enhanced shoot and leaf K⁺ of the salt-stressed sunflower plants, but it did not improve leaf and root Na⁺, Cl⁻, Mg²⁺, P, Ca²⁺, N as well as K⁺/Na⁺ ratios. The most effective dose of K+S for improving growth and achene yield was found to be 1.5% K+0.62% S and 1% K+0.41% S, respectively. Improvement in growth of sunflower plants due to exogenously applied K₂SO₄ was found to be linked to enhanced photosynthetic capacity, water use efficiency, leaf turgor and relative water content.     

SOS1 gene overexpression increased salt tolerance in transgenic tobacco by maintaining a higher K(+)/Na(+) ratio

Crop productivity is greatly affected by soil salinity, so improvement in salinity tolerance of crops is a major objective of many studies. We overexpressed the Arabidopsis thaliana SOS1 gene, which encodes a plasma membrane Na⁺/H⁺ antiporter, in tobacco (Nicotiana tabacum cv. Xanthi-nc). Compared with nontransgenic plants, seeds from transgenic tobacco had better germination under 120 mM (mmol L⁻¹) NaCl stress; chlorophyll loss in the transgenic seedlings treated with 360 mM NaCl was less; transgenic tobacco showed superior growth after irrigation with NaCl solutions; and transgenic seedlings with 150 mM NaCl stress accumulated less Na⁺ and more K⁺. In addition, roots of SOS1-overexpressing seedlings lost less K⁺ instantaneously in response to 50 mM NaCl than control plants. These results showed that the A. thaliana SOS1 gene potentially can improve the salt tolerance of other plant species.     

Estimating contribution of anthocyanin pigments to osmotic adjustment during winter leaf reddening

The association between plant water stress and synthesis of red, anthocyanin pigments in leaves has led some plant biologists to propose an osmotic function of leaf reddening. According to this hypothesis, anthocyanins function as a solute in osmotic adjustment (OA), contributing to depression of osmotic potential (Ψ_π) and maintenance of turgor pressure during drought-stressed conditions. Here we calculate the percent contribution of anthocyanin to leaf Ψ_π during OA in two angiosperm evergreen species, Galax urceolata and Gaultheria procumbens. Both species exhibit dramatic leaf reddening under high light during winter, concomitant with declines in leaf water potential and accumulation of solutes. Data previously published by the authors on osmotic potential at full turgor (Ψ_π,100) of G. urceolata and G. procumbens leaves before and after leaf reddening were used to estimate OA. In vivo molar concentrations of anthocyanin, glucose, fructose, and sucrose measured from the same individuals were converted to pressure equivalents using the Ideal Gas Law, and percent contribution to OA was estimated. Estimated mean OA during winter was −0.7 MPa for G. urceolata and −0.8 MPa for G. procumbens. In vivo concentrations of anthocyanin (3–10 mM) were estimated to account for ∼2% of OA during winter, and comprised <0.7% of Ψ_π,100 in both species. Glucose, fructose, and sucrose combined accounted for roughly 50 and 80% of OA for G. urceolata and G. procumbens, respectively, and comprised ∼20% of Ψ_π,100. We observed that a co-occurring, acyanic species (Vinca minor) achieved similar OA without synthesizing anthocyanin. We conclude that anthocyanins represent a measurable, albeit meager, component of OA in red-leafed evergreen species during winter. However, due to their low concentrations, metabolic costliness relative to other osmolytes, and striking red color (unnecessary for an osmotic function), it is unlikely that they are synthesized solely for an osmoprotectant role.     

Application of a multi-cylinder evapotranspirometer method for evapotranspiration measurements in wetlands

This paper introduces a multi-cylinder evapotranspirometer method, which can directly measure evapotranspiration (ET) from emergent plants in different species and states as well as simultaneously measure evaporation (E_W) from an open water surface. Values of daily ET from three contrasting reed (Phragmites australis) stands, with different leaf area indexes (LAI), were obtained through in situ measurements of the Baiyangdian wetland using this method during the growing seasons in 2008 and 2009. The results showed that the ET rate of the reed belt was very high, even exceeding 20 mm d⁻¹ under extreme weather conditions. Depending on the LAI change, the annual ET from the different reed canopies ranged from 970 to 2035 mm, whereas the ET/E_W ratios ranged from 2.05 to 3.98. Accuracy analysis results showed that the errors of the measurement from this method were no more than 2 mm. The relative errors of the measurement were correspondingly from 0.04% to 0.33%. It is indicated that the accuracy of our measurement is good enough for the requirements of the ET measurement.     

The ectomycorrhizal fungus (Paxillus involutus) modulates leaf physiology of poplar towards improved salt tolerance

Ectomycorrhizas (EMs) are mutualistic associations between soil fungi and plant roots. Although the physical interaction occurs only in roots, mycorrhizas may alter the physiology of the whole plant, resulting in changes in host responses to abiotic stress. To elucidate the influence of an ectomycorrhizal fungus on leaf physiology and performance under salt stress, we analysed the levels of nutrient elements, phytohormones, carbohydrates, amino compounds and fatty acids in leaves of Populus × canescens. The poplars were cultivated either in the presence or absence of Paxillus involutus and either with or without salt stress imposed by 150 mM NaCl. Leaves of ectomycorrhizal plants displayed higher quantum yield of photochemistry (Φ_PSII), increased concentrations of phosphorus and potassium, decreased concentrations of galactose, increased concentrations of the stress metabolite γ-amino butyric acid and a lower unsaturated-to-saturated fatty acid ratios than those of non-ectomycorrhizal plants. Salt exposure of P. × canescens led to leaf chlorosis and shedding, decreases in Φ_PSII, K⁺-to-Na⁺ ratio, 9Z-hexadecenoic acid, 9Z-octadecenoic acid and unsaturated-to-saturated fatty acid ratio, and increases in ABA, glucose, fructose and some amino compounds. Under salinity leaves of ectomycorrhizal plants showed an alleviation of leaf chlorosis, improved water status, higher Φ_PSII and K⁺-to-Na⁺ ratio, less accumulation of major amino compounds and lower unsaturated-to-saturated fatty acid ratios than those of non-mycorrhizal plants. These results indicate that ectomycorrhizas attenuate salinity induced injury in leaves of P. × canescens, which may be ascribed to the improved nutrient status, osmo-regulation and changes in fatty acid composition in leaves of ectomycorrhizal plants.     

The ecological adaptability of <Emphasis Type="Italic">Phragmites australis</Emphasis> to interactive effects of water level and salt stress in the Yellow River Delta

Soil salinity and waterlogging are two major environmental problems in estuarine wetlands. To prevent the typical wetland plants from degradation by soil salinization and salt waterlogging and more effectively use the plants to provide wetland ecosystem services, we examined the ecological adaptability of Phragmites australis, a characteristic plant species in the Yellow River Delta, to the interactive effects of water level and salt stress. The results showed that P. australis adapts to salt and water table stressed environments through slowing down the growth rate, maintaining the tiller number, and adjusting the biomass allocation of different organs. The highest plant height and the largest leaf area were at 0 cm water table treatment; the 0.5 % NaCl treatment increased the aboveground biomass; higher water table increased the fibrous root biomass allocation, but largely decreased the leaf biomass. The exclusion of toxic inorganic ions such as Na⁺ and Cl^? and the accumulation of organic solutes are also important mechanisms to aid survival in saline wetlands. On average 35.1 % of Cl^? and 53.9 % of Na⁺ accumulated in belowground organs. The study could provide fundamental guidance for wetland restoration projects and wetland sustainable use in coastal zones such as the Yellow River Delta.     

Sodium,potassium, chloride and proline concentrations of chloroplasts isolated from a halophyte,Mesembryanthemum crystallinum L.

Concentrations of four major solutes (Na⁺, K⁺, Cl^-, proline) were determined in isolated, intact chloroplasts from the halophyte Mesembryanthemum crystallinum L. following long-term exposure of plants to three levels of NaCl salinity in the rooting medium. Chloroplasts were obtained by gentle rupture of leaf protoplasts. There was either no or only small leakage of inorganic ions from the chloroplasts to the medium during three rapidly performed washing steps involving precipitation and re-suspension of chloroplast pellets. Increasing NaCl salinity of the rooting medium resulted in a rise of Na⁺ und Cl^- in the total leaf sap, up to approximately 500 and 400 mM, respectively, for plants grown at 400 mM NaCl. However, chloroplast levels of Na⁺ und Cl^- did not exceed 160–230 and 40–60 mM, respectively, based upon a chloroplast osmotic volume of 20–30 l per mg chlorophyll. At 20 mM NaCl in the rooting medium, the Na⁺/K⁺ ratio of the chloroplasts was about 1; at 400 mM NaCl the ratio was about 5. Growth at 400 mM NaCl led to markedly increased concentrations of proline in the leaf sap (8 mM) compared with the leaf sap of plants grown in culture solution without added NaCl (proline 0.25 mM). Although proline was fivefold more concentrated in the chloroplasts than in the total leaf sap of plants treated with 400 mM NaCl, the overall contribution of proline to the osmotic adjustment of chloroplasts was small. The capacity to limit chloroplast Cl^- concentrations under conditions of high external salinity was in contrast to an apparent affinity of chloroplasts for Cl^- under conditions of low Cl^- availability.Abbreviation Chl chlorophyll     

Salt-tolerant reed plants contain lower Na<Superscript>+</Superscript> and higher K<Superscript>+</Superscript> than salt-sensitive reed plants

Reed plants (Phragmites australis Trinius) grow not only in fresh and brackish water areas but also in arid and high salinity regions. Reed plants obtained from a riverside (Utsunomiya) were damaged by 257 mM NaCl, whereas desert plants (Nanpi) were not. When the plants were grown under salt stress, the shoots of the Utsunomiya plants contained high levels of sodium and low levels of potassium, whereas the upper part of the Nanpi plants contained low levels of sodium and high levels of potassium. One month salt stress did not affect potassium contents in either Utsunomiya or Nanpi plants, but it did dramatically increase sodium contents only in the Utsunomiya plants. The ratio of K⁺ to Na⁺ was maintained at a high level in the upper parts of the Nanpi plants, whereas the ratio markedly decreased in the Utsunomiya plants in the presence of NaCl. Accumulation of Na⁺ in the roots and Na⁺ efflux from the roots were greater in the Nanpi plants than in the Utsunomiya plants. These results suggest that the salt tolerance mechanisms of Nanpi reed plants include an improved ability to take up K⁺ to prevent an influx of Na⁺ and an improved ability to exclude Na⁺ from the roots.     

Changes in leaf gas exchange, water relations, biomass production and solute accumulation in Phragmites australis under hypoxic conditions

The physiological responses to hypoxic stress were studied in the common reed, Phragmites australis (Cav.) Trin. ex Steudel. Growth, leaf gas exchange, water (and ion) relations and osmotic adjustment were determined in hydroponically grown plants exposed to 10, 20 and 30 days of oxygen deficiency. The highest growth of reed seedlings was found in normoxic (aerobic) conditions. Treatment effects on biomass production were relatively consistent within each harvest. Leaf water potential and osmotic potential declined significantly as hypoxia periods increased. However, leaf turgor pressure showed a consistent pattern of increase, suggesting that reed plants adjusted their water status by osmotic adjustment in response to root hypoxia. After 20 and 30 days in the low oxygen treatment, net CO₂ assimilation and stomatal conductance were positively associated and the former variable also had a strong positive relationship with transpiration. Short-term hypoxic stress had a slight effect on the ionic status (K⁺, Ca²⁺ and Mg²⁺) of reed plants. In contrast, soluble sugar concentrations increased more under hypoxic conditions as compared to normoxia. These findings indicate that hypoxia slightly affected the physiological behavior of reed plants.     

Fatty acid composition of lipids in vegetative organs of the halophyte Suaeda altissima under different levels of salinity

Qualitative and quantitative composition of fatty acids (FA) in the lipids of vegetative organs of the halophyte Suaeda altissima (L.) Pall. grown at different NaCl concentrations in nutrient solution was studied. Along with this, the biomass of these organs, the content of water and Na⁺, Cl^?, and K⁺ ions in them, and the ultrastructure of root and leaf cells were determined. At both low (1 mM) and high (750 mM) NaCl concentrations in nutrient solution, plants could maintain growth and water content in organs, demonstrating a noticeable increase in the dry weight and a slight increase in the water content at 250 mM NaCl. At all NaCl concentrations in nutrient solution, S. altissima tissues contained a relatively high K⁺ amount. Under salinity, Na⁺ and Cl^? ions contributed substantially into the increase in the cell osmotic pressure, i.e., a decrease in their water potential; in the absence of salinity, K⁺ fulfilled this function. In the cells of both roots and leaves, NaCl stimulated endo- and exocytosis, supposedly involved in the vesicular compound transport. 750 mM NaCl induced plasmolysis and changes in the membrane structure, which can be interpreted as degradation processes. Under optimal NaCl concentration in medium (250 mM), the content of lipids in plant aboveground organs per fresh weight was more than 2.5-fold higher than under 1 or 750 mM NaCl, whereas in the roots opposite patten was observed. When plants were grown under non-optimal conditions, substantial changes occurred in the qualitative and quantitative FA composition in lipids of both aboveground organs and roots. Observed changes are discussed in relation to processes underlying S. altissima salt tolerance and those of disintegration occurring at the high external NaCl concentration (750 mM).