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     

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     

Physiological responses in two populations of Andropogon glomeratus Walter B.S.P. to short-term salinity

Summary Andropogon glomeratus is a C₄ nonhalophytic grass which exhibits population differentiation for tolerance to short-term salinity exposure. To investigate possible physiological mechanisms whch enable salt-tolerant individuals to survive short-term inundation, gas exchange and water relations parameters were measured before and during a 5-day watering treatment of half-strength synthetic seawater in plants from a tolerant and a non-tolerant population. Photosynthetic recovery was followed for 10 days after the salinity treatment. Photosynthetic CO₂ uptake was substantially inhibited in both populations. Stomatal conductances decreased and intercellular CO₂ concentrations increased, indicating non-stomatal factors were primarily responsible for the decrease in CO₂ uptake. After termination of the salinity treatment photosynthetic capacity increased more rapidly in the tolerant population and reached the pretreatment level after 6 days, whereas the nontolerant population did not recover fully after 10 days. A-Ci curves measured before and after the salinity treatment indicated a decrease in the carboxylation efficiency, and suggested a proportionately greater metabolic inhibition relative to the increase in the stomatal limitation. Osmotic adjustment occurred in a 2-day period in the tolerant population, but there was no change in the osmotic potentials or the water potential at the point of turgor loss in the nontolerant population. Thus short-term salt tolerance in the marsh population is associated with rapid osmotic adjustment and recovcry of photosynthetic capacity shortly after the end of the salinity exposure, rather than maintenance of greater photosynthesis during the salinity treatment.     

Characterization of esophageal desalination in the seawater eel,Anguilla japonica

To characterize mechanisms of esophageal desalination, osmotic water permeability and ion fluxes were measured in the isolated esophagus of the seawater eel. The osmotic permeability coefficient in the seawater eel esophagus was 2·10^-4 cm·s^-1. This value was much lower than those in tight epithelial, although the eel esophagus is a leaky epithelium with a tissue resistance of 77 ohm·cm^-2. When the esophagus was bathed in normal Ringer solutions on both sides no net ion and water fluxes were observed. However, when mucosal NaCl concentration was increased by a factor of 3, Na⁺ und Cl^- ions were transferred from mucosa to serosa (desalination). If only Na⁺ or Cl^- concentration in the mucosal fluid was increased by a factor of 3, net Na⁺ and Cl^- fluxes were reduced to 30–40%, indicating that 60–70% of the net Na⁺ and Cl^- fluxes are coupled mutually. The coupled NaCl transport seems to be effective in desalting the luminal high NaCl. The remaining 30–40% of the total Na⁺ and Cl^- fluxes seems to be due to a simple diffusion, because these components are independent of each other and follow their electrochemical gradients, and also because these fluxes remain even after treatment with NaCN or ouabain. A half of the coupled NaCl transport could be explained by a Na⁺/H⁺–Cl^-/HCO ₃ ^- double exchanger on the apical membrane of the esophageal epithelium, because mucosal amiloride and 4.4-diisothiocyanatostilbene-2,2-disulphonic acid inhibited the net Na⁺ and Cl^- fluxes by approximately 30%. The other half of the coupled NaCl transport, which follows their electrochemical gradients, still remains to be explained.Abbreviations DIDS 4,4-diisothiocyanatostilbene-2,2-disulphonic acid - NMDG N-methyl-d-glucosamine - P _Cl Cl^- permeability coefficient - PD transepithelial potential difference - P _Na Na⁺ permeability coefficient - P _osm osinotic permeability coefficient - TALH thick ascending limb of Henle's loop     

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.     

油菜素内酯对盐渍下油菜幼苗生长的调控效应及其生理机制

为了探讨油菜素内酯对植物耐盐性的调控,以甘蓝型油菜"南盐油1号"为试验材料,研究了外源24-表油菜素内酯(24-EBL)对100、200 mmol/L Na Cl胁迫下油菜幼苗干重(DW)、相对含水量(RWC)、渗透调节能力(OAA)、叶片气体交换参数、气孔限制值(Ls)等的调节效应,还测定了不同器官的Na+、K+、Cl-含量,并计算各器官的K+/Na+和SK,Na。结果表明:(1)在不同浓度的盐胁迫下,油菜幼苗DW显著下降,胁迫下外源喷施10-12、10-10、10-8、10-6mol/L 24-EBL作用下,油菜植株干重均不同程度的上升,且植株干重都在10-10mol/L 24-EBL(EBL2)处理下达到最大值,分别比100、200 mmol/L Na Cl胁迫下增加29%和20%。与对照相比,非盐胁迫下外源喷施10-12、10-10、10-8、10-6mol/L 24-EBL,油菜幼苗植株干重与对照相比均无显著变化。(2)不同Na Cl浓度胁迫下,油菜叶片的RWC显著下降,外施EBL2可显著提高油菜叶片的RWC和OAA。(3)不同浓度Na Cl胁迫下,油菜幼苗叶片净光合速率(Pn)、气孔导度(Gs)、胞间CO2浓度(Ci)和蒸腾速率(Tr)均不同程度下降,而Ls显著上升,而外喷EBL2可不同程度的提高Pn、Gs、Ci、Tr,降低Ls。(4)与对照相比,Na Cl胁迫下油菜幼苗叶片、叶柄和根的Na+和Cl-含量均显著上升,Na Cl浓度愈高,Na+和Cl-含量上升愈显著。而K+含量均下降,外源EBL2可显著降低幼苗各器官的Na+和Cl-含量,对幼苗叶片K+含量没有影响,但提高了叶柄和根中的K+含量。上述表明,合适浓度的24-EBL外喷可明显提高油菜的耐盐水平,且不同浓度Na Cl胁迫下,最适24-EBL浓度均为10-10mol/L。主要是因为外源喷施24-EBL能显著改善离子稳态和渗透调节能力,从而改善盐胁迫下油菜幼苗的光合作用、水分状况,提高其耐盐性。而24-EBL对盐处理下油菜植株气孔限制的显著改善是其促进其光合、水分利用的重要原因,也是其对100 mmol/L Na Cl处理的油菜生长调控效果优于200 mmol/L Na Cl处理的重要原因之一。结果还显示,在叶片中,24-EBL外施可通过排Na+和Cl-来维持植株离子稳态,而对K+影响不大;在根、茎中可通过排Na+、排Cl-、吸K+维持稳态。     

Effects of root-zone solutes on Eucalyptus camaldulensis and Eucalyptus bicostata seedlings: Responses to Na+, Mg2+ and Cl-

Specific-ion effects in salt-treated eucalypts were examined with two species known to differ in salt tolerance viz. E. camaldulensis (more tolerant) and E. bicostata (less tolerant). Sand-cultured plants were irrigated with different nutrient solutions designed to impose either osmotic stress (concentrated macronutrients with balanced cations and anions) or specific ion stress from either NaCl or MgCl₂, or from nutrient solutions rich in particular ions viz. Na⁺, Mg²⁺ and Cl^- (balancing counter ions were provided in all cases). Half-strength Hoagland nutrient solution served as control. All treatments were applied at osmotic pressures of approximately 0.52 MPa by appropriate concentrations of each solution. In general, salt-induced growth reductions were greater for E. camaldulensis than for E. bicostata, although E. camaldulensis showed strongest exclusion of Na⁺, Mg²⁺ and Cl^- from shoots. Application of NaCl and concentrated macronutrients resulted in similar growth reductions. E. bicostata seedlings exposed to high Cl^- concentrations in the presence of Mg²⁺ and concentrated cations suffered significantly more shoot and root reduction than those exposed to other salts. Treatment with solution rich in Cl^- resulted in extensive leaf damage, which suggested that Cl^- may have exerted a specific effect. No specific Na⁺ effect was observed for either species, even though shoot Na⁺ concentrations were considerably higher for E. bicostata than for E. camaldulensis. Root growth was considerably less for plants treated with Mg²⁺ salts and this effect was associated with low root Ca²⁺ concentrations.     

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.     

Leaf gas exchange,water relations,nutrient content and growth in citrus and olive seedlings under salinity

The effects of salinity on growth, leaf nutrient content, water relations, gas exchange parameters and chlorophyll fluorescence were studied in six-month-old seedlings of citrus (Citrus limonia Osbeck) and rooted cuttings of olive (Olea europaea L. cv. Arbequina). Citrus and olive were grown in a greenhouse and watered with half strength Hoagland’s solution plus 0 or 50 mM NaCl for citrus, or plus 0 or 100 mM NaCl for olive. Salinity increased Cl⁻ and Na⁺ content in leaves and roots in both species and reduced total plant dry mass, net photosynthetic rate and stomatal conductance. Decreased growth and gas exchange was apparently due to a toxic effect of Cl⁻ and/or Na⁺ and not due to osmotic stress since both species were able to osmotically adjust to maintain pressure potential higher than in non-salinized leaves. Internal CO₂ concentration in the mesophyll was not reduced in either species. Salinity decreased leaf chlorophyll a content only in citrus.     

Solute Accumulation in Tobacco Cells Adapted to NaCl

Cells of Nicotiana tabacum L. var Wisconsin 38 adapted to NaCl (up to 428 millimolar) which have undergone extensive osmotic adjustment accumulated Na⁺ and Cl⁻ as principal solutes for this adjustment. Although the intracellular concentrations of Na⁺ and Cl⁻ correlated well with the level of adaptation, these ions apparently did not contribute to the osmotic adjustment which occurred during a culture growth cycle, because the concentrations of Na⁺ and Cl⁻ did not increase during the period of most active osmotic adjustment. The average intracellular concentrations of soluble sugars and total free amino acids increased as a function of the level of adaptation; however, the levels of these solutes did not approach those observed for Na⁺ and Cl⁻. The concentration of proline was positively correlated with cell osmotic potential, accumulating to an average concentration of 129 millimolar in cells adapted to 428 millimolar NaCl and representing about 80% of the total free amino acid pool as compared to an average of 0.29 millimolar and about 4% of the pool in unadapted cells. These results indicate that although Na⁺ and Cl⁻ are principal components of osmotic adjustment, organic solutes also may make significant contributions.     

Changes in growth and water-soluble solute concentrations in Sorghum bicolor stressed with sodium and potassium salts

Sorghum bicolor L. Moench, RS 610, was grown in liquid media salinized with NaCl, KCl, Na₂SO₄, K₂SO₄ or with variable mixtures of either NaCl/KCl or Na₂SO₄/K₂SO₄ at osmotic potentials ranging from 0 to -0.8 MPa. The purpose was to study the effects of different types and degrees of salinity in growth media on growth and solute accumulation. In 14-day-old plants the severity of leaf growth inhibition at any one level of osmotic potential in the medium increased according to the following order: NaCl < Na₂SO₄ < KCl = K₂SO₄. Inhibition of growth by mixtures of Na⁺ and K⁺ salts was the same as by K⁺ salts alone. Roots responded differently. Root growth was not affected by Na⁺ salts in the range of 0 to -0.2 MPa while it was stimulated by K⁺ salts. The major cation of leaves was K⁺ because S. bicolor is a Na⁺-excluder, while Na⁺ was the major cation in roots except at low Na⁺/K⁺ ratios in media. Anions increased in tissues linearly in relation to total monovalent cation, but not with a constant anion/cation ratio. This ratio increased as the cation concentrations in tissues increased. Sucrose in leaf tissue increased 75 fold in Chloride-plants (plants growing in media in which the only anion of the salinizing salts was Cl^?) and 50 fold in Sulphate-plants (the only anion of the salinizing salts was SO₄^2-). Proline increased 60 and 18 fold in Chloride- and Sulphate-plants, respectively, as growth media potentials decreased from 0 to -0.8 MPa. The concentrations of both sucrose and proline were directly proportional to the amount of total monovalent cation in the tissue. Sucrose concentrations began increasing when total monovalent cations exceeded 100 μmol (g fresh weight)^?1 (the monovalent cation level in non-stressed plants), but proline did not start accumulating until monovalent cation concentrations exceeded 200 μmol (g fresh weight)^?1. Therefore, sucrose seemed to be the solute used for osmotic adjustment under mild conditions of saline stress while proline was involved in osmotic adjustment under more severe conditions of stress. Concentrations of inorganic phosphate, glucose, fructose, total amino acids and malic acid fluctuated in both roots and leaves in patterns that could be somewhat correlated with saline stress and, sometimes, with particular salts in growth media. However, the changes measured were too small (at most a 2–3 fold increase) to be of importance in osmotic adjustment.     

Combined effect of NaCl-salinity and hypoxia on growth,photosynthesis, water relations and solute accumulation in Phragmites australis plants

Aim of the present study was to investigate the effects of two key environmental factors of estuarine ecosystems, salinity and hypoxia, on the physiological attributes in reed plants (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 hypoxia at varying NaCl-salinity concentrations (0, 50, 100, and 200 mM). Plants grew well under hypoxia treatment with standard nutrient solution without added salt and at NaCl concentrations up to 100 mM. Reed plants were able to produce and allocate phytomass to all their organs even at the highest salt level (200 mM NaCl). In plants subjected to hypoxia at various water potentials no clear relationships were found between growth and photosynthetic parameters except for g_s, whereas growth displayed a highly significant correlation with plant–water relations. A and g_s of reed plants treated with hypoxia at varying water potential of nutrient solutions were positively correlated and the former variable also had a strong positive relationship with E. Leaf Ψ_w and Ψ_π followed a similar trend and declined significantly as water potential of watering solutions was lowered. Highly significant positive correlations were identified between leaf Ψ_w and photosynthetic parameters. At all NaCl concentrations, the increase in total inorganic ions resulted from increased Na⁺ and Cl⁻ while K⁺, Ca²⁺, and Mg²⁺ concentrations decreased with increasing osmolality of nutrient solutions. Common reed has an efficient mechanism of Na⁺ exclusion from the leaves and exhibited a high leaf K⁺/Na⁺ selectivity ratio over a wide range of salinities under hypoxia treatment. In Phragmites australis grown in 200 mM NaCl, K⁺ contributed 17% toΨ_π, whereas Na⁺ and Cl⁻ accounted for only 11% and 6%, respectively. At the same NaCl concentration, the estimated contribution of proline to Ψ_π was less than 0.2%. Changes in leaf turgor occurred with a combined effect of salinity and hypoxia, suggesting that reed plants could adjust their water status sufficiently.     

Effects of salinity on uptake and distribution of Na+, Cl- and K+ in two wheat cultivars

Plants of two wheat (Triticum aestivum L.) cultivars differing in salt tolerance were grown in sand with nutrient solutions. 35-d-old plants were subjected to 5 levels of salinity created by adding NaCl, CaCl₂ and Na₂SO₄. Growth reduction caused by salinity was accompanied by increased Na⁺ and Cl^- concentrations, Na⁺/K⁺ ratio, and decreased concentration of K⁺. The salt tolerant cv. Kharchia 65 showed better ionic regulation. Salinity up to 15.7 dS m^-1 induced increased uptake of Na⁺ and Cl^- but higher levels of salinity were not accompanied by further increase in uptake of these ions. Observed increases in Na⁺ and Cl^- concentrations at higher salinities seemed to be the consequence of reduction in growth. Uptake of K⁺ was decreased; more in salt sensitive cultivar. This was also accompanied by differences in its distribution.     

Water relations and xylem transport of nutrients in pepper plants grown under two different salts stress regimes

Two iso-osmotic concentrations of NaCl and Na₂SO₄ were used for discriminating between the effects of specific ion toxicities of salt stress on pepper plants (Capsicum annuum L.) grown in hydroponic conditions, in a controlled-environment greenhouse. The two salts were applied to plants at different electrical conductivities, and leaf water relations, osmotic adjustment and root hydraulic conductance were measured. Leaf water potential (_w), leaf osmotic potential (_o) and leaf turgor potential (_p) decreased significantly when EC increased, but the decrease was less for NaCl- than for Na₂SO₄-treated plants. The reduction in stomatal conductance was higher for NaCl-treated plants. There were no differences in the effect of both treatments on the osmotic adjustment, and a reduction in root hydraulic conductance and the flux of solutes into the xylem was observed, except for the saline ions (Na⁺, Cl^– and SO₄ ^2–). Therefore, pepper growth decreased with increasing salinity because the plants were unable to adjust osmotically or because of the toxic effects of Cl^–, SO₄ ^2– and/or Na⁺. However, turgor of NaCl-treated plants was maintained at low EC (3 and 4 dS m^–1) probably due to the maintenance of water transport into the plant (decrease of stomatal conductance), which, together with the lower concentration of Na⁺ in the plant tissues compared with the Na₂SO₄ treatment, could be the cause of the smaller decrease in growth.     

Solutes Involved in Osmotic Adjustment to Increasing Salinity in Suspension Cells of Alternanthera philoxeroides Griseb

Cell recovery from osmotic stress was studied in suspension cell cultures from Alternanthera philoxeroides [Mart.] Griseb. Changes in different classes of cellular solutes were measured after cells were transferred from 0 to 200 mM NaCl (high salt) to obtain an integrated picture of the solute pools involved in osmotic adjustment. By 2 h, cellular [Na⁺] and [Cl⁻] had increased several-fold, potentially accounting for the osmotic adjustment that produced a rapid recovery of cell turgor. There was a four-fold increase in the concentration of quaternary ammonium compounds (QAC) by 12 h and a slower increase for several days afterward. Betaine aldehyde dehydrogenase (BADH) is required for synthesis of glycine betaine, a QAC produced by a range of organisms in response to osmotic stress. Western-blot analysis for BADH suggested that glycine betaine was a significant component of the QAC solutes. The amount of BADH was generally similar at different sampling times for control and high salt cells, unlike previous reports of stimulation by osmotic stress in intact plants of some species. Between 3 and 7 days after cell transfer to high salt, other organic solutes increased in concentration and [Na⁺] and [Cl⁻] decreased. In A. philoxeroides, high [Na⁺] and [Cl⁻] produce rapid osmotic adjustment but organic solutes apparently replace these potentially harmful inorganic ions after the recovery of turgor.     

Stomatal and Nonstomatal Components to Inhibition of Photosynthesis in Leaves of Capsicum annuum during Progressive Exposure to NaCl Salinity

Young bell pepper (Capsicum annuum L.) plants grown in nutrient solution were gradually acclimated to 50, 100, or 150 moles per cubic meter NaCl, and photosynthetic rates of individual attached leaves were measured on several occasions during the salinization period at external CO₂ concentrations ranging from approximately 70 to 1900 micromoles per mole air. Net CO₂ assimilation (A) was plotted against computed leaf internal CO₂ concentration (C_i), and the initial slope of this A-C_i curve was used as a measure of photosynthetic ability. During the 10 to 14 days after salinization began, leaves from plants exposed to 50 moles per cubic meter NaCl showed little change in photosynthetic ability, whereas those treated to 100 or 150 moles per cubic meter NaCl had up to 85% inhibition, with increase in CO₂ compensation point. Leaves appeared healthy, and leaf chlorophyll content showed only a 14% reduction at the highest salinity levels. Partial stomatal closure occurred with salinization, but reductions in photosynthesis were primarily nonstomatal in origin. Photosynthetic ability was inversely related to the concentration of either Na⁺ or Cl⁻ in the leaf laminas sampled at the end of the experimental period. However, the concentration of Cl⁻ expressed on a tissue water basis was greater, exceeding 300 moles per cubic meter, and Cl⁻ was more closely associated (R² = 0.926) with the inhibition of photosynthetic ability. Leaf turgor was not reduced by salinization and leaf osmotic potential decreased to a slightly greater extent than the osmotic potential decreases of the nutrient solutions. Concentration of accumulated Na⁺ and Cl⁻ (on a tissue water basis) accounted quantitatively for maintenance of leaf osmotic balance, assuming that these ions were sequestered in the vacuoles.     

Dried field populations of Nostoc flagelliforme (Cyanophyceae) require exogenous nutrients for their photosynthetic recovery

The effects of nutrients on the photosynthetic recovery of Nostoc flagelliforme during re-hydration were investigated in order to see if their addition was necessary. Net photosynthesis was negligible in distilled water without nutrient-enrichment. Addition of K⁺ resulted in significant enhancement of net photosynthesis, whereas other nutrients (Fe³⁺, Mg²⁺, Na⁺, NO₃ ^-, PO₄ ^3-, Cl^-) and trace-metals (A₅) showed little effect. The recovered net photosynthetic activity increased with the increased K⁺, and reached the maximum at concentrations above 230 μM. Desiccation and re-hydration did not affect the dependence of photosynthetic recovery on K⁺. It was concluded that dried field populations of N. flagelliforme require exogenous addition of potassium for photosynthetic recovery and that growth may be potassium-limited in nature. This revised version was published online in August 2006 with corrections to the Cover Date.     

Interaction between CO2 enrichment and salinity stress in the C4 non-halophyte Andropogon glomeratus (Walter) BSP

Abstract Increasing atmospheric CO₂ may result in alleviation of salinity stress in salt-sensitive plants. In order to assess the effect of enriched CO₂ on salinity stress in Andropogon glomeratus, a C₄ non-halophyte found in the higher regions of salt marshes, plants were grown at 350, 500, and 650 cm³ m^?3 CO₂ with 0 or 100 mol m^?3 NaCl watering treatments. Increases in leaf area and biomass with increasing CO₂ were measured in salt-stressed plants, while decreases in these same parameters were measured in non-salt-stressed plants. Tillering increased substantially with increasing CO₂ in salt-stressed plants, resulting in the increased biomass. Six weeks following initiation of treatments, there was no difference in photosynthesis on a leaf area basis with increasing CO₂ in salt-stressed plants, although short-term increases probably occurred. Stomatal conductance decreased with increasing CO₂ in salt-stressed plants, resulting in higher water-use efficiency, and may have improved the diurnal water status of the plants. Concentrations of Na⁺ and Cl^? were higher in salt stressed-plants while the converse was found for K ⁺. There were no differences in leaf ion content between CO₂ treatments in the salt-stressed plants. Decreases in photosynthesis in salt-stressed plants occurred primarily as a result of decreased internal (non-stomatal) conductance.     

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。     

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.