Effects of NaCl on ion relations and carbohydrate status of roots and on osmotic regulation of roots and shoots of Atriplex amnicola

Abstract Atriplex amnicola was grown at 25, 200 or 400 mol m³ NaCl. Root tissues at different stages of development were investigated for concentrations of K⁺, Na⁺ and Mg²⁺, and in some cases for Cl^?. Sugar and starch concentrations were measured for plants grown at 25 or 400 mol m³ NaCl. In the ‘slightly vaeuolated’ root tips, Na⁺ was only 40 mol m^?3 at an external concentration of 400 mol m^?3 NaCl. The concentrations of K⁺ were not affected substantially by external NaCl between 25 mol m^?3 and 400 mol m^?3. The ‘highly vacuolated’ root tissues had substantially higher concentrations of K⁺, Na⁺ and Cl^? in plants grown at 200 and 400 mol m ³ NaCl than in plants grown at 25 mol m^?3 NaCl. Concentrations of Cr and of the sum of the cations in recently expanded tissue were similar to those in the bulk of the roots, consisting mainly of old cells. However, the K⁺: Na⁺ decreased with age; at 400 mol m^?3 external NaCl with a K⁺: Na⁺ of 0.012, the K⁺: Na⁺ in recently expanded 12 mm root tips was as high as 1.6, compared with 0.7 for the bulk of the roots. These ion data were used to estimate cytoplasmic and vacuolar concentrations of K⁺ and Na ⁺. Such calculations indicated that between 25 mol m³ and 400 mol m^?3 external NaCl the concentration of the sum of (Na⁺+K⁺) in the cytoplasm was maintained at about 180–200 mol m^?3 (cell water basis). In contrast, the (Na⁺+ K⁺) concentration in the vacuole was 170 mol m^?3 for plants grown at 25 mol m^?3 NaCl and 420 mol 400 mol m^?3 NaCl. The expanding root (issues exhibited greatly decreased soluble sugars and starch between dusk and dawn. Ai both times, sugar and starch concentrations in these tissues were 2.5–4.0 times greater in plants grown at 400 mol m^?3 NaCl compared with plants grown at 25 mol m^?3 NaCl. In contrast, carbohydrate concentrations in expanded root tissues were very similar at 25 and 400 mol m^?3 and showed little diurnal fluctuation. This paper considers the causes for the slower growth of A. amnicola at 400 than at 25 mol m”³ NaCl, using the data for the roots described here, and those for the shoots presented in the preceding paper (Aslam et al., 1986). There is no support for possible adverse effects by high internal ion concentrations. Instead, there may be deficiencies in supply of organic solutes for osmotic regulation; during part of the night a limited supply of such solutes may well restrict the rate of expansion of cells in plants growing at 400 mol m^?3 NaCl. There is insufficient evidence to decide whether this limitation in the expanding tissues is particularly prominent for the roots or for the shoots.     

Salt accumulation and depletion in the root-zone of the halophyte Atriplex nummularia Lindl.: influence of salinity,leaf area and plant water use

Background and aims

Salt is known to accumulate in the root-zone of Na⁺ excluding glycophytes under saline conditions. We examined the effect of soil salinity on Na⁺ and Cl^? depletion or accumulation in the root-zone of the halophyte (Atriplex nummularia Lindl).

Methods

A pot experiment was conducted in soil to examine Na⁺ and Cl^? concentrations adjacent to roots at four initial NaCl treatments (20, 50, 200 or 400 mM NaCl in the soil solution). Plant water use was manipulated by leaving plants with all leaves intact, removing approximately 50 % of leaves, or removing all leaves. Daily evapotranspiration was replaced by watering undrained pots to weight with deionised water. After 35-38 days, samples were taken of the bulk soil and of soil loosely- and closely-adhering to the roots.

Results

In plants with leaves intact grown with 200 and 400 mM NaCl, average Na⁺ and Cl^? concentrations in the closely adhering soil were about twice the concentrations of the bulk soil. Ion accumulation increased with final leaf area and with cumulative transpiration over the duration of the trial. By contrast, in plants grown with the lowest salinity treatment (20 mM NaCl), Na⁺ and Cl^? concentrations decreased in the closely adhering soil with increasing leaf area and increasing cumulative water use.

Conclusions

Our data show that Na⁺ and Cl^? are depleted from the root-zone of A. nummularia at low salinity but accumulate in the root-zone at moderate to high salinity, and that the ions are drawn towards the plant in the transpiration stream.     

Changes in ion and water content of individual shoot organs in a salt-tolerant and a salt-sensitive clone of Agrostis stolonifera L. during and subsequent to treatment with sodium chloride

Abstract Individual leaves and stems were analysed for Na⁺, Cl^?, K⁺ and water content in two clones of Agrostis stolonifera differing in salt resistance, during 14 d of treatment with NaCl, 100 and 200 mol m^?3, and a further 7 d in a salt-free medium. Great differences in ion and water content were revealed between individual organs, and organ-by-organ analysis also emphasized the differences between the clones better than whole shoot analysis. In both clones, Na⁺ and Cl^? accumulated to the greatest degree in the older leaves, but for corresponding organs, the concentrations were lower in the more tolerant clone. In the sensitive clone, the lowest leaves dehydrated in 200 mol m^?3 NaCl and failed to recover, while the plants of the more resistant clone maintained viable water content in all organs. In the resistant clone, K⁺ concentration decreased less in response to salt treatment than in the more sensitive clone. For a full appreciation of the plants' reactions, it was found necessary to express the analytical data on several bases, namely, per unit dry-weight, unit water, and total ion-content.     

Differential effects of Na+, Mg2+, K+, Ca2+ and osmotic stress on the wild type and the NaCl-tolerant mutants stl1 and stl2 of Ceratopteris richardii

In order to identify physiological components that contribute to salinity tolerance, we compared the effects of Na⁺, Mg²⁺ and K⁺ salts (NaCl, Na₂SO₄, MgCl₂, MgSO₄, KCl and K₂SO₄), Ca₂₊ (CaSO₄), mannitol and melibiose on the wild type and the single-gene NaCl-tolerant mutants stl1 and stl2 of Ceratopteris richardii. Compared with gametophytic growth of the wild type, stl2 showed a low level of tolerance that was restricted to Na⁺ salts and osmotic stress. stl2 exhibited high tolerance to both Na⁺ and Mg²⁺ salts, as well as to osmotic stress. In response to short-term exposure (3 d) to NaCl, accumulation of K⁺ and Na⁺ was similar in the wild type and stl1. In contrast, stl2 accumulated higher levels of K⁺ and lower levels of Na⁺. Ca²⁺ supplementation (1.0 mol m^?3) ameliorated growth inhibition by Na⁺ and Mg²⁺ stress in wild type and stll, but not in stl2. In addition, under Na⁺ stress (175 mol m^?3) wild-type, stll and stl2 gametopbytes maintained higher tissue levels of K⁺ and lower levels of Na⁺ when supplemented with Ca²⁺ (1.0 mol m^?3). stl2 gametophytes were extremely sensitive to K⁺ supplementation. Growth of stl2 was greater than or equal to that of the wild type at trace concentrations of K⁺ but decreased substantially with increasing K⁺ concentration. Supplementation with K⁺ from 0 to 1.85 mol m^?3 alleviated some of the inhibition by 75 mol m^?3 NaCl in the wild type and in stl1. In stl2, growth at 75 mol m^?3 NaCl was similar at 0 and 1.85 mol m^?3 K⁺ supplementation. Although K⁺ supplementation above 1.85 mol m^?3 did not alleviate inhibition of growth by Na⁺ in any genotype, stl2 maintained greater relative tolerance to NaCl at all K⁺ concentrations tested.     

The Response of Atriplex amnicola to the Interactive Effects of Salinity and Hypoxia

The growth of Atriplex amnicola, its water and ion relations,and carbohydrate use were investigated in response to the interactiveeffects of salinity and root zone hypoxia in an experiment conductedin nutrient culture. One week of hypoxia in the root zone atboth 50 and 400 mol m^–3 NaCl caused the cessation of rootgrowth, a reduction in shoot growth, and adversely affectedwater relations, but not ion relations or carbohydrate concentrations.Two weeks of hypoxia at 400 mol m^–3 NaCl resulted in thedeath of root tips, a 20–fold increase in the resistanceto water flow from the exterior of the roots to the leaves,and a further deterioration in water relations. There was alsoa doubling of Cl^– concentrations in the xylem sap anda doubling of Na⁺ and Cl^– concentrations in the leaves.An increase in the concentration of starch in the leaves, andsugars in the leaves, stems and roots, indicated that therewere problems with carbohydrate use rather than supply. Underthe prevailing conditions of low vapour pressure deficit, iontoxicity was the most probable cause of injury to A. amnicolain hypoxic solutions at high salinity. The response of A. amnicolato the interactive effects of salinity and hypoxia were similarto those reported for non-halophytes, but occurred at highersalinities. Key words: Atriplex, hypoxia, salinity, water relations, ion transport, carbohydrate     

Salt-Induced Hypodermal Transfer Cells in Roots of Prosopis farcta and Ion Distribution within Young Plants

Prosopis farcta was grown on hydroculture with additions of 0.5, 10, 50, and 100 mM NaCl and without salt treatment. In plants from a 0.5 mM NaCl treatment, Cl^? was taken up into stems and leaves, but Na⁺ was withheld from the shoot. At 10 mM NaCl, shoot K⁺ concentration was below that of the control; Na⁺ and Cl^? were taken up to stems and cotyledons in nearly equimolar amounts. However, in the leaves, Na⁺ concentrations were only half of those of Cl^?. With increasing salt stress, Na⁺ and Cl^? were transported to the shoot, but kept at relatively low levels in the roots. Na⁺/ K⁺ ratios in roots did not increase proportionally to those in the solution. At an external Na⁺/K⁺ of > 5 and a root Na⁺/K⁺ of >1 (10 mM NaCl treatment), K⁺ selectivity was induced which rose exponentially with increasing salt stress; and cell wall protuberances were discovered in the hypodermis at the zone of side root formation. These transfer cells were found neither in roots from the 0.5 mM NaCl treatment nor in the controls. Their possible role in the Na⁺/K⁺ selectivity of the roots of Prosopis farcta is discussed.     

Na+, K+ and Cl- in Xylem Sap Flowing to Shoots of NaCl-Treated Barley

Munns, R. 1985. Na⁺, K⁺ and Cl^– in xylem sap flowing toshoots of NaCl-treated barley.—J. exp. Bot. 36: 1032–1042. Na⁺, Cl^– and K⁺ concentrations were measured in xylemsap obtained by applying pressure to the roots of decapitatedbarley plants grown at external [NaCl] of 0, 25, 50, 100, 150and 200 mol m^–3. For any given NaCl treatment, ion concentrationsin the xylem sap were hyperbolically related to the flux ofwater. Ion concentrations in sap collected at very low volumefluxes (without applied pressure) were 5–10 times higherthan in sap collected at moderate fluxes (under pressure). Fora given moderate volume flux, Na+ concentration in the xylemsap, [Na⁺]_x, was only 4.0 mol m^–3 at external [NaCl] of25–150 mol m^–3, and increased to 7.0 mol m^–3at 200 mol m^–3. [Cl-]x showed a similar pattern. Thisshows there would be little difference in the rate of uptaketo the shoot of plants at 25–150 mol m^–3 externalNaCl and indicates little change even at 200 mol m^-3 NaCl becausetranspiration rates would be much lower. Thus the reduced growthof the shoot of plants at high NaCl concentrations is not dueto higher uptake rates of Na⁺ or Cl^–. The fluxes of Na⁺, Cl^– and K^– increased non-linearlywith increasing volume flux indicating little movement of saltin the apoplast. The flux of K⁺ increased even when [K⁺]_x wasgreater than external [K⁺], indicating that membrane transportprocesses modify the K⁺ concentration in the transpiration streamas it flows through the root system. Key words: -Xylem sap, Na⁺, K⁺, Cl^– fluxes, salinity, barley     

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.     

Growth and solute accumulation in 3-week-old seedlings of Agropyron elongatiun stressed with sodium and potassium salts

Agropyron elongatum [Host. (Beauv.)] [^cv. Arizona Glendale, was grown in liquid medium salinized with either NaCl, KCI, or a 50:50 mixture of these two salts at osmotic potentials ranging from 0 to –1.6 MPa. The amount of growth in 21 days was measured, and extracts were made of the shoots at this time. The extracts were assayed for low-molecular-weight organic compounds (glucose, fructose, sucrose, be-taine, proline) and inorganic solutes (Na⁺, K⁺, Cl^?, P.). The purpose was to determine if there was any correlation between the harmful effect of salinity on growth and the concentrations of solutes in tissues. Growth inhibition of A. elongatum was roughly proportional to the osmotic potential of the growth medium and was independent of the ionic composition of the salinizing salts. Total monovalent cation (the sum of Na⁺ and K⁺) concentrations and the ratio of these two cations in leaves were mainly a function of the ionic compostion of the salt in growth media, and, to a lesser degree, of osmotic potentials. F At an osmotic potential of –0.2 MPa, total monovalent cation in leaves was the same as in non-stressed plants. However, if the salinizing salt contained NaCl, there was an increase in foliar Na⁺ with a balancing decrease in K⁺. At stress levels between –0.4 and –1,6 MPa, and, if the media were salinized with either 100% NaCl or a 50:50 mixture of NaCl and KCI, total monovalent cation concentrations remained constant at a value that was twice that in non-stressed plants. Although total monovalent cation concentrations were equal in plants grown under these two salinity conditions, the K⁺/Na⁺ ratios shifted from a value of 1:2 in plants grown in 100% NaCl to 3:1 in plants subjected to the 50:50 mixture. If 100% KCI was used to salinize media, total monovalent cation was 80% of its concentration in NaCl-treated plants in the range of –0.4 to -1.2 MPa. At –1.6 MPa due to 100% KCI, total monovalent cation was double that in plants subjected to -0.4 MPa. In the range of osmotic potentials from–0.2 to –1.2 MPa, the chloride:cation ratio was 1:2. At –1.6 MPa the ratio changed to 3:4. Proline started accumulating in leaves of A. elongatum when the tissue concentration of total monovalent cation exceeded 200 μ (g fresh weight)^?1. Above this threshold value of total monovalent cation, the proline concentration of leaves was 6% of the amount of total monovalent cation that exceeded 200 umol (g fresh weight)¹.     

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.     

Concentrations and Transport of Solutes in Xylem and Phloem along the Leaf Axis of NaCl-treated Hordeum vulgare

Hordeum vulgare cv. California Mariout was established in sandculture at two different NaCl concentrations (0.5 mol m^–3‘control’ and 100 mol m^–3) in the presenceof 6.5 mol m^–3 K ⁺. Between 16 and 31 d after germination,before stem elongation started, xylem sap was collected by useof a pressure chamber. Collections were made at three differentsites on leaves 1 and 3: at the base of the sheath, at the baseof the blade, i.e. above the ligule, and at the tip of the blade.Phloem sap was collected from leaf 3 at similar sites throughaphid stylets. The concentrations of K ⁺, Na⁺, Mg2⁺ and Ca²⁺were measured. Ion concentrations in xylem sap collected at the base of leaves1 and 3 were identical, indicating there was no preferentialdelivery of specific ions to older leaves. All ion concentrationsin the xylem decreased from the base of the leaf towards thetip; these gradients were remarkably steep for young leaves,indicating high rates of ion uptake from the xylem. The gradientsdecreased with leaf age, but did not disappear completely. In phloem sap, concentrations of K⁺ and total osmolality declinedslightly from the tip to the base of leaves of both controland salt-treated plants. By contrast, Na⁺ concentrations inphloem sap collected from salt-treated plants decreased drasticallyfrom 21 mol m^–3 at the tip to 7.5 mol m^–3 at thebase. Data of K/Na ratios in xylem and phloem sap were used to constructan empirical model of Na⁺ and K⁺ flows within xylem and phloemduring the life cycle of a leaf, indicating recirculation ofNa⁺ within the leaf. Key words: Hordeum vulgare, xylem transport, phloem transport, NaCl-stress     

Sodium-induced calcium deficiency in salt-stressed corn

Abstract The effect of the Na⁺/Ca²⁺ ratio in the root media on salt-stressed corn (Zea mays L. cvs DeKalb XL-75 and Pioneer 3906) was determined in greenhouse experiments. Plants grown in a complete nutrient solution salinized with 86.5 mol m^?3 NaCl exhibited severe Ca²⁺ deficiency symptoms at the four-leaf stage. The symptoms disappeared when part of the NaCl was replaced with 10 mol m^?3 CaCl₂ (Na⁺/Ca²⁺ molar ratio = 5.7). Salt stress at an iso-osmotic potential of ?0.4 MPa substantially decreased shoot growth at all solution Na⁺/Ca²⁺ ratios from 34.6 to 0.26. However, the dry weights of blades at 26 d of age were much less when plants were salinized with NaCl alone, particularly that of DeKalb XL-75 which was more susceptible to Na-induced Ca²⁺ deficiency than was Pioneer 3906. The growth of sheaths was similarity reduced by sail stress at all Na⁺/Ca²⁺ ratios. The symptoms of Ca²⁺ deficiency were correlated with low Ca²⁺ concentrations in the leaf tissue. Ca²⁺ concentrations in the developing blades of NaCl-stressed plants were much lower than in control plants. As the Na⁺/Ca²⁺ ratio in the solution was decreased, Ca²⁺ levels increased in both the blades and sheaths while Na⁺ concentrations greatly decreased. DeKalb XL-75 was much less effective than Pioneer 3906 in restricting the uptake of Na⁺. The results clearly indicate that NaCl stress may cause lesions and unique plant responses that are not manifested on agronomic plants grown on saline soils.     

Plant growth and yield of cucumber plants grafted on different commercial and local rootstocks grown under salinity stress

This study aimed to determine the effects of different rootstocks and soilless media on the plant growth and yield of cucumber and on the leaf ion (Na⁺, Ca⁺⁺, K⁺ and Cl^?) concentrations. Four commercial rootstocks (TZ148 F₁, RS841 F₁, Nun9075 F₁ and Avar F₁) and two local landraces (Local-1 and Local-3 belonging to Cucurbita moschata L.) were used as rootstock and grafted and non grafted plants were tested in three different salinity conditions (2.5 dS m^?1, 5.0 dS m^?1 and 7.5 dS m^?1) on three different soilless media (cocopeat, perlite and rockwool) in spring period under greenhouse conditions. Salinity found to reduce root and shoot dry weight, and yield of plants in all growing media. TZ148, Nun9075 and Local-3 are found to improve tolerance of cucumber plants to saline conditions (5.0 and 7.5 dS m^?1) when used as rootstocks. Root and shoot dry weight, yield, Ca⁺⁺ in leaves and K⁺/Na⁺ ratio in leaves were significantly decreased, but Na⁺ and Cl^? concentration in leaves were increased under salt stress. Rootstock potential of Local-3 is also found to be quite good for cucumber under saline conditions.     

Sodium transport measured in plasma membrane vesicles isolated from wheat genotypes with differing K+/Na+ discrimination traits

Right-side-out plasma membrane vesicles were isolated from wheat roots using an aqueous polymer two-phase system. The purity and orientation of the vesicles were confirmed by marker enzyme analysis. Membrane potential (Ψ)-dependent ²²Na⁺ influx and sodium/proton (Na⁺/ H⁺) antiport-mediated efflux across the plasma membrane were studied using these vesicles. Membrane potentials were imposed on the vesicles using either K⁺ gradients in the presence of valinomycin or H⁺ gradients. The ΔΨ was quantified by the uptake of the lipophilic cation tetraphenylphosphonium. Uptake of Na⁺ into the vesicles was stimulated by a negative ΔΨ and had a K_m for extrav-esicular Na⁺ of 34.8 ± 5.9 mol m³. The ΔΨ-dependent uptake of Na⁺ was similar in vesicles from roots of hexaploid (cv. Troy) and tetraploid (cv. Langdon) wheat differing in a K⁺/Na⁺ discrimination trait, and was also unaffected by growth in 50 mol m^?3 NaCl. Inhibition of ΔΨ-dependent Na⁺ uptake by Ca²⁺ was greater in the hexaploid than in the tetraploid. Sodium/proton antiport was measured as Na⁺-dependent, amiloride-inhibited pH gradient formation in the vesicles. Acidification of the vesicle interior was measured by the uptake of ¹⁴C-methylamine. The Na⁺/H⁺ antiport had a K_m, for intravesicular Na⁺ of between 13 and 19 mol m^?3. In the hexaploid, Na⁺/H⁺ antiport activity was greater when roots were grown in the presence of 50 mol m^?3NaCl, and was also greater than the activity in salt-grown tetraploid wheat roots. Antiport activity was not increased in a Langdon 4D chromosome substitution line which carries a trait for K⁺/Na⁺ discrimination. It is concluded that neither of the transport processes measured is responsible for the Na⁺/K⁺ discrimination trait located on the 4D chromosome of wheat.     

Effect of NaCl and KCl salts on the growth and solute accumulation of the halophyte Atriplex nummularia

Atriplex nummularia plants are able to grow well in the absence of significant amounts of Na⁺. Medium levels of salinity (100 mM NaCl or KCl) did not cause substantial inhibition of growth but increasing concentrations of salt induced a progressive decline in length and weight of the plants. This inhibition was significantly higher in KCl grown plants than in NaCl grown plants. In addition, although it has been proposed that both K⁺ and Na⁺ are involved in the osmotic adjustment of plants in response to high soil salinity, we show that Na⁺ ions contribute more efficiently than K⁺ ions to perform this function. Our results also indicate that most of the osmotic adjustment of the plant was due to the accumulation of inorganic ions. The strong inhibition of Rb⁺ transport caused by internal sodium suggests that this cation could be efficiently used by the plant and, as a consequence, the transport of other monovalent cations is down-regulated.     

Characterizing the growth of <Emphasis Type="Italic">Sarcoptes scabiei</Emphasis> infrapopulations

The plant stress hypothesis posits that a herbivore’s reproductive success increases when it feeds on stressed plants, while the plant vigor hypothesis predicts that a herbivore preferentially feeds on more vigorous plants. We examined these opposing hypotheses by growing spider mites (Tetranychus urticae) on the leaves of stressed and healthy (vigorous) cucumber plants. Host plants were grown under controlled conditions at low, moderate, and high concentrations of NaCl (to induce salinity stress), at low, moderate, and high fertilizer concentrations (to support growth), and without these additions (control). The effects of these treatments were evaluated by measuring fresh and dry plant biomass, carotenoid and chlorophyll content, antioxidant enzyme activity, and concentrations of PO₄^3?, K⁺, and Na⁺ in plant tissues. The addition of low concentrations of fertilizer increased dry mass, protein, and carotenoid content relative to controls, suggesting a beneficial effect on plants. The highest NaCl treatment (2560 mg L^?1) resulted in increased Na⁺ and protein content relative to control plants, as well as reduced PO₄^3?, K⁺, and chlorophyll levels and reduced catalase and ascorbate peroxidase enzyme activity levels. Analysis of life table data of T. urticae mites raised on leaves from the aforementioned plant groups showed the intrinsic rate of increase (r) for mites was 0.167 day^?1 in control specimens, 0.125 day^?1 for mites reared on plants treated with a moderate concentration of fertilizer (10 mL L^?1), and was highest (0.241 day^?1) on plants grown under moderate salinity conditions (1920 mg L^?1 NaCl). Reproductive success of T. urticae did not differ on plants watered with a moderate concentration of NaCl or a high concentration of fertilizer. The moderately-stressed plants formed a favorable environment for the development and reproduction of spider mites, supporting the plant stress hypothesis.     

Kinetics of chloride transport in the cyanobacterium Synechococcus R-2 (Anacystis nidulans, S. leopoliensis) PCC 7942

The kinetics of the light-driven Cl^? uptake pump of Synechococcus R-2 (PCC 7942) were investigated. The kinetics of Cl^? uptake were measured in BG-11 medium (pH_o, 7·5; [K⁺]_o, 0·35 mol m^?3; [Na⁺]_o, 18 mol m^?3; [Cl^?]_o, 0·508 mol m^?3) or modified media based on the above. Net³⁶Cl^? fluxes (?Cl^?_o,i) followed Michaelis-Menten kinetics and were stimulated by Na⁺ [18 mol m^?3 Na⁺ BG-11 ?Cl^?_max= 3·29±0·60 (49) nmol m^?2 s^?1 versus Na⁺-free BG-11 ?Cl^?_max= 1·02±0·13 (54) nmol m^?2 s^?1] but the Km was not significantly different in the presence or absence of Na⁺ at pH_o 10; the Km was lower, but not affected by the presence or absence of Na⁺ [Km = 22·3±3·54 (20) mmol m^?3]. Na⁺ is a non-competitive activator of net ?Cl^?_o,i. High [K⁺]_o (18 mol m^?3) did not stimulate net ?Cl^?_o,i or change the Km in Na⁺-free medium. High [K⁺]_o (18 mol m^?3) added to Na⁺ BG-11 medium decreased net ?Cl^?_o,i [18 mol m^?3K⁺ BG-11; ?Cl^?_max= 2·50±0·32 (20) nmol m^?2 s^?1 versus BG-11 medium; ?Cl^?_max= 3·35±0·56 (20) nmol m^?2 s^?1] but did not affect the Km 55·8±8·100 (40) mmol m^?3]. Na⁺-stimulation of net ?Cl^?_o,i followed Michaelis-Menten kinetics up to 2–5 mol m^?3 [Na⁺]_o but higher concentrations were inhibitory. The Km for Na⁺-stimulation of net ?Cl^?_o,i [K_1/2(Na⁺)] was different at 47 mmol m^?3 [Cl^?]_o (K_1/2[Na⁺] = 123±27 (37) mmol m^?3]. Li⁺ was only about one-third as effective as Na⁺ in stimulating Cl^? uptake but the activation constant was similar [K_1/2(Li⁺) = 88±46 (16) mmol m^?3]. Br^? was a competitive inhibitor of Cl^? uptake. The inhibition constant (Ki) was not significantly different in the presence and absence of Na⁺. The overall Ki was 297±23 (45) mmol m^?3. The discrimination ratio of Cl^? over Br^? (δCl^?/δBr^?) was 6·38±0·92 (df = 147). Synechococcus has a single Na⁺-stimulated Cl^? pump because the Km of the Cl^? transporter and its discrimination between Cl^? and Br^? are not significantly different in the presence and absence of Na⁺. The Cl^? pump is probably driven by ATP.     

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     

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).     

Influence of inorganic nitrogen sources on K+/Na+ homeostasis and salt tolerance in sorghum plants

This work aimed to study the regulation of K⁺/Na⁺ homeostasis and the physiological responses of salt-treated sorghum plants [Sorghum bicolor (L.) Moench] grown with different inorganic nitrogen (N) sources. Four days after sowing (DAS), the plants were transferred to complete nutrient solutions containing 0.75 mM K⁺ and 5 mM N, supplied as either NO₃ ^? or NH₄ ⁺. Twelve DAS, the plants were subjected to salt stress with 75 mM NaCl, which was applied in two doses of 37.5 mM. The plants were harvested on the third and seventh days after the exposure to NaCl. Under the salt stress conditions, the reduction of K⁺ concentrations in the shoot and roots was higher in the culture with NO₃ ^? than with NH₄ ⁺. However, the more conspicuous effect of N was on the Na⁺ accumulation, which was severely limited in the presence of NH₄ ⁺. This ionic regulation had a positive influence on the K⁺/Na⁺ ratio and the selective absorption and transport of K⁺ in the plants grown with NH₄ ⁺. Under control and salt stress conditions, higher accumulation of free amino acids and soluble proteins was promoted in NH₄ ⁺ grown roots than NO₃ ^? grown roots at both harvesting time, whereas higher accumulation of soluble sugars was observed only at 7 days of salt stress exposure. Unlike the NH₄ ⁺ grown plants, the gas exchanges of the NO₃ ^? grown plants were reduced after 7 days of salt stress. These results suggest that external NH₄ ⁺ may limit Na⁺ accumulation in sorghum, which could contribute to improving its physiological and metabolic responses to salt stress.