Sodium Exclusion from the Shoots by Roots of Zea mays (cv. LG 11) and its Breakdown with Oxygen Deficiency

The effects of sodium chloride salinity and root oxygen deficiency(anoxia) were studied in 11-12d old maize plants (Zea mays L.cv. LG 11) in nutrient solution culture. Transport of ²²Na bythe roots to the shoot in 24 h was markedly increased by anoxiawhen the external concentration of NaCl was in the range 0·1-10·9mol m^–3. Anoxia severely inhibited uptake of ⁴²K by rootsand its transport to the shoot, so that the ratio of Na⁺/K⁺moving into the shoot was increased by a factor of approximately10. When the external concentration of NaCl was increased to2.4 mol m^–3, the roots showed much less ability to excludeNa⁺ under aerobic conditions, and anoxia caused no further increasein the movement of Na⁺ to the shoot. It is concluded that atthe higher concentration the ability of the roots to excludeNa⁺, presumably through an active mechanism in the xylem parenchymacells or in the root cortex and transporting Na⁺ to the outersolution, is saturated by excessive inward diffusion of Na⁺.The ratio of Na⁺/K⁺ transported to the shoot increased by afactor of 600 when the concentration of NaCl was increased from2·4 mol m^–3 to 40 mol m^–3 and roots weremade anoxic. Such imbalances in the supply of cations to theshoot, particularly when roots are oxygen-deficient, may contributeto salinity damage. Key words: Anaerobic, Anoxic, Oxygen deficiency, Roots, Salinity, Salt stress, Sodium chloride, Zea mays     

Induction of Increased Salt Tolerance in Sorghum bicolor by NaCl Pretreatment

Following 20 d of exposure to 75 or 150 mol m^–3 NaCl Sorghumbicolor (L.) Moench plants become capable of growing in mediumcontaining 300 mol m^–3 NaCl. Control plants, which havenot been pretreated, or plants pretreated for less than 20 ddie within 2 weeks when exposed to 300 mol m^–3 NaCl. Weconsider this induction of a capacity to survive in and toleratea high NaCl concentration as an adaptation to salinity. We suggestthat adaptation to salinity is more than osmotic adjustmentand that it takes longer to develop than osmotic adjustment.Concomitantly with the appearance of the ability to grow inhigh salinity, adaptation also comprises the development ofa capacity to regulate internal Na⁺ and Cl^– concentrations,even when external salinity is high. Shoot mean relative growthrates are similar for both control plants and for adapted plantsgrowing in 300 mol m^–3 NaCl, although their shoot Na⁺and Cl^– concentrations are quite different. Based on thesedata, we propose that adaptation of Sorghum to high salinityresults from a modulation of genome expression occurring duringextended exposure to non-lethal NaCl concentrations. Key words: Sorghum bicolor (L.) Moench, NaCl, salt tolerance, adaptation to salinity     

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     

Exogenous ABA as a Modulator of the Response of Sorghum to High Salinity

Treatment of Sorghum bicolor (L.) Moench, cv. 610, with abscisicacid (ABA) during the first week of sahnization with 150 molm^–3 NaCl induced enhancement of growth and acceleratedadaptation to high salinity (300 mol m^–3 NaCl) Adaptationis defined as the development of the ability of the plant tosurvive, grow, and set seeds upon exposure to a NaCl concentrationwhich is lethal for the unadapted plant In the absence of ABAthe saline pretreatment requires 20 d for the development ofadaptation (Amzallag et al., 1990), with ABA treatment the sameresult is achieved within approximately one week The exposureof the plants to non-lethal salinity (150 mol m^–3 NaCl)apparently triggers a transient sensitivity to ABA lasting forabout 8 to 10 d following the beginning of sahnization Thisperiod coincides with an increase in leaf PEP carboxylase activitywhich seems to occur faster if the plants are treated with ABA.Exogenous ABA-induced enhancement of growth and control of shootNa⁺ concentration, occur at a lower ABA concentration (10 mmolm^–3) than the induction of adaptation to salinity whichoc curs at 40 mmol m^–3 or above. The lowered shoot Na⁺concentration which is induced by a low ABA concentration isnot sufficient to induce survival of the plants in high salinity(300 mol m^–3 NaCl). Key words: Growth, adaptation to salinity, ABA     

Possible reasons for relative salt stress tolerance in nodules of white lupin cv. Multolupa

The effects of different NaCl concentrations on the growth andnitrogen fixation activity of white lupin (Lupinus albus [L.])was studied over a 6 d period. Plant growth parameters, photosynthesisand shoot respiration were unaffected by NaCl concentrationsup to 150 mol m^–3. However, nitrogenase activity decreasedwith increased NaCl concentration up to 100 mol m_–3, whilstthe O₂ diffusion resistance increased with 100 mol m^–3NaCl, but showed no further change when 150 mol m^–3 NaClwas applied for 6 d. Increases in NaCl concentration decreasednodular starch content while increasing sucrose content, suggestingan osmotic regulation. These changes were associated with a77% decrease in sucrose synthase activity. The effect on theO₂ diffusion resistance was paralleled by changes in glycoproteincontent of the nodules, as determined by immunogold localizationand ELISA. X-ray microanalysis studies of nodules showed that,following a 6 d exposure to 150 mol m^–3 NaCl, Na⁺ ionswere largely excluded from the infected zone, whilst only lowlevels of Cl^- ions penetrated into this region. Na⁺ entry intoroots and leaves was also at a low level. Leghaemoglobin contentdecreased with saline stress, as did superoxide dismutase; whichdecreased by 36% following exposure to 100 mol m^–3 saltfor 6 d. These results are discussed in relation to the relativesalt tolerance of the Multolupa/ISLU-16 symbiosis. Key words: Salt stress, nodules, nitrogen fixation, oxygen diffusion, carbohydrates, Lupinus albus     

Determination of Volume of Dunaliella Cells by Lithium Dilution Measurements and Derivation of Internal Solute Concentrations

A method has been developed to measure the cell volume of theunicellular green alga Dunaliella parva 19/9 using Li⁺ measurementsonly. Concentrations of internal solutes can also be calculatedif they are assayed in the same samples as Li⁺. We found thatD. parva cells grown in 0.4 kmol m^–3 NaCl have an averageaqueous cell volume of 65.1 ?2.9 µm³, a K⁺ concentrationof 126?6 mol m^–3, a Na⁺ concentration of 11?11 mol m^–3and a glycerol concentration of 615?27 mol m–3 (n= 12).Algae grown in 1.5 kmol m^–3 NaCl have an average aqueouscell volume of 131 ?7.5 µm³, a K⁺ concentration of 109?4mol m^–3, a Na⁺ concentration of 10?39 mol m^–3 anda glycerol concentration of 1 425?59 mol m^–3 (n = 12).These results indicate that D. parva cells adapted to high salinitieshave larger cell volumes than those adapted to lower salinities.However, there is no evidence for a significant difference ininternal Na⁺ concentration, despite the almost 4-fold differencein the concentration of external NaCl. The intracellular glycerolconcentration alone accounts for 65% and 54%, respectively,of the osmotic balance in low and high salt grown cells. Key words: Dunaliella, cell volume, intracellular solutes     

Ion Transport in Suaeda maritima: Its Relation to Growth and Implications for the Pathway of Radial Transport of Ions across the Root

The ion relations of the halophytc Suaeda maritima are described.When plants grew in 340 mol m^–3 sodium chloride (—1•76MPa) leaf solute potentials decreased, and were sustained around—2•5 MPa Inorganic ion concentration (mostly of sodiumchloride) accounted for this. Comparable shoot ion concentrationsof potassium, nitrate and sulphate occurred when plants grewon different salinity types characterized by these ions. Netsodium transport and shoot sodium concentration increased dramaticallywith increases in external sodium chloride concentration upto 85 mol m^–3; thereafter, further increases in externalsodium chloride concentration had relatively little effect uponeither shoot sodium concentration or upon net transport of sodiumto the shoot. The net transport of sodium plus potassium onlydoubled when the external concentration of sodium plus potassiumincreased from 24 to 687 mol m^–3 Shoot ion concentrationswere remarkably constant with time, external concentration andsalinity type. The membrane flux rates and symplasmic ion concentrations neededto sustain the observed net transport of sodium (of some 10mmol g^–1 dry wt. of roots d^–1) are calculated fromanatomical and stereological data for the root system of thisspecies. The minimum net sodium chloride flux to load the symplasmwould be 260 nmol m^–2s^–1 if the whole cortical andepidermal plasmalemmal surface area were used uniformly, butthe flux rate required would be 3000 nmol m^–2s^–1if uptake took place only at the root surface. A flux rate ofat least 1000 nmol m^–2s^–1 is needed between symplasmand xylem. The symplasmic concentration of NaCl would be atleast 80 mol m^–3. It is argued (1), that both symplasmicand xylem loading are likely to be passive processes mediatedby ion channels rather than active carriers, (2), that net iontransport at 340 mol m^–3 sodium chloride is close to themaximum which is physiologically sustainable and (3), that growthof this halophyte is limited by NaCl supply from the root. Key words: Suaeda maritima, halophyte, salinity, roots, radial ion transport     

Salt Tolerance in the HalophyteHalosarcia pergranulatasubsp.pergranulata

Halosarcia pergranulata(P. G. Wilson) subsp.pergranulatais amember of the Salicornioideae and is native to Australia. Salttolerance inH. pergranulatasubsp.pergranulatawas assessed bygrowing plants for 83 d at seven NaCl concentrations from 10to 800 mol m^-3. Shoot biomass was greatest for plants grownat 10 to 200 mol m^-3NaCl, while at salinities of 300 mol m^-3orhigher it was inhibited. There was little increase in succulencein response to NaCl, and it even declined at the highest salinities.The K⁺[ratio]Na⁺molar ratio in succulent shoot tissues decreasedfrom 0.30[ratio]1 in plants grown at 10 mol m^-3NaCl to 0.02[ratio]1in plants at 600 mol m^-3, due to a three-fold increase in tissueNa⁺concentration and a five-fold decline in tissue K⁺. The osmoticpotential of sap (     

Effects of Sodium Chloride Stress on Callus Cultures of Cicer arietinum L. cv. BG-203: Growth and Ion Accumulation

Growth and ion accumulation were measured in callus culturesof Cicer arietinum L. cv. BG-203, grown on media supplementedwith 0–200 mol m^–3 NaCl. Fresh and dry weights decreasedat concentrations ranging from 100–200 mol m^–3,the reduction being greater during the third and fourth weeksof culture. Slight stimulation of growth was observed at 25and 50 mol m^–3 NaCl. There was also a decrease in tissuewater content (fresh weight: dry weight) at 100–200 molm^–3 NaCl. The concentration of Na⁺ and Cl^– in thetissue increased with increasing salinity of the medium. Mostof the accumulation of these ions occurred by the first weekwhile significant growth inhibition became apparent by onlythe third week of culture. Tissue K⁺ and Mg²⁺ decreased withincreasing salinization, the decrease being greater in K⁺ levels.Levels of Ca²⁺, however, were maintained throughout the experimentalrange. Key words: Cicer arietinum, NaCl stress, Callus cultures, Ion accumulation     

External Potassium Supply is not Required for Root Growth in Saline Conditions: Experiments with Ricinus communis L. Grown in a Reciprocal Split-Root System

Ricinus communis L. (castor bean) plants were grown in the absence(control) and in the presence of 100molm^–3NaCl with areciprocal split-root system, in which K⁺ was supplied to oneand NO₃^– to the other part of the root system. In theseplants shoot and, to a lesser extent, total root growth wereinhibited compared to plants with non-split roots. Without andwith NaCl, growth of roots receiving NO₃^– but noK⁺ (‘minusK/plus N-roots’) was substantially more vigorous thanunder the reverse conditions (‘plus K/minus N-roots¹).100mol m^–3 NaCl inhibited growth of minus K/plus N-roots¹to the same extent as that of non-split roots, indicating thatexternally supplied K⁺ was not required for root growth undersaline conditions. In growth media without added K⁺ the rootdepleted the external low K ⁺ levels resulting from chemicalsdown to a minimum value C_mln (1.0 to 1.4 mmol m^–3); inthe presence of 100 mol m^–3 NaCl, C_min, was higher (10–18mmol m^–3) and resulted from an initial net loss of K ⁺.C_min, was pH-dependent The distribution of K⁺, Na⁺ and Mg²⁺along the root was measured. In meristematic root tissues, K⁺ concentrations were scarcely affected by external K⁺ or byNaCl, where Na ⁺ concentrations were low, but somewhat elevatedat low external K+ and/or high NaCl. In differentiated, vacuolatedtissues K ⁺ concentrations were low and Na⁺ concentrations high,if K ⁺ was not supplied externally and/or NaCl was present.The longitudinal distribution of ions within the root was usedto estimate cytoplasmic and vacuolar ion concentrations. Thesedata showed a narrow homoeostasis of cytoplasmic K+ concentrations(100–140 mol m^–3) independent of external K ⁺ supplyeven in the presence of 100 mol m ^–3 NaCl. CytoplasmicNa ⁺ concentrations were maintained at remarkably low levels.Hence, external K⁺ concentrations above C_min, were not requiredfor maintaining K/Na selectivity, i.e. for controlling Na⁺ entry.The results are discussed with regard to mechanisms of K/Naselectivity and to the importance of phloem import of K⁺ forsalt tolerance of roots and for cytoplasmic K⁺ homoeostasis. Key words: Ricinus communis, nitrate, potassium, root (split-root), salt tolerance, phloem transport     

The Combined Effects of Salinity and Root Anoxia on Growth and Net Na+ and K+-accumulation in Zea mays Grown in Solution Culture

The effects of excess salinity and oxygen deficiency on growthand solute relations in Zea mays L. cv. Pioneer 3906 were examinedin greenhouse experiments. The roots of plants 14 d old growingin nutrient solution containing additions of NaCl in the range1.0–200 mol m^–3 were either exposed to a severedeficiency of O₂ by bubbling with nitrogen gas (N₂ treatment),or maintained with a supply of air (controls), for a periodof 1–7 d. The threshold NaCl concentration resulting inappreciable inhibition of leaf extension, and shoot f. wt gainin controls was between 10 and 25 mol m^–3. At 25 mol m^–3NaCl the ratio of Na+/K+ transported to shoots was about 20times greater than in plants in 1.0 mol m^–3 NaCl. Theeffect of addition of NaCl to the nutrient solution was to enhanceNa+ movement but simultaneously depress the rate of K+ transportto shoots (per g f. wt roots). Interactions between NaCl levels and aeration treatment wereshown by analyses of variance to be statistically significantfor leaf extension, shoot and root f. wt gains, Na+ and K+ concentrationsin shoots and roots. When roots were N₂-treated, shoot and rootgrowth were depressed, the effect of aeration treatment beinggreatest at NaCl concentrations of 50 mol m^–3 or less.Additionally, N₂-treatment greatly accelerated Na- transportto shoots while depressing K+ transport still further, so thatat 10 mol m^–3 NaCl the ratio Na+/K+ acquired by the shootswas 230 times greater than in controls. Over the concentrationrange 1.0 to 50 mol m^–3 NaCl, the ratio Na+/K+ transportedto shoots by anoxic roots increased by a factor of 860. Mechanisms controlling changes in solute flux to the shoot,and the significance in relation to plant tolerance of excesssalts or oxygen deficiency are discussed. Anaerobic, corn, flooding, maize, oxygen-deficiency, salinity     

Effect of NaCl Salinity on Somatic Embryo Development in Sapindus trifoliatus L.

The effect of NaCl salinity on growth and development of somaticembryos of Sapindus trifoliatus L. was examined. Incorporationof 25 and 50 mol m^–3 NaCl into the medium greatly increasedthe growth and development of somatic embryos and both theseconcentrations favoured the production of secondary embryoids.However, supplementation of 100 mol m^–3 NaCl to the mediumdid not have any significant effect on the growth and developmentof somatic embryos. On the other hand, the culturing of proembryostructures in medium containing 200 mol m^–3 NaCl resultedin complete death within 7 d of salt exposure. Analysis of somatic embryos revealed that, upon salinization,they accumulated Na⁺ and Cl^– in significant amounts butthe content of Na⁺ was much less compared to that of Cl^–.Addition of NaCl (up to 50 mol m^–3) in the medium resultedin a considerable increase in the K⁺ content of somatic embryos.The content of proline in somatic embryos, however, increasedsubstantially in response to salinization. The amount of freesterols, steryl glycosides, steryl esters, and phospholipidsalso rose to higher values in salt-affected somatic embryos.The results suggest that somatic embryos of S. trifoliatus cantolerate concentrations of NaCl up to 100 mol m^–3 withoutaffecting growth and that they have sufficient cellular mechanismsto tolerate salinity at relatively high levels. Key words: Salinity, somatic embryo, sterols, phospholipids     

Salt Tolerance in the Succulent, Coastal Halophyte, Sarcocornia natalensis

The effects of 0, 50, 100, 200, 300, 400 and 500 mol m^–3NaCl on growth and ion accumulation in the succulent, coastalhalophyte Sarcocornia natalensis (Bunge ex Ung.-Sternb.) A.J. Scott were investigated. Increase in salinity from 0 to 300 mol m^–3 NaCl stimulatedproduction of fresh, dry, and organic dry mass, increased succulenceand shifted resource allocation from roots to shoots. Growthwas optimal at 300 mol m^–3 and decreased with furtherincrease in salinity. Water contributed to a large proportion of the increase in freshmass. Inorganic ions, especially Na⁺ and Cl– contributedsubstantially to the dry mass. At 300 mol m^–3 NaCl inorganicions contributed to 37% of total dry mass and NaCl concentrationin the shoots was 482 mol m^–3. Expressed sap osmotic potentialsdecreased from –2.10 to –3.95 MPa as salinity increasedfrom 0 to 300 mol m^–3 NaCl. Massive accumulation of inorganicions, especially Na⁺ and Cl^–, accounted for 86% of theosmotic adjustment at 300 mol m^–3 NaCl. Salinity treatments decreased the concentrations of K+ in shoots.Plant Na+ :K+ ratios increased steadily with salinity and reacheda maximum of 16.6 at 400 mol m3 NaCl. It is suggested that the exceptional salt tolerance of S. natalensisis achieved by massive inorganic ion accumulation which providessufficient solutes for osmoregulation, increased water fluxand turgor-induced growth. Key words: Sarcocornia natalensis, salt tolerance, halophyte     

Effect of Salinity on Growth, Nodulation and Nitrogen Yield of Chickpea (Cicer arietinum L.)

Chickpea cultivar ILC 482 was inoculated with salt-tolerantRhizobium strain Ch191 in solution culture with different saltconcentrations added either immediately with inoculation or5 d later. The inhibitory effect of salinity on nodulation ofchickpea occurred at 40 dS m^–1 (34.2 mol m^–3 NaCl)and nodulation was completely inhibited at 7 dS m^–1 (61.6mol m^–3 NaCl); the plants died at 8 dS m^–1 (71.8mol m^–3 NaCl). Chickpea cultivar ILC 482 inoculated with Rhizobium strain Ch191^spcstrwas grown in two pot experiments and irrigated with saline water.Salinity (NaCl equivalent to 1–4 dS m^–1) significantlydecreased shoot and root dry weight, total nodule number perplant, nodule weight and average nodule weight. The resultsindicate that Rhizobium strain Ch191 forms an infective andeffective symbiosis with chickpea under saline and non-salineconditions; this legume was more salt-sensitive compared tothe rhizobia, the roots were more sensitive than the shoots,and N₂ fixation was more sensitive to salinity than plant growth. Key words: Cicer arietinum, nodulation, N₂ fixation, Rhizobium, salinity     

Influence of the Form of Nitrogen Supply on Root Uptake and Translocation of Cations in the Xylem Exudate of Maize (Zea mays L)

Concentrations of inorganic cations are often lower in plantssupplied with NH₄⁺ as compared with NO₃^–. To examine whetherthis is attributable to impaired root uptake of cations or lowerinternal demand, the rates of uptake and translocation of K,Mg, and Ca were compared in maize plants (Zea mays L.) withdifferent growth-related nutrient demands. Plants were grownin nutrient solution with either 1·0 mol m^–3 NO₃^–or NH₄⁺ and the shoot growth rate per unit weight of roots wasmodified by varying the temperature of the shoot base (SBT)including the apical shoot meristem. The shoot growth rate per unit weight of roots, which was takenas the parameter for the nutrient demand imposed on the rootsystem, was markedly lower at 12°C than at 24°C SBT.As a consequence of the lower nutrient demand at 12°C SBT,uptake rates of NO₃^– and NH₄⁺ declined by more than 50%Compared with NO₃^– supply, NH₄⁺ nutrition depressed theconcentrations of K and particularly of Ca in the shoot, bothin plants with high and with low nutrient demand. This indicatesa control of cation concentration by internal demand ratherthan by uptake capacity of the roots. Translocation rates of K, Mg and Ca in the xylem exudate werelower in NH₄⁺- than in NO₃^–-fed plants. Net accumulationrates of Ca in the shoot were also decreased, whereas net accumulationrates of K in the shoot were even higher in NH₄⁺-fed plants.It is concluded that reduced cation concentrations in the xylemsap of plants supplied with NH₄⁺ are due to the lower demandof cations for charge balance. The lower K translocation tothe shoot is compensated by reduced retranslocation to the roots.For Ca, in contrast, decreased translocation rates in NH₄⁺-fedplants result in lower shoot concentration. Key words: Nitrogen form, cation nutrition, charge balance, xylem exudate, recirculation     

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     

Salt Tolerance in the Halophyte Suaeda maritima L.Dum.: Abscisic Acid Concentrations in Response to Constant and Altered Salinity

Endogenous abscisic acid contents were measured by gas-liquidchromatography in shoots of Suaeda maritima growing both inthe steady state over a range of salinities and over a time-coursefollowing an increase in the culture solution salinity of betweenapproximately 100 and 400 mol m^–3 NaCl. In steady-stateplants, the ABA content was maximal in the absence of salt at41 ng g^–1 fr. wt., declining to a minimum at 200 mol m^–3NaCl of 24 ng g^–1 fr. wt. Increase of culture solutionsalinity resulted in a marked increase in shoot ABA which wasmaximal after 6 h or 24 h in plants previously growing at 200mol m^–3 NaCl and in the absence of salt, respectively.Additionally, culture solution water potentials were loweredby 1.0 MPa (equivalent to raising the salt concentration byaround 200 mol m^–3); this resulted in a similar increasein endogenous ABA content to that brought about by an iso-osmoticsalt increase. Results are discussed in relation to the possiblerole of ABA in halophyte salt tolerance mechanisms. Key words: Suaeda, halophyte, abscisic acid, salt tolerance     

Influence of Age of Culture and Light Intensity on Solute Concentrations in Two Dunaliella Strains

Two strains of Dunaliella, one halotolerant and one halophilic,were grown in batch culture at NaCl concentrations varying from500 mol m^–3 to 3000 mol m^–3. Measurements were madeof the following solutes: glycerol, Na⁺, K⁺, Mg²⁺, Cl^–,phosphate in the cells of logarithmic and of stationary-phasecultures. The method used was to separate the cells from thebulk of the medium by differential density centrifugation. Soluteconcentrations were calculated using Blue Dextran as a markerfor extracellular space. It was found that in log-phase cells,glycerol accounted for one-half to two-thirds of the total cellsolute concentration, the remainder being largely accountedfor by Na⁺ and Cl^–. In the stationary phase glycerol felland Na⁺, plus Cl^–, rose. Light intensity was found toaffect cell volume and solute content. The means whereby soluteconcentrations are controlled is discussed. Key words: Osmoregulation, Ion concentrations, Dunaliella     

Potassium Transport in Enteromorpha intestinalis (L.) Link: MEASUREMENT OF INTRACELLULAR K+, EXCHANGE FLUXES AND THERMODYNAMIC ANALYSIS

Potassium transport has been studied in the marine euryhalinealga, Enteromorpha intestimlis cultured in seawater and in low-salinitymedium (Artificial Cape Banks Spring Water, ACBSW; 25·5mol m^–3 Cl^–, 20·4 mol m^–3 Na⁺, 0·5mol m^–3 K⁺). K⁺ fluxes were measured using ⁴²K⁺ and ⁸⁶Rb⁺although ⁸⁶Rb⁺ does not act as an efficient K⁺ analogue in thisplant. ⁴²K⁺ experiments on seawater plants typically exhibiteda single protoplasmic exchange phase whereas ⁸⁶Rb⁺ exhibitedtwo exchange phases. Compartmental analysis of ⁸⁶Rb⁺ effluxexperiments on seawater-grown Enteromorpha plants were usedto deduce the intracellular partition of K⁺ between the cytoplasm(279±38 mMolal) and vacuole (405±68 mMolal). Theplasmalemma K⁺ flux in plants in seawater was greater in thelight than in the dark (563±108 nmol m^–2 s^–1versus 389±66·7 nmol m^–2 s^–1). Inlow-salinity plants, separate cytoplasmic and vacuolar exchangephases were apparent. Analysis of ⁴²K⁺ efflux experiments onlow-salinity plants yielded a cytoplasmic K⁺ of 222±38mMolal and a vacuolar K⁺ of 82±11 mMolal. The plasmalemmaand tonoplast flux was 23±4·5 nmol m^–2 s^–1. The Nernst equation showed that, although K⁺ was close to electrochemicalequilibrium, active accumulation of K⁺ across the plasmalemmaoccurred in plants in seawater and ACBSW both in the light anddark. K⁺ was also actively transported inwards across the tonoplastin low-salinity plants. The electrochemical potential for K⁺across the plasmalemma ranged from 2·41±0·60kJ mol^–1 in plants grown in seawater in the light to 5·79±0·87kJ mol^–1 for plants in ACBSW in the light. Although K⁺is close to electrochemical equilibrium, the flux of K⁺ in plantsin both seawater and ACBSW media is high, hence the power consumptionof K⁺ transport is high. The permeability of K⁺ (P_K⁺) was significantlyhigher in the light than in the dark in plants in seawater (about7·0 versus 2·5 nm s^–1) but in plants inlow-salinity (ACBSW) medium the permeability was independentof light (about 12 nm s^–1). The energy requirements ofactive K⁺ transport by ATP-dependent pumps is discussed. Key words: Enteromorpha, Potassium transport, Ionic relations, Saltwater, Low salinity, Thermodynamics     

Effects of NaCl on Growth, Nitrogen Incorporation and Chemical Composition of Inoculated and NH4NO3 Fertilized Vicia faba (L. ) Plants

Vicia faba cv. Maris Bead was grown either on fixed nitrogenor on ammonium nitrate. After 4 weeks growth, nutrient solutionswere supplemented with 50, 75 and 100 mol m^–3 NaCl for15 d. Five harvests were made at weekly intervals, beginningat 4 weeks. Effects of salinity were directly related to dose,plant growth (fresh and dry weight) being depressed in bothN-fixing and N-fertilized plants. The number of nodules perplant and the proportion of those formed which developed intothe active nitrogen fixing state were depressed by salt stress.Increased size of nodules in salt-stressed plants only partlycompensated for the lower specific nitrogenase activity. Theeffects of salinity on plant nitrogen content were more pronouncedon N-flxing than on N-fertilized plants. The former took upmore Na⁺ and Cl^– than the latter: the implications ofthis and of ionic imbalance are discussed. Key words: Vicia faba, Growth, Salt stress, Nodulation