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     

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     

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     

Salt Tolerance in the Triticeae: Leymus sabulosus

Elymus dahuhcus, Leymus giganteus, L. angustus, L. sabulosusand, to a lesser extent, L. triticoides, were found to tolerate200 mol m^–3 NaCl in solution culture. Elymus dahuricusdiffered from the Leymus species in its ion-uptake characteristics,showing a greater uptake of Cl and Na and a greater loss ofK from the shoots. In a more detailed experiment on Leymus sabulosusit was found that transpiration rates altered rapidly in responseto changes in external salinity whereas the accumulation ofNa and Cl in the leaves exhibited a lag of several days. Insalt stressed L. sabulosus Cl partially replaced the high levelsof nitrate found in the leaves of control plants. Glycinebetainelevels increased in the leaves from 8.0 mol m^–3 plantsap in the controls to 28 mol m^–3 plant sap at 250 molm^–3 NaCl. Key words: Salt stress, Transpiration, Solute accumulation, Leymus     

Interaction of Salinity and Anaerobiosis in Barley and Rice

Barley and rice at the early tillering stage were exposed simultaneouslyto anaerobiosis and high [NaCl]. Barley was grown at 0.5, 70,and 125 mol m^–3 NaCl, and rice at 2, 20, 40, and 80 molm^–3 NaCl. Surprisingly, anaerobiosis only slightly aggravatedthe adverse effects of high [NaCl] on root and shoot growthof both species. For rice and barley grown under aerobic conditions, high [NaCl]increased [Na⁺] and [Cl^–] and decreased [K+] in both rootsand shoots. However, the changes in ion concentrations in theshoots were smaller for rice than for barley. For roots of barley, anaerobiosis decreased [Na⁺], [Cl^–],and [K⁺] at both low and high [NaCl], possibly as a result ofinhibition of active ion accumulation. For barley shoots, anaerobiosisincreased [Na⁺] and [Cl^–], but only at high salinity;in contrast, [K⁺] was reduced by anaerobiosis at both low andhigh [NaCl]. These results indicate that anaerobiosis slightlyincreased the permeability of the barley root system to Na+and Cl^–. For rice, the most important interaction between salinity andanaerobiosis occurred in the shoots, where anaerobiosis increased[Na⁺] and decreased [K⁺], particularly at 40 and 80 mol m^–3NaCl, while there was no interaction between anaerobiosis andsalinity for Cl^– uptake. It is therefore suggested thatanaerobic treatment of rice decreased the selectivity for K⁺over Na⁺ of cation transport to the shoots, at least for plantsgrown at high salinities.     

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     

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     

Interaction Between Mineral Nutrients, Cytokinin and Gibberellic Acid During Growth of Sorghum at High NaCI Salinity

Sorghum bicolor (L.) Moench, cv. 610, adapted to high salinitywas able to grow at 300 mol m^–3 NaCl only when half-strengthHoagland's solution was enriched with mineral nutrients. Theoptimal growth rate was observed in full strength Hoagland'ssolution; at higher or lower concentrations growth rates werelower. In contrast, growth rate of plants exposed to 150 molm^–3 NaCl was not affected by similar modification of theHoagland solution concentration. At high salinity, additionof cytokinin (CK) or gibberellic acid (GA), or a mixture ofboth, can induce the same effect on growth as the increasedmineral nutrient concentration. Phytohormones and increasedmineral concentration have similar effects, possibly becausean imbalance in phytohormones, rather than a mineral deficiency,limits growth at 300 mol m^–3 NaCl in the presence of half-strengthHoagland solution. The change in mineral concentration in thenutrient medium, in addition to its nutritional effect, alsoapparently acts as a signal involved in hormonal balance whichallows growth at high salinity. Exposure of Sorghum to 300 molm^–3 NaCl causes a decrease in the range of nutrient concentrationswhich can sustain growth. Adjustment of the nutrient concentrationmay induce the synthesis of endogenous CK and GA concentrationsrequired for growth. In contrast, addition of CK or GA at similarconcentrations during the adaptation (pretreatment) period inhibitsgrowth and prevents the adaptation process. The response tothe exogenous phytohormone treatments depends on the time elapsedfrom the beginning of salinization. Key words: Adaptation to salinity, cytokinin, gibberellic acid, mineral nutrition, growth, Sorghum, NaCl     

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     

Spatial and Temporal Aspects of Growth in the Primary Root of Cotton Seedlings: Effects of NaCl and CaCl2

Seedlings of cotton (Gossypium hirsutum L. cv. Acala SJ-2) weregrown in modified Hoagland nutrient solution with various combinationsof NaCl and CaCl₂. Marking experiments and numerical analysiswere conducted to characterize the spatial and temporal patternsof cotton root growth at varied Na/Ca ratios. At 1 mol m^–3Ca, 150 mol m^–3 NaCl reduced overall root elongation rateto 60% of the control, while increasing Ca to 10 mol m^–3at the same NaCl concentration restored the elongation rateto 80% of the control. Analysis of the spatial distributionof elongation revealed that the presence of 150 mol m^–3NaCl in the medium shortened the growth zone by about 2 mm fromthe approximate 10 mm in the control and also reduced the relativeelemental elongation rate (i.e. the longitudinal strain rate,defined as the derivatives of displacement velocity of a cellularparticle with respect to position on root axis). Supply of 10mol m^–3 Ca at the high salt condition restored partiallythe relative elemental elongation rate, but not the length ofthe growth zone. Compared to the control, the growth trajectoriesshowed that at 1 mol m^–3 CaCl2 it took more time for acellular particle to move through the growth zone at 150 molm^–3 NaCl, while at 10 mol m^–3 CaCl it took lesstime and there was no difference between the NaCl treatments Key words: Gossypium hirsutum, salinity stress, root growth kinematics     

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     

X-Ray Microanalysis and Ultrastructural Studies of Cell Compartments of Dunaliella parva

Hajibagheri, M. A., Gilmour, D. J., Collins, J. C. and Flowers,T. J. 1986. X-ray microanalysis and ultrastructural studiesof cell compartments of Dunaliella parva. -J. exp. Bot. 37:1725–1732. Ultrastructural studies of the unicellular green alga Dunaliellaparva showed the presence of cytoplasmic vacuoles. X-ray microanalysiswas performed on sections of cells which had been freeze substitutedin acetone. It was found that the concentrations of both Naand Cl were much higher in the vacuoles than in the cytoplasm.When cells were grown in 0·4 kmol m^–3 NaCl theNa and Cl concentrations in the vacuoles were 349 and 283 molm ^–3 respectively, whilst cytoplasmic Na and Cl concentrationswere 37 and 26 mol m^–3. Corresponding values for cellsgrown in 1·5 kmol m^–3 NaCl were 392 mol m^–3Na and 325 mol m^–3 Cl in the vacuoles and 36 mol m^–3Na and 30 mol m^–3 Cl in the cytoplasm. Immediately afterexposure to an increase in external salinity Na and Q concentrationsincreased in both vacuoles and cytoplasm. The results are discussedwith reference to compartmental models for the ionic relationsof Dunaiiella. Key words: X-ray microanalysis, ultrastructural studies, Dunaliella parva     

Malate Accumulates in the Vacuole of Chara australis During Uptake of Ammonium From Chloride-free Solution

Internodal cells of Chara australis can accumulate ammoniumto high concentrations (10 to 70 mol m^–3) in their vacuoles.When Cl^– is included in the bathing solution, changesin the cellular concentrations of ammonium, K⁺, Cl^– andNa⁺ have been shown to meet the requirements for electroneutralityand to account for the changes in vacuolar osmotic pressureassociated with ammonium uptake. If accumulation occurs in theabsence of external Cl^–, however; changes in the inorganicions do not meet these criteria. Malate is found in the vacuolesof cells accumulating amine in the absence of external Cl^–and its presence (at 0·5 to 8·5 mol m^–3)allows us to account for electroneutrality and for changes inthe osmotic potential. Key words: Malate, Chara, electroneutrality, ammonium     

Age, Fluence Rate, and Anthocyanin Production in Zea mays Seedlings

Increase in fluence rates of white light over the range of 5to 80 µmol m^–2 s^–1 brought about a correspondingincrease in amounts of anthocyanin production in shoots of Zeamays L. seedlings. Roots also exhibited a similar relationshipbetween increased fluence rate and increased anthocyanin productionover the range of 5 to 40 µmol m^–2 s^–1 whereasfluence rates above 40 µmol m^–2 s^–1 broughtabout decreases in anthocyanin production. Rates of productionand amounts of accumulation of anthocyanin in both shoots androots were found to vary with the age of the seedlings at thetime of exposure to light. Age, fluence rates, anthocyanin, seedlings, Zea mays     

Interactive effects of salinity, nitrogen and sulphur on the organic solutes in Spartina alterniflora leaf blades

Glycinebetaine, proline, asparagine, sucrose, glucose, and dimethylsulphoniopropionate(DMSP) were the major organic solutes in Spartina alternifloraleaf blades. To investigate the physiological role(s) of thesesolutes, the effects of salinity, nitrogen, and sulphur treatmentson leaf blade solute levels were examined. Glycinebetaine wasthe major organic solute accumulated in leaf blades grown at500 mol m^–3 NaCl, although asparagine and proline alsoaccumulated when the supply of nitrogen was sufficient. Thesesolutes may play a role in osmotic adjustment. In contrast,DMSP levels either did not change or were reduced in responseto the 500 mol m^–3 NaCl treatment. Furthermore, elevatednitrogen supply decreased leaf blade DMSP levels, which wasopposite to the response of glycinebetaine, proline, and asparagine.A 1000-fold increase in external sulphate concentration hadno effect on the leaf blade levels of DMSP, glycinebetaine,proline, or asparagine. These findings suggest that the majorphysiological role of DMSP in S. alterniflora leaf blades isnot for osmotic adjustment, even under conditions of nitrogendeficit and excess sulphur. Instead, DMSP which was presentat 45—130 µmol g^–1 dry weight, may play arole as a constitutive organic osmoticum. Key words: Spartina alterniflora, dimethylsulphoniopropionate, glycinebetaine, nitrogen, salinity     

Changes of Cell Wall Composition and Polymer Size in Primary Roots of Cotton Seedlings Under High Salinity

The aim of this study was to investigate changes in cell wallchemical composition and polymer size in the root tip of intactcotton seedlings (Gossypium hirsutum L. cv. Acala SJ-2) grownin saline environments, in order to relate the interaction betweenhigh salinity and root growth to possible changes in cell wallmetabolism. Cotton seedlings were grown in modified Hoagland nutrient solutionwith various combinations of NaCl and CaCl₂. Cell walls werefractionated into four fractions (pectin, hemicellulose 1 and2, cellulose), and analysed for their total sugar content, neutralsugar composition and size of polysaccharides. At 1 mol m^–3Ca, 150 mol m^–3 NaCl resulted in a significant increasein the cell wall uronic acid content, but a reduction in cellulosecontent on a per unit dry weight basis. Supplemental Ca overcamethe inhibitory effect of high Na on cellulose content. The neutralsugar composition of the cell wall fractions showed no majorchanges caused by varied Na/Ca ratios. Determinations of polysaccharidepolymer size showed that high Na at 1 mol m^–3 Ca led toan increase in the amount of polysaccharides of intermediatemolecular size and a decrease in that of small size in the hemicellulose1 fraction, indicating a possible inhibition of polysaccharidedegradation by high Na. This change was not observed in the10 mol m^–3 Ca treatments. The results reveal a relationshipbetween the effects of high salinity on root growth and cellwall metabolism, particularly in regard to cellulose biosynthesis Key words: Gossypium hirsutum, salinity, root, cell wall     

Ion Fluxes Across the Transfusion Zone of Secreting Limonium Salt Glands Determined from Secretion Rates, Transfusion Zone Areas and Plasmodesmatal Frequencies

Faraday, C. D., Quinton, P. M. and Thomson, W. W. 1986. Ionfluxes across the transfusion zone of secreting Limonium saltglands determined from secretion rates, transfusion zone areasand plasmodesmatal frequencies.—J. exp. Bot. 37: 482–494. The epidermal salt-secreting glands of Limonium (Plumbaginaceae)are enclosed in a cuticular envelope. Ions and metabolites enterthe glands from the mesophyll through gaps in the cuticularenvelope, the transfusion zones. Net influxes of ions acrossthe transfusion zone were calculated from measurements of secretionrates and transfusion zone areas. When leaves of L. pereziiF. T. Hubb. were treated with 300 mol m^–3 NaCl, transfusionzone influxes of Na⁺ K⁺, Ca⁺⁺ and Cl^– as high as 7?0?10^–5,1.7?10^–5, 5?8?10^–7 and 8.5?10^–5 mol m^–2s^–1 respectively, were calculated. Assuming a transmembranepathway, these fluxes would be some of the highest reportedfor ions in plant cells. Key words: Salt glands, ion fluxes, ultrastructure     

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     

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 Halophyte Suaeda maritima L. Dum. Growth, Ion and Water Relations and Gas Exchange in Response to Altered Salinity

Clipson, N. J. W. 1987. Salt tolerance in the halophyte Suaedamaritima L. Dum. Growth, ion and water relations and gas exchangein response to altered salinity.—J. exp. Bot. 38: 1996–2004. Shoot and root fresh and dry weights and shoot sodium, chlorideand potassium contents were measured and shoot relative growthrates calculated in seedlings of Suaeda maritima over a periodof 11 d following a raising of culture solution salinity from0 to 200 mol m₃– NaCl. Growth, growth rates and sodiumand chloride contents, as compared to plants growing in theabsence of salt were increased whilst potassium contents declined.Shoot sodium accumulation rate and the rate of transport ofsodium from root to shoot, osmotic potential, and rates of photosynthesisand transpiration were also measured for up to 72 h after transferof plants originally growing at 0 and 200 mol₃– NaCl to200 and 400 mol m₃– NaCl respectively. Ion uptake andtransport rates were maximal 6-12 h after transfer and thendeclined to new steady-state levels within 48 h; osmotic potentialswere lowered over a 72 h period on average by approximately1·0 MPa; and after 9 h photosynthetic and transpirationrates were reduced by about 20percnt; and 30% respectively.Results are discussed in terms of the ability of halophytesto adjust to fluctuating salinity and to salt tolerance mechanismsin general. Key words: Suaeda maritima, salinity, gas exchange, growth, ion and water relations