Tissue-Dependent Expression of the Rice wx+ Gene Promoter in Transgenic Rice and Petunia

The waxy (wx) locus, which controls the amylose synthesis, isknown to be expressed specifically in the endosperm and pollen.To study the tissue-specific regulation of the wx⁺ gene, weintroduced a fusion gene that consisted of the upstream sequenceof the wx⁺ gene and the gene for rß-glucuronidase(GUS) into cells of rice (Oryza sativa L.) and petunia (Petuniahybrida L.). GUS activity was examined in the regenerated transgenicrice and petunia plants. In transgenic rice, the upstream sequenceof the wx⁺ gene was sufficient to direct the tissue-specificexpression of GUS in the endosperm and pollen, and the controlof expression was quantitative. By contrast, in transgenic petunia,the same fusion gene was expressed in pollen but not in theendosperm. These results suggest that the putative cis-actingelements that direct pollen-specific expression are common toor similar in both monocotyledonous and dicotyledonous plants,whereas ciy-elements responsible for the endosperm-specificexpression of the rice wx⁺ gene do not function in petunia,in which development of the endosperm differs from that in rice. ⁴Present address: Division of Biological Sciences, GraduateSchool of Science, Hokkaido University, Kita-ku, Sapporo, 060Japan     

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     

Storage-protein Deposition in the Developing Rice Caryopsis in Relation to the Transport Tissues

The developing caryopsis of rice (Oryza sativa L.) was examinedhistologically at successive stages of grain-filling in orderto identify the factors which determine the distribution ofstorage protein in the endosperm, and which terminate the depositionof endosperm protein. The storage protein was deposited at theperiphery of the endosperm, and this distribution was apparentlycaused by the radial pattern of cell development in the endosperm,and by the proximity of the peripheral endosperm cells to thenucellar epidermis. The nucellar epidermis directly surroundsthe endosperm and functions as the pathway for amino acid transportto the endosperm. During the later stages of caryopsis developmentthe nucellar epidermis became compressed by being ‘sandwiched’between the expanding endosperm and the rigid hull (the tightlylocked palea and lemma) which encloses the caryopsis. It isproposed that this compression of the nucellar epidermis blocksthe supply of amino acids to the endosperm and thereby terminatesthe deposition of storage protein in the rice grain. Oryza sativa, rice, caryopsis (development), endosperm, grain filling, nucellar epidermis, storage protein     

Regulation of the Partitioning of Dry Matter and Calcium in Cucumber in Relation to Fruit Growth and Salinity

The regulation of the partitioning of dry matter and calciumin relation to fruit growth was investigated in cucumber plantsgrown in the salinity range of 3-8 mS cm^-1 in NFT (NutrientFilm Culture), with or without a fruit pruning treatment. Thedry weight gain of the plants was proportional to the outdoorintegral irradiance, with a common daily rate of 1 g MJ^-1 m^-2in two crops grown under summer (18 MJ m^-2 d^-1) and autumn (7MJ m^-2 d^-1) conditions. Within the salinity range studied, thereduction of plant dry weight was 9% mS^-1 cm^-1. However, fruitdry weight was only reduced at salinities above 5·5 mScm^-1, although the daily dry matter accumulation by fruit, asa percentage of total dry matter accumulation, was increased.Salinity reduced the dry matter accumulation in the young shootproportionally more than in the fruit. Although the total plantCa content was reduced by 13% mS^-1 cm^-1, the Ca content of theyoung shoot was reduced by 16·6%, compared to 11% inthe fruit. Pruning fruit reduced neither plant dry weight norCa uptake. The growth of the remaining fruit, and to a lesserdegree of the young shoot, accounted for all surplus assimilates.Thus, fruit were the dominant sinks for assimilates whilst themature leaves were the strongest sinks for Ca. Nevertheless,the fruit sustained the capacity to import Ca better than theyoung shoot, when supplies of both assimilates and Ca were reducedby high salinity.Copyright 1994, 1999 Academic Press Cucumber, Cucumis sativus L., salinity, fruit pruning, dry matter and calcium     

The Use of 14C-Ethane Diol as a Quantitative Tracer for the Transpirational Volume Flow of Water and an Investigation of the Effects of Salinity upon Transpiration, Net Sodium Accumulation and Endogenous ABA in Individual Leaves of Oryza sativa L.

Yeo, A. R., Yeo, M. E., Caporn, S. J. M., Lachno, D. R. andFlowers, T. J. 1985. The use of ¹⁴C-ethane diol as a quantitativetracer for the transpirational volume flow of water and an investigationof the effects of salinity upon transpiration, net sodium accumulationand endogenous ABA in individual leaves of Oryza sativa L.—J.exp. Bot. 36: 1099–1109. Oryza sativa L. (rice) seedlings growing in saline conditionsexhibit pronounced gradients in leaf sodium concentration whichis always higher in the older leaves than the younger ones.Individual leaf transpiration rates have been investigated todiscover whether movement of sodium in the transpiration streamis able to explain these profiles from leaf to leaf. The useof ¹⁴C labelled ethane diol to estimate transpiration was evaluatedby direct comparison with values obtained by gas exchange measurements.Ethane diol uptake was linearly related to the transpirationalvolume flow and accurately predicted leaf to leaf gradientsin transpiration rate in saline and non-saline conditions. ¹⁴C-ethanediol and ²²NaCl were used to compare the fluxes of water andsodium into different leaves. The youngest leaf showed the highesttranspiration rate but the lowest Na accumulation in salineconditions; conversely, the older leaves showed the lower transpirationrates but the greater accumulation of Na. The apparent concentrationof Na in the xylem stream was 44 times lower into the youngerleaf 4 than into the older leaf 1. Exposure to NaCl (50 molm^–3) for 24 h elicited an increase in endogenous ABA inthe oldest leaf only, but no significant changes occurred inthe younger leaves. Key words: —Salinity, rice, Oryza sativa L., transpiration, volume flow, abscisic acid     

Effects of Salinity on Growth, Water Relations and Ion Accumulation of the Subtropical Perennial Halophyte, Atriplex griffithii var. stocksii

The effects of salinity on growth, water relations, glycinebetainecontent, and ion accumulation in the perennial halophyte Atriplexgriffithii var. stocksii were determined. The following questionswere addressed: (1) What effect does salinity have on growthresponses at different ages? (2) Is A. griffithii an ion accumulator?(3) Does A. griffithii accumulate glycinebetaine in responseto salinity? Atriplex griffithii plants were grown in pots at0, 90, 180 and 360  m M NaCl in sand culture in a plantgrowth chamber and plants were harvested after 30, 60 and 90d. Plant total dry weight was significantly inhibited at 360m M NaCl. Root growth showed a substantial promotion at 90 mM NaCl. The water potential and osmotic potential of shootsbecame more negative with increasing salinity and time of growth.The Na⁺and Cl^-content in both shoots and roots increased withincreases in salinity. Increased treatment levels of NaCl induceddecreases in Ca⁺, K⁺and Mg²⁺in plants. Atriplex griffithii accumulateda large quantity of ions, with the ash content reaching 39%of the dry weight in leaves. Inorganic ion accumulation is significantin osmotic adjustment and facilitates water uptake along a soil-plantgradient. Glycinebetaine concentration was low in roots, andin stems it increased with increases in salinity. Total amountsof glycinebetaine in leaves increased with increases in salinity,and its concentration increased substantially at 360 m M NaCl.Copyright 2000 Annals of Botany Company Atriplex griffithii, glycinebetaine, growth, ions, water relations.     

Salinity Reduces Water Use and Nitrate-N-use Efficiency of Citrus

Five-month-old Cleopatra mandarin (Citrus reticulata Blanco)(CM) and Volkamer lemon (Citrus volkameriana Ten. and Pasq.)(VL) seedlings were grown in a glasshouse in 2·3-1 potsof Candler fine sand. Plants were irrigated with either non-saline(EC_e = 0·23 dS m^-1) or saline (6·13 dS m^-1) waterusing 3:1 NaCl:CaCl₂ solution over a 4-week period. A singleapplication of K¹⁵NO₃ (19·64 atom % excess ¹⁵N) at 212mg N1^-1, was substituted for a normal weekly fertilization after3 weeks and plants were harvested 7 d later. The transpirationrate, uptake of nitrogen, growth and nitrogen-use efficiency(NUE) on a dry weight basis (mg d. wt mg^-1 N) of both specieswas reduced by salinity. Based on growth, water-use and chloride(Cl) accumulation in leaves, VL was more salt-sensitive thanCM, but ¹⁵N uptake was equally reduced by salinity in both species.Salinity reduced ¹⁵N uptake relatively more than shoot growthover the 7-d period, such that the ¹⁵NUE (mg d. wt µg^-115N) of new shoot growth of both species increased. There wasno evidence of Cl antagonism of nitrate (NO₃) uptake but totalplant ¹⁵NO₃ uptake was positively correlated with whole planttranspiration in both species. Thus, it appears that reductionsin NO₃ uptake are more strongly related to reduced water usethan to Cl antagonism from salt stress.Copyright 1993, 1999Academic Press Sodium, chloride, salinity, calcium, nitrate, ¹⁵NO₃ uptake, nitrogen allocation, nitrogen-use efficiency, water use, Citrus reticulata, Citrus volkameriana     

Sink Activity Estimation by Sink Size and Dry Matter Increase During the Ripening Stage of Barley (Hordeum vu/gare) and Rice (Oryza sativa)

During the ripening stage of barley and rice, the sink activitywas defined as the dry matter increase per units sink size,leaf area and time, as follows: NAR = A.SinkW+NAR', where NAR is the net assimilation rate (g d.wt dm^–2d^–1);A is the sink activity [g d.wt g^–1d.wt (ear) dm^–2d^–1]; Sink W is ear wt per plant at heading (g d.wt);and NAR' is net assimilation rate excluding the assimilate ofsink organ (g d.wt dm^–2 d^–1). Plant material with 16 combinations of mutually different sink(ear) and source (leaf) size were produced at heading for eachcrop: parts of each leaf and ear were removed to produce fourgrades in barley, and also a part of each leaf was removed producingfour grades for four rice varieties showing different ear size.NAR and NAR' were determined during 26 and 21 d in barley andrice after heading, respectively. Sink activity (A), representedas the assimilation rate induced by the sink organ, was estimatedfrom the relationship between SinkW and NAR using the previousequation. The sink activity was significantly higher in ricewith a value of 0–0.028 g d.wt g^–1 d.wt (ear) dm^–2d^–1 vs. 0–0.0017 in barley, suggesting that therelative role of leaves for grain filling is considerably higherin rice than in barley. The sink activity obtained in the studymight be introduced into a model to predict the yields of barleyand rice. Hordeum vulgare L, barley, Oryza saliva L, rice, dry matter, NAR, sink, source, sink activity, model     

Salt Tolerance in the Halophyte, Suaeda maritima (L.) Dum.: The Influence of the Salinity of the Culture Solution on the Content of Various Organic Compounds

Plants of the halophyte Suaeda maritima were grown in tap wateror in a culture solution in the presence or absence of sodiumchloride and the levels of sugars, amino acids, organic acidsand quaternary ammonium compounds determined in relation tothe balance between cytoplasmic and vacuolar water potentials.The sugar content (some 7 µmol. g f. wt^–1) was unaffectedby the salinity of the growth medium as was the overall contentof amino acids (about 4 µmol. g f. wt^–1). The organicacid content was maximal in plants kept in tap water alone wherethe dominant acid was malic. Plants grown in culture solutioncontained the same acids, although addition of sodium chlorideto the medium brought about the apparent loss of glycolic acidand the appearance of oxalic acid. Only a single quaternaryammonium compound, glycinebetaine, was apparently present inthe tissues: the content of betaine doubled (to 37·5µrmol. g f. wt^–) when sodium chloride was addedto the culture solution. The content of these various compoundsis discussed in relation to the relative values of the cytoplasmicand vacuolar components of the overall tissue water potential Suaeda maritima, halophyte, salt tolerance, betaine, organic compounds, water potential     

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     

Osmotic adjustment in marine yeast

The effect of environmental salinity on cell growth, and onthe composition and accumulation of compatible solutes, or osmotica,of five yeast strains (Aureobasidium pullulans, Candida sp.,Cryptococcus albidus var. albidus, Debaryomyces hansenii andRhodotorula rubra) was compared. All these yeast were isolatedfrom manne environments, but were able to grow in the absenceof salt and should therefore be considered as halotolerant strains.According to their specific cell growth rates at different saltconcentrations, these strains vary in their capacity to osmoticallyadjust to modifications in external salinity. Candida sp. appearsto be the most sensitive since the maximum salt concentrationat which it can grow is 1.54 mol 1^-1 NaCl; however, it showedthe highest specific cell growth in the range of 0 to 1.54 mol1^-1 NaCl. Aureobasidium pullulans, on the other hand, showedthe lowest specific growth rate, but the highest halotolerancerange from 0 to 5.13 mol 1^-1 NaCl. Debaryomyces hansenii, incontrast, showed higher specific growth at this salinity rangeCryptococcus albidus var. albidus and Rhodotorula rubra showedsimilar specific cell growth rate values and halotolerance between0 and 2.45 mol 1^-1 NaCl. The protein and carbohydrate contentof the biomass of the different yeast cells, as a result ofexternal salinity vanation, remained practically constant. Themost important effects of the increase in salt concentrationin the culture medium were the reduction of cell volume andthe accumulation of low-molecular-weight metabolites (LMWM).which appear to act as osmoregulators. Glycerol was found asthe major compatible solute in the different marine yeasts studiedherein with a total contribution of 64–96% of the internalcell osmolarity. Other LMWM, like carbohydrates and amino acids,contributed to a lesser extent to compensate for the rise inosmotic pressure promoted by the salinity of the external environment.     

Ionic Relations of Garden Orache, A triplex hortensis L.: Growth and Ion Distribution at Moderate Salinity and the Function of Bladder Hairs

The growth of garden orache, A triplex hortensis was studiedunder conditions of mild NaCl or Na₂SO₄ salinity. Growth, drymatter production and leaf size were substantially stimulatedat 10 mM and 50 mM Na⁺ salts. Increased growth, however, appearedto be due to a K⁺-sparing effect of Na⁺ rather than to salinityper se. The distribution of K⁺ and Na⁺ in the plant revealeda remarkable preference for K+ in the roots and the hypocotyl.In the shoot the K/Na ratio decreased strongly with leaf age.However, the inverse changes in K⁺ and Na⁺ content with leafage were dependent on the presence of bladder hairs, which removedalmost all of the Na⁺ from the young leaf lamina. Measurementsof net fluxes of K⁺ and Na⁺ into roots and shoots of growingAtriplex plants showed a higher K/Na selectivity of the netion flux to the root compared to the shoot. With increasingsalinity the selectivity ratio S_{K, Na}^* of net ion fluxes tothe roots and to the shoots was increased. The data suggestthat recirculation of K⁺ from leaves to roots is an importantlink in establishing the K/Na selectivity in A. hortensis plants.The importance of K⁺ recirculation and phloem transport forsalt tolerance is discussed. Key words: Atriplex hortensis, Salinity, Potassium, Sodium, K⁺ retranslocation, Bladder hairs, Growth stimulation     

Senescence of Rice Leaves XXIV. Involvement of Calcium and Calmodulin in the Regulation of Senescence

Effects of compounds that influenced calcium uptake and calmodulininhibitors on the senescence of detached rice leaves were examined.Chelators, ethyleneglycol-bis-(ß-aminoethyl ether)-N,N,N',N'-tetraaceticacid (EGTA) and l,2-bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraaceticacid (BAPTA), significantly promoted senescence of detachedrice leaves in the dark and light. The effect of EGTA can bereversed by treating detached rice leaves with calcium. Verapamil,a calcium channel blocker, and lanthanum chloride, a calciumantagonist, promoted dark-induced, and suppressed BA- and light-retardedsenescence of detached rice leaves. Calcium ionophore A23187 [GenBank] and ruthenium red, believed to raise cytosolic level of Ca²⁺,were quite effective in retarding dark-induced and ABA-promotedsenescence of detached rice leaves. Calmodulin inhibitors, W-7,compound 48/80, chlorpromazine and trifluoperazine, significantlypromoted dark-induced, and suppressed BA- and light-retardedsenescence of detached rice leaves. It is concluded that cytosoliclevel of Ca²⁺ may regulate senescence of detached rice leavesthrough a calmodulin-dependent mechanism. (Received June 13, 1990; Accepted August 3, 1990)     

The Mineral Ion Relations of Mangroves I. Root Cell Compartments in a Salt Excluder and a Salt Secreter Species at Low Salinities

The efflux kinetics of ²²Na and ³⁶Cl from 48 h pre-loaded Rhizophoramangle and Avicennia germinans mangrove seedling roots grownin low salinity conditions have been documented. Estimates ofthe percent isotope distributed throughout the whole plant,the uptake rates, the amounts calculated to be present in theroot cell compartments, and the rate constants and half-timesof efflux were made. Little to no ²²Na or ³⁶Cl was noted asbeing distributed to leaf tissue in the red mangrove, Rhizophoramangle, substantiating its characterization as a non-secreting,salt excluding species. Significantly greater net uptake ratesfor Na and Cl were observed for the black mangrove, Avicenniagerminans, a non-excluding, salt-secreting species. The typicalintracellular compartmentation found in higher plant root tissueswas noted to be present in these mangroves and the efflux kineticsclearly indicated that Na and Cl were handled differentiallyby these compartments and their membranes. Rhizophora manglerevealed greater apparent contents of Na than Cl in both thevacuolar and cytoplasmic phases (5.4 and 7.7 fold greater, respectively).The inverse was found for Avicennia germinans, with the apparentvacuolar compartment amount for Cl being 4.6 times greater thanthe Na amount and the cytoplasmic Cl amount was 1.5 times morethan Na contents. The rate constants of efflux showed a patternof significantly greater Na than Cl efflux from each respectivered mangrove compartment, while the black mangroves had a patternof greater efflux rates of Cl than Na in each compartment. Thehalf-times of efflux for Na from the black mangrove cytoplasmiccompartment were 3.5 times longer, while vacuolar half-timesof efflux were near unity for Na and Cl. The results are discussedin terms of Scholander's model of salt secreting and salt excludingspecies. (Received March 26, 1984; Accepted June 26, 1984)     

Salt Adaptation of K+ Channels in the Plasma Membrane of Tobacco Cells in Suspension Culture

The patch-clamp technique was used to study and compare thecharacteristics of cation channels in the plasma membrane ofcultured lines of tobacco (Nicotiana tabacum L. cv. Bright Yellow-2)cells that were unadapted (NaCl-unadapted cells) and adaptedto 50 and 100 mM NaCl (Na50-adapted and Na100-adapted cells).In these three types of tobacco cell, the outward whole-cellcurrent activated by depolarization was dominated mainly bythe activity of the outward rectifying K⁺ channels with a single-channelconductance of 20 pS. The steady-state amplitude of the outwardwhole-cell currents at all the positive potentials examineddecreased in the following order: NaCl-unadapted cells>Na50-adaptedcells>Na100-adapted cells. There were no significant differencesbetween the NaCl-unadapted and the Na50-adapted cells in termsof the ratio of permeabilities of these channels to K⁺ and Na⁺ions. Furthermore, no significant differences in terms of thesingle-channel conductance of these channels were observed amongthe NaCl-unadapted, the Na50-adapted and the Na100-adapted cells.These observations suggest that adaptation to salinity of tobaccocells in suspension results in reduced permeability of the K⁺channels to both K⁺ and Na⁺ ions, without any change in theK⁺/Na⁺ selectivity and single-channel conductance of these channels. ¹Present address: Research Laboratory of Applied Biochemistry,Tanabe Seiyaku Co., Ltd.16-89 Kashima 3-chome, Yodogawaku, Osaka,532 Japan     

Salt Tolerance in Simmondsia chinensis: Water Balance and Accumulation of Chloride, Sodium and Proline Under Low and High Salinity

The response of jojoba [Simmondsia chinensis (Link) Schneid]plants to salinity was studied in solution culture. At concentrationsof 0, 100, 200 and 600 m-mol l^–1 NaCI it was found thatjojoba plants have high tolerance to NaCl. The growth of theseplants was not affected by salinity. They accumulated largeamounts of Cl^–, Na⁺ and proline. These amounts decreasedrapidly in plants transferred back to control medium. Potassiumcontent decreased in NaCl-treated plants and tended to increaserapidly to the control level in plants transferred to controlmedium. The effect of salinity on water balance was not appreciable.As suggested for other xerophytic species, it could be assumedthat the high tolerance of jojoba to salinity plays an importantrole in its ability to endure periods of drought. The role ofproline during or after stress remains an open question. Simmondsia chinensis (Link) Schneid, jojoba, salt tolerance, sodium accumulation, chloride ion accumulation, proline accumulation, xerophytism, drought tolerance     

Salt Tolerance in Cell Suspension Cultures of the Halophyte Kosteletzkya virginica

Tolerance to NaCl was studied in cell suspension cultures ofKosteletzkya virginica (L.) Presl. (Malvaceae), a dicotyledonoushalophyte that grows in tidal marshes of the eastern UnitedStates. Growth of salinized cultures was significantly inhibitedat high (255 mol m^–3 NaCl), but not at lower externalsalinities. Adjustment of cell suspensions to Nacl was rapid,with the duration of the normal growth cycle unaffected by salinity.Maximum biomass was attained when cultures were exposed to NaClduring early log growth. Patterns of inorganic ion accumulationreflected the utilization of both Na⁺ and K⁺ as osmotica, withNa⁺ content substantially increasing when cells were grown atan external salinity sufficient to reduce growth. K⁺ uptakeselectivity was high and Na⁺/K⁺ ratios were low in salt-treatedcultures even though K⁺ content was somewhat lower comparedto unsalinized cultures. Free proline and microsomal lipid contentincreased in salt-treated cell cultures. Key words: Kosteletzkya virginica, halophyte, salt tolerance, cell suspension culture     

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