The Ionic Relations of Acetabularia mediterranea

The concentrations of K⁺, Na⁺, and Cl^– in the cytoplasmand the vacuole of Acetabularia mediterranea have been measured,as have the vacuolar concentrations of SO₄^–– andoxalate. The electrical potential difference between externalsolution, and vacuole and cytoplasm has been measured. The resultsindicate that Cl^– and SO₄^–– are probably transportedactively into the cell, and that active transport of Na⁺ isoutwards. The results for K⁺ are equivocal. The fluxes of K⁺,Na⁺, Cl^–, and S0₄^–– into the cell and theeffluxes of Na⁺ and Cl^– have been determined. The Cl^–fluxes are extremely large. In all cases the plasmalemma isthe rate-limiting membrane for ion movement. A technique isdescribed for the preparation of large, completely viable cellfragments containing only cytoplasm, with no vacuole.     

Ontogenetic Changes in the Chemical Composition of Ricinus communis Grown with NO-3 or NH+4 as N Source

Ricinus communis L. var. Gibsonii was grown in Long Ashton nutrientmedium with either 12mol m^–3 NO^–₃ or 8.0 mol m^–3NH⁺₄ as N source. Two plants from each N treatment were harvestedtwice a week and analysed for C, N, P, S, NO^–₃, SO^2–₄Cl^–K⁺Na⁺, Ca²⁺ Mg²⁺ and ash alkalinity. Statistical analysis of thedata showed that the effect of age and N source was differentfor the chemical variables analysed. Thus [Na⁺] was unaffectedby age or N source, and for both N sources [Mg²⁺] started atthe same level and decreased at the same rate as the plantsmatured. With NH⁺₄ as N source, [SO^2–₄] was higher thanwith NO^–₃, but did not alter with age. The concentrations,in mmol g^–1 dry wt, of C, organic N, K⁺ and Ca²⁺ weredifferent for the two N sources, but the levels of these variablesaltered with age in the same way for both N sources; i.e. therewas no age x N interaction. In the case of P, NO^–₃, Cl^– and COO^–, however,age-related variations were different for the two N sources.It is concluded, inter alia, that [Na⁺] is determined by external[Na⁺] alone, and that K⁺, Ca²⁺ and Cl^– are the inorganicions actively involved in charge balance during ion uptake bythe roots. Key words: Ontogeny, Chemical composition, Plant nutrition     

Effect of NaCI Salinity on Flows and Partitioning of C, N, and Mineral Ions in Whole Plants of White Lupin, Lupinus albusL.

Plants of Lupinus albus L., cv. Ultra, were grown hydroponicallywith NO₃^–-nutrition for 51 d under control (0.05 mol m^–3Na⁺ and 10 mol m^–3 Cl^–) and saline (40 mol m^–3NaCI) conditions. Plants were harvested 41 and 51 d after germinationand analysed for content and net increment of C, N and the mineralcations K⁺, Na⁺, Mg²⁺, and Ca²⁺ and the anions Cl^–, NOJ,malate, phosphate, and SO₄^2–. Roots, stem interaodes,petioles and leaflets were analysed separately. During the studyperiod net photosynthesis, respiratory losses of CO₂ from shootand root and the composition of the spontaneously bleeding phloemsap and the root pressure xylem exudate were also determined.Using molar ratios of C over N in the transport fluids, incrementsof C and N, and photosynthetic gains as well as respiratorylosses of C, the net flows of C and N in the xylem and phloemwere then calculated as in earlier studies (Pate, Layzell andMcNeill, 1979a). Knowing the carbon flows, the ratios of ionto carbon in the phloem sap, and ion increments in individualorgans, net flows of K⁺, Na⁺, and Cl^– over the study periodwere also calculated. Salt stress led to a general decrease of all partial componentsof C and N partitioning indicating that inhibitions were notdue to specific effects of NaCI salinity on photosynthesis oron NO₃ uptake. However, there were differences between variouslyaged organs, and net phloem export of nitrogenous compoundsfrom ageing leaves was substantially enhanced under saline conditions.In addition, NO₃^–reduction in the roots was specificallyinhibited. Uptake and xylem transport of K⁺ was more severelyinhibited than photosynthetic carbon gain or NO₃^– uptakeby the root. K⁺ transport in the phloem was even more severelyrestricted under saline conditions. Na⁺ and Cl^– flowsand uptake, on the other hand, were substantially increasedin the presence of salt and, in particular, there were thenmassive flows of Na^– in the phloem. The results are discussedin relation to the causes of salt sensitivity of Lupinus albus.The data suggest that both a restriction of K⁺ supply and astrongly increased phloem translocation of Na⁺ contribute tothe adverse effects of salt in this species. Restriction ofK⁺ supply occurs by diminished K⁺ uptake and even more by reducedK⁺ cycling within the plant. Key words: Lupinus albus, salt stress, phloem transport, xylem transport, partitioning, carbon, nitrogen, K⁺, Na⁺, CI^–     

Stimulatory Effect of Chloride Ions on NADP Malic Enzyme from Leaves of two C4 Species of Cyperus

NADP malic enzyme (EC 1.1.1.40 [EC] ) from leaves of two C₄ speciesof Cyperus (C. rotundus and C. brevifolius var leiolepis) exihibiteda low level of activity in an assay mixture that contained lowconcentrations of Cl^–. This low level of activity wasmarkedly enhanced by increases in the concentration of NaClup to 200 mM. Since the activity of NADP malic enzyme was inhibitedby Na₂SO₄ and stimulated by relatively high concentration ofTris-HCl (50–100 mM, pH 7–8), the activation ofthe enzyme by NaCl appears to be due to Cl^–. Variationsin the concentration of Mg²⁺ affected the K_A (the concentrationof activator giving half-maximal activation) for Cl^–,which decreased from 500 mM to 80 mM with increasing concentrationsof Mg²⁺ from 0.5 mM to 7 mM. The K_m for Mg²⁺ was decreased from7.7 mM to 1.3 mM with increases in the concentration of NaClfrom zero to 200 mM, although the increase of V_max was not remarkable.NADP malic enzyme from Cyperus, being similar to that from otherC₄ species, was able to utilize Mn²⁺. The K_m for Mn²⁺ was 5mM, a value similar to that for Mg²⁺. The addition of 91 mMNaCl markedly decreased the K_m for Mn²⁺ to 20 +M. NADP malicenzyme from Setaria glauca, which contains rather less Cl^–than other C₄ species, was inactivated by concentrations ofNaCl above 20 mM, although slight activation of the enzyme wasobserved at low concentrations of NaCl at pH7.6. (Received February 20, 1989; Accepted June 12, 1989)     

Diurnal K+ and Anion Transport in Phaseolus Pulvinus

Diurnal movement of Phaseolus leaf is caused by deformationof the laminar pulvinus located at the joint of the leaf bladeand the petiole. The plants were cultured in solutions withvarious ion compositions, and changes of K⁺, Na⁺, Ca²⁺, Mg²⁺,Cl^–, NO₃– and P₁ concentrations both in the upperand lower parts of the laminar pulvinus were measured. Culturein 10 mM KCl solution caused an increase in K⁺ and Cl^–concentrations both in the upper and lower parts without anysignificant change in the concentration of NO₃^–; culturein 10 mM KNO₃ solution caused an increase in K⁺ and NO₃^–concentration without any significant change in the concentrationof Cl^–; and culture in 10 mM KH₂PO₄ solution caused anincrease in K⁺ and P₁ concentrations without any significantchange in the concentrations of NO₃- and Cl^–. K⁺ moved from the upper to lower parts or from the lower toupper parts diurnally in all plants cultured in any solutionmentioned above. The main inorganic anion that accompanied thisK⁺ movement was Cl^– in KCl solution, and NO₃^– inKNO₃ solution. When the seedlings were cultured in distilledwater or in KH₂PO₄ solution, neither Cl^– NO₃^– norP₁ accompanied this K⁺ movement. In these cases, mainly H⁺ and/ororganic anions are supposed to move in exchange for and/or incombination with K⁺ movement. (Received November 8, 1982; Accepted June 13, 1983)     

Effect of K+, its Counter Anion, and pH on Sodium Efflux from Barley Root Tips

Sodium efflux from ²²Na⁺-loaded root tips root tips of Hordeumvulgare L. was markedly increased by replacing 10mM Na₂SO₄ inthe washing solution by K₂SO₄ with the same electrical conductivity.This increase was inhibited by both an uncoupler and an inhibitorof oxidative phosphorylation but not by ouabain. Potassium ionsdid not enhance Na⁺ efflux in the presence of a rapidly absorbedcounter anion, such as Cl^–, instead of . Efflux of ²²Na⁺ could also be enhanced by a low pH in theabsence of K⁺; this was prevented by uncouplers, but not byan inhibitor of the mitochondrial ATPase. It seems that K⁺ indirectly enhances Na⁺ efflux. It is suggestedthat metabolic K⁺ uptake in excess of the counter anion resultsin a proton gradient across the plasmalemma (acid outside) inducingH⁺/Na⁺ antiport.     

Ion Composition of the Chara Internode

Ion compositions of the cytoplasm and the vacuole of Chara australiswere analyzed according to Kishimoto and Tazawa (1964) and Kiyosawa(1979a). The ions in the cytoplasm and the vacuole analyzedwere K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl^–, NO₃^– and H₂PO₄^–.Assuming that the volume of the cytoplasm V_p is 10% of thatof the whole cell V, the concentrations of K⁺, Na⁺, Ca²⁺, Mg²⁺,Cl^–, NO₃^– and H₂PO₄^– in the cytoplasm averaged70, 15, 13, 4.6, 31, 2.2 and 16 mM, respectively. If the volumeof the cytoplasm was assumed to be 5% of that of the whole cell,their averaged concentrations were 139, 31, 25, 9.2, 62, 4.4and 33 mM, respectively. The averaged ion compositions of thecell sap were K⁺, 111; Na⁺, 47; Ca²⁺, 4.4; Mg²⁺, 8.9; Cl^–,91; NO^–₃, 3.3 and H₂PO₄^–, 6.0 mM. These values,taking the concentrations and the charges of the protein (Kiyosawa1979b) and amino acids (Sakano and Tazawa 1984) into accountand assuming the presence of some uni- or oligovalent anionsand/or small nonelectrolyte molecules, could explain fairlywell both the electroneutrality and the osmotic pressure ofthe cell, except when V_p/V = 5%. (Received May 18, 1987; Accepted September 29, 1987)     

The Effect of Salinity Changes Upon the Physiology of Eulittoral Green Macroalgae from Antarctica and Southern Chile: II INTRACELLULAR INORGANIC IONS AND ORGANIC COMPOUNDS

The effects of hypo- and hypersaline treatments ranging from7–68% on the intracellular inorganic ion and organic soluteconcentrations were determined in the eulittoral green macroalgaeUlothrix implexa, Ulothrix subflaccida, Enteromorpha bulbosa,Acrosiphonia arcta, and Ulva rigida from Antarctica and SouthernChile. The main inorganic cations were K⁺, Na⁺, and Mg²⁺ inall species. The major osmolyte in E. bulbosa, A. arcta, andU. rigida was K⁺ at increasing salinities. In both Ulothrixspecies, however, K⁺ levels declined during hypersaline stressand Na⁺ concentrations rose significantly. The main inorganicanions were Cl^-, SO²_4-, and PO³_4- in all algae, while E. bulbosaand U. rigida also contained NO⁺₃. A. arcta showed an extremelyhigh SO^2-₄ content. The organic solutes proline, sucrose, andß-dimethylsulphoniopropionate (DMSP) played an importantrole in osmotic acclimation. The occurrence of three organicosmolytes suggests an additional function of these solutes ascryoprotectants in the cold-water macroalgae investigated.     

The Effects of Salinity upon Ion Content and Ion Transport of the Marine RedAlga Porphyra purpurea(Roth) C.Ag.

Ion contents and concentrations (K⁺, Na⁺, Cl^–, Ca²⁺, Mg²⁺,SO^2–₄, NO^–₃, HPOJ^2–₄, amino and organic acids)of P. purpurea have been studied in relation to salinity variation.Cells were shown to accumulate large amounts of K⁺ and Cl^–against their respective gradients of electrochemical potentialin all dilute and concentrated seawater media. Active influxof SOJ^2–₄, NO^–₃, and HPOJ^2–₄ is also suggested,while Na⁺ is actively excluded from cells under hyposaline andhypersaline conditions. The relative proportions of individualcomponents of the internal osmotic potential were found to changeaccording to the external salt concentration. KCL forms themajor fraction of _j} in concentrated seawater media while K⁺-aminoacids form the major fraction in dilute seawaters. Other intracellularsolutes comprise less than 15% oft_j, in all media. Unidirectional fluxes of K⁺ and Cl^– were studied by radioisotopicmeans. Fluxes of K⁺ and Cl^– are reduced in hyposalinemedia, as is absolute KCL content per cell. Intracelhilar KCLcontent was also found to be markedly dependent upon externalK⁺ concentration, rather than water potential. Changes in KC1levels induced by salinity variation occur over a 6 h period.     

Ionic composition and pH of the vacuolar sap in marine dinoflagellate Noctiluca

Ionic composition of the vacuolar sap of Noctiluca miliariswas as follows: [Na⁺] = 487.3 mM, [K⁺]=24.1 mM, [Ca²⁺]=6.6 mM,[Mg²⁺]=2.8 mM, [Cl^–]=500mM, [NH₄⁺]=15–25 mM, and[SO₄^2–]=undetectable. To measure the vacuolar pH of singleliving cells, a pH-sensitive glass microelectrode was used.The vacuolar pH value was 3.50 ±0.18. When the cellswere transferred from normal sea water into osmotically adjusted50% sea water for one day, the vacuolar ion concentrations remainedalmost constant. Upon immersing the cells in osmotically unadjustedsea water of various concentrations for one day, the observedincrements or decrements of the vacuolar ion concentrationscould be accounted for largely by the migration of water outof or into the cells. The intrinsic ionic composition of thevacuole seems to be constant against changes in ion concentrationsof the bathing medium. (Received October 20, 1975; )     

Unequal distribution of potassium and anions within the Phaseolus pulvinus during circadian leaf movement

Ion and saccharide concentrations in the upper and lower partsof the laminar pulvinus of the primary leaf of Phaseolus vulgariswere measured in relation to the circadian movement. Concentrations of K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl^–, organic acid,NO₃^–, H₂PO₄^–, fructose and fructose-yielding saccharidesin the pulvinus were 75–120, 0.3–0.7, 5–8,6–12, 40–60, 60–73, 19–35, 2–9and 1–5 mM, respectively, and the osmotic pressure ofthe pulvinus was considered to be due to these ions. The cell volume in the expanding part was larger than that inthe contracting part. The change of the cell volume alteredthe molar concentration in the cell sap and therefore the amountof solutes actually transported from the upper to the lowerpart and vice versa was estimated from the concentration expressedin moles per gram of dry weight. Results showed that K⁺, Cl^–, organic acid (or H⁺) andNO₃^– moved from the upper to lower parts or vice versain the pulvinus in relation to its deformation, keeping theelectroneutrality among those ions, whereas C_a2⁺ and Mg²⁺ didnot move. The difference in the K⁺ concentration between theupper and lower parts when the leaf was up or down amountedto 30% of the whole osmotic pressure. This lead to the conclusionthat the endogenous clock-controlled unequal distribution ofK⁺, Cl^–, organic acid (or H⁺) and NO₃^– in the pulvinuscould be the force for the circadian leaf movement. (Received August 7, 1979; )     

Ion Content of the Halotolerant Alga Dunaliella salina

The intracellular concentration of the major ions in Dunaliellasalina cells were determined, following the removal of extracellularions by ion-exchange minicolumns. Log phase cells, grown inmedia containing 1–4 molar NaCl, contained 30–50mM chloride and 200–350 mM magnesium (5 mM in medium).Phosphorus, which is present intracellularly mostly as polyphosphate,was present in amounts of 60–100 fmoles per cell, equivalentto a concentration of 600–1,000 mM (0.2 mM in medium).Previous data indicated that such cells contained 20–40mM Na⁺, 150–300mM K⁺, 20mM SO^2–₄, and very low concentrationsof Ca2⁺ and charged nitrogenous compounds. Mg²⁺ and K⁺ seemto serve as the major counter ions for the intracellular negativecharge present in the massively accumulated polyphosphates.The former accounts for about 2/3 of the required positive charge.This is supported by the observation that limitation in thephosphate or K⁺ supply in the medium lead to a parallel decreasein the accumulation of intracellular phosphorus, Mg²⁺ or K⁺. ¹Present address: Department of Vegetables, The Volcani Center,Bet-Dagan 50250, Israel. (Received June 13, 1988; Accepted August 25, 1988)     

Apoplastic Solute Concentrations of Organic Acids and Mineral Nutrients in the Leaves of Several Fagaceae

Ion chromatographic methods determined organic acids and mainnutrient minerals in the apoplastic solution from leaves ofseveral Fagaceae (Quercus ilex L., Quercus cerris L., Quercusvirgiliana (Ten.) Ten, and Fagus sylvatica L.). The anions oforganic acids found in high amounts (250 to 650 µM) werequinate, malate, and oxalate. Lactate, pyruvate, formate andacetate were detected in relatively low amounts with concentrationsbetween 20 and 200 µM. The total concentration of organicacids in the apoplastic sap ranged between 1.5 and 2 mM. Thetotal concentration of inorganic cations (K⁺, Mg²⁺, NH₄⁺, Ca²⁺,Na⁺) and anions (C1^–, NO₃^–, SO^2–₄ and PO^3–₄)in the apoplastic sap varied between 5 and 10 mM, and 0.35 and1.8 mM, respectively. We conclude that the concentration oforganic acid ions in the leaf apoplast depends mainly on theexchange with the leaf cells and is influenced by the electrochemicalgradient between the symplast and the apoplast in relation tothe water potential of the leaf. The determination of formateand acetate in the apoplastic compartment of leaves lend weightto the argument that the production of these acids by treesis a important emission source to the atmosphere. (Received June 9, 1998; Accepted April 8, 1999)     

Osmotic and Ionic Regulation in Chara L-cell Fragments

Ion absorption from rather complicated artificial pond water(APW) by cell fragments having a lower osmotic pressure thanthe intact internodal cell (L-cell fragments) was studied. L-cellfragments were prepared by taking advantage of trans cellularosmosis and ligating the cell with thread. The results wereas follows: (1) L-cell fragments absorbed more K⁺ than Na⁺ fromaKCL + NaCl mixture in the presence of Ca²⁺, Mg²⁺ and SO₂₄ inthe light; (2) the influx of KCI was larger than that of KNO₃;(3) the amount of positive charge carried by K⁺, Na⁺ and Mg²⁺across the cell membrane balanced well with the amount of negativecharge carried by Cl^– in Cl^–-containing and NO₃^–-free APW; (4) no conclusion could be made as to whether ornot the rule of electro neutrality held for the K⁺, Na⁺, Ca²⁺and NO₃^– fluxes across the cell membrane, because dilutedKNO₃ is unstable; (5) L-cell fragments in KCl-containing APWsurvived longer than those in KNO₃-containing and Cl^–-free APW; (6) after incubation in KNO₃-containing and Cl^–-freeAPW, L-cell fragments absorbed a great amount of KCI immediatelyafter being transferred to KCl-containing and NO₃^– -freeAPW; and (7) lowering the turgor pressure of the intact cellby raising the external osmotic pressure did not induce ionflux into the cell. Thus, we concluded that the L-cell fragmentsabsorbed ions from the external solution not because of theirlower turgor pressure, but because of the diluted ion concentrationof the cytoplasm and the vacuole. The electroneutrality ruleheld, at least, for K⁺, Na⁺, Mg²⁺ and Cl^– influxes acrossthe cell membrane inthe KCl-containing and NO₃^–-free APW.These results were analyzed on the basis of an extended poremodel which presumed the existence of ATP-dependent processesin the membrane, and suggested that K⁺, Na⁺ and Mg₂₊ inflowsinto an L-cell fragment are likely to be induced by active Cl^–inflow. (Received May 18, 1987; Accepted September 29, 1987)     

The intercellular distribution of vacuolar solutes in the epidermis and mesophyll of barley leaves changes in response to NaCl

Concentrations of inorganic and organic solutes were measuredin sap extracted from individual mesophyll and epidermal cellsof the third leaf of barley. During the development of the thirdleaf plants were grown in various salt solutions (NaCl; 2, 50,100, and 150 mM, KCI; 100 mM or KNO₃; 100 mM). Leaves were analysed2–4 d after full expansion. Cell-sap was extracted usinga modified pressure probe and analysed for its osmolality, concentrationsof P, Na⁺ K⁺ Ca²⁺, and Cl^– and, in some cases, of nitrate,hexoses and total amino acids. Salt treatment caused differentialchanges in the concentrations of solutes in mesophyll and epidermalcells, but did not affect the basic pattern of solute compartmentationbetween these tissues. Calcium was found at osmotically significantconcentrations only in the epidermis, whereas P and organicsolutes were almost exclusively found in the mesophyll. Chlorideand Na⁺ accumulated preferentially in the epidermis, althoughmesophyll concentrations also increased considerably. At 150mM external NaCl, mesophyll cells contained 302 mM Na and 167mM Cl^–, compared to 29 mM Na⁺ and 16 mM Cl^– in thecontrol. Mesophyll Cl^– levels were even higher in the100 mM KCl treatment (216 mM) where mesophyll and epidermalK⁺ accumulated to 424 and 491 mM, respectively. These huge increasesin mesophyll Na⁺ Cl^– and K⁺ were not associated with abreakdown in leaf performance since net rates of photosynthesisdecreased only by less than 20%. Under control (2 mM NaCl) conditions,solutes followed patterned gradients between the various epidermalcell types. The extent of these gradients changed with leafage. During 50 mM NaCl treatment, gradients in Cl^–, nitrateand malate concentrations progressively disappeared, with malateconcentrations approaching zero. Potassium and Na⁺ exhibitedaltered distribution profiles, whereas Ca²⁺ distribution wasunaffected. NaCl-dependent increases in osmolalities differedbetween cells. Exposure of plants to 150 mM NaCl caused qualitativelysimilar changes in both epidermal solute and osmolality profiles,although absolute values differed from those at 50 mM NaCl.In particular, epidermal Cl^– and Na⁺ increased to about500 mM and K⁺ disappeared (<<5 mM) from the vacuole ofcertain epidermal cell types completely. Key words: Barley leaf epidermis, mesophyll, salt stress, single-cell analysis, vacuolar solutes     

Relative Importance of Ion Exclusion, Secretion and Accumulation in Spartina alterniflora Loisel.

The extent to which Spartina alterniflora Loisel. excluded,secreted or accumulated the major seawater ions (Cl^-, SO^2-₄,Na⁺, K⁺, Mg²⁺, and Ca²⁺) was investigated under varying salinitytreatments. From a quantitative viewpoint, ion exclusion wasmost prominent and accounted for 91–97% of the theoreticalmaximum ion uptake as a result of transpiration and growth.Of those ions taken up, approximately half was secreted fromthe shoots. Relative to K⁺, a disproportionate amount of Na⁺was excluded at the roots and secreted by the shoots. The concentrationwithin the tissues of S. alterniflora did not change with salinitytreatment for the majority of the ions examined, but Na⁺ wasmore than twice as concentrated at 40 g dm^-3 than at lOgdm^-3.Calculations of the flux of ions from salt marsh sediments tothe flood water via shoot secretion or stem/leaf turnover indicatethat these processes may be important to the ecology of S. alternifloraas mechanisms that limit the accumulation of salt within theroot zone.     

Lamprothamnium, a Euryhaline Charophyte: I. OSMOTIC RELATIONS AND MEMBRANE POTENTIAL AT STEADY STATE

The charophyte Lamprothamnium papulosum (Wallr.) J. Gr. is foundat salinities varying from nearly fresh water to twice thatof sea water. It can maintain its turgor constant at 302 mosmolkg^–1 (0.73 MPa) when exposed to external osmotic pressuresof 550 to 1350 mosmol kg^–1 (1.3–3.3 MPa). Turgorshows a tendency to rise slightly at lower osmotic pressure(388 mosmol kg^–1 of turgor at 150 mosmol kg^–1 externalosmolality). K⁺ and Cl^– are the main solutes in the vacuole,and are most important in controlling internal osmotic pressure.Mg²⁺, Ca²⁺, and SO^2–₄ are present in significant amountsbut their concentrations do not change with changes in externalsalinity. Na⁺ is present in lower concentration than K⁺, andplays a minor role in regulating turgor. Sucrose is presentin significant concentrations, but changes little with changesin salinity. Two enzymes involved in sucrose metabolism, sucrosephosphate synthetase (EC 2.4.1.14 [EC] ), and sucrose synthetase (EC2.4.1.13 [EC] ) are active in whole cell extracts of Lamprothamnium.As in the fresh water charophytes, Lamprothamnium membrane potentialmay be depolarized (close to E_K) or hyperpolarized, and presumablyof electrogenic origin. Both types of potential are found atall salinities tested.     

Response of Wheat Seedlings to Low O2 Concentrations in Nutrient Solution: II. K +/Na+ SELECTIVITY OF ROOT TISSUES9

This paper reports the effects of low O₂ concentration (0–01,0–055, and 0.115mol m^–3) in nutrient solutions onK⁺/Na⁺ selectivity of growing and mature root tissues of 6-to 8-d-old, intact, wheat (Triticum aestivum cv. Gamenya) seedlings. Increases in anaerobic catabolism and decreases in O₂ uptake,K⁺ uptake and K⁺/Na⁺ selectivity were all more pronounced and/oroccurred at higher external O₂ concentrations in the apex (0–2mm) than in the expanding tissues (2–4 mm); these growingtissues were, in turn, more affected than the expanded tissuesof the roots (4–12 mm). Selectivity for K⁺ over Na⁺ in roots and shoots was particularlysensitive to O₂ deficiency. For example, in apical tissues (0–2mm) K ⁺ /Na⁺ selectivity was already reduced at 0.115 mol m^–3O₂, yet at this O₂ concentration there was no effect on eithergrowth or (K⁺/Na⁺) uptake. Upon transfer from 0.01 to 0.26 mol m^–3 O₂, a detailedstudy of the 12 mm root tips showed that 70% of these tips regainedhigh (K⁺ + Na⁺) concentrations and K⁺/^Na+ ratios. In contrast,there was no recovery in the remaining 30% of the 12 mm roottips. Net K⁺ transport to the shoots during the period afterre-aeration was negative for the population as a whole. Theseverity of these effects supports the view that the root tipsand the stele were more susceptible to O2 deficiency than wasthe cortex of the fully-developed root tissues. Key words: Hypoxia, K⁺/Na⁺ selectivity, expanded and expanding tissues     

Isolation and Characterization of Sodium Chloride-Resistant Callus Culture of Vigna radiata (L.) Wilczek var. radiata

Callus cultures were initiated from seedling root segments ofmungbean (Vigna radiata (L.) Wilczek var. radiata) cv. K 851on modified PC-L2 basal medium. Growing cells were exposed toincreasing concentrations of NaCl in the medium. A concentrationof 300 mol m^–3 NaCl proved completely inhibitory to growthof the calli. On incubation for 25 d, cells which could toleratethis concentration of NaCl grew to form cell clones. Selectedclones were characterized with regard to their growth behaviour,K⁺, Na⁺ and free proline content when grown under stress aswell as on normal media and were compared with the normal sensitivecallus. The selected callus was capable of growing on mediumcontaining NaCl at the inhibitory concentration. The K⁺ contentof the selected callus was lower in the case of the NaCl mediumthan for the normal medium. However, the selected clones maintainedhigher K⁺ and Na⁺ levels, with increased salinization comparedwith the wild-type cells. Salt-selected cells accumulated higherlevels of free proline under NaCl stress compared to wild-typecells. Under normal conditions, however, the amounts of freeproline in selected and non-selected calli were comparable. Key words: Vigna radiata, callus culture, NaCl stress     

Ion and Glycerol Concentrations in 12 Isolates of Dunaliella

Ginzburg, M., and Ginzburg, B. Z., 1985. Ion and glycerol concentrationsin 12 isolates of Dunaliella.—J. exp. Bot. 36: 1064–1074. Twelve isolates of Dunaliella with average cell volumes rangingfrom 50 to 1400x10^–18 m³ were grown in batch culture at0.5 M or 2.0 M NaCl. Glycerol and ions (Na⁺, K⁺, Mg²⁺, CI^–,phosphate) were measured in log-phase cultures. The contentsof Mg²⁺, K⁺ and phosphate per cell were found to be a functionof cell-volume. Cell glycerol, Na⁺ and Cl^– were functionsof cell-volume and of the NaCl concentration in the medium.Solute concentrations were calculated from the measured cell-volumesand from the ³H₂O content of pellets corrected for intercellularspace using Blue Dextran. Cell glycerol was found to accountfor about one-half of the expected osmolarity, the remainderbeing largely accounted for by Na⁺ and CI^–. Key words: —Dunaliella, isolates, glycerol, ion concentrations