Some Effects of Root Anatomy on K, Na and Cl Loading of Citrus Roots and Leaves

Loading of K, Na and Cl into fibrous roots of salt-treated citrusgenotypes, Rangpur lime (Citrus reticulata var. austera hybrid?)and Etrog citron (C. medica L.) was investigated in relationto root anatomy, in particular, the differentiation of the epidermal-hypodermallayers with distance from the root tip. The influence of durationof salinity treatment on the characteristics of K, Na and Claccumulation in leaves of the two genotypes was explored intwo experiments respectively, covering the short term (14 d)and long term (12 weeks). This study focused on two regions of the fibrous root, a segment2–12 mm from the root tip, immediately basipetal to thezone of elongation and a differentiated region of the maturesuberized, fibrous root, 40–50 mm from the root tip. Inthe distal root segment (2–12 mm) the epidermis and hypodermisof both genotypes was observed as two closely packed, uniseriatelayers of living cells. In the proximal root segment (40–50mm) the differentiated hypodermis was evident as a uniseriatelayer of thick-walled lumina interspersed with ‘passagecells’ which were frequently associated with clustersof viable epidermal cells. The characteristics of Na and Cl loading in the two root zonesdiffered profoundly during the short term loading (acclimation)phase. Attainment of quasi-steady-states for Na and Cl in thedistal region (with the exception of Na in Etrog citron) wasrapid as was Na equilibration of the proximal root segmentsin both genotypes. In contrast, Cl loading in the proximal regiontook c. 14 d to reach a quasi-steady-state by which time Cllevels were 2 to 3 times higher in the proximal than in thedistal root segments. The superior tolerance of Rangpur lime to long term salinitywas highly correlated to Cl exclusion from the leaves. However,during the first 14 d of acclimation to 50 mol m^–3 NaClthere was no segregation of the two genotypes based upon leafCl levels. Expression of differential accumulation of Cl inleaves appeared to be a time dependent process and was manifestonly after Cl saturation of the proximal root which representsthe bulk of the fibrous root system. The salt tolerance of Rangpurwas also associated with high selectivity of fibrous roots forK. over Na. A pronounced loss of K from cortical cells in theproximal root segment of salt-stressed Etrog citron was alsoevident by X-ray microanalysis. Key words: Citrus, anatomy, salinity, roots, X-ray microanalysis     

Phospholipids, free sterols and adenosine triphosphatase of plasma membrane-enriched preparations from roots of citrus genotypes differing in chloride exclusion ability

Plasma membrane-enriched preparations from fibrous roots of three citrus genotypes differing in their abilities for chloride exclusion, and grown in the presence of 0,50 or 100 mM NaCl for 4 weeks, were analysed for phospholipid and free sterol content and vanadate-sensitive adenosine triphosphatase (ATPase) activity over a range of temperatures. The best chloride excluder, Rangpur lime (Citrus reticulaia Blanco var. austera hyb.?), had significantly higher maximal ATPase activity than both the moderate chloride excluder. Kharna khatta (Citrus kharna Raf.), and the worst chloride excluder, Etrog citron (Citrus medico L.), at all assay temperatures below 28°C. Salt treatment had no effect on maximal ATPase activity of either Rangpur lime or Etrog citron but resulted in increased activity of the enzyme in Kharna khatta at temperatures below 28°C. Arrhenius plots of ATPase activity from the three citrus genotypes showed that, in controls, the activation energy (E.,) of Rangpur lime ATPase was significantly lower than that of both Kharna khatta and Etrog citron. The thermotropic phase transition temperature (T_f) for Rangpur lime (27°C) was also lower than for the other citrus genotypes (31°C). Salt treatment resulted in increases in both Ea and T, for Rangpur lime, decreases in both parameters for Kharna khatta and no change of either parameter for Etrog citron. An inverse relationship between E_a and the phospholipid to free sterol ratio was evident for plasma membrane preparations from all three citrus genotypes in the presence and absence of salt treatment suggesting that changes in membrane fluidity, particularly those induced by free sterols, have the potential to influence active as well as passive ion transport processes and thus may play a significant role in the chloride exclusion mechanism.     

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     

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     

NaCl effects on 4-desmethylsterol composition of plasma-membrane-enriched preparations from citrus roots

Abstract The free 4-desmethylsterol composition of plasma-membrane-enriched preparations from white fibrous roots of Rangpur lime (Citrus reticulata var. austera hybrid?), Kharna khatta (C. kharna Raf.) and Etrog citron (C. medica L.) seedlings grown in the presence of 0, 50, or 100 mol m^?3 NaCl for 28 d was quantitated by gas chromatography (GC) on analytical capillary (SE-54 fused silica) columns and the sterols were identified by combined gas chromatography-mass spectrometry (GC-MS). Only three 4-desmethylsterols were positively identified by GC-MS, viz. campesterol, stigmasterol and sitosterol. Cholesterol could not be positively identified in any of the membrane preparations. Campesterol levels were generally similar for all treatments and for all three genotypes, approximating 30% of the total free 4-desmethylsterol content of the plasma membranes. At all levels of salinity (0, 50 or 100 mol m^?3 NaCl) sitosterol levels decreased in the order Rangpur lime > Kharna khatta > Etrog citron and stigmasterol levels decreased in the reverse order. The ratio of sitosterol to stigmasterol was highest in Rangpur lime and lowest in Etrog citron at each level of salinity and was reduced by salt treatment in all three genotypes. Salt-induced reductions in the ratio of ‘more planar’ to ‘less planar’ sterols correlated inversely with the accumulation of Cl^? in the leaves of the three genotypes suggesting a role for plasma membrane sterols in the Cl^? exclusion mechanism. A model relating sterol structure, membrane sterol composition and membrane permeability to Cl^? exclusion ability in citrus is presented.     

Salt Stress Causes Acceleration of Purine Catabolism and Inhibition of Pyrimidine Salvage in Zea mays Root Tips

Nucleotide metabolism was studied in apical 5.0 mm root tipsof corn plants (Zea mays L., cv. Pioneer 3906) hydroponicallycultured for 7 d and then salinized for 19 d at a rate calculatedto reduce the osmotic potential (_o) of the solutions by O.1MPad^–1 to a final _o = -0.4 MPa. Saline treatments withtwo different molar ratios of Ca₂₊/Na⁺ were employed, viz.,0–03 (2.5 mol m^–3 CaCl₂ + 86.5 mol m^–3 NaCl)for the NaCl treatment and 0.73 (31.5 mol m^–3 CaCl₂ +43.1 mol m^–3 NaCl) for the NaCl + CaCl₂ treatment. Bothsalt treatments reduced root growth by more than 30%. The capacityof roots to provide purine nucleotides either by de novo synthesisor by re-utilization of existing bases, e.g. salvage of hypoxanthineto adenine nucleotides, was not affected by either salt treatment.However, catabolism of hypoxanthine was accelerated more than3.5-fold by both salt treatments, demonstrating an increasedcapacity for purine catabolism which would shift the normal1: 1 ratio of synthesis: degradation of purine nucleotides observedfor the roots of healthy control plants to less than 0.2 duringsalt stress. The ratio of pyrimidine nucleotide synthesis: degradationwas also reduced. In this case, the unfavourable shift towardnucleotide degradation resulted because both salt treatmentsreduced salvage capacity by more than 25%, but had no compensatingeffect on de novo synthesis or catabolism of pyrimidines. Key words: Salinity, osmotic potential, nucleotide metabolism     

Effect of Salt Stress on Callus Cultures of Oryza sativa L.

Kavi Kishor, P.B 1988. Effect of salt stress on callus culturesof Oryza sativa L.—. exp. Bot 39 235–240 Callus cultures of rice adapted to grow under increasing NaClstress were found to accumulate considerable amounts of freeproline, compared with unadapted cells. Salt-adapted cells grownfor 10 passages (25 d each) on NaCl-free medium accumulatedproline on re-exposure to salt as did cells which were growncontinuously on NaCl. On replacing NaCl (100 mol m^–3)with 100 mol m^–3 of KC1, fresh and dry weights as wellas free proline content of salt-adapted callus declined comparedto that attained on 100 mol m^–3 NaCl medium. However,equimolar concentrations of NaCl and KC1 (when added together)produced an increase in growth and free proline accumulationin salt adapted callus. Omission of Ca²⁺ from the growth mediuminhibited the growth of salt-adapted cells in the presence ofNaCl, while it had little effect on the growth of non-adaptedcells in the presence of NaCl. ABA increased the fresh and dryweights of the non-adapted callus only in the presence of 200mol m^–3 of NaCl but not in the absence of NaCl. ABA failedto evoke the same response in salt adapted cells in the presenceof the salt. Tissues exhibited good growth under inhibitorylevels of NaCl (500 mol m^–3) only when glycine betaine,choline and proline were added to the medium but showed no growthin the presence of sarcosine, glycine and dimethylglycine. Key words: Oryza saliva, callus cultures, NaCl stress     

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     

Kinetics of Root Elongation of Maize in Response to Short-Term Exposure to NaCl and Elevated Calcium Concentration

To study the effect of salt (NaCl) on root elongation we developeda device that measures this effect by means of a Linear VariableDifferential Transformer (LVDT). To test the efficacy of thedevice we performed experiments demonstrating that (a) ratesof elongation of primary maize (Zea mays L.) roots were comparableto elongation rates of primary roots growing freely in solutionculture; and (b) chilling and low O₂ concentrations of the solutionelicited the expected responses. Inhibition of root elongation by 75 mol m^–3 NaCl was gradual.At an iso-osmotic concentration, mannitol did not inhibit rootgrowth, suggesting that the inhibition was not due to osmoticfactors but rather to effects of salt on metabolism. The additionof supplemental Ca (10 mol m^–3) ameliorated this stressfulcondition. Timing of the application of Ca was critical. Treatmentwith Ca after addition of NaCl only partially restored growth,but pretreatment with Ca completely prevented the inhibitionof growth by salt stress. Key words: Root growth, Zea mays L., salinity     

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     

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     

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     

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

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

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     

Salt Tolerance in the Triticeae: The Contribution of the D Genome to Cation Selectivity in Hexaploid Wheat

Inorganic cation concentrations were measured in shoots of hexaploidbread wheat (Triticum aestivum L.) and its presumed ancestorsgrown at 100 mol m^–3 external NaCl. Aegilops squarrosaand T. aestivum had high K/Na ratios while T. dicoccoides andAe. speltoides had low K/Na ratios. T. monococcum although havinga high K/Na ratio, had the highest total salt load of the fivespecies tested. The effect of the D genome (from Ae. squarrosa)was further investigated in seedlings of synthetic hexaploidwheats, and was again found to improve cation selectivity. Differentresponses were obtained from root and shoot tissue in this experiment.One synthetic hexaploid and its constituent parents were grownto maturity at 100 mol m^-3 NaCl and the yields recorded. Despitecomplications due to increased tillering in the stressed hexaploid,it was possible to show that the addition of the D genome enhancedyield characteristics in the hexaploid wheat. An experimentwith synthetic hexaploids derived from the tetraploid wheatvariety "Langdon" and several Ae. squarrosa accessions revealeddifferences in vegetative growth rates between the differentsynthetic hexaploids in the presence or absence of 150 or 200mol m^–3 external NaCl. The possibility of transferringsalt tolerance genes from Ae. squarrosa to hexaploid wheat usingsynthetic hexaploids as bridging species is discussed. Key words: Salt stress, wheat, D genome, Aegiops squarrosa, synthetic hexaploids     

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     

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     

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     

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