Salt Retention by Bean Hypocotyl

The ultrastructure of hypocotyl, epicotyl, and petiole of bean(Phaseolus vulgaris, L.) was investigated in plants grown ina basic solution in the absence or presence of high levels ofchloride salts. The hypocotyl tissue of both control and salt-treatedplants showed frequent vesiculation similar to that previouslyobserved in the root and hypocotyl of the halophyte, Salicorniaeuropea, L. These vesicles were not previously observed in theroot and leaf of bean plants that were grown under identicalconditions in the absence of high levels of chloride salt. Experiments concerning the localization of chloride as electron-densesilver-complex showed that the vesicles contain a chloride concentrationas high as the cytoplasmic phase or the free space. These resultsare discussed in relation to the ionic retention property ofthe bean hypecotyl and the role of vesiculation in salt resistanceof plants.     

Salt Tolerance in the Halophyte Suaeda maritima L. Dum.: Intracellular Compartmentation of Ions

The time-course of exchange of sodium and potassium ions fromroot and leaf material of the halophyte Suaeda maritima hasbeen followed and the data analysed according to the phenomenologyof efflux, or compartmental, analysis. Sodium ions were exchangedmuch more slowly (c. 4 times) from the vacuoles of leaf cellsof plants grown in sodium chloride than were potassium ionsfrom the vacuoles of leaf cells of plants grown either in similarconcentrations of potassium chloride or in low concentrationsof potassium. In plants grown in sodium chloride, sodium ionswere exchanged 9 times more slowly from the vacuoles of leafcells than from the vacuoles of root cells. The concentration of sodium ions in the cytoplasm of leaf cellsof plants growing in 340 mol m^–3 sodium chloride was estimatedto be 165 mol m^–3 when the average concentration in theleaf tissue was about 600 mol m^–3. As measured by movement from mature to developing leaves inintact plants; there was less in vivo retranslocation of ²²Naand ³⁶CI in plants growing in sodium chloride than there wasof ⁸⁶Rb in plants growing either in potassium chloride or innon-saline conditions. The results are discussed in terms of the concept and energeticsof compartmentation of ions in the cells of halophytes.     

Avoidance of sodium accumulation by the stomatal guard cells of the halophyte Aster tripolium

X-ray microanalysis has revealed that the sodium content ofthe stomatal guard cells of Aster tripolium remains much lowerthan that of other leaf cells when the plants are grown at highsalinity. Large amounts of sodium did, in contrast, accumulatein epidermal and subsidiary cells, and particularly in the mesophylltissue, suggesting that a mechanism exists to limit the extentof its entry into guard cells. Even in plants grown at highsalinity, the content of potassium was much higher than thatof sodium in the guard cells, consistent with the view thatthis is a major ion involved in determining stomatal movementsin this halophyte. Determinations were also made for the nonhalophyte Commelinacommunis, and it was found that the guard cells accumulatedlarge amounts of sodium when it was presented to them as analternative to potassium. It is suggested that the acquisition by the guard cells of someability to restrict the intake of sodium ions may be an importantcomponent of sodium-driven regulation of transpiration, andhence of salinity tolerance, in A. tripolium. Key words: Salinity tolerance, sodium, potassium, stomata, Aster tripolium     

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     

Salt Tolerance in Suaeda maritima (L.) Dum: THE EFFECT OF SODIUM CHLORIDE ON GROWTH, RESPIRATION, AND SOLUBLE ENZYMES IN A COMPARATIVE STUDY WITH PISUM SATIVUM L

The effect of sodium, chloride on the growth of a halophyte,Suaeda maritima (L.) Dum., was compared with its effect on Pisumsativum L. cv. Alaska under controlled environmental conditions.The salt stimulated the growth of Suaeda maximally at concentrationsof 170 to 340 mM while the growth of Pisum was inhibited evenby 100 mM. Both species accumulated ions in the tops and themaximum concentrations of Na⁺ and Cl^– rose in Suaeda to860 mM (based on the water content) and 730 mM and in Pisumto 170 mM and 300 mM respectively. Respiration in both specieswas inhibited as the NaCl level in the culture solution wasraised. Four supernatant enzymes (malic dehydrogenase, glucose-6-phosphatedehydrogenase, peroxidase, and acid phosphatase) prepared fromPisum and from Suaeda (grown either in the absence of addedNaCl or in the presence of 340 mM NaCl) were assayed in variouslevels of sodium chloride. The dehydrogenases were markedlyinhibited by increasing salt concentrations while there wasa smaller effect on the peroxidase and acid phosphatase. Therewas no difference in the effect of salt on the enzymes preparedfrom the two species although one is halophilic and the otherhalophobic.     

Salt tolerance in Suaeda maritima (L.) Dum: A COMPARISON OF MITOCHONDRIA ISOLATED FROM GREEN TISSUES OF SUAEDA AND PISUM

Mitochondria were isolated from green leaves and stems of theglycophyte Pisum sativum and the halophyte Suaeda maritima.The preparations oxidized malate, succinate, and 2-oxoglutarateas well as externally added NADH. Acceptor control ratios wereabout 2.8 for mitochondria from Pisum and 1.8 for mitochondriafrom Suaeda oxidizing malate+pyruvate in 125 mM sodium chloride.The mitochondrial fraction was contaminated with chloroplastfragments which resulted in relatively low rates of oxygen uptakewhen these were expressed on a protein basis. The addition of sodium chloride at concentrations greater than200 mM considerably reduced the rates of oxygen uptake by bothspecies in the presence and absence of phosphate acceptor (ADP).Acceptor control ratios were reduced and there was a markeddecline in the ADP/O ratio. Sucrose at equivalent molar concentrationshad a much less drastic effect on the mitochondria. There was no significant difference in the effects of thesetwo solutes on mitochondria from the two species and the similarityof response is discussed in relation to the cytoplasmic ioncontent of the halophyte.     

Selectivity and Kinetics of Ion Uptake by Barley Plants Following Nutrient Deficiency

Barley plants grown without an external supply of phosphorus,sulphur, chlorine or nitrogen subsequently absorbed these nutrients,as phosphate, sulphate, chloride and nitrate, more rapidly thandid nutrient, sufficient control plants under similar conditions.With phosphorus, sulphur and chlorine, increased absorptionwas restricted to the nutrient which had been deficient, orto close chemical analogues of it, the uptake of other anionsbeing unaffected or decreased. The selectivity of enhanced nitrateuptake by nitrogen-deficient plants was not examined. The differencesin the rates of phosphate, sulphate and chloride absorptionby plants of differing nutrient status were due principallyto changes in the maximum transport capacity for these anionsper unit weight of root, although in plants grown without externalchloride there was some evidence that the roots also developedan increased affinity for that ion. Hordeum vulgare, barley, mineral nutrient deficiency, ion absorption, kinetics of ion uptake, phosphate, sulphate, chloride, arsenate, bromide, selenate     

Lipids from Bean, Barley and Sugar Beet in Relation to Salt Resistance

A comparison was made between the lipid and fatty acid composition of the salt-sensitive bean (Phaseolus vulgaris L. cv. Saxa), the less salt-sensitive barley (Hordeum vulgaris L. cv. Wisa) and the salt-tolerant sugar beet (Beta vulgaris L. cv. Kawemono). Sugar beet roots showed a higher content of sterol components and sulfolipid as compared with bean and barley roots. The lipids of sugar beet roots contained more linoleic acid and less linolenic acid than those of bean and barley roots. For barley and sugar beet roots a higher amount of extra-long chain fatty acids was observed than for bean roots. It was concluded that differences in membrane structure are correlated with differences in membrane permeability to sodium and chloride and in salt-resistance of the studied species.     

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-stimulated Phosphoenolpyruvate Carboxylase in Cakile maritima

The effects of NaCl and other salts, in vivo and in vitro, on the activity of phosphoenolpyruvate carboxylase from the coastal C₃ halophyte Cakile maritima Scop, were investigated. Plants grown with 100 mM NaCl in their growth medium yielded some 30% higher rates of phosphoenolpyruvate carboxylase activity than did salt-depleted plants. Activity of the enzyme was stimulated when NaCl was added to the reaction mixture in concentrations of up to 200 mM. The magnitude of this in vitro stimulation was similar for plants grown in the presence or absence of NaCl. The effect seems to be caused by chloride rather than by sodium ions.     

Properties of Membranes from the Halophyte Suaeda maritima: I. CYTOCHEMICAL STAINING OF MEMBRANES IN RELATION TO THE VALIDITY OF MEMBRANE MARKERS

The fine structure and certain cytochemical properties of theshoots from the halophyte Suaeda maritima have been examined.No major fine structural differences were observed between plantsgrown in the presence or absence of salt. Considerable evidenceof vesiculation was observed, particularly in cells of the stelartissue from the stems. The specificity of the phosphotungsticacid-chromic acid stain for plasma membranes was examined andsome doubt raised as to its widespread applicability as a plasmamembrane marker in plant cells. The suitability of other membranemarkers such as ruthenium red and ATPase activity were investigated.     

Nitrate Reduction in the First Leaf and Roots of Barley Seedlings Grown in Sand and in Culture Solution

The in vivo method has been used to determine activity of nitratereductase in Hiproly and Proctor barley. Differences in activitybetween the cultivars were small and less than those due togrowing conditions. Activity in plants grown in culture solutionwas greater than that for sand-grown plants, especially in theroot The in vivo method gave values for nitrate reductase activitywhich are less than those found by the in vitro method, andevidence is presented to show that the in vivo method underestimatesthe rate of formation of organic nitrogen in barley seedlings.It is shown that significant nitrate reductase activity occursin roots but it is nevertheless concluded that the main siteof nitrate assimilation is in the leaves of this material.     

Increased vacuolar and plasma membrane H+-ATPase activities in Salicornia bigelovii Torr. in response to NaCl

The halophyte Salicornia bigelovii Torr. shows optimal growthand Na⁺ accumulation in 200 mM NaCl and reduced growth underlower salinity conditions. The ability to accumulate and compartmentalizeNa⁺ may result, in part, from stimulation of the H⁺ -ATPaseson the plasma membrane (PM-ATPase) and vacuolar membranes (V-ATPase).To determine if these two primary transport systems are involvedin salt tolerance, shoot fresh weight (FW) and activity of thePM- and V-ATPases from shoots in Salicornia grown in 5 and 200mM NaCI were compared. Higher PM-ATPase activity (60%) and FW(60%) were observed in plants grown in 200 mM NaCI and thesestimulations in growth and enzyme activity were specific forNa⁺ and not observed with Na⁺ added in vitro. V-ATPase activitywas significantly stimulated in vivo and in vitro (26% and 46%,respectively) after exposure to 200 mM NaCl, and stimulationwas Na⁺ -specific. Immunoblots indicated that the increasesin activity of the H⁺ -ATPases from plants grown in 200 mM NaCIwas not due to increases in protein expression. These studiessuggest that the H⁺-ATPases in Salicornia are important in salttolerance and provide a biochemical framework for understandingmechanisms of salt tolerance in plants. Key words: Salicornia, H⁺-ATPases, salt tolerance     

Stereological Analysis of Leaf Cells of the Halophyte Suaeda maritima (L.) Dum

A stereological analysis of cells from the mesophyll, vascularbundles and central parenchyma in leaves of the halophyte Suaedamaritima (L.) Dum is described. The volume fraction of vacuolewas greater in plants grown under saline conditions when comparedwith those under non-saline conditions, and there was a concurrentincrease in the surface density of the tonoplast. The volumefraction of chloroplasts and cell wall fell under saline conditions,while that of the intercellular spaces increased. Salinizationof the growth medium was accompanied by a large increase inthe fraction of the cell volume occupied by the mitochondria:the increase in surface density of mitochondrial membranes wassome 72% when averaged over all the cell types analysed. Key words: Salt tolerance, Halophyte, Suaeda maritima, Stereology     

The Effect of Ions on Growth and Leaf Succulence of Atriplex hortensis var. cupreata

When plants of Atriplex hortensis var. cupreata were grown insolutions containing at least 100 mmoll^–1 of various saltsit was found that sodium was the ion most effective in stimulatingleaf succulence, irrespective of whether the anion was chloride,bromide or sulphate. Potassium was the next most effective ion.Magnesium and calcium were without effect. Dry weight productioncould be greatly reduced by sodium and potassium but stimulatedby magnesium. The results are compared with those previouslyreported for C₄ species of Atriplex.     

Salt Tolerance in the Halophyte, Suaeda maritima (L.) Dum.: Properties of Malic Enzyme and PEP carboxylase

Malic enzyme and phosphenol pyruvate carboxylase activitieshave been isolated and characterized from the shoots of Suaedamaritima plants grown in culture solution (with and withoutNaCl) or in tap water. The enzymes isolated from the lattershowed increases in both specific activity and K_m values incomparison with plants grown in culture solution: however, theaddition of NaCl to the culture solution had no significanteffect on either enzyme. Malate levels were high in plants grownin tap water, reduced by an ordeT of magnitude by the additionof culture solution and then halved by the addition of NaCl. Both enzymes were inhibited in vitro by NaCl, although the additionof high concentrations of betaine and proline to the assay mediumdid not further inhibit enzyme activity. The significance ofthese results is discussed in relation to the proposed roleof betaine and proline as cytoplasmic osmoregulators. Suaeda maritima, halophyte, salt tolerance, malic enzyme, PEP carboxylase     

Effects of NaCl salinity on 15N-nitrate fluxes and specific root length in the halophyte Plantago maritima L.

The effect of salinity on nitrate influx, efflux, nitrate net uptake rate and net nitrogen translocation to the shoot was assessed in a ¹⁵N steady state labelling experiment in the halophyte Plantago maritima L. raised for 14 days on solution supplied with 50, 100 and 200 mol m^–3 sodium chloride or without sodium chloride. Additionally, salinity induced changes in root morphology were determined. Specific root length increased upon exposure to elevated sodium chloride concentrations due to variations in biomass allocation and length growth of the tap root. Changes in root morphology, however, had a minor effect on nitrate fluxes when expressed on a root fresh weight basis. The decreased rate of nitrate net uptake in plants grown on elevated levels of sodium chloride was almost entirely due to a decrease in nitrate influx. Expressed as a proportion of influx, nitrate efflux remained unchanged and was even lower at the highest salinity level. At all sodium chloride concentrations applied the initial rate of nitrogen net translocation to the shoot decreased relative to the rate of nitrate net uptake. It is concluded that under steady state conditions the negative effect of sodium chloride on the rate of nitrate net uptake at non growth-limiting salinity levels was due to the interaction between sodium chloride and nitrate transporters in the root plasma membrane and/or processes mediating the translocation of nitrogen compounds, possibly nitrate, to the shoot.     

The Effect of Salinity on Growth of Phaseolus vulgaris L.: I. Anatomical Changes in the First Trifoliate Leaf

When plants of Phaseolus vulgaris were grown in culture solutioncontaining 48 m mol l^–1 sodium chloride, the first trifoliateleaves were always smaller in area than those of control plants.The leaves of the salt-treated plants however could become thicker.This increase in thickness was brought about by the increasein the thickness of the spongy parenchyma layer. The palisadeparenchyma layer was always thinner than that in the controlleaves. While these latter leaves expanded predominantly bycell division, this only held for the early stages of expansionof the leaves of salt-treated plants. In this case cell divisionceased when the leaves were about half their maximal size andfurther increase in area was brought about by an increase involume of the spongy parenchyma cells.     

The Effects of Brown Rust and Phosphate on Cold Acclimation in Winter Barley

The green leaf area of winter barley, cv. Sonja, sampled fromthe field at different times during winter was always greatestin plants grown at high soil phosphate and smallest in plantsgrown at low soil phosphate, and at each fertilizer level wasgreater in healthy plants than in plants infected by rust (Pucciniahordei). In leaves that survived the coldest period of winter,the percentage area that was damaged was increased by rust infectionwhich prevented the ameliorating effects of high soil P. Rustand low P interacted to reduce the increases in leaf area andshoot d. wt that occurred when higher temperatures prevailedin spring. Under controlled conditions in the laboratory, phosphate reducedthe injury suffered when plants not acclimated to low temperatureswere exposed to freezing conditions, but this effect was removedby rust infection. After rust infection, freezing temperatureswere damaging even to acclimated plants, particularly if grownwith low soil P. Evidence of visible symptoms, and quantitativemeasurements of electrolyte efflux from intact leaves, chlorophyllfluorescence in vivo, and ethane and ethylene evolution fromcold-acclimated plants, showed that infection raised the minimumtemperature at which tissues could survive without injury. Infectedleaves were more sensitive to low temperature post-sporulationthan presporulation. Measurements of electrolyte efflux andchlorophyll fluorescence on plants growing under cold conditionsshowed that infection inhibited the processes of acclimationto low temperatures. Winter barley, Puccinia hordei, injury, low temperature, acclimation     

Acclimation of Photosynthate Partitioning and Photosynthetic Rates to Changes in Length of the Daily Photosynthetic Period

Pangola, soya bean and spinach plants were grown in long andshort day photosynthetic periods. Reciprocal shifts betweenlong and short day grown plants were made to study acclimationin the rate of leaf starch synthesis with change in daylength.The rate of leaf starch accumulation is a function of the lengthof the daily photosynthetic period. Acclimation, that is a changein partitioning with a change in length of the photosyntheticperiod, occurs in a variety of species. Acclimation in the rateof starch accumulation occurs rapidly in pangola and is apparentlycomplete the day after a change in length of the daily photosyntheticperiod. Soya bean and spinach leaves require a few days in thenew environment for an acclimation to occur. Digitaria decumbens Stent., Glycine max (L.) Merr., Spinacia oleracea L., pangola, soya bean, spinach, specific leaf weight, starch, photosynthesis