Sodium Exclusion by Chenopodium Species

The uptake of sodium, potassium and chloride in Chenopodiumalbum L. and Chenopodium schraderianum Roemer and Schultes wasfollowed over 2 weeks. Ion concentrations and ion fluxes werecompared to those observed in Atriplex prostrata Boucher exDC. and Suaeda maritima (L.) Dum. as halophilic Chenopodiaceae,and to Phaseolus aureus Roxb. and Trifolium alexandrinum L.as sodium-excluding Fabaceae. Seedlings of all species werecultivated in quartz sand at 10 mmol dm^–3 of potassium,sodium, and chloride. For Fabaceae low uptake rates of alkali ions and sodium retentionin roots are substantiated in Phaseolus. Results for Atriplexand Suaeda illustrate high uptake rates of alkali ions and preferentialtransport of sodium to the shoots. In contrast to halophilic chenopods, Chenopodium album andC.schraderianum show low sodium concentrations in shoots and ahigh K-Na-selectivity of net ion fluxes. Evidence for sodiumexclusion by their roots is presented. Sodium exclusion by Chenopodiumspecies is not as efficient as in Phaseolus, but is within therange of that found in other Fabaceae. Unlike other glycophytes,the Chenopodium species show the high rates of alkali ion uptakewhich have been found in their halophilic relatives. Key words: Chenopodiaceae, Fabaceae, ion uptake, salt exclusion, K-Na-selectivity     

Effects of Salinity on Some Citrus Scion-Rootstock Combinations

Chloride and sodium concentrations, water relations and gasexchange parameters were measured on leaves of Clementine (CitrusClementine Hort. ex. Tan) and Navel orange [C. sinensis (L.)Osb] scions grafted on Cleopatra mandarin (C. reticulata Blanco)and Troyer citrange (C. sinensis x Poncirus trifoliata) rootstocksgrown at increasing levels of NaCl in the external medium. Otherparameters affected by salinity such as growth and defoliationwere also recorded. Scions on Cleopatra mandarin accumulated less Cl^- in their leavesthan did scions on Troyer citrange. Also, leaf Cl^- levels inClementine scions were lower than in Navel orange when bothwere grafted on the same rootstock. However, sodium concentrationwas lower in scions on Troyer citrange than in Cleopatra mandarin. Leaf water potential, stomatal conductance, photosynthesis andgrowth were reduced more in grafted plants of salt-treated Navelorange than those of salt-treated Clementine. However, choiceof rootstock had little effect on salt-induced changes in theseparameters. For each scion, reduction in leaf stomatal conductancewas closely correlated with decrease in leaf water potential.Also, a significant correlation between photosynthesis and stomatalconductance was found. The results indicate that reductions in gas exchange parametersand growth at increasing salinity levels depended more on thescion type than on Cl^- or Na⁺ concentration in leaves. Otherwise,leaf injury and defoliation were closely correlated with leafCl^- concentration.Copyright 1995, 1999 Academic Press Citrus, photosynthesis, salinity, water relations     

Determination of Unidirectional Sodium Fluxes in Roots of Intact Sunflower Seedlings

The method of compartmental analysis was applied to study sodiumfluxes in roots of intact seedlings of Helianthus annuus L.By measuring sodium uptake and transport to the shoots of theseedlings in parallel experiments, transport of tracer sodiumto shoots and net accumulation of Na⁺ in the roots during theflux measurements was accounted for. The steady-state sodiumfluxes in the intact sunflower roots were similar in size tothose in excised roots but in general they were somewhat higher.This indicates more metabolic activity in the intact tissues.Using whole plants it is possible to study the response of ionfluxes in roots to ecophysiological stimuli received by theshoots, and in the present experiments the effect of continuouslight versus long-day growth conditions was investigated. Potassium,when continually present, depressed all fluxes and the cytoplasmiccontent of sodium but tended to increase the vacuolar sodiumcontent, in particular when this was related to the cytoplasmiccontent. When added to sodium-loaded roots, potassium stimulatedthe plasmalemma sodium efflux but slightly, suggesting a lowefficiency of K⁺-Na⁺ exchange across the plasmalemma in intactas well as excised sunflower roots. Subsequently, however, potassiuminduced a transient decrease in the ²²Na efflux that was followedby oscillations in tracer efflux. These changes were attributedto potassium-induced transfer of sodium to vacuoles. Moreover,the oscillations seem to indicate the operation of negativefeedback control of sodium fluxes.     

Rapid Shedding of Roots from Azolla filiculoides Plants in Response to Inhibitors of Respiration

Chemicals that are known to be inhibitors of respiration, namely,sodium azide, sodium cyanide, DNP, CCCP and DCCD, caused sheddingof roots of Azolla filiculoides plants. Complete shedding ofroots of more than 10 mm in length occurred when Azolla plantswere treated with sodium azide, DNP or CCCP at concentrationsabove 50µM, 30µM and 20µM, respectively. Theshedding in response to sodium azide, DNP and CCCP was veryrapid and was complete within 5–20 min. Microscopic studies revealed the presence of large cells atthe outer surface of the base of roots that were about to beshed. The tested-chemicals caused the expansion, rounding upand separation of these cells, probably via the rapid absorptionof water, with resultant shedding of roots. When detached roots were immersed in a solution of sodium azide,DNP or CCCP, the large cells expanded and rounded up. Thesecells were gradually separated from the roots. However, theseparation of the cells caused by DNP was inhibited by the presenceof various buffers at acidic pH. By contrast, buffers at neutralpH greatly facilitated the separation of cells irrespectiveof whether DNP was present or absent. The results suggest that the separation of cells involves anincrease in the pH of the external solution in the vicinityof the large cells. A change in ion fluxes of the large cells,which accompanies an increase in pH of the external solution,may cause the rapid absorption of water by the cells and resultin the expansion and separation of the cells. (Received June 15, 1993; Accepted October 25, 1993)     

Sodium Recirculation and Loss from Phaseolus vulgaris L.

In a split-root experiment, ²²Na was supplied to Phaseolus vulgarisL. roots emerging from the stem, 2.5 cm above the main roots.Sodium exported from these upper roots was translocated a shortdistance upward in the stem and downward to the main roots.Most of the ²²Na arriving in the main roots was lost to themedium. Sodium loss from P. vulgaris roots into KCI or NaCl was similarand was not affected by oligomycin. The results confirm a previous hypothesis regarding the mechanismof sodium exclusion from the tops of sodium non-accumulatorplants. Phaseolus vulgaris L., bean, sodium transport     

Gas Transport in the Marsh Grass, Spartina alterniflora

Spartina plants have continuous gas spaces from the leaves tothe tips of the roots. Oxygen values in the roots are as lowas 3 per cent and increase toward the stem. Carbon dioxide valuesare highest in the rhizome and decrease up the stem and towardthe root tips. Oxygen and carbon dioxide moved through the plantsat equal rates for equal gradients, and these rates agree withmeasurements made on plants in the marsh. Calculated oxygenand carbon dioxide fluxes for the observed gradients in theobserved gas spaces agreed with measured fluxes. We concludethat gases move in and out of Spartina roots by diffusion throughuninterrupted gas spaces within the plant.     

Pressure-Induced Water and Solute Flow Through Plant Roots

Water and salt flows through detopped sunflower, tomato andred kidney bean roots under applied pressure were studied usinga pressure chamber. Values of J_v for these root systems weremeasured applying variable pressure on the root medium, andL_p calculated. The K, Na and Cl fluxes under applied pressure were comparedwith those in intact plants at the same water flow rates. Tento 100 times higher Na and Cl fluxes were observed through detoppedroots under pressure as compared to those in the unpressurized,intact plants. It is suggested that the roots under pressureare not completely analogous to intact plant roots, and thatpressure-induced flow may not be a reliable method of determiningcharacteristics of ion flow in roots in relation to water flow. Key words: Volume flow, Hydraulic conductivity, K selectivity     

Unidirectional Ca2+ Fluxes in Roots of Rye (Secale cereale L). A Comparison of Excised Roots with Roots of Intact Plants

The unidirectional Ca²⁺ fluxes across the plasma membrane andtonoplast were determined in both excised roots and roots ofintact seedlings of rye (Secale cereale L. cv. Rheidol). Theunidirectional Ca²⁺ fluxes across the plasma membrane and tonoplastmeasured in excised roots were of a similar order of magnitudeto those determined in roots of intact plants. Influx and effluxof Ca²⁺ across the root plasma membrane were similar (estimatedto be between 0·7 and 3·4 µmol g     

Sodium Absorption and Distribution in Forage Grasses of Different Potassium Status

The absorption and distribution of sodium were examined in threegrasses grown in flowing solution culture with different suppliesof potassium. There were marked differences between the speciesin the rate of absorption by their roots, timothy absorbingat a much slower rate than either ryegrass or cocksfoot. Inall species, the rate of Na absorption was greatest when therewas a maintained supply of K and/or when the K contents of theplants were high. Transport of Na from roots to shoots of timothywas restricted; it was less restricted in the other speciesand large proportions of the Na moved from roots to shoots whenK was not supplied to the plants. Sodium transported from theroots accumulated in old leaves and not in the younger leaves.When K was no longer supplied, the growth of ryegrass was maintainedin the plants previously grown with Na plus K; Na supplied insteadof K, however, did not maintain growth. Cocksfoot grown withNa grew less well than when grown without Na when plants wereno longer supplied with K; the growth of timothy was unaffectedby Na. Dactylis glomerata L., Lolium perenne L., Phleum pratense L., cocksfoot, ryegrass, timothy, absorption of ions, distribution of ions, potassium, sodium     

Does Cytokinin Transport from Root-To-Shoot in the Xylem Sap Regulate Leaf Responses to Root Hypoxia?

We have examined the hypothesis that cytokinins transportedfrom roots to shoots affects leaf growth, stomatal conductance,and cytokinin concentration of leaves of Phaseolus and a hybridpoplar (Populus trichocarpa x Populus deltoides) with hypoxicroots. Because cytokinins may interact with other substances,potassium and calcium concentrations were determined in xylemsap of Populus plants with hypoxic and aerated roots while gibberellin(GA) concentrations were measured in shoot tissues. Root hypoxiadecreased leaf growth and closed stomata in both species. Inboth species, fluxes of cytokinins out of the roots were reduced,but no differences in bulk leaf concentrations were measuredbetween the hypoxic and aerated plants. Shoots with aeratedroots contained slightly higher concentrations of GA₁ and GA₃than shoots from hypoxic plants. There were no differences incalcium or potassium concentrations in xylem sap between aerationtreatments. Exogenously applied cytokinins did not alleviatethe growth or stomatal responses caused by root hypoxia. Informationon the site(s) and mechanism(s) of cytokinin action and theways in which cytokinins are compartmentalized within plantcells will be required to understand the physiological significanceof cytokinin transport in the transpirational stream. Key words: Cytokinins, hypoxia, Populus, Phaseolus     

Effects of cadmium on gas exchange and phytohormone contents in citrus

The effect of increased Cd²⁺ concentrations in the watering solution on citrus physiology was studied by using two citrus genotypes, Cleopatra mandarin and Carrizo citrange. Cadmium content in roots and leaves was tested together with measurements of leaf damage, gas exchange parameters, and hormonal contents. Citrus roots efficiently retained Cd²⁺ avoiding its translocation to the shoots and Cleopatra mandarin translocated less Cd²⁺ than Carrizo. With increasing Cd²⁺ concentration all gas exchange parameters were decreased more in Carrizo than in Cleopatra mandarin. Cd-induced increases in abscisic acid and salicylic acid contents were observed in leaves but not in roots of both genotypes.     

Shoot-Dependent Regulation of Sodium and Potassium Fluxes in Roots of Whole Barley Seedlings

Unidirectional fluxes and the cytoplasmic and vacuolar contentsof potassium and sodium in root cells of intact barley seedlings(Hordeum vulgare L., cv. Villa) were determined by use of compartmentalanalysis. In addition, the net vacuolar accumulation J_cv andthe xylem transport ø_cx of K⁺ and Na⁺ were measured.Both of these data were needed for the evaluation of the effluxdata. Fluxes and compartmental contents of K⁺ and Na⁺ were comparableto data obtained with excised roots. The effect of the shoot-to-rootratio—as varied by partial excision of the seedlings seminalroots—on the fluxes and contents was investigated. Highershoot-to-root ratios induced an increase in xylem transport,in plasmalemma influx, and also in the cytoplasmic content ofK⁺ and Na⁺. With potassium the plasmalemma efflux was almostunaltered while the tonoplast fluxes and vacuolar content weredecreased (in presence of Na⁺). With sodium, on the other hand,the plasmalemma efflux and the tonoplast fluxes were also increasedin the plants having one root and a high shoot-to-root ratio.These changes occurred even under conditions of low humidity,when transpiration was low and guttation occurred. The latterwas also increased at the high shoot-to-root ratio. The observedchanges could be due to a relieved feedback control of ion fluxesby the shoot and mediated in part by a relatively higher supplyof photosynthates in the plants having one root In addition,hormonal signals were suggested to participate. In particulara possibly decreased level of cytokinins in the plants havingonly one root could contribute to the signal. The observed changesappear to be responses of the plant to an alteration that canoccur under natural conditions when the root system is damaged.     

Effect of NaCl concentrations in irrigation water on growth and polyamine metabolism in two citrus rootstocks with different levels of salinity tolerance

Six-months-old, uniform sized seedlings of two citrus rootstocks; Cleopatra mandarin (Citrus reshni Hort. ex Tan) and Troyer citrange (Poncirus trifoliata × Citrus sinensis) were irrigated with half-strength Hoagland nutrient solution containing 0, 40 or 80 mM NaCl for 12 weeks. Shoot height, leaf number and fresh weights of the seedlings, and relative chlorophyll contents, chlorophyll fluorescence yields (Fv/Fm), net photosynthetic and respiration rates in the leaves decreased with the increase in salinity level in the irrigation water. The decrease was greater in Troyer citrange as compared to Cleopatra mandarin. The concentrations of sugars i.e. fructose, glucose and sucrose in the leaves of Cleopatra mandarin and both leaves and roots of Troyer citrange decreased with the increase in salinity level. However, the concentrations in the roots of Cleopatra mandarin increased with the increase in salinity level. Free proline content in the leaves of Troyer citrange and root tissue of Cleopatra mandarin also increased with the increased salinity level. Among the polyamines, spermine titer increased in the leaves of both rootstocks as a response to salinity treatments. Na⁺ concentrations were higher in leaf and root tissue of Cleopatra mandarin, while that of Cl⁻ were higher in Troyer citrange.     

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     

Changes in the Chlorophyll Contents of Leaves and in Levels of Cytokinins in Root Exudates during Ripening of Rice Cultivars Nipponbare and Akenohoshi

Changes in fluxes of cytokinins in exudates transported viathe xylem from roots of rice plants cvs. Nipponbare (a standardJapanese cultivar) and Akenohoshi (a slowly senescing cultivar)were measured by mass spectrometry with deuterium-labeled standards.The fluxes of zeatin (Z), trans-ribosylzeatin (trans-RZ), N⁶-isopentenyladenine(iP), and "conjugated Z" (Z in the hydrolysates of highly polarfractions) decreased from heading to the late ripening stagein both cultivars. At the late ripening stage, iP and Z couldno longer be detected, while the flux of N⁶-isopentenyladenosine(iPA) increased slightly. In Akenohoshi, conjugated Z was thepredominant cytokinin from heading to the middle of the ripeningstage. The flux of each of the cytokinins in Akenohoshi washigher than that in Nipponbare at every time point, with theexception of the flux of iPA just after heading. The total concentrationof cytokinins in the xylem exudate of Akenohoshi was higherthan that of Nipponbare after the middle of ripening stage.The chlorophyll content of the third leaves, which were senescingrapidly, was significantly correlated with the flux of totalcytokinins per plant or per unit leaf area. These results suggestthat the larger amounts of cytokinins, in particular conjugatedZ, transported from the roots to the shoots caused the slowsenescence of leaves in Akenohoshi during the ripening stage. (Received May 9, 1994; Accepted July 1, 1995)     

Salinity-calcium interactions on growth and ionic concentration of Citrus plants

Two-year-old Navel orange scions (Citrus sinensis (L.) Osbeck) budded to either Cleopatra mandarin (C. reticulata) and Troyer citrange (C. sinensis × P. trifoliata) rootstocks were used in this experiment. Cleopatra manda in rootstock was considered more tolerant to salinity than Troyer citrange, and this property was attributed to a greater capacity to exclude chloride ions.Plants were grown under glasshouse conditions and supplied with nutrient solution containing either no or 45 mM NaCl. Calcium concentration was increased from 3 to 30 mM. Sodium, potassium, calcium and chloride concentrations in plant organs were analyzed after 90 days of treatment.Supplemental Ca was found to mitigate the adverse effects of salinity on plant growth, defoliation or leaf injury.Chemical analysis indicated that in plants grafted on Troyer citrange Ca restricted uptake and subsequent translocation of Na to the leaves and increased K concentration in both roots and leaves. However, in Cleopatra mandarin-grafted plants increasing Ca levels seemed to reduce transport of Na from roots to leaves, and Na accumulation in roots was associated with reduced concentration of K in this rootstock.Organ chloride analysis showed that Cl accumulation in leaves of plants grafted on both rootstocks was reduced when external Ca concentration increased, whereas Cl concentration in roots remained constant or increased. The data of distribution of Cl in plants showed that a high external Ca level increased Cl accumulation in the basal stem and roots, and reduced the transport of Cl from roots to leaves.     

Acid-Efflux Patterns of Primary and Secondary Roots of Ricinus communis (Euphorbiaceae)

Graviresponding primary roots of castor bean (Ricinus communis)were characterized by more acid efflux on their upper (i.e.rapidly growing) sides than their lower sides. Acid-efflux patternsof the upper and lower sides of horizontally oriented lateralroots were symmetrical. The onset of graviresponsiveness bysecondary roots correlated positively with the development ofasymmetric patterns of acid efflux similar to those of gravirespondingprimary roots. The addition of 1 mM sodium orthovanadate (aninhibitor of auxin-induced proton efflux) to the growth mediumabolished gravicurvature and the development of acid-effluxasymmetry by primary and secondary roots. These results suggestthat (i) the absence of an auxin-induced asymmetry of acid effluxmay be the factor responsible for uncoupling graviperceptionfrom gravitropism in lateral roots, and (ii) the developmentof an auxin-induced asymmetry of acid efflux may mediate theonset of graviresponsiveness by secondary roots of R. communis. Ricinus communis, castor bean, acid efflux, root gravitropism     

A Study of the Exudation of Excised Maize Roots after Removal of the Epidermis and Outer Cortex

The fluid exudation rates and the ionic composition of the exudatesof isolated maize roots were compared with those of similarroots from which the epidermal and outer cortical cells hadbeen removed. The results indicate that in low ionic strengthmedia the salt fluxes into the exudation stream are severaltimes larger in the control than in the treated roots. As theionic strength of the bathing medium increases to 10 mM KClor greater, the salt fluxes become equal. A mechanism to accountfor this behaviour is discussed. The values of L_p, the hydraulic conductivity of the roots toradial water flow, are 0.26 x 10^–6 cm sec^–1 atm^–1for treated and 0.14 x 10^–6 cm sec^–1 atm^–1for control roots, but a statistical technicality precludeda significance test on this apparent difference. The kinetics of tritiated water exchange from external mediumto the exudation fluid in both control and treated roots werenot significantly different. The entry of labelled water seemsto be achieved by the fluid exudation rate in both cases; thusthe barrier to water movement to the exudate compartment remainsintact after removal of the epidermis.     

The Interactions Between Monovalent Cations and Calcium During Their Adsorption on Isolated Cell Walls and Absorption by Intact Barley Roots

The adsorption of sodium, potassium, rubidium and calcium ionsat different concentrations was measured on cell walls frombarley roots (Hordeum vulgare L. cv. Union), prepared by detergenttreatment. It was found that sodium and calcium interacted verystrongly during their simultaneous adsorption, whereas potassiumdid not interfere with calcium. This has led us to concludethat calcium and sodium are adsorbed on identical sites in thecell wall, whereas potassium is adsorbed at another site. Rubidiumseems to be less specific for both sites and interferes onlymoderately with calcium. The adsorption on cell walls of thesecations was compared with their adsorption on intact roots at2 °C, where beside the cell wall, sites may be availableat the outer surface of the membrane, and further measurementswere made of absorption at 25 °C. The fact that sodium interactswith calcium and potassium alters the ratio of K to Na in thecell wall compared to their concentrations in the medium. Thepreferential shift towards potassium when calcium is presentcould be very important for the rates of initial uptake in lowsalt barley roots, since the membrane is in contact with a differentproportion of K to Na in the cell wall from the one suppliedin the medium. Hordeum vulgare L., barley, absorption of cations, adsorption, calcium, sodium, potassium rubidium