Changes in the Cytoplasmic and Vacuolar pH in Intact Cells of Mung Bean Root-Tips under High-NaCl Stress at Different External Concentrations of Ca2+ Ions

The cytoplasmic pH and the vacuolar pH in root-tip cells ofintact mung bean seedlings under high-NaCl stress were measuredby in vivo ³¹P-nuclear magnetic resonance (³¹P-NMR) spectroscopy.When roots were incubated with high levels (100 mM) of NaClat the control external concentration (0.5 mM) of Ca²⁺ ions,the vacuolar pH increased rapidly from 5.6 to 6.2 within 3 h,while the cytoplasmic pH only decreased by a mere 0.1 pH uniteven after a 24-h incubation under high-NaCl conditions. Theincrease in vacuolar pH induced by the high-NaCl stress wasdiminished by an increase in the external concentration of Ca²⁺ions from 0.5 mM to 5 mM. The intracellular concentration ofNa⁺ ions in the root-tip cells increased dramatically upon perfusionof the root cells with 100 mM NaCl, and high external levelsof Ca²⁺ ions also suppressed the in flow of Na⁺ ions into thecells. The vacuolar alkalization observed in salt-stressed rootsmay be related to the inhibition of an H⁺-translocating pyrophosphatasein the tonoplast, caused by the increase in the cytoplasmicconcentration of Na⁺ ions. It is suggested that, although thevacuolar pH increased markedly under salt stress, the cytoplasmicpH was tightly regulated by some unidentified mechanisms, suchas stimulation of the H⁺-translocating ATPase of the plasmalemma,in roots of mung bean under salt stress. (Received April 18, 1992; Accepted July 6, 1992)     

Stimulation of the Extrusion of Protons and H+-ATPase Activities with the Decline in Pyrophosphatase Activity of the Tonoplast in Intact Mung Bean Roots under High-NaCl Stress and Its Relation to External Levels of Ca2+ Ions

Extrusion of protons as a response to high-NaCl stress in intactmung bean roots was investigated at different external concentrationsof Ca²⁺ ions ([Ca²⁺]_ex). The extrusion of protons was graduallyenhanced in the roots exposed to 100 mM NaCl, and high [Ca²⁺]_exdiminished this enhancement of the extrusion. Vesicles of plasmalemmaand tonoplast were prepared from the roots and the H⁺-translocatingATPase (H⁺-ATPase) activities associated with the two typesof membrane and the H⁺-pyrophosphatase (H⁺-PPase) activity ofthe tonoplast were assayed. The plasmalemma ATPase was stimulatedin parallel with dramatic increases in the intracellular concentrationof Na⁺([Na⁺]_in). High [Ca²⁺]ex prevented the increase in [Na⁺]inand diminished the stimulation of ATPase activity. The tonoplastATPase showed a rapid response to salt stress and was similarlystimulated even at high [Ca²⁺]M. The activities of both ATPaseswere, however, insensitive to concentrations of Na⁺ ions upto 100 HIM. By contrast, H⁺-PPase activity of the tonoplastwas severely inhibited with increasing [Na⁺]in under salt stressand recovered with high [Ca²⁺]ex. These findings suggest thathigh-NaCl stress increases the intracellular concentration ofNa⁺ ions in mung bean roots, which inhibits the tonoplast H⁺-PPase,and the activity of the plasmalemma H⁺-ATPase is thereby stimulatedand regulates the cytoplasmic pH. (Received March 26, 1991; Accepted December 13, 1991)     

Effects of External Ca2+ on K+ Permeability of the Elongating Region of Mung Bean Roots under High KCl Stress

Simultaneous measurements of the extracellular potential andthe K⁺(⁸⁶Rb) efflux, and of the intracellular and extracellularpotentials of the cortical cells were used to study the effectsof external Ca²⁺ on the plasma membrane K⁺(⁸⁶Rb) permeabilityin two-day-old mung bean (Vigna mungo L. Hepper, ‘Blackmatpe’) roots under high KCl stress. The K⁺ efflux wasenhanced by a high KCl solution (>7.5 mM), and addition of0.5 mM Ca²⁺ could suppress this efflux. The removal of membrane-associatedCa⁺ from the root surface with EDTA led to a recovery of theK⁺ efflux along with a marked decrease in the extracellularpotential. (Received November 19, 1986; Accepted March 6, 1987)     

高盐胁迫对罗布麻生长及离子平衡的影响

采用网室盆栽试验,研究了不同浓度NaCl（100～400 mmol·L^-1）胁迫30 d对罗布麻植株生物量积累、生长速率、根系活力、盐分和矿质离子吸收、分布等的影响.结果表明：100 mmol·L^-1 NaCl处理30 d,罗布麻植株鲜质量和生长速率显著下降,但对其干质量没有影响;随着盐度的增加,罗布麻植株干质量、鲜质量和生长速率均显著降低.100～200 mmol·L^-1 NaCl胁迫下,罗布麻根系活力明显高于对照;300～400 mmol·L^-1 NaCl盐胁迫下,其活力显著降低.随着盐浓度的增加,罗布麻根、茎和叶片Na⁺含量逐渐增加、K⁺含量缓慢降低;叶片Ca²⁺、Mg²⁺含量明显降低,茎部Ca²⁺和根部Mg²⁺含量有不同程度的增加.盐胁迫明显降低了罗布麻根、茎和叶片K⁺/Na⁺、Ca²⁺/Na⁺和Mg²⁺/Na⁺的比率,植株选择性吸收和运输K⁺、Ca²⁺的能力显著提高.罗布麻植株很强的拒盐能力,以及对K⁺、Ca²⁺的选择性吸收和运输是其具有高盐适应性的主要原因.     

Influx of na, k, and ca into roots of salt-stressed cotton seedlings : effects of supplemental ca

High Na⁺ concentrations may disrupt K⁺ and Ca²⁺ transport and interfere with growth of many plant species, cotton (Gossypium hirsutum L.) included. Elevated Ca²⁺ levels often counteract these consequences of salinity. The effect of supplemental Ca²⁺ on influx of Ca²⁺, K⁺, and Na⁺ in roots of intact, salt-stressed cotton seedlings was therefore investigated. Eight-day-old seedlings were exposed to treatments ranging from 0 to 250 millimolar NaCl in the presence of nutrient solutions containing 0.4 or 10 millimolar Ca²⁺. Sodium influx increased proportionally to increasing salinity. At high external Ca²⁺, Na⁺ influx was less than at low Ca²⁺. Calcium influx was complex and exhibited two different responses to salinity. At low salt concentrations, influx decreased curvilinearly with increasing salt concentration. At 150 to 250 millimolar NaCl, ⁴⁵Ca²⁺ influx increased in proportion to salt concentrations, especially with high Ca²⁺. Potassium influx declined significantly with increasing salinity, but was unaffected by external Ca²⁺. The rate of K⁺ uptake was dependent upon root weight, although influx was normalized for root weight. We conclude that the protection of root growth from salt stress by supplemental Ca²⁺ is related to improved Ca-status and maintenance of K⁺/Na⁺ selectivity.     

Effects of Some Amino Acid Analogues on the Uptake and Transport of K+ and Ca2+ in Wheat and Mung Bean Seedlings: I. CORTICAL CELL FLUXES AND TRANSPORT TO THE STELE IN EXCISED ROOT SEGMENTS, AS AFFECTED BY p-FLUOROPHENYLALANINE

Effluxes of K⁺ and Ca²⁺ from root segments of both wheat, Triticunaestivum L. cv. Capelle and mung bean, Vigna radiata (L.) Wilczek,were measured in the presence or absence of 20 mol m^–3para-fluorophenylalanine (p-FPA). The results were used to estimatethe compartment contents and transmembrane K⁺ and Ca²⁺ fluxesin root cortex cells. Using the Ussing-Teorell flux equationas the criterion, it was concluded that entry of K⁺ from theoutside solution to the cytoplasm, and from the cytoplasm tothe vacuole were active in both wheat and mung bean. Also, inboth species, Ca²⁺ entered the cytoplasm passively across theplasmalemma and was actively pumped back to the external solution.However, interpretation of the direction of active transportacross the tonoplast depends upon an assumption about Ca²⁺ activityin the cytoplasm. The only qualitative effect of p-FPA was to alter the drivingforce for K⁺ influx, across the plasmalemma in wheat, from anactive to a passive one. Quantitative effects of the analoguewere seen for K⁺ fluxes in both wheat and mung bean and forCa²⁺ fluxes in wheat. The p-FPA reduced transport of K⁺ in bothspecies, while transport of Ca²⁺ was unaffected. The implicationsof these results for the ‘two pump hypothesis’ arediscussed. Key words: Triticum aestivum, Vigna radiata, Two pump hypothesis     

NaCl胁迫对圆柏幼苗生长和离子吸收及分配的影响

以当年生圆柏幼苗为实验材料,采用温室调控盆栽土培法研究了不同浓度NaCl(0、100、200、300mmol·L-1)胁迫21d对其生长情况及不同器官(根、茎、叶)中K~+、Na~+、Ca~(2+)和Mg~(2+)的吸收和分配的影响,以探讨圆柏幼苗对盐环境的生长适应性及耐盐机制。结果表明:(1)随着NaCl胁迫浓度的增加,圆柏幼苗生长,包括株高、地径、相对生长量以及生物量的积累均呈下降趋势,而其根冠比却增加。(2)在各浓度NaCl胁迫处理下,圆柏幼苗根、茎、叶中Na~+含量较对照均显著增加,而且叶中Na~+含量显著高于茎和根,叶中Na~+含量是根中的5倍。(3)随着NaCl胁迫浓度的升高,圆柏幼苗各器官中K~+、Ca~(2+)和Mg~(2+)含量以及K~+/Na~+、Ca~(2+)/Na~+及Mg~(2+)/Na~+比值均呈下降趋势。(4)在NaCl胁迫条件下,圆柏幼苗根系离子吸收选择性系数SK,Na、SCa,Na、SMg,Na显著提高,茎、叶离子转运选择性系数SCa,Na、SMg,Na则逐渐降低,叶中离子转运选择性系数SK,Na则随着NaCl胁迫浓度的升高显著降低,大量Na~+进入地上部,减缓了盐胁迫对根系的伤害。研究认为,圆柏幼苗的盐适应机制主要是通过根系的补偿生长效应及茎、叶对Na~+的聚积作用来实现的,同时也与根对K~+、Ca~(2+)、Mg~(2+)的选择性运输能力增强和茎、叶稳定的K~+、Ca~(2+)、Mg~(2+)的选择性运输能力有关。     

Interactions among Ca2+, Na+ and K+ in salinity toxicity: quantitative resolution of multiple toxic and ameliorative effects

Root elongation by wheat seedlings (Triticum aestivum L. cv. Scout 66) was not inhibited by NaCl or KCl up to 130 mM in culture solutions or by high Na⁺ (2 mg g^-1 FW) or K⁺ (4 mg g^-1 FW) in the root tissue, provided that [Ca²⁺]>2 mM in the rooting medium. At [NaCl], [KCl], or [mannitol] >250 mOs, root elongation was progressively inhibited, irrespective of high [Ca²⁺]. In contrast, shoot elongation was sensitive to any diminution of water potential, and Ca²⁺ alleviated the toxicity only weakly. At solute concentrations <250 mOs, the following interactions were observed. Ca²⁺ alleviated Na⁺ and K⁺ toxicity to roots by at least three separate mechanisms. K⁺ was more toxic to roots than Na⁺, but Na⁺ was more toxic to shoots. Low levels of K⁺ relieved Na⁺ toxicity, but low levels of Na⁺ enhanced K⁺ toxicity. Tissue concentrations of Na⁺ were reduced by Ca²⁺ and K⁺ in the rooting medium, and tissue concentrations of K⁺ were enhanced by Ca²⁺ and Na⁺. Several hypotheses relating to salinity toxicity can be evaluated, at least for wheat seedlings. The osmoticant hypotheses (salinity intoxication occurs because of diminished water potential) is true for shoots at all salinity levels, but is true for roots only at high salinity. The Ca²⁺-displacement hypothesis (Na⁺ is toxic because it displaced Ca²⁺ from the cell surface) is correct, but often of minor importance. The K⁺-depletion hypothesis (Na⁺ is toxic because it causes a loss of K⁺ from plant tissues) is false. The Cl^--toxicity hypothesis (the apparent toxicity of Na⁺ is induced by associated Cl^-) is false. The results indicate that, apart from osmotic effects, high levels of Na⁺ in the rooting medium and in the tissues are not toxic unless Ca²⁺ is also deficient, a condition probably leading to inadequate compartmentation and excessive cytoplasmic accumulation. This study related growth to ion activities at plasma-membrane surfaces. These activities were computed by a Gouy-Chapman-Stern model then incorporated into non-linear growth models for growth versus toxicants and ameliorants.Key words: Calcium, potassium, salinity, sodium, toxicity      

Effects of Ions and Membrane Potential on the Elongation of the Unicellular Green Alga Closterium

Cells of the unicellular green alga Closterium ehrenbergii elongatedexclusively at septa and for 4–5 hours after cell division.Cell elongation was strongly inhibited by a decrease in eitherthe external concentration of Ca²⁺ or pH, and was also inhibitedby several competitive Ca²⁺ channel blockers. Changes in concentrationsof other external ions had no effect on the elongation. Theaverage concentrations of ions in the intracellular fluid ofthe interphase cell before cell division was as follows (inmM): K⁺=56.5, Na⁺=4.8, Ca²⁺=2.4, Mg²⁺=1.3, Cl^–=59.5; thepH was 7.4. The levels of K⁺, Na⁺ and Cl^– ions decreasedsignificantly with cell elongation, suggesting that this process,which proceeds with water uptake, surpasses ion absorption.The plasma membrane potential (Vm) in both the interphase cellsand in the elongating cells was in the range of –90 to–105 mV (interior negative). The Vm was entirely determinedby the simple diffusion of K⁺. A decrease in the external concentrationof Ca²⁺ caused depolarization, probably by an indirect effectof low Ca²⁺. Changes in the extracellular level of H⁺ and othercations barely affected Vm. Thus, external Ca²⁺ and H⁺ are concludedto affect cell elongation but not via a change in the Vm acrossthe plasma membrane. (Received February 29, 1988; Accepted June 8, 1988)     

Salt, nutrient uptake and transport, and ABA of Populus euphratica; a hybrid in response to increasing soil NaCl

The uptake and transport of salt ions (Na⁺, Cl^-), macronutrients (K⁺, Ca²⁺, Mg²⁺) and abscisic acid (ABA) response to increasing soil salinity were examined in 2-year-old seedlings of Populus euphratica and a hybrid, P. talassica Kom 2 (P. euphratica + Salix alba L.). Leaf burn symptoms appeared in the hybrid after 8 days of exposure to salinity when soil NaCl concentration increased to 206 mM, whereas P. euphratica exhibited leaf damage after day 21 when soil NaCl exceeded 354 mM. Leaf necrosis was the result of excess salt accumulation since the injury followed an abrupt increase of endogenous salt levels. Compared with the hybrid, P. euphratica exhibited a greater capacity to exclude salt ions from leaves under increasing salinity, especially Cl^-. Salt treatment altered nutrient balance of the hybrid, leaf K⁺, Ca²⁺ and Mg²⁺ concentrations significantly declined and the same trends were observed in roots with the exception of K⁺. Although K⁺ levels decreased in salinised P. euphratica, increasing salinity did not affect the levels of Ca²⁺ and Mg²⁺ in leaves, but did increase the uptake of these nutrients when salt stress was initiated. NaCl-induced increase of ABA concentration in xylem sap [ABA] was observed in the two tested genotypes, however xylem [ABA] increased more rapidly in P. euphratica and a fivefold increase of xylem [ABA] was recorded after the first day of exposure to salt stress. Therefore, we conclude that the increase of Ca²⁺ uptake may be associated with the rise of ABA, and thus contributes to membrane integrity maintenance, which enables P. euphratica to regulate uptake and transport of salt ions under high levels of external salinity in the longer term.     

Aluminum Stress Increases K+ Efflux and Activities of ATP- and PPi- Dependent H+ Pumps of Tonoplast-Enriched Membrane Vesicles from Barley Roots

Aluminum stress significantly stimulated K⁺ effux from barleyroots that had been preloaded with K⁺ The stress also increasedPP₁- and ATP-dependent H⁺ pump activities of tonoplast enrichedmembrane vesicles from the roots. Ca²⁺ ions reduced increasesin K⁺ effux and both H⁺ pump activities under these conditions. (Received April 25, 1992; Accepted August 4, 1992)     

NaCl处理对西伯利亚白刺幼苗生长及离子平衡的影响

以1年生西伯利亚白刺水培幼苗为材料,研究了不同浓度NaCl(0、200、400mmol·L~(-1))处理对幼苗生长及不同器官(根、茎、叶)中Na~+、K~+、Ca~(2+)、Mg~(2+)的吸收、运输与分配的影响,探讨西伯利亚白刺的盐适应机制。结果表明:(1)200mmol·L~(-1) NaCl处理促进了西伯利亚白刺幼苗的生长及叶片肉质化程度,400mmol·L-1 NaCl处理显著抑制其生长。(2)随着NaCl处理浓度的升高,西伯利亚白刺幼苗根、茎、叶中Na~+含量显著增加,且叶中Na~+含量显著高于茎和根中;根系中K~+含量显著增加;根、茎、叶中Ca~(2+)、Mg~(2+)含量在200mmol·L~(-1) NaCl处理下保持平稳或上升,而在400mmol·L-1 NaCl处理下显著下降。(3)各器官中K~+/Na~+、Ca~(2+)/Na~+和Mg~(2+)/Na~+比值总体随NaCl处理浓度的升高呈下降趋势,且根部离子比值始终高于叶片和茎。(4)随着NaCl处理浓度的升高,西伯利亚白刺幼苗根-茎SK,Na显著下降,而根-茎SCa,Na、SMg,Na及茎-叶SK,Na、SCa,Na、SMg,Na逐渐提高。研究发现,西伯利亚白刺的盐适应机制主要是通过植株的补偿生长效应及叶片对Na~+的聚积作用实现的,同时也与根系对K~+的扣留及茎叶对K~+、Ca~(2+)、Mg~(2+)选择性运输能力增强有关。     

Salt-imposed restrictions on the uptake of macroelements by roots of Arabidopsis thaliana

The aim of this investigation was to identify the growth limiting factors in Arabidopsis thaliana subjected to a mild salt stress. Two natural accessions (Col and N1438) were compared. In spite of their morphological and developmental similarity, they have been previously shown to differ in the response of their superoxide dismutase genes to salt stress (Physiol Plant 132:293–305, 2008). Thirty-day-old seedlings were grown for 15 days using a split-root configuration in which the root system was divided into two equal parts: the first was immersed in a complete nutrient solution with 50 mM NaCl added, while the second part was immersed in either complete or incomplete K-, Ca-, or N-free medium. Using this approach, we demonstrated that K⁺ and Ca²⁺ uptake was impaired in the roots subjected to NaCl. There was no indication of the salt-induced inhibition of N uptake. If K⁺ or Ca²⁺ were available from salt-free medium, plants were able to grow at normal rate and accumulate large amounts of Na⁺ in the shoots. These results indicate that the sensitivity of Arabidopsis growth to mild salinity was probably due to an inhibition of K⁺ or Ca²⁺ root transport by salt rather than due to salt accumulation in shoots. Furthermore, the salt sensitivity of ion transport in roots seemed to depend on the genotype, since K⁺ was limiting for Col growth, in contrast to N1438, the growth of which was limited by Ca²⁺.     

Significance of Ca2+ and K+ in Micrasterias Growth and Morphogenesis

Significance of Ca²⁺ and K⁺ for the complex morphogenesis ofMicrasterias, which takes place through multipolar tip growth,was investigated. Studies with different external Ca²⁺ concentrationsand Ca²⁺ channel inhibitors LaCl₃ and verapamil indicate thatCa²⁺ and Ca²⁺ channels are essential in the development, whiletreatments with different K⁺ concentrations and K⁺ channel inhibitorTEA demonstrate that potassium or K⁺ channels are not neededin the process, albeit the existence of K⁺ channels. K⁺ is notneeded even for the regulation of turgor pressure, which wasfound to decrease clearly during cell development. The plasmamembrane ATPase inhibitors diethylstilbesterol (DES) and Na-orthovanadatestop morphogenesis and indicate the importance of ion pumpsin the developmental process. Both supraoptimal, external K⁺and Ca²⁺ cause abundant Ca²⁺ precipitate formation in chloroplasts,which shows that chloroplasts are important in regulation ofcytoplasmic Ca²⁺ metabolism and that K⁺ activates the uptakeof Ca²⁺ through Ca²⁺ channels. (Received June 13, 1995; Accepted September 13, 1996)     

Application of 39K NMR Spectroscopy to Potassium Transport in Mung Bean Root Tips

The intracellular K⁺ concentration and its change in mung bean[Vigna mungo (L.) Hepper] root tips were investigated non-invasivelywith ³⁹K nuclear magnetic resonance spectroscopy using a membraneimpermeable shift reagent, dysprosium (III) tripolyphosphate[Dy(PPP_i)^7–₂]. The K⁺ resonance was shifted to highermagnetic field in proportion to the concentration of the shiftreagent. In addition to a reference capillary peak for measuringthe K⁺ concentration, two well-resolved peaks (intra- and extracellularK⁺ resonances) were observed in the 39K NMR spectra of mungbean root tips. The intracellular K⁺ concentration was determinedto be 41 mM, which was similar to the value obtained by flamephotometry. When 20 mM KCl was added to the external medium,the intensity of the intracellular K⁺ resonance gradually increasedand the net K⁺ uptake rate was calculated to be 4.1 micromolesper gram fresh weight per hour. After removal of KCl from theperfusion medium, the intracellular K⁺ concentration considerablydecreased. With ³¹P NMR method, 2.5 mM Dy(PPP_j)^7–1₂ and20 mM KCl had little effect on the ATP level in the cells. Wehave indicated that the ³⁹K NMR method can be used to determinethe K⁺ levels and net fluxes of the K⁺ transport in perfusedroot tips successively. (Received April 6, 1988; Accepted September 29, 1988)     

Root elongation in saline solution related to calcium binding to root cell plasma membranes

To gain a better understanding of the relations between root elongation and the amount of Ca²⁺ bound to the plasma membrane (PM), melon plants were grown in aerated solutions containing different concentrations of CaCl₂ with various concentrations of NaCl or mannitol. With increasing external concentrations of NaCl or mannitol, root elongation was suppressed. Addition of CaCl₂ to the external medium alleviated the inhibition of root elongation by high concentrations of Na⁺, but not of mannitol. Root elongation in media containing high concentrations of NaCl was correlated with the computed amount of Ca²⁺ bound to the PM. A model describing relative root elongation (RRL) under salt stress was developed. This model takes into account the osmotic potential in the growing solution (based on the mannitol experiments) and the computed amount of Ca²⁺ bound to the PM. Calcium binding was calculated by applying a Gouy-Chapman-Stern sorption model using the same parameters deduced from studies on PM vesicles. This model combines electrostatic theory with competitive binding at the PM surface. The model for RRL allowed the computation of a critical value for the fraction of negative sites binding Ca²⁺ on the PM needed for nearly optimal (95%) root elongation. Any decrease below this critical value decreased the RRL. Root elongation of Honey Dew (salt-resistant cv.) was greater than that of Eshkolit Ha'Amaqim (salt-sensitive cv.) under NaCl stress. Nearly optimal root growth for Honey Dew and Eshkolit Ha'Amaqim occurred when 40% and 51% of total membrane charged sites were bound by Ca²⁺, respectively. The effect of osmotic potential on the suppression of root elongation was the same for the two cultivars. To our knowledge, this report provides the first fully quantitative estimates of PM-bound Ca²⁺ relative to salt toxicity.     

Repression of the K+ Uptake and Cation-Stimulated ATPase Activity Associated with the Plasma Membrane-Enriched Fraction of Cucumber Roots Due to Ca2+ Starvation

The uptake of K⁺ by cucumber plants decreased markedly duringCa²⁺ starvation. A plasma membrane-enriched fraction, judgedfrom the distribution of marker enzymes, was prepared from controland Ca²⁺-starved roots. The Mg²⁺- and K⁺-Mg²⁺-ATPase activitiesassociated with the plasma membrane-enriched fraction of controlroots were maxima at pH 6.5. Various monovalent cations andpotassium salts of monovalent anions stimulated Mg²⁺-ATPaseactivity. Vanadate, DES and DCCD inhibited K⁺- Mg²⁺-ATPase activity.Of the divalent cations and phosphate esters tested, Mg²⁺ andATP were most effective for the stimulation of ATPase by K⁺,whereas Ca²⁺ was ineffective in replacing Mg²⁺. Mg²⁺- and K⁺-Mg²⁺-ATPase activities associated with the plasmamembrane enriched fraction of Ca²⁺-starved roots were much lowerthan those of control roots. K_m values of K⁺-Mg²⁺-ATPase forATP were comparable for control and Ca²⁺-starved roots. The K⁺-stimulated activity of Mg²⁺-ATPase in Ca²⁺-starved rootswas approximately one fourth that of the control, whereas therate of stimulation was only slightly lower in Ca²⁺-starvedroots. (Received May 9, 1984; Accepted September 17, 1984)     

NaCl胁迫下沙枣幼苗生长和阳离子吸收、运输与分配特性

沙枣(Elaeagnus angustifolia L.)耐盐性强,是我国北方生态脆弱地区造林绿化的一个先锋树种。为探讨沙枣的盐适应机制,研究了不同浓度NaCl(0、100和200 mmol/L)胁迫30d对其水培幼苗生物量累积以及不同组织(根、茎、叶)K+、Na+、Ca2+和Mg2+吸收、运输与分配的影响。结果表明:盐胁迫不同程度地促进了沙枣苗根系生长;100 mmol/L NaCl胁迫对幼苗生物量累积无明显影响,而200 mmol/L则显著抑制了生物量累积;盐胁迫幼苗根、茎、叶中Na+含量以及K+-Na+选择性运输系数(S K,Na)和Ca2+-Na+选择性运输系数(S Ca,Na)显著或大幅度增加,而K+、Ca2+、Mg2+含量以及K+/Na+、Ca2+/Na+和Mg2+/Na+比值则显著或大幅度下降;200 mmol/L NaCl胁迫沙枣根Na+含量和根Na+净累积量分别为22.15 mg/g干重和1.87 mg/株(是对照的16.20倍和20.06倍),根成为Na+净累积量增加幅度最大的组织和Na+含量最高的组织;200 mmol/L NaCl胁迫沙枣茎、叶中的Na+含量以及冠组织Na+净累积量分别高达5.15、7.71 mg/g干重和3.29 mg/株(是对照的7.22倍、9.58倍和5.45倍),但幼苗仍能正常生长。综合分析认为,沙枣的盐适应机制是根系拒盐和冠组织耐盐,主要通过根系的补偿生长效应、根系对Na+的聚积与限制作用以及冠组织对Na+的忍耐来实现的,同时也与根、茎和叶对K+、Ca2+选择性运输能力显著增强有关。     

Na+, K+ and Cl- in Xylem Sap Flowing to Shoots of NaCl-Treated Barley

Munns, R. 1985. Na⁺, K⁺ and Cl^– in xylem sap flowing toshoots of NaCl-treated barley.—J. exp. Bot. 36: 1032–1042. Na⁺, Cl^– and K⁺ concentrations were measured in xylemsap obtained by applying pressure to the roots of decapitatedbarley plants grown at external [NaCl] of 0, 25, 50, 100, 150and 200 mol m^–3. For any given NaCl treatment, ion concentrationsin the xylem sap were hyperbolically related to the flux ofwater. Ion concentrations in sap collected at very low volumefluxes (without applied pressure) were 5–10 times higherthan in sap collected at moderate fluxes (under pressure). Fora given moderate volume flux, Na+ concentration in the xylemsap, [Na⁺]_x, was only 4.0 mol m^–3 at external [NaCl] of25–150 mol m^–3, and increased to 7.0 mol m^–3at 200 mol m^–3. [Cl-]x showed a similar pattern. Thisshows there would be little difference in the rate of uptaketo the shoot of plants at 25–150 mol m^–3 externalNaCl and indicates little change even at 200 mol m^-3 NaCl becausetranspiration rates would be much lower. Thus the reduced growthof the shoot of plants at high NaCl concentrations is not dueto higher uptake rates of Na⁺ or Cl^–. The fluxes of Na⁺, Cl^– and K^– increased non-linearlywith increasing volume flux indicating little movement of saltin the apoplast. The flux of K⁺ increased even when [K⁺]_x wasgreater than external [K⁺], indicating that membrane transportprocesses modify the K⁺ concentration in the transpiration streamas it flows through the root system. Key words: -Xylem sap, Na⁺, K⁺, Cl^– fluxes, salinity, barley     

Repression of Proton extrusion from Intact Cucumber Roots and the Proton Transport Rate of Microsomal Membrane Vesicles of the Roots due to Ca2+ Starvation

Proton extrusion from cucumber roots decreased markedly duringCa²⁺ starvation in the presence of KC1. Vesicles with ATP-dependentproton transport activity were prepared from the microsomalmembrane fraction of control and Ca²⁺-starved roots. The protontransport rate of the vesicles from Ca²⁺-starved roots was repressedto less than half of the vesicles prepared from the controlroots. K⁺-Mg²⁺-ATPase activity associated with the vesiclesprepared from Ca²⁺-starved roots was approximately one-thirdof the activity associated with those prepared from controlroots. K_m values of the proton transport rate and K⁺-Mg²⁺-ATPasefor ATP were much higher in vesicles prepared from Ca²⁺-starvedroots. The repression of proton extrusion linked with K⁺ uptake inthe Ca²⁺-starved roots could be largely caused by the reducedproton pumping activity associated with microsomal membranesin the roots. (Received May 25, 1987; Accepted October 14, 1987)