Potassium transport in two tomato species : lycopersicon esculentum and lycopersicon cheesmanii

The commercial tomato, lycopersicon esculentum Mill. cv Walter, and its wild relative, Lycopersicon cheesmanii ssp. minor (Hook.) C.H. Mull., were grown for 30 days under controlled conditions and in solution culture varying in its content of Na⁺ and K⁺. Subsequently, ⁸⁶Rb-labeled K⁺ uptake and distribution were studied. From all solutions, `Walter' consistently absorbed <sup>86</sup>Rb-labeled K<sup>+</sup> at a higher rate in micromoles per gram fresh weight per 30 minutes than L. cheesmanii. L. cheesmanii distributed a greater proportion of the absorbed K<sup>+</sup> from its root to its shoot. When 0.6 millimolar NaNO<sub>3</sub> replaced 0.6 millimolar KNO<sub>3</sub> in the pretreatment solution, intact plants of both genotypes followed a similar pattern as when they were pretreated with K<sup>+</sup> only, but a greater percentage of the absorbed K<sup>+</sup> remained in the roots. Leaf slices of L. cheesmanii plants deprived of K<sup>+</sup> for 6 days showed a greater rate of K<sup>+</sup> uptake than did slices from `Walter' plants pretreated the same way. Stem slices of L. cheesmanii, however, had a lower uptake rate than did those of `Walter'. Both leaf and stem slices of `Walter' plants, pretreated 6 days with 0.6 millimolar NaNO₃ substituting for 0.6 millimolar KNO₃ in their growth medium, had greater rates of ⁸⁶Rb-labeled K⁺ uptake from 0.5 and 20 millimolar KCl solutions than did slices of L. cheesmanii. These marked differences in patterns of ion uptake and translocation indicate that these genotypes of tomato have evolved different mechanisms to deal with K⁺ and Na⁺ in their environments.     

Comparative studies on the sodium, potassium, and chloride relations of a wild halophytic and a domestic salt-sensitive tomato species

In long-term experiments with differentially salinized nutrient solutions, plants of Lycopersicon esculentum Mill cv. Walter failed at Na⁺ concentrations of 200 millimolar or more but tolerated K⁺ concentrations of that magnitude. The behavior of the wild, salt-tolerant Lycopersicon cheesmanii (Hook) C. H. Mull., accession number 1401, was diametrically different; it tolerated Na⁺ at 200 millimolar, but K⁺ at the same concentration proved toxic to it.     

Accumulation of potassium and sodium by barley roots in a k-na replacement series

Excised roots of barley (Hordeum vulgare, var. Campana) were incubated for 24 hr in solutions containing constant total concentrations of KCl and NaCl but in which the mole fractions of K and Na were varied in replacement series. In solutions containing 1, 10, or 50 mm concentrations of K⁺ plus Na⁺, total cation accumulation was dependent upon the total salt concentration but was relatively independent of the mole fractions of K⁺ and Na⁺. These results imply that accumulation of K⁺ and Na⁺ was limited by a common factor. In solutions containing 0.01 mm K⁺ plus Na⁺ there was a strong preference for K⁺ over Na⁺ and the sum of K⁺ and Na⁺ accumulation increased with increasing K⁺ concentration.     

Influence of Excision and Aging upon K+ Influx into Barley Roots: Recovery or Enhancement? 1

The influx of K⁺ from ⁸⁶Rb-labeled solutions in the concentration range 0.008 to 0.2 mm into roots of intact plants and excised roots of barley plants (Hordeum vulgare [L.]) previously grown in 5 mm CaSO₄ (low K⁺ roots) or 0.5 mm CaSO₄ plus 5 mm KCl (high K⁺ roots) was measured. A consistent observation of these experiments was a substantial reduction of influx (usually by about 50%) following excision. The possible leakage of K⁺ into the medium and subsequent dilution of specific activity of labeled solutions was eliminated as an explanation for influx reduction in excised low K⁺ roots. Reduction of transpirational rates was also without effect upon influx into low K⁺ roots. Excision followed by 2 hours aging in 0.5 mm CaSO₄ solution revealed that influx values recovered within the 2 hours to the values obtained in intact roots. It is concluded that much of the literature which describes the enhancement of ion uptake following excision actually describes excision damage followed by recovery.     

Sodium and potassium fluxes and compartmentation in roots of atriplex and oat

K⁺ and Na⁺ fluxes and ion content have been studied in roots of Atriplex nummularia Lindl. and Avena sativa L. cv Goodfield grown in 3 millimolar K⁺ with or without 3 or 50 millimolar NaCl. Compartmental analysis was carried out with entire root systems under steady-state conditions.

Increasing ambient Na⁺ concentrations from 0 to 50 millimolar altered K⁺, in Atriplex, as follows: slightly decreased the cytoplasmic content (Q_c), the vacuolar content (Q_v), and the plasma membrane influx and efflux. Xylem transport for K⁺ decreased by 63% in Atriplex. For oat roots, similar increases in Na⁺ altered K⁺ parameters as follows: plasma membrane influx and efflux decreased by about 80%. Q_c decreased by 65%, and xylem transport decreased by 91%. No change, however, was observed in Q_v for K⁺. Increasing ambient Na⁺ resulted in higher (3 to 5-fold) Na⁺ fluxes across the plasma membrane and in Q_c of both species. In Atriplex, Na⁺ fluxes across the tonoplast and Q_v increased as external Na⁺ was increased. In oat, however, no significant change was observed in Na⁺ flux across the tonoplast or in Q_v as external Na⁺ was increased. In oat roots, Na⁺ reduced K⁺ uptake markedly; in Atriplex, this was not as pronounced. However, even at high Na⁺ levels, the influx transport system at the plasma membrane of both species preferred K⁺ over Na⁺.

Based upon the Ussing-Teorell equation, it was concluded that active inward transport of K⁺ occurred across the plasma membrane, and passive movement of K⁺ occurred across the tonoplast in both species. Na⁺, in oat roots, was actively pumped out of the cytoplasm to the exterior, whereas, in Atriplex, Na⁺ was passively distributed between the free space, cytoplasm, and vacuole.

     

Cation pretreatment effects on nitrate uptake, xylem exudate, and malate levels in wheat seedlings

Week-old wheat seedlings absorbed at least 40% NO₃⁻ from NaNO₃ when preloaded with K⁺ than when preloaded with Na⁺ or Ca²⁺. Cultures of Triticum vulgare L. cv. Arthur were grown for 5 days on 0.2 mm CaSO₄, pretreated for 48 hours with either 1 mm CaSO₄, K₂SO₄, or Na₂SO₄, and then transferred to 1 mm NaNO₃. All solutions contained 0.2 mm CaSO₄. Shoots of K⁺-preloaded plants accumulated three times more NO₃⁻ than shoots of the other two treatments. Initially, the K⁺-preloaded plants contained 10-fold more malate than either Na⁺- or Ca²⁺-preloaded seedlings. During the 48-hour treatment with NaNO₃, malate in both roots and shoots of the K⁺-preloaded seedlings decreased. Seedlings preloaded with K⁺ reduced 25% more NO₃⁻ than those preloaded with either Na⁺ or Ca²⁺. These experiments indicate that K⁺ enhanced NO₃⁻ uptake and reduction even though the absorption of K⁺ and NO₃⁻ were separated in time. Xylem exudate of K⁺-pretreated plants contained roughly equivalent concentrations of K⁺ and NO₃⁻, but exudate from Na⁺ and Ca²⁺-pretreated plants contained two to four times more NO₃⁻ than K⁺. Therefore K⁺ is not an obligatory counterion for NO₃⁻ transport in xylem.     

Significance of Na<Superscript>+</Superscript> and K<Superscript>+</Superscript> for Sustained Hydration of Organ Tissues in Ecologically Distinct Halophytes of the Family Chenopodiaceae

The contents of Na⁺, K⁺, water, and dry matter were measured in leaves and roots of euhalophytes Salicornia europaea L. and Climacoptera lanata (Pall.) Botsch featuring succulent and xeromorphic cell structures, respectively, as well as in saltbush Atriplex micrantha C.A. Mey, a halophyte having bladder-like salt glands on their leaves. All three species were able to accumulate Na⁺ in their tissues. The Na⁺ content in organs increased with elevation of NaCl concentration in the substrate, the concentrations of Na⁺ being higher in leaves than in roots. When these halophytes were grown on a NaCl-free substrate, a trend toward K⁺ accumulation was observed and was better pronounced in leaves than in roots. Particularly high K⁺ concentrations were accumulated in Salicornia leaves. There were no principal differences in the partitioning of Na⁺ and K⁺ between organs of three halophyte species representing different ecological groups. At all substrate concentrations of NaCl, the total content of Na⁺ and K⁺ in leaves was higher than in roots. This distribution pattern persisted in Atriplex possessing salt glands, as well as in euhalophytes Salicornia and Climacoptera. The physiological significance of such universal pattern of ion accumulation and distribution among organs in halophytes is related to the necessity of water absorption by roots, its transport to shoots, and maintenance of sufficient cell water content in all organs under high soil salinity.     

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。     

Dynamics of Na+, K+, and Proline Accumulation in Salttreated Vigna sinensis (L) and Phaseolus aureus (L)

The dynamics of Na⁺, K⁺, and proline accumulation in various organs of non nodulated Vigna sinensis and Phaseolus aureus was followed during their acclimation to two levels of salinities for a period of 35 days and was correlated to the vegetative growth of the two species. The rate of Na⁺ and K⁺ absorption is at a maximum during the first 15 to 20 days of culture. K⁺ absorption is not completely inhibited even at 100 mM NaCl although the endogenous Na⁺ largely surpasses that of K⁺ in certain organs. Low salinity rather accelerates K⁺ absorption in both species. The relative growth rates (RGR) correlate with the rate of Na⁺ and K⁺ accumulation. At low salinity (10 mM NaCl), the RGR of V. sinensis is greater than that of P. aureus. However, at high salinity (100 mM NaCl) the RGR is the same for both species. The growth of the younger parts of the two species is not arrested by salt treatment. Very high accumulation of Na⁺ is avoided in organs with less vacuolated tissues. At no time does the endogenous K : Na ratio in these organs fall below 1.0. Certain organs, especially the roots, hypocotyls, and the lower parts of the stems are capable of storing large quantities of Na⁺. In V. sinensis, the accumulated Na⁺ and K⁺ are evenly distributed among the various organs while in P. aureus they are rather concentrated in the roots. External salinity creates water deficiency in the younger plant parts and as a consequence, proline accumulates especially in the youngest aerial organs - more in P. aureus than in V. sinensis. The accumulation of this amino acid in both the species is dependent on time and correlates directly, not only with the water deficit, but also with the K⁺ contents. In contrast, it does not seem to depend directly on the endogenous Na⁺ content. The relative salt tolerance of the two species and the possible role of K⁺, Na⁺ and proline in the osmotic adjustments of the two species under saline conditions are discussed.     

Short-term experiments on ion transport by seedlings and excised roots : technique and validity

The absorption of K⁺ by excised roots of barley (Hordeum vulgare L. cv California Mariout) has been systematically compared with that of entire, undisturbed seedlings. Some experiments have also been done with wheat (Triticum aestivum L.) and an amphiploid obtained from a cross between it and salt-tolerant tall wheatgrass (Lophopyrum elongatum Host Löve [syn. Agropyron elongatum Host]). For all three genotypes, the rate of K⁺ absorption measured in a 20-min period was identical for entire 8-d-old seedlings and their excised roots within the experimental error. Manipulation gentler than root excision, viz. careful transfer of seedlings from one experimental solution to another, was also without effect on the rate of K⁺ absorption. Absorption of K⁺ measured by assay of its ⁸⁶Rb label in the tissue was identical with that measured by K⁺ depletion of the experimental solutions assayed chemically. For the plant materials and conditions of these experiments, the excised root technique for studying ion transport into roots is validated. The advantages of the technique, and findings differing from the present ones, are discussed.     

Solute contents in roots and root calli of NaCl-tolerant and NaCl-sensitive tissues ofLycopersicon

Biomass, relative growth rate (RGR), organic and inorganic solute contents in control and NaCl (50–100 mM) affected roots or calli of the wild tomato genotypeLycopersicon pennellii and theLycopersicon esculentum wilty mutantflacca were compared. Under NaCl-stress, the RGR of calli fromL. pennellii was higher than that of the mutantflacca, while the root biomass of the former was lower than that of the latter. Constant water contents were found in calli and roots, irrespective of the genotypes and NaCl concentrations. Taking into account the solute contents of the apoplasm, Na⁺ accumulation was similar in the sensitive tissues (calli fromL. flacca, roots ofL. pennellii) and the tolerant ones (calli fromL. pennellii, flacca roots). Decreased K⁺ and Mg²⁺ and increased proline contents were found in both sensitive tissues. In comparison with sensitiveL. pennellii roots, salt sensitiveflacca calli showed increased total organic acid and amino acid contents.     

Responses of Atriplex spongiosa and Suaeda monoica to Salinity

The growth and tissue water, K⁺, Na⁺, Cl⁻, proline and glycinebetaine contents of the shoots and roots of two Chenopodiaceae, Atriplex spongiosa and Suaeda monoica have been measured over a range of external NaCl salinities. Both species showed some fresh weight response to low salinity mainly due to increased succulence. S. monoica showed both a greater increase in succulence (at low salinities) and tolerance of high salinities than A. spongiosa. Both species had high affinities for Na⁺ and maintained constant but low shoot K⁺ contents with increasing salinity. These trends were more marked with S. monoica in which Na⁺ stimulated the accumulation of K⁺ in roots. An association between high leaf Na⁺ accumulation, high osmotic pressure, succulence, and a positive growth response at low salinities was noted. Proline accumulation was observed in shoot tissues with suboptimal water contents. High glycinebetaine contents were found in the shoots of both species. These correlated closely with the sap osmotic pressure and it is suggested that glycinebetaine is the major cytoplasmic osmoticum (with K⁺ salts) in these species at high salinities. Na⁺ salts may be preferentially utilized as vacuolar osmotica.     

Coordination of AtHKT1;1 and AtSOS1 facilitates Na+ and K+ homeostasis in Arabidopsis thaliana under salt stress

Reducing Na⁺ accumulation and maintaining K⁺ stability in plant is one of the key strategies for improving salt tolerance. AtHKT1;1 and AtSOS1 are not only the salt tolerance determinants themselves, but also mediate K⁺ uptake and transport indirectly. To assess the contribution of AtHKT1;1 and AtSOS1 to Na⁺ homeostasis and K⁺ nutrition in plant, net Na⁺ and K⁺ uptake rate, Na⁺ and K⁺ distributions in Arabidopsis thaliana wild type (WT), hkt1;1 mutant (athkt1;1) and sos1 mutant (atsos1) were investigated. Results showed that under 2.5 mM K⁺ plus 25 or 100 mM NaCl, athkt1;1 shoot concurrently accumulated more Na⁺ and less K⁺ than did WT shoot, suggesting that AtHKT1;1 was critical for controlling Na⁺ and K⁺ distribution in plant; while atsos1 root accumulated more Na⁺ and absorbed lower K⁺ than did WT root, implying that AtSOS1 was determiner of Na⁺ excretion and K⁺ acquisition. Under 0.01 mM K⁺, athkt1;1 absorbed lower Na⁺ than did WT with 100 mM NaCl, suggesting that AtHKT1;1 is involved in Na⁺ uptake in roots; while atsos1 shoot accumulated less Na⁺ than did WT shoot no matter with 25 or 100 mM NaCl, implying that AtSOS1 played a key role in controlling long-distance Na⁺ transport from root to shoot. We present a model in which coordination of AtHKT1;1 and AtSOS1 facilitates Na⁺ and K⁺ homeostasis in A. thaliana under salt stress: under the normal K⁺, the major function of AtHKT1;1 is Na⁺ unloading and AtSOS1 is mainly involved in Na⁺ exclusion, whereas under the low K⁺, AtHKT1;1 may play a dominant role in Na+ uptake and AtSOS1 may be mainly involved in Na⁺ loading into the xylem.     

NaCl Induces a Na/H Antiport in Tonoplast Vesicles from Barley Roots

Evidence was found for a Na⁺/H⁺ antiport in tonoplast vesicles isolated from barley (Hordeum vulgare L. cv California Mariout 72) roots. The activity of the antiport was observed only in membranes from roots that were grown in NaCl. Measurements of acridine orange fluorescence were used to estimate relative proton influx and efflux from the vesicles. Addition of MgATP to vesicles from a tonoplast-enriched fraction caused the formation of a pH gradient, interior acid, across the vesicle membranes. EDTA was added to inhibit the ATPase, by chelating Mg²⁺, and the pH gradient gradually dissipated. When 50 millimolar K⁺ or Na⁺ was added along with the EDTA to vesicles from control roots, the salts caused a slight increase in the rate of dissipation of the pH gradient, as did the addition of 50 millimolar K⁺ to vesicles from salt-grown roots. However, when 50 millimolar Na⁺ was added to vesicles from salt-grown roots it caused a 7-fold increase in the proton efflux. Inclusion of 20 millimolar K⁺ and 1 micromolar valinomycin in the assay buffer did not affect this rapid Na⁺/H⁺ exchange. The Na⁺/H⁺ exchange rate for vesicles from salt-grown roots showed saturation kinetics with respect to Na⁺ concentration, with an apparent K_m for Na⁺ of 9 millimolar. The rate of Na⁺/H⁺ exchange with 10 millimolar Na⁺ was inhibited 97% by 0.1 millimolar dodecyltriethylammonium.     

Nitric Oxide Mediates Root K+/Na+ Balance in a Mangrove Plant,Kandelia obovata,by Enhancing the Expression of AKT1-Type K+ Channel and Na+/H+ Antiporter under High Salinity

It is well known that nitric oxide (NO) enhances salt tolerance of glycophytes. However, the effect of NO on modulating ionic balance in halophytes is not very clear. This study focuses on the role of NO in mediating K⁺/Na⁺ balance in a mangrove species, Kandelia obovata Sheue, Liu and Yong. We first analyzed the effects of sodium nitroprusside (SNP), an NO donor, on ion content and ion flux in the roots of K. obovata under high salinity. The results showed that 100 μM SNP significantly increased K⁺ content and Na⁺ efflux, but decreased Na⁺ content and K⁺ efflux. These effects of NO were reversed by specific NO synthesis inhibitor and scavenger, which confirmed the role of NO in retaining K⁺ and reducing Na⁺ in K. obovata roots. Using western-blot analysis, we found that NO increased the protein expression of plasma membrane (PM) H⁺-ATPase and vacuolar Na⁺/H⁺ antiporter, which were crucial proteins for ionic balance. To further clarify the molecular mechanism of NO-modulated K⁺/Na⁺ balance, partial cDNA fragments of inward-rectifying K⁺ channel, PM Na⁺/H⁺ antiporter, PM H⁺-ATPase, vacuolar Na⁺/H⁺ antiporter and vacuolar H⁺-ATPase subunit c were isolated. Results of quantitative real-time PCR showed that NO increased the relative expression levels of these genes, while this increase was blocked by NO synthesis inhibitors and scavenger. Above results indicate that NO greatly contribute to K⁺/Na⁺ balance in high salinity-treated K. obovata roots, by activating AKT1-type K⁺ channel and Na⁺/H⁺ antiporter, which are the critical components in K⁺/Na⁺ transport system.     

Mesurement of longitudinal ion profiles in single roots of Hordeum and Atriplex by use of flameless atomic absorption spectroscopy

Summary A method is described by which the Na⁺ and K⁺ content in 0.5 mm sections of single roots of Hordeum distichon L. and Atriplex hortensis L. can be determined by use of flameless atomic absorption spectroscopy. By this method the longitudinal profiles of K⁺ and Na⁺ along low salt roots and roots which had been equilibrated with or grown in K⁺-free 1 mM Na⁺-solution were determined. The profiles reveal that high K⁺/Na⁺ ratios in the cytoplasm are maintained also in K⁺-free solutions. In solutions containing 1 mM Na⁺ a high K⁺/Na⁺ selectivity was found to be dependent on sufficient aeration. From the ion profiles the cytoplasmic (110 mM) and vacuolar (20 mM) K⁺ concentration in low salt barley roots—values which are unobtainable by compartmental analysis—could be estimated.     

Cytoplasmic streaming in the root cortex and its role in the delivery of potassium to the shoot

The influence of cytochalasin B (CB), a potent inhibitor of cytoplasmic streaming, on ⁸⁶Rb-labelled K⁺ translocation by detopped Lycopersicon esculentum Mill., Cucumis sativus L. and Zea mays L. plants was examined by measuring the radioactivity in xylem exudate before and after the addition of CB to the medium bathing the roots. CB caused complete cessation of cytoplasmic streaming in root segments within 15 min but was without effect on either total ⁸⁶Rb uptake or exudation. Thus factors other than cytoplasmic streaming limit the movement of K⁺ across the symplast of the root of higher plants.     

Na+ and K+ transport in Nitrosomonas europaea and Nitrobacter agilis

Potassium-depleted cells of Nitrosomonas europaea and Nitrobacter agilis were prepared by diethanolamine treatment and contained less than 5 mM intracellular K⁺. The addition of K⁺ to K⁺-depleted cells of N. europaea and N. agilis resulted in a depolarization of membrane potential (ΔΨ) by about 5 and 10 mV, respectively. This depolarization was, however, compensated by an equivalent increase in transmembrane pH gradient (ΔpH), so that the total proton-motive force (Δp) remained constant, indicating that K⁺ transport was electrogenic in both bacteria. Using ²²Na⁺-loaded cells, it is shown that both bacteria lack a respiration-dependent Na⁺ pump; however, antiporters for Na⁺/H⁺, K⁺/Na⁺ and K⁺/H⁺ were detected. Of these, at least the K⁺/Na⁺ antiporter required an electrochemical gradient for its operation. It is also shown that the unprotonated form of NH₄⁺ is transported into these bacteria by a simple diffusion mechanism.     

Rubidium and Potassium Absorption by Bean-leaf Slices Compared to Sodium Absorption

At salt concentrations of 0.1 mM as well as of 5.0 mM, the ²²Na⁺ absorption capacity of bean (Phaseolus vulgaris L. cv. ‘Brittle Wax’) leaf tissue increased during the period of leaf expansion and decreased rapidly after leaf maturation. The absorption capacity for ⁸⁶Rb⁺ and ⁴²K⁺ was highest in very young leaves and decreased continuously in expanding and in mature leaves. The ⁸⁶Rb⁺ absorption capacity of mature leaves was not increased by detopping the plants; this senescence-retarding treatment more than doubled ²Na⁺ absorption. The absorption of ²²Na⁺ by bean-leaf slices was not enhanced by light, whereas ⁸⁶Rb⁺ and ⁴²K⁺ absorption was much affected. Previously absorbed ⁸⁶Rb⁺ and ⁴²K⁺ were more available for exchange than ²²Na⁺.     

Long-term effects of plant hormones on K+ levels and transport in young wheat plants of different K+ status

Long-term effects of 1-naphtaleneacetic acid (NAA), benzyladenine (BA), gibberellic acid (GA₃), abscisic acid (ABA) and ethylene on K⁺ levels, K⁺ uptake and translocation to the shoot were studied in young wheat plants (Triticum aesticum L. cv. Martonvásári-8) grown at different K⁺ supplies. Na⁺ levels and K⁺/Na⁺ selectivity were also investigated. Both in shoots and roots, NAA, BA and ABA decreased K⁺ and Na⁺ levels more effectively in high-K⁺ plants than in low-K⁺ plants. GA, and ethylene did not influence K⁺ and Na⁺ levels. K⁺/Na⁺ selectivity in roots of low-K⁺ plants was increased in favour of K⁺ by BA, NAA and to a lesser extent by ABA. In high-K⁺ plants only BA increased the K⁺/Na⁺ ratio, whereas the effects of the other hormones were the opposite (NAA) or less pronounced (ABA). K⁺(⁸⁶Rb) uptake was inhibited by NAA and BA in low-K⁺ plants but not in high-K⁺ plants. K⁺(⁸⁶Rb) uptake was inhibited throughout by 10 μM ABA. K⁺(⁸⁶Rb) translocation to the shoot was influenced by the hormones similarly to the uptake patterns, with the exception of ABA, which inhibited translocation in low-K⁺ plants but not in high-K⁺ plants. The results show that hormonal effects may quantitatively and qualitatively be modified by K⁺ levels in the plant and that internal K⁺ concentration may play a role in the mechanisms regulating the effects of NAA, BA and ABA but probably not in those of GA₃ or ethylene.