Effects of aluminium on growth and kinetics of K+(86Rb) uptake in two cultivars of wheat (Triticum aestivum) with different sensitivity to aluminium

Two cultivars of wheat (Triticum aestivum L. cvs Kadett and WW 20299) were grown for 9 days with 20% relative increase in nutrient supply per day at pH 4.1. Aluminium at 50 μ M retarded the growth of roots more than that of shoots in both cultivars, thus decreasing the root/shoot ratio. The inhibition was largest in WW 20299. With long term Al treatment (9 days), K_m for K⁺(⁸⁶Rb) influx increased five times in both cultivars and V_max decreased in WW 20299. Efflux of K⁺(⁸⁶Rb) was little affected. When the roots were treated with aluminium for two days, only relative growth rate of roots was retarded, while growth of shoots was unaffected and influx of K⁺(⁸⁶Rb) adjusted to the actual K⁺ demand of the plants. It is concluded that the effects of aluminium on K⁺ uptake in these wheat cultivars are not primary factors contributing to aluminium sensitivity. However, in soil with Al the demand for a comparatively high concentration of K⁺ to maintain an adequate K⁺ uptake rate, in combination with a slow growth rate of the roots, may secondarily lead to K⁺ deficiency in the plants.     

Influence of light and darkness and the experimental design on kinetics of K+ (86Rb) influx in roots of intact spring wheat

Seedlings of spring wheat ( Triticum aestivum L. cv. Svenno) were cultivated at 20°C in continuous light or darkness with the roots in nutrient solutions for six days. The plants were starved for K⁺ during different periods of time to produce plants with various K⁺ status. In one cultivation light-grown plants were pretreated in darkness, and vice versa, before the uptake experiment. In all experiments, roots were put in a complete nutrient medium containing 2.0 m M K⁺ radiolabelled with ⁸⁶Rb. The uptake time was varied (5, 60 or 120 min).
The K⁺ concentration in the roots, [K⁺]_root, increased during the course of the uptake experiments, especially in light and at initially low [K⁺]_root, At the same time K⁺ (⁸⁶Rb) influx in the roots decreased. The simoidal relationship obtained between K⁺ (⁸⁶Rb) influx and [K⁺]_root was affected by these changes, and Hill plots gave various Hill coefficients, n_H, depending on the duration of the uptake experiments. n_H from three apparently straight line segments of the same plot, in different [K⁺]_root - intervals, indicated a falling degree of interaction between the binding sites as [K⁺]_root increased. For the dark-grown plants negative cooperativity could not be demonstrated.     

Growth, contents of K+ and kinetics of K+(86Rb) uptake in barley cultured at different low supply rates of potassium

Plants of barley ( Hordeum vulgare L. cv. Salve) were grown with 6.5–35% relative increase of K⁺ supply per day (RKR) using a special computer-controlled culture unit. After a few days on the culture solution the plants adapted their relative growth rate (RGR) to the rate of nutrient supply. The roots of the plants remained in a low salt status irrespective of the rate of nutrient supply, whereas the concentration of K⁺ in shoots increased with RKR. Both V_max and K_m for K⁺(⁸⁶Rb) influx increased with RKR. It is concluded that with a continuous and stable K⁺ stress, the K⁺ uptake system is adjusted to provide an effective K⁺ uptake at each given RKR. Allosteric regulation of K⁺ influx does not occur and efflux of K⁺ is very small.     

Effect of K+ and H+ stress and role of Ca2+ in the regulation of intracellular K+ concentration in mung bean roots

The effects of external K⁺, H⁺ and Ca2⁺ concentrations on the intracellular K+ concentration, [K⁺]i, and the K⁺-ATPase activity in 2-day-old mung bean roots [ Vigna mungo (L.) Hepper] were investigated. [K⁺]i, in mung bean roots was markedly decreased by external K⁺ or H⁺ stress and did not recover the initial value even after the stress was removed. This decrease in [K⁺]i, gradually disappeared with the addition of (Ca2⁺. Ca2⁺ may offset the harmful effects of ion stress. Ca2⁺ seems to have two effects on K+ transport; control of K⁺ permeability and activation of K⁺ uptake, although K⁺-ATPase activity was inhibited by Ca2⁺ concentrations higher than 10–4 M. We suggest that Ca2⁺ activates K⁺ uptake indirectly through the acidification of the cytoplasm.     

Lack of active K+ uptake in aeroponically grown wheat seedlings

The K⁺ (⁸⁶Rb⁺) uptake and the growth of intact wheat seedlings ( Triticum aestivum L. cv. GK Szeged) grown in 0.5 m M CaCl₂ solution and of seedlings grown on wet filter paper in Petri dishes were compared under different experimental conditions. Aeroponic (AP) and hydroponic (HP) conditions brought about striking differences in the growth of the roots, whereas the shoot growth was not influenced. The dry weight of the roots was higher for the AP plants than for the HP plants. The AP grown seedlings exhibit a low rate of K⁺ uptake, which seems to be a passive process. The effect of 2, 4–dinitrophenol (2, 4–DNP) clearly shows the absence of an active component of the K⁺ uptake in roots grown in air with a high relative humidity. In plants grown under AP conditions the effect of Ca²⁺ on the K⁺ uptake is unfavourable, i.e. there is an inhibition (negative Viets effect). Results relating to the effect of 2,4–DNP suggest that the "negative Viets effect" is a feature of the passive K⁺ uptake. The data suggest that the AP growth conditions play a very important role in the induction and/or development of the ion transport system(s), which becomes impaired under the AP conditions.     

Growth and accumulation of N, K+, Ca2+ and Mg2+ in barley exposed to various nutrient regimes and root/shoot temperatures

Six cultivars of spring barley ( Hordeum vulgare L. cvs Salve, Nümberg II, Bomi, Risø 1508, Mona and Sv 73 608) were grown in water culture for three weeks with various combinations of mineral supply and differential roots/shoot temperatures during the growth period. Most important for growth and accumulation of N, K⁺, Ca²⁺ and Mg²⁺ was the mineral supply, followed by the root temperature and the choice of cultivar. Treatments with low mineral supply or low root temperature induced a uniform reduction in growth and accumulation of the ions studied. The effects of low mineral supply and low root temperature on growth and N accumulation was additive, which indicates that these factors exert their influence independently of each other.
Roots grown at 10°C were smaller and Rb⁺(⁸⁶Rb) influx was higher than in roots grown at 20°C. It is suggested that the control of Rb⁺(⁸⁶Rb) influx is affected by the root temperature and the age of the plants. The higher ⁸⁶Rb⁺ (⁸⁶Rb) influx into the low temperature roots could not compensate for the smaller root size. However, the lower total mineral accumulation made up for the needs of the smaller plants and cannot explain the reduction in growth.     

Effect of potassium status on K+ (Rb)+ uptake and transport in sunflower roots

Young sunflower plants ( Helianthus annuus L. cv. Halcón), grown in nutrient solution at two K⁺ levels (0.25 and 2.5 m M ) were used to study the effect of K⁺ content in the root on uptake and transport of K⁺ to the exuding stream of decapitated plants. Roots of plants grown in low K⁺ gave higher exudation flux, higher K⁺ concentration in exudate and higher K⁺ flux than high K⁺ roots. After 6 h of uptake the K⁺ flux in low K⁺ roots was about three times that in high K⁺ roots. When the roots were kept in a nutrient solution in which Rb⁺ replaced K⁺, low K⁺ roots exuded much more Rb⁺ than K⁺ after the first 2 h, whereas high K⁺ roots exuded about similar amounts of K⁺ and Rb⁺. In intact plants grown at three different K⁺ levels (0.1, 1.0 and 10.0 m M ), there was an inverse relationship between the K⁺ level in the nutrient solution and the Rb⁺ accumulated in the roots or transported to the shoot. The results suggest that the transport of ions from xylem parenchyma to stele apoplast may be controlled by ions coming down from the shoot in sieve tubes.     

Long-term effects of abscisic acid on K+ transport in young wheat plants of different K+ status

The effects of abscisic acid (ABA) on growth, uptake and translocation of potassium ions, K⁺,Mg²⁺-ATPase activity and transpiration were investigated in young wheat ( Triticum aestivum L. cv. Martonvásári-8) plants grown at different K⁺ supplies. Long-term treatment with ABA (10 μ M ) reduced growth in high-K⁺ plants, but had less effect under low-K⁺ conditions. K⁺(⁸⁶Rb) uptake was inhibited by about 70 and 40% in low- and high-K⁺ plants, respectively. The stimulation by K⁺ of the Mg²⁺-ATPase activity in the root microsomal fraction was lost with ABA treatment. It is suggested that the inhibitory effect of ABA on K⁺ uptake may be related to this effects on the K⁺,Mg²⁺-ATPase. Translocation of K⁺ to the shoot was inhibited in low-K⁺ plants only, and it was not affected in high-K⁺ plants. In parallel to this, ABA treatment reduced transpiration by about 50% in low-K⁺ plants, whereas a much smaller effect was seen in high-K⁺ plants. These observations suggest that the regulation by ABA of the stomatal movements is strongly counteracted by high-K⁺ status.     

Separation of metabolic and non-metabolic steps of Rb+ uptake in spring wheat roots with different K+ status

Uptake of Rb⁺ from a complete nutrient solution with 2.0 mM Rb⁺ was studied in roots of spring wheat seedlings ( Triticum aestivum L. cv. Svenno) with different K⁺ levels. The relationship between Rb⁺ uptake and concentration of K⁺ in the roots indicated a negative feedback mechanism operating through allosteric control. The Rb⁺ uptake process in root cells was divided into two steps: (1) binding of the ion in the free space, and (ii) transmembrane transport into the cytoplasm. Metabolic and non-metabolic components of uptake were separated by addition of the metabolic inhibitor 2,4-dinitrophenol (DNP) to the nutrient solution. It is suggested that metabolic Rb⁺ uptake requires energy in two uptake steps (for binding to the carrier entity in the free space and for transmembrane transport) or in one step only (for transmembrane transport), dependent on the K⁺ status of the roots. The change from metabolic to non-metabolic binding in the free space is accomplished by changing the conformational state of the carrier (slow/fast transitions). There may be a hysteretic effect on metabolic Rb⁺ uptake through a slow transition between carrier states. This is superimposed on the negative cooperativity, strengthening further cooperativity at intermediate K⁺ levels in the roots. Non-metabolic Rb⁺ uptake probably consists of two components, a carrier-mediated (facilitated diffusion) and a parallel diffusive component.     

Cation-stimulated H+ efflux by intact roots of barley

Abstract. Rates of proton extrusion and potassium (⁸⁶Rb) influx by intact roots of barley ( Hordeum vulgare cvs . Fergus, Conquest and Betzes) plants were simultaneously measured in short-term (15min) experiments. The nature and extent of apparent coupling between these ion fluxes was explored by manipulating conditions of temperature, pH and cation composition and concentration during flux determinations. In addition, the influence of salt status upon these fluxes was examined. At low K⁺ concentrations (0.01 to 1 mol m⁻³), H⁺ efflux and K⁺ influx were strongly correlated in both low- and high-K⁺ roots, although K⁺: H⁺ exchange stoichiometries were almost consistently greater than 2:1. At higher concentrations (1 to 5 mol m⁻³), H⁺ efflux was either reduced or remained unchanged while K⁺ influxes increased. In the presence of Na₂SO₄, rates of H⁺ extrusion demonstrated similar cation dependence, although below 10 mol m⁻³ Na₂SO₄, H⁺ fluxes were generally 50% lower than in equivalent concentrations of K₂SO₄. These observations are considered in the context of current hypotheses regarding the mechanisms of k⁺/H⁺ exchange.     

Effects of copper on active and passive Rb+ influx in roots of winter wheat

The effects of copper (CuCl₂) on active and passive Rb⁺(⁸⁶Rb⁺) influx in roots of winter wheat grown in water culture for 1 week were studied. External copper concentrations in the range of 10–500 μ M in the uptake nutrient solution reduced active Rb⁺ influx by 20–70%, while passive influx was unaffected (ca 10% of the Rb⁺ influx in the Cu-free solution). At external Rb⁺ concentrations of up to 1 m M , Cu exposure (50 μ M decreased V_max to less than half and increased K_m to twice the value of the control. Short Cu exposure reduced the K⁺ concentration in roots of low K⁺ status. Pretreatment for 5 min in 50 μ M CuCl₂ prior to uptake experiments reduced Rb⁺ influx by 26%. After 60 min pretreatment with Cu, the corresponding reduction was 63%. Cu in the cultivation solution impeded growth, especially of the roots. The Cu concentration in the roots increased linearly with external Cu concentration (0–100 μ M ) while Cu concentration in the shoots was relatively unchanged. The K⁺ concentration in both roots and shoots decreased significantly with increased Cu in the cultivation solutions. Possible effects of Cu on membranes and ion transport mechanisms are discussed.     

Effects of salinity and replacement of K+ by Na+ on lipid composition in two sugar beet inbred lines

The effects of NaCl and replacement of K⁺ by Na⁺ on the lipid composition of the two sugar beet inbred lines FIA and ADA were studied (a) with increasing additions of NaCl to the basal medium, and (b) with increasing replacement of K⁺ by Na⁺ at the same total concentration as in the basal medium. Direct relations were noted between NaCl concentration of the nutrient solution and the phospholipid concentration in the roots of FIA, the genotype characterized by a low K⁺/Na⁺ ratio, as well as between NaCl in the medium and the phospholipid concentration in the shoots of ADA, the genotype with a high K ⁺/Na ⁺ ratio. The sulfolipid level in the roots of FIA was maintained at higher NaCl concentrations, while it was decreased in ADA. The glycolipid concentration in the shoots of ADA and the degree of unsaturation of the fatty acids of the total lipid fraction were decreased by salinity, indicating reduced biosynthesis of chloroplast glycolipids and/or accelerated oxidation of these lipids in the presence of NaCl.
In the Na⁺ for K⁺ replacement experiment a low content of K⁺ in the medium resulted in decreased levels of total lipids, phospholipids and sulfolipid in the roots of both genotypes, which did not relate to root growth. K⁺-leakage from the roots at low K⁺-level in the medium may be reduced by the increase in saturation of the lipids. In the shoots of ADA increased levels of total lipids, phospholipids and Sulfolipid were noted at a low K⁺-concentration of the nutrient solution.     

Control of Na+ and K+ transport in Spergularia marina I. Transpiration effects

In this paper we begin our study of factors controlling Na⁺ and K⁺ uptake in the halophyte Spergularia marina (L.) Griseb., with emphasis on plants growing at moderate salinity (0.2x sea water). The involvement of transpiration was considered first because of its potential to account for much or all of the transport of ions, and particularly of Na⁺, to the shoot under these growth conditions. Transpiration was constant with time through most of the light period, quickly dropping to 6% of the day time rate at night. ²²Na⁺ uptake, on the other hand, showed much less day/night variation, and relative transport to the shoot was constant. After establishing that transpiration was linearly related to leaf weight, possible transpiration effects were further considered as correlations between leaf weight and transport to the shoot. Under constant, day-time conditions, with linear effects of time and plant size removed, total transport of ²²Na⁺ to the shoot (per plant) was not correlated to leaf weight. A similar result was found when transport was expressed per gram of root, and when partitioning of total label to the shoot was considered. Finally, the correlation was considered between leaf weight and a Na⁺/K⁺ enrichment factor defined as the Na⁺/K⁺ ratio in the leaves divided by that in the roots. This correlation was also insignificant. The results indicate that analysis of control of Na⁺ and K⁺ uptake and transport in this experimental system need not consider effects of transpiration.     

ENERGETICS OF AMINO ACID TRANSPORT INTO BRAIN SLICES: EFFECTS OF K+ DEPLETION AND Rb+ OR Cs+ SUBSTITUTION ON AMINO ACID UPTAKE

Abstract— Mouse brain slices were depleted of K⁺ by three 10-min incubations-in oxygenated HEPES-buffered medium lacking glucose and K⁺. Addition of K⁺ or Rb⁺ (or Cs⁺, to a smaller degree) with glucose, or with succinate, malate, and pyruvate (SMP) before incubation at 37°C with ¹⁴C-amino acids restored active low-affinity transport of d -Glu, α-aminoisobutyrate (AIB), GABA, Gly, His, Val, Leu, Lys, and Orn. Ouabain at 1–2μ m with Rb⁺ was more inhibitory with SMP than with glucose, suggesting that the glycoside may affect specific energy coupling to transport. Valinomycin, in contrast, showed no specificity of inhibition of amino acid uptake with glucose or SMP and K⁺ or Rb⁺. Cs⁺ partially restored amino acid uptake, but Li⁺ was less effective than Cs ⁺. NaF at 10 m m with SMP + Rb⁺, or SMP + K⁺ did not inhibit amino acid uptake. Therefore, it was possible to dissociate glycolysis and Na⁺, K ⁺ -ATPase activity from amino acid transport. The ion replacements for K ⁺ that supported active amino acid transport indicate that the specificity of ions in possible ionic gradients for transport energetics should be reexamined.     

Actual escape area and lateral escape from the xylem of the alkali ions Na+, K+, Rb+ and Cs+ in tomato

Approximation of the total escape area of the xylem in an inbred line of tomato (Ly-copersicon escutentum Mill. cv. Tiny Tim) with help of the frequency distribution of xylem vessel radii provides the possibility to calculate realistic escape constant values from uptake experiments of several elements into tomato stem segments. Comparison of the lateral escape rates of ²⁴Na⁺, ⁴²K⁺, ⁸⁶Rb⁺ and ¹³⁴Cs⁺ indicate that Na⁺ escape is rate-limited by its uptake into a rather constant number of surrounding cells, regardless of changes in the total escape area of the xylem vessels. The escape of K⁺, Rb⁺ and Cs⁺ seems to be proportional to the surface area of the xylem vessels and their escape is apparently controlled by their transport across the cell walls of the transport channels. The calculated small values for the escape rate constants (apparent permeability of the xylem cell walls, ca 2–3 · 10−⁹ m s−⁷) are probably due to the presence of lignin in the xylem cell walls, the discrimination between ions as a result of differing affinities and selectivities and the presence of other solutes in the applied solution.     

An effect of Na+ on K+ uptake in intact seedlings of Zea mays

Models for the regulation of K⁺ uptake in higher plant roots have become more complex as studies have moved from the level of excised low-salt roots to that of intact plants grown under fully autotrophic conditions. In this paper we suggest that some of the differences between the conditions are qualitative, possibly requiring fundamental changes to the model, rather than simply quantitative.
The uptake of K⁺ by low-salt roots of Zea mays L. [(A619 x Oh 43) x A632], was independent of Na⁺ concentration over a wide range. However, independence of Na⁺ was not the case in plants grown on complete nutrient medium in the light: inclusion of Na⁺ in the uptake medium enhanced K⁺ uptake. In the presence of Na⁺, K⁺ uptake rates were similar in whole plants with high root K⁺ contents to rates in excised or intact, low-salt roots.     

Free space uptake and influx of Ni2+ in excised barley roots

The effects of switches between high and low nutrient supplies on growth and mineral nutrition of winter wheat ( Triticum aestivum L. cv. Martonvásári-8) were followed in four main developmental phases: tillering, shooting, heading and grain filling. Growth of the shoots was significantly affected by switches. Under low nutrient supply the life cycle was shortened. Root growth was only slightly affected by switches, but an early high nutrient supply followed by low nutrient supply gave an impetus for root development. In general, the growth data indicate that the nutrient status of the plants is determined by the nutrient level supplied during shooting. A high level of nutrients during shooting leads also to high vegetative growth, whereas the best grain yield was obtained by a high dose of nutrients during tillering followed by low nutrient conditions during the shooting stage and later. K⁺(⁸⁶Rb) influx in the roots decreased with age. The potential for K⁺ (⁸⁶Rb) influx was low in plants of high-salt status, but it became high in response to switching to low supply at shooting, whereas later switches had no influence on this function in high-salt plants. The highest K⁺(⁸⁶Rb) influx was found in plants starting with high nutrient supply followed by low-salt conditions; this plant group was outstanding also with respect to its high grain yield.     

Effect of gibberellic acid on K+ (Rb+) uptake and transport in sunflower roots

Four-week-old sunflower plants ( Helianthus annuus L. cv. Halcón), grown in different nutrient solutions, were used to study the effects of gibberellic acid (GA₃) on K⁺ (Rb⁺) uptake by roots or transport to the shoot. Gibberellic acid application to the nutrient solution did not affect the exudation process of excised roots. When GA₃ was sprayed on leaves 2 to 6 days before excising the roots, the rate of exudation and the K⁺ flux increased. When the exudation study was done keeping the roots in a nutrient solution in which Rb⁺ replaced K⁺, the GA₃ effects were evident also on Rb⁺ uptake and transport. In intact plants, GA₃ increased the Rb⁺ transported to the shoot but did not affect Rb⁺ accumulation in the root. It is suggested that these GA₃ effects can be explained if it is assumed that GA₃ acts on the transport of ions to the xylem vessels.     

Puccinellia tenuiflora maintains a low Na+ level under salinity by limiting unidirectional Na+ influx resulting in a high selectivity for K+ over Na+

Puccinellia tenuiflora is a useful monocotyledonous halophyte that might be used for improving salt tolerance of cereals. This current work has shown that P. tenuiflora has stronger selectivity for K⁺ over Na⁺ allowing it to maintain significantly lower tissue Na⁺ and higher K⁺ concentration than that of wheat under short- or long-term NaCl treatments. To assess the relative contribution of Na⁺ efflux and influx to net Na⁺ accumulation, unidirectional ²²Na⁺ fluxes in roots were carried out. It was firstly found that unidirectional ²²Na⁺ influx into root of P. tenuiflora was significantly lower (by 31–37%) than in wheat under 100 and 150 m m NaCl. P. tenuiflora had lower unidirectional Na⁺ efflux than wheat; the ratio of efflux to influx was similar between the two species. Leaf secretion of P. tenuiflora was also estimated, and found the loss of Na⁺ content from leaves to account for only 0.0006% of the whole plant Na⁺ content over 33 d of NaCl treatments. Therefore, it is proposed that neither unidirectional Na⁺ efflux of roots nor salt secretion by leaves, but restricting unidirectional Na⁺ influx into roots with a strong selectivity for K⁺ over Na⁺ seems likely to contribute to the salt tolerance of P. tenuiflora .     

Involvement of epidermal cells in stomata movement: The effect of ABA

ABA affected K⁺ and solute transport between guard cells and epidermal cells as indicated by K⁺ staining and plasmolysis. ABA enhanced K⁺ (⁸⁶Rb) uptake into epidermal cells. To find out whether the ABA enhanced accumulation of K⁺ (⁸⁶Rb) in epidermal cells is active, uptake in the presence of exogenous ATP was studied. These studies hinted that K⁺ (⁸⁶Rb) uptake by epidermal cells is a passive process, while its release is an active one. This was verified by applying iodoacetate, which interferes with energy supply. The epidermal cells thus seem to play a role in stomatal movement.