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1.
Cation pretreatment effects on nitrate uptake, xylem exudate, and malate levels in wheat seedlings 总被引:1,自引:1,他引:0
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. 相似文献
2.
Organic Acids and Ionic Balance in Xylem Exudate of Wheat during Nitrate or Sulfate Absorption 总被引:1,自引:0,他引:1
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Experiments were designed to study the importance of organic acids as counterions for K+ translocation in the xylem during excess cation uptake. A comparison was made of xylem exudate from wheat seedlings treated 72 hours with either 1.0 millimolar KNO3 or 0.5 millimolar K2SO4, both in the presence of 0.2 millimolar CaSO4. Exudation from KNO3 plants had twice the volume and twice the K+ and Ca2+ fluxes or rate of delivery to shoots, as K2SO4 plants. Malate flux was 25% higher in K2SO4 than in KNO3 exudate. Malate was the principal anion accompanying K+ or Ca2+ in K2SO4 treatment, while in the KNO3 treatment, NO3− was the principal anion. The contribution of SO42− was negligible in both treatments. In a second experiment, exudate was collected every 4 hours during the daytime throughout a 72-hour treatment with KNO3. Malate was the only anion present in exudate at first, just after the CaSO4 pretreatment had ended. Malate concentration decreased and NO3− concentration increased with time and these concentrations were negatively correlated. By 62 hours, NO3− represented 80% of exudate anions. K+ and NO3− concentrations in exudate were strongly correlated with K+ and NO3− uptake, respectively. The first 36 hours of absorption from KNO3 solution resembled the continuous absorption of K2SO4, in that malate was the principal counterion for translocation of K+. 相似文献
3.
Fast-2, a membrane mutant of Paramecium aurelia, is due to a single-gene mutation and has behavioral abnormalities. Intracellular recordings through changes of external solutions were made. The mutant membrane hyperpolarized when it encountered solutions with low K+ concentration. This hyperpolarization and other associated activities were best observed in Ca- or Na-solutions devoid of K+. Membrane potential was plotted against the concentration of K+ (0.5 to 16 mM) in solutions of fixed Na+ or Ca++ concentration. The slopes of the curves for the mutant membrane were steeper than those for the wild type at the lower concentrations of K+. Inclusion of 2 mM tetraethylammonium chloride (TEA-Cl) counteracted the mutational effects. Spontaneous action potentials in Ba-solution and the electrically evoked action potentials in various solutions are normal in this mutant. We conclude that the resting permeability to K+ relative to the permeabilities to Na+ and Ca++ has been increased by the mutation. 相似文献
4.
On the mechanisms of sodium ion transport by the irrigated gills of rainbow trout (Salmo gairdneri) 总被引:1,自引:1,他引:1
Sodium uptake by rainbow trout gills has been investigated with a small-volume system enabling rapid, successive flux measurements in different solutions. Sodium influx obeys a Michaelis-Menten type relation, with a Km of 0.46 mM, and uptake proceeds unimpaired in the absence of penetrating counter-ions. This suggests a coupled cation exchange. Ammonia output is about the same as the Na+ influx when external [Na+] is 1 mM, but at higher or lower Na+ influxes, the correlation does not hold. A progressive downward shift in the pH of the irrigating medium as Na+ influx increases indicates that the exchanging cation is hydrogen. In support of this, acetazolamide, which inhibits Na+ uptake, also prevents the downward pH shift. The potential across the gill is about 10 mv, body fluids positive, in NaCl solutions up to 10 mM, and is little affected by changes in Na+ concentration below that. Finally, evidence for locating the rate-limiting step at the outer membrane of the epithelium is presented. 相似文献
5.
Plasmalemma electrical properties were used to investigate K+ transport and its control in internodal cells of Chara corallina Klein ex Willd., em R.D.W. Cell exposure to solutions containing 10 mm KCl caused the potential, normally −250 millivolts (average), to depolarize in two steps. The first step was a 21 millivolt depolarization that lasted from 1 to 40 minutes. The second step started with an action potential and left the membrane potential at −91 millivolts, with a 10-fold reduction in resistance. We suggest that the second step was caused by the opening of K+ -channels in the membrane. This lowered the resistance and provided a current pathway that partially short-circuited the electrogenic pump. Although largely short-circuited, the electrogenic pump was still operating as indicated by: (a) the depolarized potential of −91 millivolts was more negative than Ek (=−42 millivolts in 10 mm K+); (b) a large net K+ uptake occurred while the cell was depolarized; (c) both the electrogenic pump inhibitor, diethylstilbestrol, and the sulfhydryl-reagent N-ethylmaleimide (which increased the passive membrane permeability) further depolarized the potential in 10 mm KCl.A two-phase recovery back to normal cell potentials occurred upon lowering the K+ concentration from 10 to 0.2 mm. The first phase was an apparent Nernst potential response to the change in external K+ concentration. The second phase was a sudden hyperpolarization accompanied by a large increase in membrane resistance. We attribute the second phase to the closing of K+ -channels and the removal of the associated short-circuiting effect on the electrogenic pump, thereby allowing the membrane to hyperpolarize. Further experiments indicated that the K+ -channel required Ca2+ for normal closure, but other ions could substitute, including: Na+, tetraethylammonium, and 2,4,6-triaminopyrimidine. Apparently, K+ -channel conductance is determined by competition between Ca2+ and K+ for a control (gating?) binding site. 相似文献
6.
Accumulation of potassium and sodium by barley roots in a k-na replacement series 总被引:1,自引:1,他引:0
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Hiatt AJ 《Plant physiology》1969,44(11):1528-1532
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. 相似文献
7.
Influx of na, k, and ca into roots of salt-stressed cotton seedlings : effects of supplemental ca
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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. 相似文献
8.
Detached internodes of Chara corallina survived in solutions containing 100 mol m?3 NaCl when the external concentration of Ca2+ was greater than 1 mol m?3. Na+ influx was roughly proportional to external Na+ up to 100 mol m?3 NaCl. Na+ influx involved two components: a Ca2+-insensitive influx which allowed the passage of Na+ independently of external Ca2+; and a Ca2+-inhibitable mechanism where Na+ influx was inversely proportional to external Ca2+. The Ca2+-inhibitable Na+ influx was similar to the Ca2+-inhibitable K+ influx. Mg2+ and Ba2+ were able to substitute for Ca2+ in partially inhibiting Na+ influx in the absence of external Ca2+. The effect of Ca2+ appears specific to Na+ and K+ influx since the effects of a Ca2+-free solution on the influx of some other cations, anions and neutral compounds is small. It is suggested that Na+ influx via the Ca2+-inhibitable mechanism represents Na+ leakage through K+ channels and that cell death at high salinity occurs due to a cytotoxic Na+ influx via this mechanism. 相似文献
9.
Keitaro Kiyosawa 《Physiologia plantarum》1996,97(1):180-184
Movements of ions are considered to be governed by the electroneutrality rule. Therefore, a cation moving across the cell membrane into the cell either passively or actively should move together with its counterion, an anion, in equal amounts of charge or in exchange for another cation inside the cell. This means that the net influx of the cation in question should be affected by the permeability of its counterion and/or another cation inside the cell. To examine osmotic and ionic regulation in Chara cells, cell fragments of Chara having a lower osmotic pressure than normal (L-cell fragments) were prepared. The L-cell fragments were individually put into various dilute electrolyte solutions and their osmotic potentials were measured with a turgor balance. Concentrations of K+, Na+, Ca2+, Mg2+, Cl?, NO?3. and SO2?4. in the external electrolyte solutions in which L-cells had been incubated were also analysed by ion chromatography. The results showed that in 0.5 mM KCL + 0.1 mM CaCl2 solution, Chara L-cell fragments absorbed K+ and Cl? to maintain electroneutrality and then regained their osmotic potential very rapidly. When the anion was Cl, the cation absorbed at the highest rate was K+ On the other hand, when the cation was K, the anion absorbed at the highest rate was Cl, Other ions Ca2+, SO2?4 and NO?3 showed much less permeability than K+ and Cl ?for the Chara plasma membrane. The conclusion from these findings was that due to the constraint of electroneutral transport, the uptake rate of a salt into L-cells is limited by the permeability of the least permeable ion. 相似文献
10.
Poole RJ 《Plant physiology》1969,44(4):485-490
The flux ratio (influx/efflux) of K+ across the plasmalemma of beet cells at an external potassium concentration of 0.6 mm does not respond to changes of membrane potential in the manner expected for the free diffusion of ions. The K+ efflux is affected by the presence of adsorbed Ca2+, but is apparently unrelated to the electrical potential or to the net uptake of potassium. The K+ efflux is greater than the efflux of the sulfate and organic anions which are accumulated with potassium, and is partially dependent on the presence of external potassium. Thus the loss of 42K from the cell does not appear to be a leakage of freely diffusing K+ ions, nor a leakage of ion pairs, but a carrier-mediated transport or exchange of potassium across the cell membrane. 相似文献
11.
Effect of Ionic Composition of Suspending Solution on Virus Adsorption by a Soil Column 总被引:4,自引:3,他引:1
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The effect of various electrolytes on the adsorption of poliovirus was measured in 250-cm-long soil columns with ceramic samplers at different depths. Viruses suspended in deionized water moved much farther through the soil than those suspended in tap water, whereas movement in sewage water was intermediate. The salt content of the tap water and sewage water promoted virus adsorption, but evidently the organic compounds in sewage retarded adsorption. When viruses were suspended in chloride solutions of K+, Na+, Ca+, and Mg2+, virus adsorption increased as the cation concentration and valence increased. The depth of virus penetration was related to the ionic strength of the solutions. Virus penetration data for NO3−, SO42−, and H2PO4− salts of K+, Na+, and Ca2+ indicated that other anions were more effective than Cl− in promoting virus adsorption. Also, NH4+ was more effective than other cations in limiting the penetration depth of viruses. It seems that ions composed of radicals are more effective than ions composed of single atoms in promoting virus adsorption. Al3+ was the most effective ion in limiting virus penetration, probably owing to flocculation of the viruses. Adding AlCl3 concentrations to secondary sewage effluent to provide an Al3+ concentration of 0.1 mM reduced the virus penetration depth to 40 cm. These studies show that the ionic composition of the suspending solutions must be considered in predicting virus penetration depths, and it may be practical to add low concentrations of a flocculating agent such as AlCl3 to sewage water to limit virus movement through very porous soils. 相似文献
12.
Gokarn YR Fesinmeyer RM Saluja A Razinkov V Chase SF Laue TM Brems DN 《Protein science : a publication of the Protein Society》2011,20(3):580-587
Specific-ion effects are ubiquitous in nature; however, their underlying mechanisms remain elusive. Although Hofmeister-ion effects on proteins are observed at higher (>0.3M) salt concentrations, in dilute (<0.1M) salt solutions nonspecific electrostatic screening is considered to be dominant. Here, using effective charge (Q*) measurements of hen-egg white lysozyme (HEWL) as a direct and differential measure of ion-association, we experimentally show that anions selectively and preferentially accumulate at the protein surface even at low (<100 mM) salt concentrations. At a given ion normality (50 mN), the HEWL Q* was dependent on anion, but not cation (Li+, Na+, K+, Rb+, Cs+, GdnH+, and Ca2+), identity. The Q* decreased in the order F− > Cl− > Br− > NO3− ∼ I− > SCN− > ClO4− ≫ SO42−, demonstrating progressively greater binding of the monovalent anions to HEWL and also show that the SO42− anion, despite being strongly hydrated, interacts directly with the HEWL surface. Under our experimental conditions, we observe a remarkable asymmetry between anions and cations in their interactions with the HEWL surface. 相似文献
13.
Isolated protoplasts from pulvinar motor cells of Mimosa pudica were studied using conventional whole-cell patch clamp techniques. With internal solutions weakly buffered for Ca2+ (0.2 mm EGTA), a run-down of the outward delayed rectifier K+ current was induced by hyperpolarizing the holding potential, and this effect was strongly promoted by high external Ca2+ concentrations. This rundown could be reversed by coming back to less hyperpolarized holding potentials or by lowering the external [Ca2+]. Such rundown was absent when pipette internal solutions strongly buffered (10 mm EGTA) for Ca2+ were used. Ionomycin induced run-down of the K+ current with internal solutions containing 0.2 mm but not 10 mm EGTA. The hyperpolarization-associated rundown was reversibly blocked by Gd3+ and La3+.We thank Christophe Untereiner and Denis Wagner for expert technical assistance in facilitating the experiments and data acquisition and analysis. 相似文献
14.
Summary The Ca++-mediated increase in K+-permeability of intact red blood cells (Gardos effect) was initiated by exposing cells to known concentrations of Ca++ (using EGTA buffers) in the presence of the ionophore A23187. The potency of quinine, an inhibitor of the response, was found to depend on the external K+ concentration. In K+-free solutions the concentration of quinine to achieve 50% inhibition (K
50) was 5 m, but at 5mm K+ the required concentration was increased 20-fold to 100 m. An increase in internal Na+ had the opposite effect, allowing a high potency of quinine despite the presence of external K+. Alterations in the internal K+ level, on the other hand, were without effect on theK
50, suggesting that the membrane potential is not a factor. This conclusion is supported by the lack of effect on quinine inhibition of substitution of Cl– by NO
3
–
, a considerably more permeant anion. The data are consistent with the hypothesis that quinine inhibits by competitively displacing K+ from an external binding site, the reported K+-activation site for the Ca++-mediated K+-permeability. 相似文献
15.
Irradiation of a washed suspension of cultured rose (Rosa damascena var. Gloire de Guilan) cells with about 1,680 joules per square meter of short wave ultraviolet (UV) light (254 nanometers) caused K+ to appear in the external medium. Short-term tracer (86Rb+) experiments confirmed the earlier suggestion (Wright, Murphy 1978 Plant Physiol 61: 434-436) that UV increases the efflux of K+; there was also a small decrease in influx of K+. There was a partial recovery of fluxes from the effects of UV radiation, but no net accumulation of K+ within 16 to 18 hours after the irradiation. The K+ appearing in the medium was matched by an equivalent amount of HCO3−; it was suggested that HCO3− was the principal counterion for the K+ flux induced by UV. Inhibitors of ATP synthesis (10−5 molar carbonyl cyanide m-chlorophenyl hydrazone; 0.05 millimolar KCN plus 0.75 millimolar salicylhydroxamic acid) strongly reduced the UV-stimulated K+ leakage, suggesting that the leakage was dependent in some way on ATP concentration inside the cells. The UV-induced K+ leakage was also dependent on temperature and the presence of Ca2+ in the external medium. 相似文献
16.
The internal potential of flexor cells in slices of the laminar pulvini of Phaseolus coccineus has been recorded by standard microelectrode techniques in 100 eq m-3 external salt solutions of various ionic compositions. The measured values are between-15 and-60 mV depending on the external medium. Treating the results with the Goldman equation yields the following relative permeabilities: K+, 1.00; Na+, 0.24; Cl-, 0.19; NO
3
-
, 1.6. The membrane potential was only slightly sensitive to external pH and Ca2+. Metabolic inhibitors (azide, cyanide and salicylhydroxamic acid, carbonyl cyanid m-chlorphenyl hydrazone) caused only slight depolarizations (ca. 4 mV), which differed from the ion-induced changes by their slow time courses. The results are consistent with the hypothesis that the relatively impermeable Cl- is actively transported and osmotically efficient, whereas the well-permeable K+ passively follows Cl- to maintain electroneutrality and is osmotically of only minor significance.Abbreviations SHAM
salicylhydroxamic acid
- CCCP
carbonyl cyanid m-chlorphenyl hydrazone 相似文献
17.
Aluminum is a major constituent of most soils and limits crop productivity in many regions. Amelioration is of theoretical as well as practical interest because understanding amelioration may contribute to an understanding of the mechanisms of toxicity. In the experiments reported here 2-day-old wheat (Triticum aestivum L. cv Tyler) seedlings with 15-millimeter roots were transferred to solutions containing 0.4 millimolar CaCl2 at pH 4.3 variously supplemented with AlCl3 and additional amounts of a chloride salt. Root lengths, measured after 2 days in the test solutions, were a function of both Al activity and the cation activity of the added salt. Percent inhibition = 100 {Al3+}/({Al3+} + Km + α{C}β) where {Al3+} is the activity of Al3+ expressed in micromolar, {C} is the activity of the added cation expressed in millimolar, and Km (= 1.2 micromolar) is the {Al3+} required for 50% inhibition in the absence of added salt. For Ca2+, Mg2+, and Na+ the values of α were 2.4, 1.6, and 0.011, respectively, and the values for β were 1.5, 1.5, and 1.8, respectively. With regard to relative ameliorative effectiveness, Ca2+ > Mg2+ ≈ Sr2+ K+ ≈ Na+. Other cations were tested, but La3+, Sc3+, Li+, Rb+, and Cs+ were toxic at potentially ameliorative levels. The salt amelioration is not solely attributable to reductions in {Al3+} caused by increases in ionic strength. Competition between the cation and Al for external binding sites may account for most of the amelioration. 相似文献
18.
In contrast to intact etiolated pea seedling tissue (Pisum sativum L.), excised segments immersed in a complete nutrient solution show marked increases in ion content, largely of K+ and NO3−, over a 72-hour period. During this time there is increase in cell electropotential difference, PD. During the initial 6 to 8 hours there is a lag in ion uptake; cell PD, however, increases rapidly from approximately −50 to −100 mv then increases more slowly. The increase in PD precedes and thus may be a prerequisite for the rapid ion accumulation phase. Cell PD increases in either water or nutrient solution but eventually reaches higher levels in the latter. Following water pretreatment of sufficient duration K+ accumulation shows no lag period. The lag phase noted here appears dissimilar to that of storage tissues. 相似文献
19.
Modification of heart sarcolemmal Na+/K+-ATPase activity during development of the calcium paradox 总被引:3,自引:0,他引:3
This study examined the status of sarcolemmal Na+/K+-ATPase activity in rat heart under conditions of Ca2+-paradox to explore the existence of a relationship between changes in Na+/K+-pump function and myocardial Na+ as well as K+ content. One min of reperfusion with Ca2+ after 5 min of Ca2+-free perfusion reduced Na+/K+-ATPase activity in the isolated heart by 53% while Mg2+-ATPase, another sarcolemmal bound enzyme, retained 74% of its control activity. These changes in sarcolemmal ATPase activities were dependent on the duration and Ca2+ concentration of the initial perfusion and subsequent reperfusion periods; however, the Na+/K+-ATPase activity was consistently more depressed than Mg2+-ATPase activity under all conditions. The depression in both enzyme activities was associated with a reduction in Vmax without any changes in Km values. Low Na+ perfusion and hypothermia, which protect the isolated heart from the Ca2+-paradox, also prevented reperfusion-induced enzyme alterations. A significant relationship emerged upon comparison of the changes in myocardial Na+ and K+ content to Na+/K+-ATPase activity under identical conditions. At least 60% of the control enzyme activity was necessary to maintain normal cation gradients. Depression of the Na+/K+-ATPase activity by 60-65% resulted in a marked increase and decrease in intracellular Na+ and K+ content, respectively. These results suggest that changes in myocardial Na+ and K+ content during Ca2+-paradox are related to activity of the Na+/K+-pump; the impaired Na+/K+-ATPase activity may lead to augmentation of Ca2+-overload via an enhancement of the Na+/Ca2+-exchange system. 相似文献
20.
Paul Jensén 《Physiologia plantarum》1982,56(3):259-265
Effects of interrupted K+ supply on different parameters of growth and mineral cation nutrition were evaluated for spring wheat (Triticum aestivum L. cv. Svenno). K+ (2.0 mM) was supplied to the plants during different periods in an otherwise complete nutrient solution. Shoot growth was reduced before root growth after interruption in K+ supply. Root structure was greatly affected by the length of the period in K+ -free nutrient solution. Root length was minimal, and root branching was maximal within a narrow range of K+ status of the roots. This range corresponded to cultivation for the last 1 to 3 days, of 11 in total, in K+ -free nutrient solution, or to continuous cultivation in solution containing 0.5 to 2 mM K+. In comparison, both higher and lower internal/external K+ concentrations had inhibitory effects on root branching. However, the differing root morphology probably had no significant influence on the magnitude of Ca2+, Mg2+ and Na+ uptake. Uptake of Ca2+ and especially Mg2+ significantly increased after K+ interruption, while Na+ uptake was constant in the roots and slowly increased in the shoots. The two divalent cations could replace K+ in the cells and maintain electroneutrality down to a certain minimal range of K+ concentrations. This range was significantly higher in the shoot [110 to 140 μmol (g fresh weight)?1] than in the root [20 to 30 μmol (g fresh weight)?1]. It is suggested that the critical K+ values are a measure of the minimal amount of K+ that must be present for physiological activity in the cells. At the critical levels, K+ (86Rb) influx and Ca2+ and Mg2+ concentrations were maximal. Below the critical K+ values, growth was reduced, and Ca2+ and Mg2+ could no longer substitute for K+ for electrostatic balance. In a short-term experiment, the ability of Ca2+ to compete with K+ in maintaining electroneutrality in the cells was studied in wheat seedlings with different K+ status. The results indicate that K+, which was taken up actively and fastest at the external K+ concentration used (2.0 mM), partly determines the size of Ca2+ influx. 相似文献