Net Uptake Of Potassium Research Articles

SELECTIVITY AND PARTITIONING OF POTASSIUM AND SODIUM IN SESAME

Net uptake and partitioning of sodium (Na+) and potassium (K+) in plants of two sesame cultivars (Sesamum indicum cv. ‘PB-1’ and cv. ‘UCR’) exposed to 20 mM sodium chloride (NaCl) were studied over a period of 28 days. Both cultivars showed a marked discrimination between K+ and Na+ during uptake. The reduction of K+ in the plants caused by the NaCl treatment was of similar magnitude in the two cvs. The cv. ‘UCR’ showed lower Na+ concentrations in the shoot tissues than ‘PB-1’ and K+/Na+ selectivity ratios were higher in cv. ‘UCR’ than in cv. ‘PB-1’. At the last sampling on day 28 there was a marked decrease of shoot growth in cv. ‘PB-1’ in comparison to the cv. ‘UCR’. Leaves of cv. ‘PB-1’ showed clear toxic symptoms, while those of cv. ‘UCR’ did not. It is concluded that Na+ exclusion from the shoot contributes to salt tolerance of sesame, cv. ‘UCR’.

Crop Response to Long‐Term Potassium Application as Affected by Potassium‐Supplying Power of the Selected Soils in Northern China

Potash resources in China are very scarce. It is especially important to correctly evaluate the potential potassium‐supplying power of soils in northern China in order to use soil potassium sufficiently and potash fertilizer properly. Regional differences in crop yield responses to long‐term potassium application in northern China were determined in this study. Twenty‐five representative soil samples from 13 provinces, municipalities, and autonomous regions of major agricultural regions in northern China were collected from the surface layer (0–20 cm) before crop seeding in 1993. A soil potassium‐depletion study was carried out in a pot experiment with successive planting of corn seedlings for 10 harvests in the 25 soils. Since 1993, field trials on wheat and corn response to long‐term potassium application were conducted at the fixed sites of HLJ‐SC (Shuangcheng of Heilongjiang), JL‐LFZ (Liufangzi of Jilin), HB‐XJ (Xinji of Hebei), SX‐LF (Linfen of Shanxi), QH‐NKY (Nongkeyuan of Qinghai), and XJ‐CJ (Changji of Xinjiang). Soil‐available potassium, slowly available potassium, total potassium, main clay minerals, cation exchange capacity, particle size, other available nutrients, and potassium concentration in plants were measured. The results showed that potential potassium‐supplying powers of the 25 tested soils, which were respectively evaluated by the contents of slowly available potassium in soils and the amount of total net potassium uptake in the pot experiment, generally tended to increase from eastern to western regions in northern China. Significant wheat yield responses to long‐term potassium application in the field trials were found since 2000 in the north‐central region but not observed until 2004 in the northwestern region. Significant corn yield responses to long‐term potassium application in the field trials were found starting in soils of the northeastern region, following in soils of the north‐central region, and then in soils of the northwestern region. These were consistent with potential potassium‐supplying power of the soils, which tended to increase from east to west regions.

Rate of Nitrogen Application During the Growing Season and Spraying Plants with Urea in the Autumn Alters Uptake of Other Nutrients by Deciduous and Evergreen Container-grown Rhododendron Cultivars

The influence of fall sprays with urea on the uptake of nutrients other than nitrogen (N) was assessed using 1-year-old container-grown Rhododendron L. (Rhododendron ‘H-1 P.J.M’) and azalea (Rhododendron ‘Cannon's Double’) grown with different rates of N. Plants were grown with a complete fertilizer containing different N rates from May to Sept. 2004 sprayed or not with urea in the fall of 2004 and grown with a complete fertilizer containing different N rates in the spring of 2005. Urea sprays altered uptake of nutrients other than just N although fertilizer application with other nutrients ceased before plants were sprayed with urea. Across a wide range of plant sizes and N status, urea sprays increased net phosphorus (P), copper (Cu), and manganese (Mn) uptake and decreased net potassium (K) and magnesium (Mg) uptake during the year of urea application. Spraying plants with urea altered nutrient demand and storage in different plant structures during the winter. For azalea, urea sprays increased P demand by roots, Mn demand by 2004 stems, and Cu demand by stems. Urea also decreased storage of K in roots and 2004 stems of azalea and Mg in roots. For rhododendron, urea sprays increased P demand by 2003 stems and 2004 leaves and Mn demand by 2004 leaves. Urea sprays also decreased storage of K and Mg in 2004 leaves of rhododendron. For both cultivars, urea sprays increased mobilization of iron (Fe) from storage and demand for Fe in stems. Spraying Rhododendron with urea in the fall altered uptake and demand for certain nutrients during the following spring. Urea sprays in the fall of 2004 increased uptake and possibly demand for P, K, and sulfur during the spring of 2005 for both cultivars, the uptake of calcium by rhododendron, and the uptake of Mg and Mn by azalea. Our results indicate that when growers spray plants with urea in the fall, spring fertilizer practices may need to be modified to account for increased uptake or demand of certain nutrients.

Utilisation of nutrients by embryos of the enigmatic Australian viviparous skink Niveoscincus coventryi.

The Eugongylus species group of Australian lygosomine skinks provides an unparalleled opportunity to study the evolution of placentotrophy. Viviparity and placentotrophy have evolved in two lineages, currently recognised as the genera Pseudemoia and Niveoscincus. The genus Niveoscincus is important because it is the only lineage of squamates in which variation in placental morphology and in the pattern of embryonic nutrition is known. Niveoscincus coventryi has the least complex placental morphology among species currently assigned to the genus. We quantified the net uptake of nutrients across the placenta of N. coventryi for comparison with other species in the genus and with other viviparous and oviparous lizards. The pattern of embryonic nutrition of N. coventryi is similar to other viviparous lizards with simple placentae in that there is no net uptake of dry matter during development but there is a net uptake of water, calcium, potassium, and sodium. There is no net uptake of lipid, nitrogen (an index of protein), or magnesium. We conclude that N. coventryi is predominantly lecithotrophic. Further, if N. coventryi is the sister taxon to Tasmanian Niveoscincus, then the distribution of patterns of embryonic nutrition among members of this clade suggests that the evolution of placentotrophy occurred during radiation of this lineage in Tasmania.

Effects of insulin-like growth factor I on basal and stimulated glucose fluxes in rat liver.

Effects of insulin-like growth factor I (IGF-I) and insulin on glucose and potassium fluxes were examined by measuring transhepatic glucose and potassium balance in isolated perfused rat livers. At 1 nM, both IGF-I and insulin decreased basal glucose release by approximately 64% (P < 0.05). Adrenaline (epinephrine)-stimulated glucose release (42.6 +/- 4.5 micromol/g of liver within 30 min) was inhibited (P < 0.05) by approximately 32 and approximately 52% during IGF-I and insulin exposure, which was accompanied by reduced cAMP release (-71 and -80%, P < 0.05). IGF-I- and insulin-induced reduction of glucose release only decreased during calcium-free perfusion, but not during inhibition of phosphoinositide 3-kinase by wortmannin. Both IGF-I and insulin induced net potassium uptake, while insulin also attenuated the response to adrenaline. In conclusion, IGF-I causes (i) insulin-like inhibition of hepatic glycogenolysis, even at low, nanomolar concentrations, which is associated with decreased cAMP release, reduced in the absence of Ca(2+), but not mediated by phosphoinositide 3-kinase, (ii) reduction of adrenaline-induced glycogenolysis and (iii) net potassium uptake under basal conditions.

Effects of insulin-like growth factor I on basal and stimulated glucose fluxes in rat liver

Effects of insulin-like growth factor I (IGF-I) and insulin on glucose and potassium fluxes were examined by measuring transhepatic glucose and potassium balance in isolated perfused rat livers. At 1nM, both IGF-I and insulin decreased basal glucose release by ≈ 64% (P &amp;lt; 0.05). Adrenaline (epinephrine)-stimulated glucose release (42.6±4.5µmol/g of liver within 30 min) was inhibited (P &amp;lt; 0.05) by ≈ 32 and ≈ 52% during IGF-I and insulin exposure, which was accompanied by reduced cAMP release (-71 and -80%, P &amp;lt; 0.05). IGF-I- and insulin-induced reduction of glucose release only decreased during calcium-free perfusion, but not during inhibition of phosphoinositide 3-kinase by wortmannin. Both IGF-I and insulin induced net potassium uptake, while insulin also attenuated the response to adrenaline. In conclusion, IGF-I causes (i) insulin-like inhibition of hepatic glycogenolysis, even at low, nanomolar concentrations, which is associated with decreased cAMP release, reduced in the absence of Ca2+, but not mediated by phosphoinositide 3-kinase, (ii) reduction of adrenaline-induced glycogenolysis and (iii) net potassium uptake under basal conditions.

Effect of rapid cooling and acidic pH on cellular homeostasis of Pectinatus frisingensis, a strictly anaerobic beer-spoilage bacterium

Pectinatus frisingensis is a strictly anaerobic mesophilic bacterium involved in bottled beer spoilage. Cellular volume, adenylate energy charge, intracellular pH and intracellular potassium concentration measurements were performed in late exponential-phase cell suspensions placed in different physiological conditions, to evaluate the capability of this bacterium to maintain cellular homeostasis. The intracellular pH was calculated from the intracellular accumulation of a [carboxyl- 14C]benzoic acid. Optimum physiological conditions were the presence of a carbon source and pH of 6.2, hostile conditions were a pH 4.5, absence of a carbon source, and rapid cooling treatment. The cell was able to maintain a higher intracellular pH than the external pH under all conditions. Intracellular volume was lower at pH 4.5 than at pH 6.2. A low net potassium efflux rate was routinely measured in starving cells, while glucose addition promoted immediate net potassium uptake from the medium. Cooling treatment resulted in sudden net potassium efflux from the cell, a decrease of the intracellular pH, and low modifications of the adenylate energy charge in metabolizing-glucose cell suspensions. Thus, cold treatment perturbs the P. frisingensis homeostasis but the bacteria were able to restore their homeostasis in the presence of a carbon source, and under warm conditions.

Cardiac contractile function and electrolyte regulation during hyperosmolal stress: an experimental study in the isolated rabbit heart.

Perturbations of the extracellular osmotic environment leads to cell volume changes. The aim of the present study was to evaluate the effects of hyperosmolality on cardiac contractile function and in particular the role of ionic mechanisms anticipated to be operative during hyperosmolal exposure. Paced rabbit hearts were perfused in the Langendorff mode and were exposed to 330, 370, 410, 450 and 600 mOsm kg-1 in 10 min. intervals intervened by 15 min. isosmolal buffer perfusion (by adding mannitol). Thereafter, 370 and 600 mOsm kg-1 perfusates were chosen for investigation of the effects of inhibition of the Na-K-2Cl co-transporter (bumetanide 1 microM and 10 microM), the Na+/H+ exchanger (5-(N-ethyl-N-isopropyl amiloride (EIPA) 100 nM) and the Na+/K(+)-ATPase (ouabain 50 nM). After a rapid and transient decrease in left ventricular developed pressure, all perfusates up to 450 mOsm kg-1 increased LVDP. The 600 mOsm kg-1 perfusate initially reduced LVDP by 50%, but LVDP increased to 85% of initial value at the end of the 10 min. perfusion. EIPA attenuated the recovery of LVDP during perfusion with 600 mOsm kg-1, whereas bumetanide did not affect cardiac contractile function. A net uptake of potassium was observed during hyperosmolal perfusion. Inhibition of the Na+/H+ exchanger resulted in a continued release of cardiac water throughout hyperosmolal perfusion. Isolated perfused rabbit hearts tolerate considerable elevations in perfusate osmolality. Our results suggest that the Na+/H+ antiporter is activated on hyperosmolal exposure with a secondary activation of the Na+/K(+)-ATPase. Since inhibition with bumetanide did not affect contractility or electrolyte movements, the Na-K-2Cl co-transporter does not seem to play an important role in cardiac response to hyperosmolality in rabbits.

Calcium‐induced net potassium uptake of pig hearts in vivo

To determine whether the catecholamine-induced myocardial potassium uptake could be mimicked by increasing extracellular and intracellular calcium concentrations in vivo, we measured changes in myocardial potassium balance in nine anaesthetized open-chest pigs with PVC-valinomycin electrodes in arterial and coronary sinus blood. CaCl2 infusion (200-400 mumol min-1) into the left coronary artery increased coronary sinus blood calcium concentration from 2.29 (2.19-2.42) to 4.63 (3.76-5.67) mmol l-1 (median, 95% confidence interval, P = 0.01) indicating a similar increment in myocardial extracellular calcium concentration. The contractility measure LV dP/dt increased 95 (76-147) %, indicating a substantial increment in intracellular calcium concentration. During the CaCl2 infusion coronary sinus potassium concentration declined to a nadir 0.12 (0.09-0.17) mmol l-1 below baseline (P = 0.008) whereas arterial concentration remained unchanged. Peak myocardial potassium uptake was 18 (7-32) mumol min-1 100 g-1 and occurred 150 (110-195) s after start of infusion. The response remained unaltered after adrenoceptor blockade by prazosin and propranolol. Prolonged CaCl2 infusion caused a net myocardial potassium loss which was accompanied by metabolic and haemodynamic indications of myocardial ischaemia. These findings are consistent with enhanced Na-K pump activity in the intact beating pig heart in response to increased extracellular and intracellular calcium concentrations.

Accumulation of potassium and calcium in rat myocardium exposed to alpha-1-adrenoceptor stimulation.

Net fluxes of potassium, calcium, sodium and chloride were examined in isolated perfused rat hearts during alpha-1-adrenoceptor stimulation. The ion measurements were performed in the non-recirculating perfusate. Hearts were exposed to alpha-1-adrenoceptor stimulation (phenylephrine 5 x 10(-5) mol/l in the presence of the beta-blocker timolol 10(-6) mol/l). During alpha-1-adrenoceptor stimulation perfusate potassium fell relatively rapidly by about 0.10 mmol/l after approximately 100 sec. followed by a slower rise. About 180 sec. after onset of alpha-1-adrenoceptor stimulation, the potassium level was about 0.06 mmol/l below the control concentration level. This reduction was eliminated by the alpha-1-adrenoceptor blocker prazosin (10(-7) mol/l). The effects on net calcium fluxes were measured at two different calcium concentrations. For both concentrations we found a small but statistically significant reduction of the calcium concentration in the perfusate after alpha-1-adrenoceptor stimulation. Neither sodium nor chloride perfusate concentrations showed statistical significant changes compared to control values. The present observations revealed the existence of alpha-1-adrenoceptor regulated mechanisms related to a net uptake of both potassium and calcium in rat heart.

An x-ray mapping study of the effects of aluminum on the distribution of calcium, potassium and phorphorus in the roots of Hordeum vulgare var. Kearney

Alumninum toxicity in plants has been shown to reduce root length and the net uptake of nitrate, ammonium, and potassium. In contrast it was demonstrated that phosphate net uptake increased with Al treatment. Additions of calcium to the growth medium were shown to counteract these effects, particularly changes in root length. However the reason(s) for the anti-toxic effect(s) of calcium ions is not understood. One possibility is that Al displaces Ca from the plasmamembrane and/or the cell wall which in turn disrupts Ca-dependent transport processes within and on the cell surface. In this study we report on the effects of Al on Ca, K and P distribution in the roots of the barley variety Kearney using x-ray mapping of freeze-dryed material and discuss the results in terms of the general mechanism of Al toxicity.Root material was obtained from 5day old plants grown in hydroponic solution with or without 50 μM Al. Excised root tips were mounted on specimen holders and plunged into liquid nitrogen after which the roots were faced off with a cyromicrotome.

Volume-regulatory potassium release from isolated perfused rat kidney.

The present study has been performed to test for cell volume regulatory potassium release from the isolated perfused rat kidney exposed to hypotonic perfusate and for its sensitivity to potassium channel blocker barium and calcium channel blocker verapamil. Replacement of 25 mmol/l NaCl with 50 mmol/l mannitol has little effect on effluent potassium activity, whereas subsequent omission of mannitol from the perfusate leads to a transient increase of effluent potassium activity, reflecting volume regulatory potassium release. Barium (1 mmol/l) leads to a marked transient decrease of effluent potassium activity, pointing to net cellular uptake of potassium. Verapamil (1 mumol/l) leads to a slight decrease of effluent potassium activity. Both barium and verapamil virtually abolish the rapid, transient increase of effluent potassium activity upon exposure to hypotonic perfusates. Thus, the substances either block or markedly retard volume regulatory potassium release. The apparent renal vascular resistance is transiently increased by exposure to hypotonic perfusates and by barium, but is reduced by verapamil. Cell volume regulation of isolated perfused mouse straight proximal tubules is retarded but not abolished by verapamil (0.1 mmol/l). In conclusion, cellular potassium release from rat kidney can be determined by continuous measurement of effluent potassium activity. The volume regulatory potassium release and cell volume regulation are impaired by both barium and verapamil. The persisting cell volume regulation could be due either to slow potassium release and/or some mechanism independent of potassium.

Water, K+, H+, lactate and glucose fluxes during cell volume regulation in perfused rat liver.

The present study has been performed to test for ion release from isolated perfused rat liver exposed to hypotonic perfusates. Replacement of 40 mmol/l NaCl in perfusate by 80 mmol/l raffinose leads to slight alkalinization and slight decrease of liver weight. Subsequent decrease of perfusate osmolarity by omission of raffinose results in an increase of liver weight and a parallel increase of effluent sodium, chloride and potassium activity pointing to net uptake of solute free water. While effluent chloride and sodium activities approach perfusate activities within less than 2 min, a second, 6 min lasting increase of effluent potassium activity is observed, pointing to potassium release by the liver. This transient increase of effluent potassium activity is paralleled by a decrease of liver weight. Throughout exposure to hypotonic perfusates, lactate, pyruvate and glucose release by the liver is significantly decreased and effluent pH is rendered alkaline. Readdition of 80 mmol/l raffinose leads to rapid decrease of liver weight and a parallel decrease of effluent sodium, chloride and potassium activities followed by a 10-20 min lasting decrease of effluent potassium activity, pointing to net uptake of potassium, which almost matches the net release observed before. The transient decrease of potassium activity is paralleled by an increase of liver weight, an increase of effluent glucose, lactate and pyruvate concentration and an acidification of the effluent. Similar decrease of effluent potassium activity, acidification of effluent and increase of effluent glucose, lactate and pyruvate concentration are observed, if perfusates are made hypertonic by addition of raffinose.(ABSTRACT TRUNCATED AT 250 WORDS)

Independent stimulation of glucose metabolism and Na+-K+ exchange by insulin in the human forearm.

Insulin promotes potassium uptake into skeletal muscle by stimulating the activity of the Na+-K+ pump. To test whether insulin-induced glucose and potassium uptake are linked processes in vivo, we used the perfused forearm technique in healthy volunteers. Local hyperinsulinemia (125 +/- 11 microU/ml for 100 min) induced a net uptake of glucose and potassium (4.79 +/- 0.61 and 0.76 +/- 0.22 mumol.min-1.100 ml-1 of forearm volume, respectively). When an intra-arterial ouabain infusion (0.72 microgram.min-1.100 ml-1, producing local levels of approximately 0.5 mM) was superimposed on the insulin infusion, potassium uptake was blocked (0.026 +/- 0.190 ml.min-1.100 ml-1, P less than 0.02), and glucose uptake was decreased (to 3.31 +/- 0.34 mumol.min-1.100 ml-1, P less than 0.03). The latter change was explained by a 30% fall in forearm blood flow (from 2.95 +/- 0.10 to 2.01 +/- 0.18 ml.min-1.100 ml-1, P less than 0.001). To separate out the effect of blood flow, in another series of studies forearm blood flow was clamped by co-infusing propranolol and phentolamine (7 and 8 micrograms.min-1.100 ml-1, respectively). Under these conditions of fixed flow (7.0 +/- 0.8 ml.min-1.100 ml-1), ouabain still abolished the stimulatory effect of insulin on potassium uptake but had only a small (and statistically insignificant) effect on forearm glucose extraction (from 20 +/- 2 to 16 +/- 2%, P = N>). We conclude that in human forearm muscle ouabain inhibits Na+-K+ exchange and depresses insulin-induced glucose uptake via an adrenergic-mediated limitation of blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of ambient ammonium on net potassium uptake by decapitated maize seedlings

SUMMARYThe effects of ambient ammonium on potassium uptake and accumulation in xylem exudate were examined in 6‐d‐old decapitated maize (Zea mays L., ev. Pioneer 3369a) seedlings, Net uptake of both K+ and NH+4 was measured by solution depletion during a 5 h treatment period. [86Rb]K+ influx during a 10 min uptake period was also measured for some treatment combinations over the 5 h period. The presence of ambient 0.2 mM NH+4initially resulted in net efflux of K+ to solution containing 0.2 mM K+, as well as to K+‐free solutions. A transition from net K+ efflux to net K+ uptake occurred after 1.25–1.5 h in solutions containing 0.2 mM K+ and 0–2 mM NH+4. After the transition, the rate of K+ uptake was ∼ 50% of that found in the absence of ambient NH+4 [86Rb]K+ influx from 0.2 mM K+ was inhibited by 50% in the presence of 0.2 mM NH+4. Increasing ambient NH+4 to 2.0 mM increased the initial net efflux of K+ and delayed the time at which transition to net uptake occurred. The combined data indicate that the inhibitory effect of ambient NH+4 on net K+ uptake resulted from an initial but temporary enhancement of K+ efflux, and a constant inhibition of K+ influx. A reciprocal inhibition of net NH+4 uptake by K+ was not observed. Net NH+4 uptake initially was associated with K+ efflux, after which a transition to net H+ occurred. In the presence of NH+4, the transition from net K+ efflux to net K+ uptake, and the associated onset of net H+ efflux took place without measurable alterations in the rate of K+ accumulation in the xylem fluid. These results suggest spatially separate compartments for K+ efflux and xylem deposition.

Root Excision Decreases Nutrient Absorption and Gas Fluxes

The roots of barley plants (Hordeum vulgare L. cv Steptoe) were monitored before and after excision for net uptake of carbon dioxide, oxygen, ammonium, potassium, nitrate, and chloride and for their content of sucrose, glucose, fructose, and malic acid. All fluxes began to attenuate within 2 hours after excision. Net potassium uptake returned to control levels 6 hours after excision, but carbon dioxide, oxygen, ammonium, and nitrate fluxes continued to diminish for the remainder of the observation period. The addition of 0.1 molar glucose or 0.1 molar sucrose to excision medium had no significant effect on these changes in ion and gas fluxes. Net chloride uptake was negligible for all treatments. Sugar and malic acid content of the root declined after excision. Sucrose and glucose levels remained depressed for the entire observation period, whereas fructose and malic acid returned to control levels after 9 hours. These results indicate that excision has profound, adverse effects on root respiration and the absorption of mineral nitrogen.

Growth, mineral uptake and skeletal calcium deposition in brown trout, Salmo trutta L., yolk‐sac fry exposed to aluminium and manganese in soft acid water

In 30‐day exposures in artificial soft water medium, survival of brown trout alevins was not affected by low pH (4.5,4.8, 5.4), by low calcium concentration (10.25 μmol l−1) or by manganese (≤20 μmol l−1), but was impaired by aluminium (6–8 μmol l−1) at low calcium concentration (10 μmol l−1) irrespective of pH (4.5 or 5.4). Manganese (6.6, 20 μmol l−1) impaired net calcium uptake and calcium deposition in the skeleton at low calcium concentration (25 μmol l−1) irrespective of pH. Aluminium (2–8 μmol l−1) impaired gross development, net uptake of calcium, potassium and sodium, and calcium deposition in the skeleton, and slightly increased the net loss of magnesium, some of these effects being more severe at calcium concentration 10 μmol l−1 than 50 μmol l−1, and some more severe at pH 5.4 than pH 4.5. Net uptake of calcium and sodium were impaired at low pH (4.5, 4.8), and skeletal calcium deposition was impaired at low calcium concentration (10 μmol l−1), but these effects of low pH and low calcium concentration were slight compared with those of the trace metals. The possible role of trace metals in reports of the deleterious effects on fish of low pH levels is discussed.

Disturbed ion balance in alevins of Atlantic salmon Salmo salar chronically exposed to sublethal concentrations of cadmium

Embryos and alevins of Atlantic salmon Salmo salar were exposed to cadmium concentrations ranging from 0.47 to 300 μg Cd/L from shortly after fertilization to near complete yolk absorption (92 days). Tissue sodium, potassium, calcium, magnesium, and water contents of embryos and alevins were determined at 9-day intervals during this period. Cadmium had no significant effect on the tissue cation or water contents of embryos. Net water uptake by alevins was significantly inhibited at cadmium concentrations ≥0.78 μg Cd/L. Net sodium uptake was significantly inhibited at all concentrations except 79 and 300 μg Cd/L, but because of the concomitant decrease in water uptake there were no significant changes in sodium to water ratios. Net potassium uptake was significantly inhibited at concentrations ≥ 8.2 μg Cd/L and net calcium uptake was significantly inhibited at concentrations ≥ 0.78 μg Cd/L. Tissue magnesium was not affected. Calcification of skeletal elements was inhibited progressively at concentrations ≥ 0.78 μg Cd/L. Low tissue potassium and calcium levels appeared to be responsible for many of the symptoms associated with cadmium poisoning and were probably the immediate cause of death.

Net uptake and partitioning of nitrogen and potassium in cultivars of barley during ageing

Experiments were carried out with barley cultivars (Hordeum vulgare L.) grown in both pot‐ and water‐culture. Net uptake of NO3− and K+ in the roots was followed in two barley cultivars grown on water‐culture for 85 days. After an initial period of low net uptake of both ions, uptake increased until a maximum was reached after 30 to 45 days. Thereafter, net uptake of NO3− and K+ steadily decreased. In the pot experiments, effects of different mineral supply on day 4 to 18 upon the development of five barley cultivars of various earliness were investigated. The effect of earliness on fresh weight production was largest when mineral supply on day 4 to 18 was limited. The influence of limited mineral supply on day 4 to 18 on K‐economy was independent of earliness of the cultivars. The maximal N‐content was reached at the same time as maximal fresh and dry weight in fairly late cultivars; in early cultivars maximum N‐level was reached later than maximum fresh and dry weight. Overall, maximal N‐content was higher in the fairly late cultivars than in the early cultivars. The highest rate of 15N‐transport was attained later in two of three fairly late cultivars than in early cultivars. Partitioning of dry weight, N and K in the shoots changed during ageing, ears being an important sink. Varietal differences in partitioning depended on the earliness of the cultivars. The largest fraction of recently supplied 15N, supplied as nitrate, and K+ (86Rb) were found in the stems. In the oldest plants of the early cultivars the transport to the ears of these isotopes was gradually impaired, reflecting the decreasing function of the long distance transport system.

The relationship between intracellular pH, the pH gradient and potassium transport in Escherichia coli.

The capacity of E. coli cells to regulate intracellular pH (pHi) during net potassium uptake has been investigated. The data show: (a) that cells sense their intracellular pH; (b) that the pH gradient (delta pH) exerts a feedback regulation on pHi; (c) that a mechanism of regulation of pHi exists which may be independent of Na+ [Zilberstein, Agmon, Schuldiner & Padan (1982) J. Biol. Chem. 257, 3687-3691]; and (d) that cells have a limited capacity to raise their intracellular pH in the absence of net K+ transport.