The Influence of Internal Ion Concentration on Potassium Accumulation and Salt Respiration of Red Beet Root Tissue

It is shown that during a period of washing in serated distilledwater disks of Red Beet root tissue acquire the capacity toabsorb potassium rapidly. Subsequently the rate of accumulationof this ion is closely related to the internal salt-contentof the material. On the other hand, whilst the level of saltrespiration increases during the preliminary washing, it isnot influenced significantly by the internal potassium concentration.The implications of these observations are discussed in relationto a possible mechanism of mineral salt absorption.     

Cation-Anion Balance during Potassium and Sodium Absorption by Barley Roots

Steady-state rates of potassium ion and sodium ion absorption by excised barley roots accompanied by various anions were compared with the rates of anion absorption and the concomitant H⁺ and base release by the roots. The cation absorption rates were found to be independent of the identities, concentrations, and rates of absorption of the anions of the external solution, including bicarbonate. Absorption of the anion of the salt plus bicarbonate could not account for the cation absorption. H⁺ is released during cation absorption and base during anion absorption. The magnitude by which one or the other predominates depends on the relative rates of anion and cation absorption under various conditions of pH, cation and anion concentration, and inhibitor concentrations. The conclusion is that potassium and sodium ions are absorbed independently of the anions of the absorption solution in exchange for H⁺, while anions are exchanged for a base. The H⁺ release reflects a specificity between K⁺ and Na⁺ absorption such that it appears to be H⁺ exchanged in the specific rate-limiting reactions of the cation absorption.     

Salt Tolerance in the Halophyte Suaeda maritima L. Dum.: Intracellular Compartmentation of Ions

The time-course of exchange of sodium and potassium ions fromroot and leaf material of the halophyte Suaeda maritima hasbeen followed and the data analysed according to the phenomenologyof efflux, or compartmental, analysis. Sodium ions were exchangedmuch more slowly (c. 4 times) from the vacuoles of leaf cellsof plants grown in sodium chloride than were potassium ionsfrom the vacuoles of leaf cells of plants grown either in similarconcentrations of potassium chloride or in low concentrationsof potassium. In plants grown in sodium chloride, sodium ionswere exchanged 9 times more slowly from the vacuoles of leafcells than from the vacuoles of root cells. The concentration of sodium ions in the cytoplasm of leaf cellsof plants growing in 340 mol m^–3 sodium chloride was estimatedto be 165 mol m^–3 when the average concentration in theleaf tissue was about 600 mol m^–3. As measured by movement from mature to developing leaves inintact plants; there was less in vivo retranslocation of ²²Naand ³⁶CI in plants growing in sodium chloride than there wasof ⁸⁶Rb in plants growing either in potassium chloride or innon-saline conditions. The results are discussed in terms of the concept and energeticsof compartmentation of ions in the cells of halophytes.     

Transport of protons and potassium ions across the membranes of bacteria <Emphasis Type="Italic">Enterococcus hirae</Emphasis> dependent on ATP and nicotinamide adenine dinucleotides

The transport of protons and potassium ions across the membranes of the bacteria Enterococcus hirae growing in an alkaline medium (pH 8.0) or under experimental conditions (pH 7.5) during glucose fermentation accomplished by a KtrI system of absorption of potassium ions, which can interact with F₀F₁-ATPase to form at H⁺-K⁺-pump, has been studied. It was found on cells with a high membrane permeability that the administration of nicotinamide adenine dinucleotides results in the potassium absorption which is insensitive to the inhibitor of F₀F₁-ATPase N,N′-dicyclohexylcarbodiimide. It is assumed that, along with the KtrI system which interacts with F₀F₁-ATPase, a separate KtrI or another K⁺ absorption system operates in these bacteria under particular conditions, which is dependent on NAD⁺ +NADH. Presumably, these interact with this system, changing its conformational state required for the transition to the “active” form.     

Physicochemical roles of soluble metal cations in the outer membrane of Escherichia coli K-12

Atomic absorption spectroscopy of isolated native and EDTA-modified (lipopolysaccharide-depleted) outer membrane revealed trace amounts of potassium, manganese, and iron (1.0-7.0 nmol/mg dry weight outer membrane). Sodium, magnesium, and calcium were approximately one order of magnitude more plentiful, but EDTA-modified outer membrane was deficient in calcium. When metal-binding assays were conducted to find the binding capacity of native and EDTA-modified outer membrane, potassium bound poorly compared with sodium. However, there was no difference in the binding of these ions between the OM preparations. In contrast, reduced amounts of magnesium, calcium, manganese, and iron III bound to the EDTA-modified OM. Partitioning of intact cells in a biphasic dextran-polyethyleneglycol system indicated that the reduced lipopolysaccharide content of the EDTA-modified outer membrane increased the hydrophobicity of the cell surface. Exposure of control and EDTA-treated cells to divalent metal salt solutions before phase partitioning also increased cell surface hydrophobicity. Freeze-etching showed that sodium ions had no effect on the membrane fractures observed in control cells, but with EDTA-treated cells, this cation increased the occurrence of small outer membrane fractures (plateaus) which are characteristic of EDTA treatment. Both magnesium and manganese increased the frequency of outer membrane cleavage in control cells, whereas calcium did not. In contrast, all three divalent metallic ions increased the frequency and extent of cleavage in the outer membrane of EDTA-treated cells.     

The salting-in hypothesis of post-hypertonic lysis

The phenomenon of slow cooling cryoinjury has remained one of the primary areas of research in cryobiology since the early 1950s when it was first investigated thoroughly. Lovelock demonstrated that cell death from freezing and thawing was mainly due to exposure to hypertonic solutions and the subsequent dilution back to isotonic conditions. He suggested that the cell became permeable to sodium in hypertonic conditions leading to a loading of sodium during the hypertonic exposure, which caused the cell to swell past its elastic limit during resuspension in isotonic media (post-hypertonic lysis). This idea was pursued by Zade-Oppen, Farrant, and others who were able to show that the membrane became leaky to cations in hypertonic media but they could not provide any mechanism that would cause the cell to load up with sodium (other than an exchange of extracellular sodium for intracellular potassium, leaving the cell with the same cation concentration that it started out with). In the absence of such a mechanism, predicting post-hypertonic lysis from osmotic simulations cannot be done.A simplified model is proposed in which the intracellular milieu is composed of both KCl and a proteinaceous component that normally forms many salt bridges between amino acids with fixed charges. When the intracellular salt concentration increases, the proteins are “salted in” to solution (salt bridges are replaced with ionic interactions) thereby decreasing the intracellular cation concentration. Cation channels in the plasma membrane are opened by exposure to a high salt concentration (either inside or outside the membrane) allowing extracellular sodium to take the place of the intracellular potassium that is interacting with anionic groups on the proteins. Dilution of the external medium (which also occurs during melting) causes water to move into the cells, diluting the cytoplasm. The proteins are then “salted out” of solution and release the salt back to free ions in solution. The cell has an excess of intracellular ions and may swell past its elastic limit due to water influx. A simulation engine is developed based on the model and compared to results in the literature for freeze–thaw injury in human red blood cells.     

PROLYTIC ION EXCHANGES PRODUCED IN HUMAN RED CELLS BY METHANOL,ETHANOL, GUAIACOL,AND RESORCINOL

When the washed red cells of heparinized human blood are exposed at 4°C. to methanol, ethanol, guaiacol, or resorcinol in hypolytic concentrations in isotonic NaCl, the prolytic loss of K at the end of 20 hours varies from about 25 per cent of the initial K content of the cells in the case of 3.1 M methanol to about 55 per cent of the initial K in the case of 0.04 M resorcinol. As in the case of the prolytic losses observed with other lysins, the K loss is rapid at first and then slows down so that what appears to be a new steady state is reached logarithmically. The K lost from the cells during the period of the prolytic loss is replaced by an approximately equivalent amount of Na, derived from the isotonic NaCl in which the cells are suspended. The Na which enters can be replaced by K by washing the cells in isotonic KCl, and this K can again be replaced by Na by washing the cells in isotonic NaCl. The remainder of the cell K., i.e. the K which was not lost during the period of the prolytic loss, is retained in the cell unaffected by these washing procedures. The capacity of red cells for undergoing disk-sphere transformations is scarcely affected by their having been exposed to hypolytic concentrations of methanol, ethanol, guaiacol, or resorcinol in isotonic NaCl, and their resistance to osmotic hemolysis and to lysis by saponin and digitonin is altered only in minor respects even when as much as 50 per cent of the cell K has been exchanged for Na. Some restriction to the movement of K between the cell and its environment is apparently modified irreversibly when the cell is exposed to hypolytic concentrations of lysins, and the modification is such that only a fraction of the cell K is affected, the fraction being a function of the lysin concentration, the duration of its action, and other factors. A modification of some part of the cell structure and of the properties dependent on its integrity is probably involved: K may be lost more readily from some cells than from others, from some parts of the cell more readily than from other parts, or the explanation may lie in changes in the extent to which Hb binds ions or in modifications of metabolic processes.     

Extracellular Potassium Activity in Attached Leaves and its Relation to Stomatal Function

Apoplastic potassium activities (a_k) in leaves of Commelinacommunis L., Vicia faba L. and Pisum sativum L. var. argenteumwere recorded with neutral-carrier-based, potassium-sensitivemicro-electrodes. Measurements were carried out in 0.3–1.4nl volumes contiguous with the extracellular space of attachedleaves and were held for periods of 7–68 min. Mean steady-statea_K values recorded from all three species were below 50 µM.Similar potassium activities were attained, regardless of theinitial values obtained after washing with distilled water orpotassium additions, and the activities recorded showed onlyminimal dependence on the relative vapour pressure difference.Tissue capacity for K⁺ absorption was increased 15–30-foldin the presence of added Ca²⁺. By contrast, cyanide reducedboth the initial rate of potassium absorption by the tissuesand their apparent capacity for the cation. These observationsindicate that the free potassium pool in the leaf apoplast issignificantly smaller than has previously been assumed. Theresults contradict the notion that high concentrations of potassiumaccumulate locally as a result of transpiration, and may indicatethe presence in the leaf tissues of potassium transport activitysensitive to Ca²⁺ and dependent on metabolism. Key words: Apoplastic potassium activity, Transpiration/K⁺ transport, Guard cells     

Resolution of Pump and Leak Components of Sodium and Potassium Ion Transport in Human Erythrocytes

Further support for the pump-leak concept was obtained. Net transport was resolved into pump and leak components with the cardiac glycoside, ouabain. The specificity of ouabain as a pump inhibitor was demonstrated by its ineffectiveness when the pump was already inhibited by lack of one of the three pump substrates, sodium ion, potassium ion, or adenosine triphosphate. In the presence of ouabain the rates of passive transport of sodium and potassium ions changed almost in proportion to changes in their extracellular concentrations when one ion was exchanged for the other. In the presence of ouabain and at the extracellular concentrations which produced zero net transport, the ratio of potassium ions to sodium ions was 1.2-fold higher inside the cells than outside. This finding was attributed to a residual pump activity of less than 2% of capacity. The permeability to potassium ions was 10% greater than the permeability to sodium ions. A test was made of the independence of pump and leak. Conditions were chosen to change the rate through each pathway separately or in combination. When both pathways were active, net transport was the sum of the rates observed when each acted separately. A ratio of three sodium ions pumped outward per two potassium ions pumped inward was confirmed.     

The salting-in hypothesis of post-hypertonic lysis

The phenomenon of slow cooling cryoinjury has remained one of the primary areas of research in cryobiology since the early 1950s when it was first investigated thoroughly. Lovelock demonstrated that cell death from freezing and thawing was mainly due to exposure to hypertonic solutions and the subsequent dilution back to isotonic conditions. He suggested that the cell became permeable to sodium in hypertonic conditions leading to a loading of sodium during the hypertonic exposure, which caused the cell to swell past its elastic limit during resuspension in isotonic media (post-hypertonic lysis). This idea was pursued by Zade-Oppen, Farrant, and others who were able to show that the membrane became leaky to cations in hypertonic media but they could not provide any mechanism that would cause the cell to load up with sodium (other than an exchange of extracellular sodium for intracellular potassium, leaving the cell with the same cation concentration that it started out with). In the absence of such a mechanism, predicting post-hypertonic lysis from osmotic simulations cannot be done.A simplified model is proposed in which the intracellular milieu is composed of both KCl and a proteinaceous component that normally forms many salt bridges between amino acids with fixed charges. When the intracellular salt concentration increases, the proteins are “salted in” to solution (salt bridges are replaced with ionic interactions) thereby decreasing the intracellular cation concentration. Cation channels in the plasma membrane are opened by exposure to a high salt concentration (either inside or outside the membrane) allowing extracellular sodium to take the place of the intracellular potassium that is interacting with anionic groups on the proteins. Dilution of the external medium (which also occurs during melting) causes water to move into the cells, diluting the cytoplasm. The proteins are then “salted out” of solution and release the salt back to free ions in solution. The cell has an excess of intracellular ions and may swell past its elastic limit due to water influx. A simulation engine is developed based on the model and compared to results in the literature for freeze–thaw injury in human red blood cells.     

Transport of protons and potassium ions across the membranes of bacteria Enterococcus hirae depends on ATP and nicotineamide adenine dinucleotides

The transport of protons and potassium ions across the membranes of the bacteria Enterococcus hirae growing in an alkaline medium (pH 8.0) or under experimental conditions (pH 7.5) during glucose fermentation accomplished by a KtrI-system of absorption of potassium ions, which can interact with F0F1-ATPase to form at H(+)-K(+)-pump, has been studied. It was found on cells with a high membrane permeability that the administration of nicotinamideadenine dinucleotides results in the potassium absorption, which is insensitive to the inhibitor of F0F1-ATPase N,N'-dicyclohexylcarbodiimide. It is assumed that, along with the KtrI system, which interacts with F0F1-ATPase, a separate or another K+ absorption system operates in these bacteria under particular conditions, which is dependent on NAD(+)+NADH. Presumably, these interact with this system, changing its conformational state required for the transition to the "active" form.     

ECOLOGICAL ADAPTATIONS OF SALT MARSH GRASS,DISTICHLIS SPICATA (GRAMINEAE), AND ENVIRONMENTAL FACTORS AFFECTING ITS GROWTH AND DISTRIBUTION

Salt grass is an important pioneer plant in early stages of succession. The sharp-pointed rhizomes with numerous epidermal silica cells, and the aerenchymatous network of the rhizome, leaf sheath, and roots facilitate development of the plant in heavy clays, shales, and inundated soils. In salt marshes of southern Utah, salt grass contributes to a hummock-building process that favors localized removal of salts by capillary action and evaporation. This process provides a narrow strip of soil that is favorable for the rooting of extended rhizomes. In laboratory experiments, maximum growth for Distichlis spicata, a perennial salt marsh grass, was obtained at 15,000 ppm soluble salts in nutrient solution cultures. Comparable concentrations of salts occurred in soils of the habitat from which plants were taken. Nearly equal concentrations of sodium and potassium were found in the plant tissue where the growth of the plants was optimal; such a ratio was maintained in the plants during most of the growing season. In the field the greatest amount of growth of salt grass takes place when temperatures are cool and soil moisture is quite high during the early spring. During mid-summer as air temperatures rise, crude protein in the plant decreases. During periods of high salt and water stress, morphological and anatomical adaptations of the stomata, salt glands, and trichomes of salt grass are important for survival. Stomata on exposed ridges of vascular bundles, where desiccation is greatest, usually are covered by four epidermal cells. In contrast, stomata found in the grooves between vascular bundles tend to be uncovered. The salt gland is composed of a large basal cell and a cap cell and actively excretes (in a diurnal rhythm) excess sodium, potassium, and chloride ions. A mechanism for salt excretion from this gland is postulated. The silica-containing trichomes on the leaves may play a role in cooling the leaf under conditions of high solar radiation and also serve to protect the plant against attack by herbivores.     

False localization of acid phosphatase activity in the nuclear envelope and endoplasmic reticulum of peritoneal macrophages

Summary Acid phosphatase cytochemistry using lead salt methods was performed on rat peritoneal macrophages obtained by the intraperitoneal injection of dextran five days previously. Lead precipitate was present in the nuclear envelope, the rough endoplasmic reticulum, Golgi apparatus and lysosomes in about 50% of these cells. The formation of reaction product appeared to be substrate-specific and was sensitive to sodium fluoride in all these sites. However, only in the nuclear envelope, the rough endoplasmic reticulum and Golgi apparatus could lead salt precipitation be prevented by (a) omission of the washing procedure following the incubation step, (b) postincubation in a medium containing sodium fluoride, or (c) washing in buffer containing lead salt. It is concluded that precipitation of lead salt does not prove the presence of acid phosphatase activity in these organelles. The formation of precipitate in these sites is probably due to a local matrix effect, facilitated by the persistence of acid phosphatase activity in the lysosomes and a suboptimal trapping efficiency of phosphate ions during the washing procedure which follows in the incubation step.     

The Effects of Aqueous Extracts of Red Beet Root on Salt Accumulation and Respiration of Discs of Red Beet Root

An account is given of the preparation of aqueous extracts ofred beet root which are shown to stimulate potassium uptakein beet discs washed for a short period, but inhibit potassiumuptake in discs washed for four days or more. Analysis of extractsshowed them to contain organic anions (especially citrate andmalate) which affect both the metabolic phase of potassium uptakeand respiration of the tissue. The effects of extracts and organicacids on uptake of manganese by beet discs is described andcompared with effects on potassium absorption. The results arediscussed with respect to current theories of salt accumulationand in relation to the hypothesis relating an inhibitor of saltaccumulation to the lag phase of ion uptake by beet discs.     

Metabolic changes in washed,isolated steles

Summary Steles isolated from maize roots grown under non-sterile conditions showed an increase in ion absorption capacity and in the rate of oxygen uptake when washed for 24 h, although the levels of protein and of several hydrolytic and respiratory tnzymes fell over the same period. Fresh isolated cortex showed higher activity than fresh steles in relation to both ion absorption and respiration. The large increase with washing in the ion absorption capacity of the steles was not observed when the tissue was isolated from roots grown under sterile conditions. These results are discussed in relation to proposed mechanisms for the radial transport of ions across the root and to the effect of micro-organisms on ion absorption studies in higher plant cells.     

Cell shrinkage and monovalent cation fluxes: role in apoptosis

The loss of cell volume or cell shrinkage has been a morphological hallmark of the programmed cell death process known as apoptosis. This isotonic loss of cell volume has recently been term apoptotic volume decrease or AVD to distinguish it from inherent volume regulatory responses that occurs in cells under anisotonic conditions. Recent studies examining the intracellular signaling pathways that result in this unique cellular characteristic have determined that a fundamental movement of ions, particularly monovalent ions, underlie the AVD process and plays an important role on controlling the cell death process. An efflux of intracellular potassium was shown to be a critical aspect of the AVD process, as preventing this ion loss could protect cells from apoptosis. However, potassium plays a complex role as a loss of intracellular potassium has also been shown to be beneficial to the health of the cell. Additionally, the mechanisms that a cell employs to achieve this loss of intracellular potassium vary depending on the cell type and stimulus used to induce apoptosis, suggesting multiple ways exist to accomplish the same goal of AVD. Additionally, sodium and chloride have been shown to play a vital role during cell death in both the signaling and control of AVD in various apoptotic model systems. This review examines the relationship between this morphological change and intracellular monovalent ions during apoptosis.     

Absorption of Cadmium and Lead Ions by Gametophyte of the MossPlagiomnium undulatum

A cytochemical analysis of heavy-metal distribution was used to establish an increased ability of the marginal and midrib cells of moss leaves to accumulate metal ions from solutions of lead and cadmium nitrate. The adjacent leaf cells accumulated metal ions more slowly. As shown by the color reaction produced by metal–dithizone complex, the concentration of the absorbed metal ions in the cells increased more than 100-fold as compared to the salt concentration in the solution. The morphological differentiation of the marginal and midrib cells was closely related to the cytosolic pH value and the absorption capacity of cells. Metal ions absorbed in excess of the capacity of absorption sites were not bound by cells and readily washed out.     

The salt glands of Tamarix usneoides E. Mey. ex Bunge (South African Salt Cedar)

Tamarix usneoides is a halophyte tree endemic to south-western Africa. This species is known to excrete a range of ions from specialized glandular structures on its leaves. To understand the mechanisms involved in the transport, sequestration and excretion of ions by the glands, a study was performed on salt gland distribution and ultrastructure. The glands are vesiculated trichomes, comprised of eight cells viz. two basal collecting cells and six excretory cells, partially bounded by a secondary cell wall that could serve as an impermeable barrier, forcing excess ions to move from the apoplast of the surrounding tissue into the cytoplasm of the basal excretory cells. It was hypothesized that the ions are moved across the excretory cells in endocytotic vesicles that fuse with the plasmalemma or form junctional complexes, allowing ion movement from one excretory cell to the next. In the apical cell, the vesicles fuse with the plasmalemma, releasing the ions into the network of cell wall ingrowths which channel the ions to the outside surface of the cell. This study shows that there are distinct structural adaptations for the processing of ions for excretion, although the mechanism by which ions enter the cells still needs to be determined.     

Induction and development of increased ion absorption in corn root tissue

Washing excised or intact primary roots of corn (Zea mays L., WF9 × M14) in aerated distilled water or dilute salt solutions for 2 hours induced doubling of the rate of accumulation of various nutrient ions and solutes. This response to washing depended upon aerobic metabolism, but involved no increase in aerobic respiration. Excision of root tissue was not required as the effect could be obtained with intact root systems. Increased phosphate absorption followed after a lag period of 30 to 40 minutes and continued for 6 hours before leveling off at about 3.5 times the initial rate. Chloramphenicol was not inhibitory to the development of increased absorption, while inhibitors of RNA and protein synthesis were. Auxins and kinetin were also inhibitory, but so was the antiauxin, 2,4,6-trichlorophenoxyacetic acid.     

The ultrastructure of the salt gland of Spartina foliosa

Summary The salt gland in Spartina foliosa is composed of two cells, a large basal cell and a smaller, dome-shaped cap cell which is located on a neck-like protrusion of the basal cell. There is no cuticular layer separating the salt gland from the mesophyll tissue. The basal cell has dense cytoplasm which contains numerous mitochondria, rod-like wall protuberances, and infoldings of the plasmalemma which extend into the basal cell and partition the basal cell cytoplasm. The protuberances originate on the wall between the basal and the cap cells and are isolated from the basal-cell cytoplasm by the infoldings of the plasmalemma. While the cap cell has no partitioning membrane system or wall protuberances, it resembles the basal cell by having dense cytoplasm and numerous mitochondria.The basal cell seems to be designed for efficient movement of ions toward the cap cell. The long, dead-end extracellular channels in the basal cell of Spartina appear comparable to surface specializations seen in the secreting epithelium of animal cells which carry out solute-linked water transport. The number of mitochondria and their close association with the plasmalemma extensions suggest that they have an important role in the transfer of ions through the basal cell.The accumulated ions would move into the extracellular spaces along an osomotic gradient where the accompanying passive flow of water would move the ions into the cap-cell wall and from there the solution would pass out through the pores in the cuticle.