Absorption of Potassium and Sodium Ions by Carrot Root Tissue Cultures

The absorption of potassium and sodium ions by cultured explantsof young secondary phloem of carrot has been examined. Muchsmaller differences were observed between slowly growing andrapidly growing tissues than in the work of Steward and Millar(1954). This discrepancy is attributed to the use by Stewardand Millar of media of dissimilar mineral salts compositionto grow the two types of tissue. At first, potassium uptake per unit of fresh weight proceededmore rapidly in the actively proliferating cultures than theslowly growing ones, but these ultimately had the greater capacityfor potassium absorption. The rapidly growing cultures showeda higher selectivity towards potassium vis-à-vis sodiumions than did those growing slowly. The effect was evident throughouta culture period of 5 weeks, but was most marked during theearly stages of growth. Some possible explanations of theseobservations are discussed.     

The Absorption of Potassium by Cells in the Apex of the Root

The purpose of this investigation is the study of the propertiesof the cell with regard to potassium absorption as the cellexpands. Serial sections each 1·5 mm. in length havebeen cut along the course of maize roots over the first 9·0mm. from the tip. The sections have been immersed in 0·01N. solution of potassium chloride in water and in 2 per cent.fructose. Absorption from these solutions has been measuredover a period of 48–72 hours. It is shown that absorptionby the first section which consists almost entirely of meristematiccells is abnormally low, and this is attributed to the absenceof a tonoplast surrounding a central vacuole in the cells ofthis section. The different initial rates with the differentsections indicate that after vacuolation in the root has occurredthe rate per unit area of surface decreases as the cell expands.When the data are reduced to a unit cell basis, however, theyshow that, per cell, absorption increases as expansion occursin the root. This is attributed to an increasing protein content,and the decrease in rate per unit area to a corresponding decreasein protein per unit area. At the same time it is shown thatduring cell growth in the root the cytoplasm differentiatesin such a way that absorption per unit protein increases. After excision, whether growth occurs or not, the protein contentdoes not increase. The final internal concentrations in thedifferent sections vary according to the growth that occurs.When vacuolation has occurred and growth is limited the finalinternal concentration is greater than it is at the beginningof the experiment. When growth occurs, on the other hand, thefinal internal concentration may be lower. This is taken toindicate that absorption depends on an inward secretion intothe vacuole which is independent of surface area and an outwarddiffusion into the medium which increases with increase in surfacearea. It is suggested that the results obtained with sugar supportthis interpretation. When sugar is provided the rate of absorptionis always stimulated and when growth does not occur the finalinternal concentration is enhanced. When growth occurs, however,sugar not only stimulates absorption but also the expansionof the cell, and the latter effect leads to a final concentrationwhich may be lower than that given in the absence of sugar.     

Absorption of Phosphate and Potassium Ions in Poplar Stems

Phosphate and potassium ions were drawn through segments ofpoplar stem using a vacuum. Analysis of the activity-time curvesfor selected points along the stem were consistent with a mathematicalmodel of mass flow combined with irreversible lateral flow alongthe conducting vessels. However, the phosphate ion could beflushed out of the stems with water, so that it was necessaryto consider this as a limiting case of a reversible-flow model.Comparison is made with the activity-time curves for ion absorptioninto plant tissue, which are considered similar in shape. Avalue of 50 µm min^–1 was obtained for the lateralvelocity, and the ratio of tracer lost laterally to tracer movingon along the pipe was calculated to be about 0.7     

The Exchangeability of Potassium and Bromide Ions in Cells of Red Beetroot Tissue

The exchangeability of potassium and bromide ions accumulatedby cells of red beetroot tissue has been examined under variousexperimental conditions by means of radioactive tracers. It is established that the cells contain a certain amount ofeasily exchanged ions which is largely independent of the saltcontent of the tissue. The remainder of the salt does not exchangeappreciably within 24 hours either during absorption or whenaccumulation is stopped by low temperature, potassium cyanide,high internal salt content, or by an insufficient preliminarywashing of the material. An hypothesis is proposed that the easily exchanged ions aredistributed throughout the intercellular spaces, cell walls,and in parts of the protoplasm, whilst those which do not readilyexchange may be situated in the cell vacuoles, or else stronglyassociated with protoplasmic constituents. The results suggestthat a considerable barrier to the free diffusion and exchangeof ions is located in the region of the tonoplast of a plantcell, and the metabolic transport of ions across this membraneis discussed. An examination of the changes which occur in the amounts ofreadily exchanged potassium during the washing of freshly cutbeet disks in aerated distilled water indicates that the protoplasmprobably acquires a capacity to fix ions more strongly as aresult of this treatment. This supports the view that an effectof washing on the capacity of cells to absorb salts metabolicallyis to increase the number of ‘absorption centres’involved.     

Potassium Fluxes during Potassium Absorption by Intact Barley Plants of Increasing Potassium Content

The presence of previously absorbed K in plants caused a marked reduction in the short term influx of ⁸⁶Rb-labeled K into roots of barley seedlings. The influx values agreed with net K absorption rates into intact plants, thus suggesting that K efflux was negligible in comparison with influx.     

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

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

The Relationship between Transpiration and the Absorption of Inorganic Ions by Intact Plants

The relationship between the rate at which water and the rubidiumand phosphate ions are absorbed by intact plants, and transferredto their shoots has been investigated in water culture undervarying conditions of transpiration and nutrient supply. When the external concentration and the nutrient status of theplants are sufficient low, wide variations in the rate of transpirationhave little effect on the transfer of nutrients to shoots; whenlittle water is being lost by transpiration the concentrationin the transpiration stream may exceed that in the externalmedium by factors exceeding 100. In contrast when the externalconcenration and the nutrient status of the plants are highthe rate of transfer of ions to shoots may vary closely withthe rate of transpiration and the concentration in the transpirationstream may be similar to, or less then, that in the externalmedium. The occurrence of concentrations of ions in the roots is transpirationstream which greatly exceed those in the medium external tothe roots is regarded as evidence that ions not transferredpassively across the roots of intact plants to a significantextent.     

Interaction Between Potassium and Calcium in Their Absorption by Intact Barley Plants. II. Effects of Calcium and Potassium Concentration on Potassium Absorption

Increasing concentrations of K (20, 200, 2000 μm) in the nutrient solution depressed Ca content and concentration in barley plants growing in nutrient solutions of low Ca concentrations (250 and 2500 μm). Increasing K from 20 to 200 μm depressed Ca absorption more than increasing K from 200 to 2000 μm K.     

Efficient Uptake of Cesium Ions by Rhodococcus Cells

Bacteria of the genus Rhodococcus were found to be able to accumulate cesium by means of active transport and nonspecific sorption on the cell surface structures. The maximum removal (up to 97%) of cesium from a medium supplemented with ammonium acetate was observed at 28°C, pH 7.8–8.6, and an equimolar content (0.2 mM) of potassium and cesium ions in the medium. The most active cesium-accumulating rhodococcal strains may be useful in biological treatment of industrial wastewaters contaminated with radionuclides.     

The Role of Calcium Ions in the Acceleration of Resting Muscle Glycolysis by Extracellular Potassium

The activation of the glycolysis of resting muscle by increased extracellular potassium is dependent upon the simultaneous presence of calcium, but not of sodium ions. This regulation of metabolism by a membrane characteristic seems to act upon an early link in the glycolytic enzyme chain.     

The Absorption and Accumulation of Salts by Living Plant Cells: IX The Absorption of Rubidium bromide by Potato Discs

Chemical methods for the quantitative determination of rubidiumin aqueous plant extracts and saps were investigated but abandonedin favour of a spectrographic technique which is fully described. The results of quantitative determinations of the rubidium andbromide absorbed by potato discs from solutions of rubidiumbromide, and the effects upon this absorption of oxygen, oftime, and of the specific surface of the discs are described.The effects of these variables upon the accumulation of bromidewhich were previously described have been confirmed. All thevariables which affect bromide absorption affect the uptakeof rubidium in a similar manner. The absorption of rubidium is of two distinct kinds. The firstphase in the absorption process is a relatively rapid uptakeof rubidium unaccompanied by bromide. This process is unaffectedby oxygen, is not confined to the surface cells, and ceasesafter a short time. The second phase occupies a protracted periodduring which both rubidium and bromide are absorbed in equivalentamounts. During this phase the absorption is confined to a fewlayers of cells at the surface and is determined by oxygen concentrationin the manner already described for the bromide ion. The two types of absorption are described as ‘inducedabsorption’ and as ‘primary absorption’ inthe sense used earlier. The former is merely a property of thesubstances in the tissue, the latter is a process which tendsto increase the free energy of the tissue, therefore demandsthat work should be done, and is a property of the organizedliving cell. The relationships of the two types of absorption process totime have been described and they can be expressed in termsof equations. The effect of the surface and thickness of discs upon the absorptionof bromide and rubidium is interpreted quantitatively. The distance from the surface of the discs at which ‘primaryabsorption’ ceases is the same for rubidium and bromide,and coincides with the values previously determined for thedepth of the layer of tissue which exhibits enhanced respiration. The ‘induced absorption’ of rubidium may be observedin discs killed by alcohol. The effect of concentration uponthis process is similar to the adsorption isotherm. The effectof concentration upon the absorption of bromide by living discsis much less conspicuous and the requirements of the absorptionisotherm are not rigidly met. The effect of concentration alsoinvolves the factor of surface and thickness of disc. Unequal absorption of the bromide and rubidium arises from thesuperimposed effect of two distinct processes one of which causesthe absorption of rubidium only and the other tends to causeequal uptake of rubidium and bromide.     

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.     

Increased Potassium Absorption Confers Resistance to Group IA Cations in Rubidium-Selected Suspension Cells of Brassica napus

Cell lines of suspension cultures of Brassica napus cv. Jet Neuf were identified for their ability to tolerate 100 millimolar Rb⁺, a level which was double the normally lethal concentration. Ten spontaneous isolates were obtained from approximately 5 × 10⁷ cells, one of which was reestablished as a cell suspension. This cell line, JL5, was also resistant to the other group IA cations— Li⁺, Na⁺, K⁺, and Cs⁺—and this trait was stable for at least 30 cell generations in the absence of Rb⁺ selection pressure. The growth characteristics were similar to those of sensitive cells under nonselective conditions. The selected JL5 cells were shown by analysis to have effected more net accumulation of K⁺ and Rb⁺ and less of Na⁺ than did the unselected cells. JL5 and unselected cells after 14 days of culture in basal medium contained 597.2 and 258.2 micromoles of K per gram dry weight, respectively. Michaelis-Menten kinetic analysis of K⁺ influx showed that JL5 possessed an elevated phase 1 V_max, but there was no alteration in its K_m. This is the first time that a plant mutation has been shown to have both increased influx and net absorption of a major essential cation.     

Absorption of Iron by Enzymically Isolated Leaf Cells

Iron uptake was studied using cells enzymically isolated from green tobacco leaves. Absorption was increased both by light and succinate as probable energy sources. Bicarbonate in the incubation mixture was inhibitory, and citrate also reduced absorption presumably by chelation with the metal. Absorption of iron was temperature sensitive and optimal at 25°C. Temperature coefficients and activation energies suggested that absorption was energy mediated. NaN₃ and DNP inhibited uptake at concentrations of 10-³M and 10^?4M, respectively. The inhibition caused by DNP was not negated by an external supply of ATP. The results suggest that iron absorption is an active metabolic process in cells enzymically isolated from green tobacco leaves. Cells from Fe-chlorotic leaves of PI 54619–5–1 soybean absorbed less iron than those derived from healthy leaves of the same variety, while leaf cells from the variety Hawkeye showed no such differences.     

Kinetics and Energetics of Light-enhanced Potassium Absorption by Corn Leaf Tissue

The effect of illumination on the absorption of K⁺ by leaf tissue of Zea mays was investigated. The rate of K⁺ absorption was enhanced by exposure of slices of corn leaf tissue to light, even of relatively low intensities. Potassium was transported inward, with virtually no efflux of previously accumulated K⁺. The evidence indicates that the transport mechanism for absorption of K⁺ is the same in the light as in the dark, but that the source of energy for absorption of K⁺ is different in the light from that in the dark. Various anti-metabolites were used to establish that the energy utilized for active ion transport in the light came partly from ATP supplied by cyclic photophosphorylation. Expenditure of ATP was required in the dark too, but this ATP was formed by oxidative phosphorylation. Establishing the ultimate source of energy for active ion uptake by higher plants might be facilitated by demonstration of an ion-transport process that is not linked directly with the transfer of electrons in the mitochondrial cytochrome chain.     

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.