Accumulation of potassium and sodium by barley roots in a k-na replacement series

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.     

Influence of Excision and Aging upon K+ Influx into Barley Roots: Recovery or Enhancement? 1

The influx of K⁺ from ⁸⁶Rb-labeled solutions in the concentration range 0.008 to 0.2 mm into roots of intact plants and excised roots of barley plants (Hordeum vulgare [L.]) previously grown in 5 mm CaSO₄ (low K⁺ roots) or 0.5 mm CaSO₄ plus 5 mm KCl (high K⁺ roots) was measured. A consistent observation of these experiments was a substantial reduction of influx (usually by about 50%) following excision. The possible leakage of K⁺ into the medium and subsequent dilution of specific activity of labeled solutions was eliminated as an explanation for influx reduction in excised low K⁺ roots. Reduction of transpirational rates was also without effect upon influx into low K⁺ roots. Excision followed by 2 hours aging in 0.5 mm CaSO₄ solution revealed that influx values recovered within the 2 hours to the values obtained in intact roots. It is concluded that much of the literature which describes the enhancement of ion uptake following excision actually describes excision damage followed by recovery.     

The role of intracellular pH in the regulation of cation exchanges in yeast

1. When yeast oxidizes propan-2-ol in the presence of KCl no uptake of K⁺ occurs. 2. When propionate is added to suspensions containing propan-2-ol, or if the suspensions are bubbled with CO₂, a considerable uptake of K⁺ occurs. 3. Maximum K⁺ uptake occurs at a propionate concentration of 2mm. 4. The addition of 20mm-propionate to the suspension lowers the intracellular pH of the yeast from a resting value in the region of 6.2 to approx. 5.6. 5. When K⁺ uptake is measured in the presence of 20mm-propionate, progressive changes in the rate of K⁺ uptake and intracellular pH occur. The optimum rate of K⁺ uptake occurs at an intracellular pH of 5.70. 6. The effect of both intra- and extra-cellular pH on K⁺–K⁺ exchange was studied and an optimum rate was found at an extracellular pH of 5.35, the corresponding intracellular pH being 6.44. 7. When a Na⁺-loaded yeast oxidizes propan-2-ol in the presence of KCl, a steady efflux of Na⁺ and influx of K⁺ occurs. The addition of 10mm-propionate to the suspension markedly inhibited the Na⁺ efflux but only slightly decreased the K⁺ influx. 8. The effect of both extra- and intra-cellular pH on Na⁺ efflux was studied with propan-2-ol and with glucose. The results can be best interpreted in terms of intracellular pH changes, and an optimum was obtained at approx. pH6.40.     

Potassium Channels in Chara corallina: CONTROL AND INTERACTION WITH THE ELECTROGENIC H PUMP

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.     

Transport of glucose and galactose in kidney-cortex cells

1. The aerobic transport of d-glucose and d-galactose in rabbit kidney tissue at 25° was studied. 2. In slices forming glucose from added substrates an accumulation of glucose against its concentration gradient was found. The apparent ratio of intracellular ([S]_i) and extracellular ([S]_o) glucose concentrations was increased by 0·4mm-phlorrhizin and 0·3mm-ouabain. 3. Slices and isolated renal tubules actively accumulated glucose from the saline; the apparent [S]_i/[S]_o fell below 1·0 only at [S]_o higher than 0·5mm. 4. The rate of glucose oxidation by slices was characterized by the following parameters: K_m 1·16mm; V_max. 4·5μmoles/g. wet wt./hr. 5. The active accumulation of glucose from the saline was decreased by 0·1mm-2,4-dinitrophenol, 0·4mm-phlorrhizin and by the absence of external Na⁺. 6. The kinetic parameters of galactose entry into the cells were: K_m 1·5mm; V_max 10μmoles/g. wet wt./hr. 7. The efflux kinetics from slices indicated two intracellular compartments for d-galactose. The galactose efflux was greatly diminished at 0°, was inhibited by 0·4mm-phlorrhizin, but was insensitive to ouabain. 8. The following mechanism of glucose and galactose transport in renal tubular cells is suggested: (a) at the tubular membrane, these sugars are actively transported into the cells by a metabolically- and Na⁺-dependent phlorrhizin-sensitive mechanism; (b) at the basal cell membrane, these sugars are transported in accordance with their concentration gradient by a phlorrhizin-sensitive Na⁺-independent facilitated diffusion. The steady-state intracellular sugar concentration is determined by the kinetic parameters of active entry, passive outflow and intracellular utilization.     

Separation and partial characterization of multiple ribonucleic Acid polymerases from soybean hypocotyl

Two major peaks of RNA polymerase activity have been routinely separated by diethylaminoethyl cellulose chromatography following solubilization from soybean (Glycine max L. var. Wayne) chromatin. The relative amounts of these two peaks depend upon the manner in which the chromatin is purified. Pelleting the chromatin through dense sucrose solutions results in not only a loss of total solubilized RNA polymerase activity but also a selective loss of the α-amanitin-sensitive form of the enzyme. Peak I elutes from a diethylaminoethyl cellulose column at a KCl concentration of approximately 0.27 m, is insensitive to α-amanitin and rifamycin, and has Mg²⁺ + Mn²⁺ optima of 5 mm and 1.25 mm, respectively. The enzyme is inhibited by KCl concentrations of about 0.03 m or greater. Peak II elutes from the column at a KCl concentration of approximately 0.35 m, is sensitive to α-amanitin, insensitive to rifamycin, and has Mg²⁺ + Mn²⁺ optima of 2 mm and 1.0 mm, respectively. Activity is inhibited by KCl concentrations of about 0.06 m or greater. Both enzymes prefer denatured calf thymus DNA, but peak II exhibits a stronger preference.     

Sodium-gradient-stimulated transport of l-alanine by plasma-membrane vesicles isolated from liver parenchymal cells of fed and starved rats. Crucial role of the adrenal glucocorticoids

The ability of liver efficiently to take up amino acids, particularly l-alanine, during starvation was studied in a cell-free system by isolating plasma-membrane vesicles in a transport-competent state from rat liver parenchymal cells. These membrane vesicles have the capacity to accumulate l-alanine against an apparent concentration gradient when exposed to an artificial and transient transmembrane Na⁺ gradient (extravesicular Na⁺ concentration greater than inside). The rate of accumulation of l-alanine is dependent on the plasma-membrane vesicle concentration, and the steady-state concentration attained is inversely related to the osmolarity of the medium. The Na⁺-mediated stimulation is not exhibited if the membrane vesicles are pre-equilibrated with NaCl, if K⁺ or Li⁺ are substituted for Na⁺, or if SO₄²⁻ replaces Cl⁻ as the counterion. The apparent active transport of l-alanine into the membrane vesicles appears to occur by an electrogenic mechanism: (1) the use of NaSCN significantly heightens the early concentrative phase of transport when compared with the effect of NaCl; (2) an enhanced active transport is also observed when a valinomycin-induced K⁺ efflux occurs concomitant with Na⁺ and l-alanine influx. Plasma-membrane vesicles isolated from liver parenchymal cells of a 24 h-starved rat exhibit an initial l-alanine transport rate that is 3–4 times that for membrane vesicles derived from a fed animal. The increased rate of l-alanine transport by plasma-membrane vesicles from starved animals can be obliterated by adrenalectomy and restored by administration of glucocorticoid. These results establish that stimulation of the gluconeogenic pathway by starvation involves a plasma-membrane-localized change affecting l-alanine transport which is regulated in part by the glucocorticoid hormones.     

Electrical potential differences in cells of barley roots and their relation to ion uptake

Single cell electropotentials of barley (Hordeum vulgare L., cv. `Compana') root cortex were measured at different external concentrations of KCl in the presence of Ca²⁺. The roots were low in salt from seedlings grown on 0.5 mm aerated CaSO₄ solution. Thus, the conditions were equivalent to those used to define the dual mechanisms found with radioactive tracer-labeled ion uptake. In 0.5 mm CaSO₄ alone, there is an increase with time of cell negativity from about -65 millivolts 15 minutes after cutting segments to about -185 millivolts in 6 to 8 hours. Two possible hypotheses, not mutually exclusive, are offered to explain this aging effect: that cutting exposes plasmodesmata which are leaky initially but which seal in time, and that some internal factors, e.g., hormones diffusing from the apex, have a regulatory effect on the cell potential, an influence which becomes dissipated in isolated segments and permits the development of a higher potential difference. In any case changes in selective ion transport must be involved. The cell potentials at KCl concentrations above 2.0 mm are more negative than would be expected for a passive diffusion potential. It is suggested that this discrepancy may be due to an electrogenic pump or to a higher K⁺ concentration in the cytoplasm than in the remainder of the cell, or perhaps to both. Whether there is a clear relationship between cell potential and mechanisms 1 and 2 of cation transport depends upon whether the cell potentials of freshly cut or of aged tissue represent the values relevant to intact roots.     

The use of potential-sensitive cyanine dye for studying ion-dependent electrogenic renal transport of organic solutes. Spectrophotometric measurements

Renal transport of four different categories of organic solutes, namely sugars, neutral amino acids, monocarboxylic acids and dicarboxylic acids, was studied by using the potential-sensitive dye 3,3′-diethyloxadicarbocyanine iodide in purified luminal-membrane and basolateral-membrane vesicles isolated from rabbit kidney cortex. Valinomycin-induced K⁺ diffusion potentials resulted in concomitant changes in dye–membrane-vesicle absorption spectra. Linear relationships were obtained between these changes and depolarization and hyperpolarization of the vesicles. Addition of d-glucose, l-phenylalanine, succinate or l-lactate to luminal-membrane vesicles, in the presence of an extravesicular>intravesicular Na⁺ gradient, resulted in rapid transient depolarization. With basolateral-membrane vesicles no electrogenic transport of d-glucose or l-phenylalanine was observed. Spectrophotometric competition studies revealed that d-galactose is electrogenically taken up by the same transport system as that for d-glucose, whereas l-phenylalanine, succinate and l-lactate are transported by different systems in luminal-membrane vesicles. The absorbance changes associated with simultaneous addition of d-glucose and l-phenylalanine were additive. The uptake of these solutes was influenced by the presence of Na⁺-salt anions of different permeabilities in the order: Cl⁻>SO₄²⁻>gluconate. Addition of valinomycin to K⁺-loaded vesicles enhanced uptake of d-glucose and l-phenylalanine in the presence of an extravesicular>intravesicular Na⁺ gradient. Gramicidin or valinomycin plus nigericin diminished/abolished electrogenic solute uptake by Na⁺- or Na⁺+K⁺-loaded vesicles respectively. These results strongly support the presence of Na⁺-dependent renal electrogenic transport of d-glucose, l-phenylalanine, succinate and l-lactate in luminal-membrane vesicles.     

Effect of ammonium and other ions on the glucose-dependent active transport of l-histidine in slices of rat-brain cortex

1. The influence of cations on the active transport into cells of rat-brain-cortex slices of l-histidine, an amino acid that is not metabolized by this tissue, has been studied. 2. Like other amino acids, l-histidine accumulated in the cells in the presence of glucose in concentrations up to over double that in the incubation medium. 3. The active transport of l-histidine was highest in a medium containing Ca²⁺ (3mm). The addition of K⁺ (27mm) led to a marked decrease in the intracellular concentration of l-histidine, though the oxygen uptake of the slices was higher. 4. The active l-histidine transport was inhibited by NH₄⁺. The inhibitory effect increased with the NH₄⁺ concentration, being about 25% at 8mm, 65% at 20mm, and 90% at 27 and 50mm. The oxygen uptake of the brain slices was depressed by only 25% by the highest NH₄⁺ concentration used, and less by lower concentrations.     

Studies of cardiac muscle with a high permeability to calcium produced by treatment with ethylenediaminetetraacetic acid

Thin strips of frog ventricle were isolated and bathed for 15 min in a solution containing 140 mM KCl, 5 mM Na₂ATP, 3 mM EDTA, and 10 mM Tris buffer at pH 7.0. The muscle was then exposed to contracture solutions containing 140 mM KCl, 5 mM Na₂ATP, 1 mM MgCl₂, 10 mM Tris, 3 mM EGTA, and CaCl₂ in amounts to produce concentrations of free calcium from 10^-4.8 M to 10^-9 M. The muscles developed some tension at approximately 10^-8 M, and maximum tension was achieved in 10^-5 M Ca⁺⁺. They relaxed in Ca⁺⁺ concentrations less than 10^-8 M. The development of tension by the EDTA-treated muscles was normalized by comparison with twitch tension at a stimulation rate of 9 per min before exposure to EDTA. In 10^-5 M Ca⁺⁺ tension was always several times the twitch tension and was greater than the contracture tension of a frog ventricular strip in KCl low Na-Ringer. Tension equal to half-maximum was produced at approximately 10^-6.2 M Ca⁺⁺. Intracellular recording of membrane potential indicated that after EDTA treatment the resting potential of cells in Ringer solution with 10^-5 M Ca or less was between 5 and 20 mv. Contracture solutions did not produce tension without prior treatment with EDTA. The high permeability of the membrane produced by EDTA was reversed and the normal resting and action potentials restored in 1 mM Ca-Ringer. Similar studies of EDTA-treated rabbit right ventricular papillary muscle produced a similar tension vs. Ca⁺⁺ concentration relation, and the high permeability state reversed with exposure to normal Krebs solution.     

Requirement for extraction of polyribosomes from barley tissue

The isolation of barley (Hordeum vulgare L.) polyribosomes, showing minimal degradation effects of endogenous RNase, required a buffer adjusted to pH 8.0 and containing 0.40 m KCl in addition to common extraction components. The extracted polyribosomes were characterized in sucrose gradients by their conversion to monosomes when incubated with pancreatic RNase and by their dependence on adequate amounts of Mg²⁺ during extraction and analysis. Factors which contributed to polyribosome stability were evaluated by the relative sedimentation rates of aggregates in sucrose gradients. Tissue extraction at KCl concentrations less than 0.40 m and below pH 8.0 resulted in an appearance of larger amounts of ribosomes in the less dense region of the sucrose gradient after centrifugation. The addition of 10 mm dithiothreitol was partially effective in preventing the loss of higher polymerized states of polyribosomes at KCl concentrations below 0.40 m. Extractions conducted at KCl concentrations greater than 0.40 m and at pH 8.0 reduced the amount of ribosomes obtained from the tissue. The monosome portion of the polyribosomal profile was partially dissociated into subunits when the tissue was extracted in 0.60 m KCl. A similar effect on monosomes was obtained when polyribosomes were incubated with cycloheximide and 0.40 m KCl, a result not observed by use of a combination of 0.10 m KCl and the drug or 0.40 m KCl alone.     

On the mechanisms of sodium ion transport by the irrigated gills of rainbow trout (Salmo gairdneri)

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 K_m 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.     

Structural requirements for active intestinal transport. The nature of the carrier–sugar bonding at C-2 and the ring oxygen of the sugar

Several weakly transported sugars were tested for transport by the Na⁺-dependent sugar carrier with slices of everted hamster intestinal tissue. Sugars were assumed to be transported by this carrier if the accumulation was diminished in the absence of Na⁺ and in the presence of the competitive inhibitor 1,5-anhydro-d-glucitol. The extent of accumulation was correlated with the number of hydroxyl groups in the d-gluco configuration if the ring oxygen was placed in the normal d-glucose position. 5-Thio-d-glucose, with a sulphur atom in the ring, was transported at about the same rate as d-glucose and had a similar K_i for d-galactose transport, but myoinositol was poorly accumulated. It is suggested that there is no hydrogen bonding at the ring oxygen atom, but that the oxygen atom is found at this position as a result of steric constraints. No sugar without a hydroxyl group in the d-gluco position at C-2 of the sugar, including d-mannose, 2-deoxy-d-glucose, 2-chloro-2-deoxy-d-glucose and 2-deoxy-2-fluoro-d-glucose, was transported by the Na⁺-dependent carrier, but these sugars and l-fucose weakly and competitively inhibit the Na⁺-dependent accumulation of l-glucose into slices of everted hamster intestinal tissue. It is concluded that the bond between the carrier and C-2 of the sugar may be covalent, and a possible mechanism for active intestinal transport is proposed.     

Cation pretreatment effects on nitrate uptake, xylem exudate, and malate levels in wheat seedlings

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.     

Role of potassium and malate in nitrate uptake and translocation by wheat seedlings

Wheat seedlings (Triticum vulgare) treated with 1 mm KNO₃ or NaNO₃, in the presence of 0.2 mm CaSO₄, were compared during a 48-hour period with respect to nitrate uptake, translocation, accumulation and reduction; cation uptake and accumulation; and malate accumulation. Seedlings treated with KNO₃ absorbed and accumulated more nitrate, had higher nitrate reductase levels in leaves but less in roots, accumulated 17 times more malate in leaves, and accumulated more of the accompanying cation than seedlings treated with NaNO₃. Within seedlings of each treatment, changes in nitrate reductase activity and malate accumulation were parallel in leaves and in roots. Despite the great difference in malate accumulation, leaves of the KNO₃-treated seedlings had only slightly greater levels of phosphoenolpyruvate carboxylase than leaves of NaNO₃-treated seedlings. NADP-malic enzyme levels increased only slightly in leaves and roots of both KNO₃- and NaNO₃-treated seedlings. The effects of K⁺ and Na⁺ on all of these parameters can best be explained by their effects on nitrate translocation, which in turn affects the other parameters. In a separate experiment, we confirmed that phosphoenolpyruvate carboxylase activity increased about 2-fold during 36 hours of KNO₃ treatment, and increased only slightly in the KCl control.     

Ecophysiological response of Crambe maritima to airborne and soil-borne salinity

Background and Aims

There is a need to evaluate the salt tolerance of plant species that can be cultivated as crops under saline conditions. Crambe maritima is a coastal plant, usually occurring on the driftline, with potential use as a vegetable crop. The aim of this experiment was to determine the growth response of Crambe maritima to various levels of airborne and soil-borne salinity and the ecophysiological mechanisms underlying these responses.

Methods

In the greenhouse, plants were exposed to salt spray (400 mm NaCl) as well as to various levels of root-zone salinity (RZS) of 0, 50, 100, 200 and 300 mm NaCl during 40 d. The salt tolerance of Crambe maritima was assessed by the relative growth rate (RGR) and its components. To study possible salinity effects on the tissue and cellular level, the leaf succulence, tissue Na⁺ concentrations, Na⁺ : K⁺ ratio, net K⁺/Na⁺ selectivity, N, P, K⁺, Ca²⁺, Mg²⁺, proline, soluble sugar concentrations, osmotic potential, total phenolics and antioxidant capacity were measured.

Key Results

Salt spray did not affect the RGR of Crambe maritima. However, leaf thickness and leaf succulence increased with salt spray. Root zone salinities up to 100 mm NaCl did not affect growth. However, at 200 mm NaCl RZS the RGR was reduced by 41 % compared with the control and by 56 % at 300 mm NaCl RZS. The reduced RGR with increasing RZS was largely due to the reduced specific leaf area, which was caused by increased leaf succulence as well as by increased leaf dry matter content. No changes in unit leaf rate were observed but increased RZS resulted in increased Na⁺ and proline concentrations, reduced K⁺, Ca²⁺ and Mg²⁺ concentrations, lower osmotic potential and increased antioxidant capacity. Proline concentrations of the leaves correlated strongly (r = 0·95) with RZS concentrations and not with plant growth.

Conclusions

Based on its growth response, Crambe maritima can be classified as a salt spray tolerant plant that is sensitive to root zone salinities exceeding 100 mm NaCl.     

Reversible Repression of Early Enzyme Synthesis in Bacteriophage T4-infected Escherichia coli

A mutant of Escherichia coli B, defective in its accumulation of K⁺, was found to synthesize protein at a rate proportional to the level of this cation in the growth medium. When bacteriophage T4-infected cells were incubated in growth medium containing 1 mm K⁺, phage deoxyribonucleic acid (DNA) was synthesized at a rate 25% that of normal, and phage protein was synthesized at a rate of 50% of normal. Deoxycytidine pyrophosphatase, a phage-directed early enzyme, shut off at a level of 55% that of normal when infected cells were incubated in medium containing 1 mm K⁺. However, deoxycytidine pyrophosphatase synthesis resumed in these cells when they were shifted to medium containing the normal K⁺ concentration (33 mm). DNA synthesis also attained the rate characteristic of this K⁺ concentration. These results suggest that phage DNA synthesis is not sufficient to repress early protein formation and also indicate that the inhibitor of early protein formation is an early function whose synthesis is sensitive to the same repression as that of the early proteins.     

Uptake of amino acids by actidione-treated yeast cells

The uptake of glycine,l-aspartic acid andl-lysine at pH 5 was not systematically affected by the presence of up to 0.1m NaCl or KCl, without or with 0.3mm actidione. The observed effects, either positively or negatively altering the rate of amino acid uptake, depended on the concentration of the ion but were always qualitatively the same for Na⁺ and K⁺. The inhibition prevailing with 0.1m ions was significantly more pronounced with Na⁺ than with K⁺. The presence of other anions (phosphate, nitrate, sulphate) had a slight but significant effect on uptake as compared with the variant using chloride. It is concluded that inSaccharomyces cerevisiae the transport of amino acids is not essentially coupled with the transport of different ions.     

Electrostatic association and donnan phenomena as mechanisms of ion accumulation

Excised roots of barley (Hordeum vulgare, var. Campana) were incubated for periods up to 24 hours in salt solutions of various concentrations and ion accumulation was determined at various time intervals. The data were consistent with the existence of 2 components of ion uptake, one accounting for ion uptake from solutions below 1 mm and both components contributing to uptake from solutions of concentrations higher than 1 mm.