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PubMed1967

Steady State Sodium and Rubidium Effluxes in Pisum sativum Roots.

Steady state effluxes of potassium and sodium ions were measured on Pisum sativum var. Alaska root segments excised from seedlings which had grown in a nutrient solution containing the major inorganic ions and either (86)Rb as a tracer for K or (22)Na as a tracer for Na. Fluxes appeared to be from 2 cellular compartments, a small compartment with a high flux rate and a larger compartment with a slow flux rate. Cell wall exchange fluxes are believed to have been negligible. Efflux rates for 11.3% and 88.7% of cellular potassium ions were 6 x 10(-7) and 1.32 x 10(-7) respectively; rates for 33.7% and 66.3% of cellular sodium ions were 1.48 x 10(-7) and 3.83 x 10(-8) respectively, (equivalents per gram fr wt per hr). The sodium flux measurements, with previous measurements of ionic concentrations and transmembrane potentials, support the theory that sodium is transported actively from Pisum roots.

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PubMed1967

Ion Absorption and Retention by Chlorella pyrenoidosa. III. Selective Accumulation of Rubidium, Potassium and Sodium.

The selective preference of Chlorella pyrenoidosa for alkali metal cations was found to have the order Rb > K > > > Na. It was demonstrated that a cation of higher preference can replace in the cell cations of lower preference by an ion interchange process.The replacement of Na from the cell by K or Rb occurred against high external Na concentrations up to 450 meq/1 Na.It is suggested that the structural selectivity of the Chlorella cell may be amplified by a chromatographic type repetitive selection process, driven by metabolically dependent unsymmetric shape changes of cellular membranes.

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PubMed1967

Sodium and rubidium as possible nutrients for sugar beet plants.

This study concerned the degree to which Na or Rb could substitute for K in the growth of sugar beet plants when K in the culture solution was low (1 meq/liter) or high (12 meq/liter).Sodium at high concentrations increased the growth of plants in a basal nutrient medium when either deficient in K or when adequately supplied with K alone. Redistribution of K from petioles to blades could not fully explain these results. Therefore, the essentiality of Na per se for growth of sugar beet plants may be inferred.Rubidium increased the growth of plants significantly when supplied in small doses to a nutrient medium deficient or adequately supplied with K. The amount of K added and the mode of Rb addition to solution cultures should be carefully considered when studying the effect of Rb on growth. High Rb concentrations were toxic, especially to the growth of fibrous roots.Sodium or Rb have been shown to enhance the growth of sugar beet plants under either low or high K conditions. Essentiality of either Na and/or Rb per se for growth of sugar beets may be inferred, but other criteria should be fulfilled also for conclusive proof.

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PubMed1970

An Anomaly in Potassium Accumulation by Barley Roots: II. Effect of Calcium Concentration and Rubidium-86 Labeling.

When excised barley roots were incubated in 0.01 to 0.1 mm KCl solutions containing 0.2 mm CaSO(4), there was a peak in the K(+) accumulation against concentration curve at 0.02 to 0.04 mm KCl. The peak in the K(+) accumulation curve was shifted to lower K(+) concentrations when Ca(2+) concentration was decreased and to higher K(+) concentrations when Ca(2+) concentration was increased. Increasing Ca(2+) concentration in the treatment solution was observed to be stimulatory, inhibitory, or neutral depending on the K(+) concentration.When (86)Rb was used as an isotopic tracer for K(+), accumulation of K(+) was grossly overestimated, and the apparent K(+) accumulation curve, as estimated with (86)Rb-labeled K(+), was hyperbolic over the concentration range of 0.01 to 0.1 mm. It was concluded that (86)Rb is a poor tracer for K(+) over the concentration range of 0.01 to 0.1 mm. Accumulation of Rb(+) in the presence of K(+) was accurately measured by (86)Rb.

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PubMed1971

Interaction of rubidium or sodium with potassium in absorption by intact sugar beet plants.

This study concerns the selective absorption of K and Rb or of K and Na by intact sugar beet (Beta vulgaris) plants from modified conventional nutrient solutions over an extended period of plant growth. Long term results agreed with those of short term experiments by other investigators using excised root systems and simple salt solutions. Potassium and Rb were mutually competitive in their absorption. High selectivity of K relative to Na absorption was observed. Sodium was excluded during the early growth period of sugar beets.

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PubMed1976

Effects of kinetin and root tip removal on exudation and potassium (rubidium) transport in roots of honey locust.

Exudation, (86)Rb transport, and water permeability were examined in excised roots of honey locust (Gleditsia triacanthos L.) treated by removing the tip 2 mm (tip-cut 2 mm) or tip 8 mm of the root, or by adding kinetin, or by both treatments. Tip removal increased the rate of exudation. Kinetin, 5 x 10(-6)m, inhibited exudation and Rb transport in tip-cut 2-mm roots; the inhibition was reversible. Kinetin inhibition of exudation was initially associated with lower K(Rb) transport and later with decreases in both ion transport and water permeability. Exudation was also inhibited at 10(-10) to 10(-7)m kinetin. Exudation from roots with intact tips was not altered by kinetin until after about 24 hours. Light during the exudation period had no significant (95%) influence on rate of exudation during the first 24 hours whether root tips were cut or kinetin applied.The results suggest the involvement of the root tip in regulating exudation in other parts of the root. This regulation might occur through cytokinin control of water permeability and the rate of ion transport.

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PubMed1978

Effects of low temperature on respiration and uptake of rubidium ions by excised barley and corn roots.

The effect of temperature upon ion uptake and respiration was investigated with excised roots of corn (Zea mays) and barley (Hordeum vulgare). A strong inhibition (Q(10) = 5 to 8) of ion uptake was observed at temperatures below 10 C. At higher temperatures more normal temperature dependencies (Q(10) = 1.3 to 2) were obtained. When the data were plotted according to the Arrhenius relationship, two different activation energies were indicated above and below 10 C. Other studies have related such changes with temperature in activation energy of processes to changes in membrane properties induced by temperature. These results suggest that such phase transitions may affect ion uptake processes. If so, then differences among species in their capacity to maintain normal root function at low soil temperature and to resist low temperature stress may be related to differences in the physical properties of cellular membranes.

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PubMed1979

Red light and auxin effects on rubidium uptake by oat coleoptile and pea epicotyl segments.

Apical segments of etiolated oat (Avena sativa L. cv. Victory) coleoptiles showed enhanced uptake of [(86)Rb(+)] when tested 30 minutes after a 5-minute red irradiation. The response was partly reversible by far red light. Uptake was sensitive to carbonyl cyanide m-chlorophenyl hydrazone, but not to isotonic mannitol. Indoleacetic acid (10(-7) molar) caused a very pronounced and rapid stimulation of uptake. Basal coleoptile segments also exhibited a red light-enhanced uptake, but not an effect of red light on changes in the pH of the medium. The [(86)Rb(+)] uptake of third internode segments from etiolated peas (Pisum sativum L. cv. Alaska) was not affected by either red light or auxin. This tissue also showed no red light effect on acidification of the medium. It is concluded that alteration of [(86)Rb(+)] flux is not a general feature of phytochrome action.

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PubMed1979

Movement to the xylem exudate of rubidium accumulated in the apex of corn roots.

Apical segments of roots of corn (Zea mays, L.) were excised and mounted in experimental salt solutions containing (86)RbCl and CaCl(2). Xylem exudates were collected hourly beginning at the 21st hour. At the 24th hour, experimental solutions were replaced with solutions of other chlorides (nonlabeled) of Ca(2+) +/- some monovalent cation.Following replacement of the labeled solutions, the rate of (86)Rb(+) release to the exudates from root segments declined by about the same proportional amount regardless of the initial steady-state output rate or the kinds of salts used to replace the RbCl. The content of (86)Rb(+) in the roots also declined with time, but to a relatively less degree. Loss of accumulated (86)Rb(+) to the various external solutions following replacement was less than 6% in 6 hours. It is concluded that movement of accumulated Rb(+) to the exudate is dependent on the concentration of Rb(+) in the root but is largely independent of exchange between accumulated ions and other ions in transit across the root.

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PubMed1979

Rubidium (potassium) uptake by Arabidopsis: a comparison of uptake by cells in suspension culture and by roots of intact seedlings.

Experiments are reported in which the uptake of (86)Rb(+), used as an analog of K(+), into cultured cells of Arabidopsis thaliana is investigated. A single transport system is found with K(m) = 0.34 millimolar and V(max) = 14 nmoles per milligram of protein per hour. This system is blocked by the metabolic inhibitor carbonyl cyanide m-chlorophenyl hydrazone (CCCP) and by cold. At high concentrations of external K(+) (above 1 millimolar), a significant fraction of total uptake is energy-independent. No evidence is found for more than one energy-dependent uptake system or for concentration-dependent modifications of a carrier as postulated in multiphasic transport models.Rb(+) uptake was also examined in cultured cells derived from an "osmotic mutant" of Arabidopsis. The system closely resembles that found in wild type cells with the exception that the Michaelis-Menten constants are higher: K(m) = 1 millimolar and V(max) = 32 nanomoles per milligram of protein per hour.The possibility that these results are artifacts associated with use of cultured cells was checked by examining (86)Rb(+) uptake by roots of intact seedlings of wild type Arabidopsis. A single energy-dependent transport system is found with K(m) = 0.42 millimolar which is not significantly different from the K(m) of cultured cells. There is also energy-independent uptake at high external ion concentration.

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PubMed1979

Ozone alteration of membrane permeability in chlorella: I. Permeability of potassium ion as measured by rubidium tracer.

The addition of ozone to a suspension of Chlorella sorokiniana causes a rapid loss of K(+), as measured by efflux of (86)Rb from prelabeled cells. The efflux of the tracer is stimulated some 15 to 20 times over that of the control. For about 100 microliters per liter ozone, about 25 minutes (6 x 10(-8) moles O(3) delivered per minute) of exposure are required for a 50% depletion of the intracellular K(+). The stimulation of K(+) efflux is nearly linearly dependent upon the amount of ozone delivered into the solution. Following short pulses of ozone (lasting 1 to 5 minutes), efflux rates return to the control level but only after about 15 minutes.While influx of K(+) is ultimately inhibited by ozone, at low concentrations or for short exposure times the tracer influex is stimulated 100 to 200%. Ozone stimulation of an active pump mechanism is unlikely in view of a concomitant decrease in respiration. Thus, this influx may represent movement of K(+) along its electrochemical gradient. Assuming that influx and efflux are in steady-state according to the Goldman equation, it was calculated that the membrane potential for K(+) of -80 to -90 millivolts in control cells drops to -40 millivolts with ozone exposure and is accompanied by a calculated increased permeability to K(+) of 2- to 3-fold.

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PubMed1979

Loss of rubidium and potassium from barley roots on sudden chilling.

Sudden chilling of roots of barley pretreated in a labeled Rb(+) solution at 25 C causes a transient loss of label from the nonfree space. The half-time of the release is about 10 minutes. Within the first few hours of uptake the loss increases proportionally to the root Rb(+) content but varies between experiments as a fraction of this content: values from 4 to 20% were observed. The same phenomenon is found for K(+) labeled with (86)Rb(+).

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PubMed1980

Effects of Boron Deficiency on Rubidium Uptake and Photosynthesis in the Diatom Cylindrotheca fusiformis.

Culturing the diatom Cylindrotheca fusiformis under boron-deficient conditions leads to changes in (86)Rb uptake and photosynthesis prior to any effect on the rate of cell division. The influx rate of (86)Rb into boron-deficient cells was 79% of the control rate after 5 to 5.5 hours culture. Despite lowered (86)Rb influx, however, boron-deficient diatoms accumulated more (86)Rb than did control cells; this was due to the deficient cells' lower efflux rate. After 24 hours culture, boron-deficient cells had accumulated 30% more (86)Rb than had control cells, while releasing (86)Rb at only one-half the control rate. Increased photosynthetic rates were another effect of boron deficiency during this early stage of culture. Prior to 20 hours boron-deficient culture, diatoms had photosynthetic rates 37% greater than those of control cells. Corresponding to the increase in photosynthesis, boron-deficient diatoms had 12% more carbohydrate than control cells after 16 hours culture.

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PubMed1989

Two modes of rubidium uptake in sunflower plants.

The Rb(+)-uptake kinetics in K(+)-starved sunflower (Helianthus annuus) plants can be explained by the addition of two Michaelis-Menten equations. In contrast, Rb(+) uptake can be described by a single Michaelis-Menten equation in normal-K(+) plants. Differences in the K(m)s and in the Arrhenius plots of Rb(+) uptake in the two types of plants suggest two uptake modes.

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PubMed1989

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 x 10(7) 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.

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PubMed2000

Lithium potassium borate and lithium rubidium borate: new non-linear optical crystals

The title compounds, LiKB(4)O(7) and LiRbB(4)O(7), are newly developed non-linear optical crystals containing two kinds of anionic groups, namely (B(3)O(8))(7-) and (B(5)O(10))(5-). The (B(3)O(8))(7-) groups form infinite spiral chains parallel to the [100] direction, which are interconnected by sharing O atoms with (B(5)O(10))(5-) groups.

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