Menadiol diphosphate, a new substrate for non-specific alkaline phosphatase in histochemistry and immunohistochemistry.

Menadiol diphosphate was introduced as a new substrate for nonspecific alkaline phosphatase, following a search for new and less expensive substrates, which give a more sensitive response and are easily synthesized in the laboratory. Menadiol released by phosphatase action can be assayed by its reduction of tetrazolium salts, or it can be coupled with diazonium salts; alternatively, the phosphate can be trapped by metal ions. The synthesis and purification of menadiol diphosphate are described, and it was shown to be sufficiently stable for qualitative and semiquantitative histochemistry, as well as for the immunohistochemistry of enzymes and cytoskeletal proteins with nonspecific alkaline phosphatase as the enzyme label. For qualitative as well as semiquantitative histochemistry and immunohistochemistry, the best results were obtained by applying the method with nitro-blue tetrazolium (NBT) to acetone-chloroform pretreated cryostat sections. Tetranitro-blue tetrazolium (TNBT), benzothiazolylphthalhydrazidyl tetrazolium (BSPT) and various diazonium salts were less suitable. Fast Blue BB and VB produced satisfactory results. Ce3+ ions and the DAB-Ni-H2O2 procedure yielded better results than Ca2+ ions in the Co-(NH4)2S visualization method. The NBT method with menadiol diphosphate is superior to existing methods employing azo, azoindoxyl or tetrazolium salts and to metal precipitation methods. The Ce3+ technique and the NBT/menadiol diphosphate method give similar results, and appear to be of equal value. In qualitative histochemistry and immunohistochemistry the NBT/menadiol diphosphate method resulted in higher quantities of precisely localized stain. Semiquantitative histochemistry with minimal incubation revealed more favorable kinetics for the menadiol diphosphate method, especially when using NBT.     

Use of nitro blue tetrazolium in the reaction of adrenaline autooxidation for the determination of superoxide dismutase activity

The addition of nitro blue tetrazolium (NBT) into the reaction of adrenaline autooxidation allows direct identification of superoxide anion formation (O₂^−⊙) as well as demonstration of kinetics of their accumulation in this superoxide-generating system. The kinetics of adrenochrome and O₂^−⊙ formation has been compared under the same conditions. Three possible approaches to the use of the adrenaline autooxidation reaction for the determination of superoxide dismutase activity (SOD) and revealing antioxidant properties of various compounds are discussed. Two of these approaches have been described previously: the spectro-photometric method of registration of adrenochrome, an end product of adrenaline autooxidation, at 347 nm (Sirota, 1999) and the polarographic method, which measures oxygen consumption used for O₂^−⊙ formation (Sirota, 2011). Here, a novel approach to this problem is presented; it is based on spectrophotometric determination of O₂^−⊙ using NBT. The employment of this approach results in a significant decrease of the pH value of carbonate buffer from 10.5 to 9.7 and a 4-fold decrease in the amounts of added adrenaline, thus creating milder conditions for the revealing and investigation of antioxidant properties of materials being examined.     

Sensitivity of various visualization methods for peroxidase and alkaline phosphatase activity in immunoenzyme histochemistry

Summary Various chromogen protocols for visualizing peroxidase and alkaline phosphatase activity in immunoenzyme histochemistry were compared with respect to their sensitivity. They were tested on tissue sections of human skeletal muscle and in an antigen spot test using antibodies against slow skeletal muscle myosin. The chromogens included 3-amino-9-ethylcarbazole (AEC), 3, 3-diaminobenzidine (DAB),p-phenylenediamine-pyrocatechol (PPD-PC) and 4-chloro-1-naphthol (CN) in peroxidase histochemistry, and 5-bromo-4-chloro-3-indolyl phosphate-nitro blue tetrazolium salt (BCIP-NBT), BCIP-tetra nitro blue tetrazolium salt (TNBT) and various combinations of substituted naphthol phosphate-diazonium salt in alkaline phosphatase histochemistry. DAB, CN, and PPD-PC were also employed with imidazole and DAB in addition to Co²⁺ and Ni²⁺ ions. The results indicate that DAB-imidazole and DAB-Co²⁺ and Ni²⁺ ions are the most sensitive chromogen protocols for visualizing peroxidase activity. Although no large differences were found between the various chromogen protocols for visualizing alkaline phosphatase activity, the protocol BCIP-TNBT is especially recommended. Furthermore, the various chromogen protocols were evaluated as to stability of chromogen solutions and final precipitates, background staining, localization properties, and enhancement of enzyme activity.     

The cerium perhydroxide-diaminobenzidine (Ce-H2O2-DAB) procedure

Summary New light microscopic visualization methods were developed for the histochemical detection of non-specific alkaline and acid phosphatase, Mg-, Ca-and Na, K-dependent adenosine triphosphatase, myosin adenosine triphosphatase, glucose-6-phosphatase, 5-nucleotidase and thiamine pyrophosphatase with cerium ions as trapping agents in cryostat and plastic sections. The techniques are based on the conversion of cerium phosphate into cerium perhydroxide by H₂O₂ which decomposes at 55°–60° C into cerium hydroxide and oxygen radicals. These radicals are able to oxidize diaminobenzidine (DAB) to DAB brown. Addition of nickel ions to the DAB-H₂O₂ mixture generates bluish-black stained nickel-DAB complexes. Compared with the classical metal precipitation, azo, azoindoxyl and tetrazolium procedures the H₂O₂-DAB and especially the H₂O₂-DAB-nickel methods provided identical or superior results in catalytic phosphatase histochemistry and immunohistochemistry when using non-specific alkaline phosphatase as the enzyme label.     

A model for NADH-tetrazolium reductase

Summary In the presence of light, reduced nicotinamide adenine dinucleotide (NADH) and riboflavin formed a complex which was able to reduce certain tetrazolium salts. Neither NADH (10^–3 M) nor riboflavin (10^–4 M) alone was able to induce tetrazolium reduction in the presence of oxygen, but in a nitrogen atmosphere photoreduction of riboflavin induced reduction of tetrazolium salts. Only electrophilic nitro and thiazolyl substituted tetrazolium salts with more positive redox potentials were reduced by the NADH-riboflavin complex, and only monoformazans were produced from the ditetrazolium salts. The reduction kinetics of these tetrazolium salts are given, and the spectral area capable for induction of electron transfer in the NADH-riboflavin complex is screened. It is concluded that the electron transfer in flavin nucleotide dependent dehydrogenase systems will probably proceed without direct interference with the apoenzyme. This may have practical implications for the histochemistry of tetrazolium reductases especially as regards fixation. The catalytic action of light on tetrazolium reduction should also be taken into consideration when tetrazolium salts are used as electron acceptors in a histochemical reaction.     

Ceriometry,a combined method for chemical oxygen demand and dissolved oxygen (with a discussion on the precision of the winkler technique)

A ceriometric method is described in which Ce³⁺ salts are used for the determination of dissolved oxygen and Ce⁴⁺ salts for the determination of the chemical oxygen demand. The interference of COD in the O₂ determination, a common feature of most Winkler determinations, is corrected. The standard deviation is typically about 1% of the mean, and bias (inaccuracy) is very small.The method is simple, quick and reliable.The precision and accuracy of the Winkler method is discussed and compared with that of the Cerium method.     

Cations and Anions as Modifiers of Ryanodine Binding to the Skeletal Muscle Calcium Release Channel

Rate and equilibrium measurements of ryanodine binding to terminal cysternae fractions of heavy sarcoplasmic reticulum vesicles demonstrate that its activation by high concentrations of monovalent salts is based on neither elevated osmolarity nor ionic strength. The effect of the ions specifically depends on their chemical nature following the Hofmeister ion series for cations (Li⁺ < NH⁺ ₄ < K⁻∼ Cs⁺≤ Na⁺) and anions (gluconate⁻ < Cl⁻ < NO₃ ⁻∼ ClO₄ ⁻∼ SCN⁻) respectively, indicating that both are involved in the formation of the salt-protein complex that can react with ryanodine. Activation by rising salt concentrations exhibits saturation kinetics with different dissociation constants (25–11 m) and different degrees of cooperativity (n= 1.5–4.0) for the respective salts. Maximal second order binding rates between 40,000 and 80,000 (m ⁻¹· sec⁻¹) were obtained for chlorides and nitrates of 1a group alkali ions with the exception of lithium supporting only rates of maximally 10,000 (M⁻¹· sec⁻¹). The nitrogen bases, NH⁺ ₄ and Tris⁺, in combination with chloride or nitrate, behave divergently. High maximal binding rates were achieved only with NH₄NO₃. The dissociation constants for the ryanodine–protein complexes obtained by measurements at equilibrium proved to depend differently on salt concentration, yet, converging to 1–3 nm for the applied salts at saturating concentrations. The salts do not affect dissociation of the ryanodine protein complex proving that the effect of salts on the protein's affinity for ryanodine is determined by their effect on the on-rate of ryanodine binding. ATP and its analogues modify salt action resulting in elevated maximal binding rates and reduction or abolition of binding cooperativity. Linear relations have been obtained by comparing the rates of ryanodine binding at different salt concentrations with the rates or the initial amplitudes (15 sec) of salt induced calcium release from actively loaded heavy vesicles indicating that the various salts promote specifically and concentration dependently channel opening and its reaction with ryanodine. Received: 9 February 1998/Revised: 24 April 1998     

The use of tetrazolium salts in the histochemical demonstration of succinic dehydrogenase activity in plant tissues

Summary Succinic dehydrogenase activity was determined in fresh or cryostat sections of tissues from Allium cepa, Vicia faba, Pisum sativum and Helianthus tuberosus using different tetrazolium salts as electron accepters. In 10 fresh or frozen sections a reaction was obtained with TNBT, NBT, MTT, and INT but not with NT, BT or TTC. In contrast a reaction was obtained with each of the tetrazolium salts in 50–150 fresh or frozen sections. The observed differences in the abilities of the tetrazolium salts to demonstrate succinic dehydrogenase activity are discussed.The sites of acceptance of electrons from the electron transport pathway in plant cells by the tetrazolium salts has been demonstrated cytochemically, and shown to differ from those observed in animal cells in that unlike animal cells, there is no apparent acceptance of electrons by MTT and INT from cytochrome C₁-C region of the pathway.     

Superoxide production by rabbit pulmonary alveolar macrophages.

Nitroblue tetrazolium (NBT) reduction by reduction by alveolar macrophages from normal and BCG-granulomatous rabbit lungs was inhibited by superoxide dismutase (SOD). Superoxide (.O₂^?) might therefore be involved, either direclty or indirectly, in the bactericidal activities of such cells. Cells from BCG-granulomatous rabbits did not, however, reduce significantly more NBT per cell than cells from normal rabbits.     

Luminescence and energy‐transfer properties of color‐tunable Ca2Mg0.25Al1.5Si1.25O7:Ce3+/Eu2+/Tb3+ phosphors for ultraviolet light‐emitting diodes

A series of Ca₂Mg_0.25Al_1.5Si_1.25O₇:Ce³⁺/Eu²⁺/Tb³⁺ phosphors was been prepared via a conventional high temperature solid‐state reaction and their luminescence properties were studied. The emission spectra of Ca₂Mg_0.25Al_1.5Si_1.25O₇:Ce³⁺,Eu²⁺ and Ca₂Mg_0.25Al_1.5Si_1.25O₇:Ce³⁺,Tb³⁺ phosphors show not only a band due to Ce³⁺ ions (409 nm) but also as a band due to Eu²⁺ (520 nm) and Tb³⁺ (542 nm) ions. More importantly, the effective energy transfer from Ce³⁺ to Eu²⁺ and Tb³⁺ ions was confirmed and investigated by emission/excitation spectra and luminescent decay behaviors. Furthermore, the energy level scheme and energy transfer mechanism were investigated and were demonstrated to be of resonant type via dipole–dipole (Ce³⁺ to Eu²⁺) and dipole–quadrupole (Ce³⁺ to Tb³⁺) reactions, respectively. Under excitation at 350 nm, the emitting color could be changed from blue to green by adjusting the relative doping concentration of Ce³⁺ and Eu²⁺ ions as well as Ce³⁺ and Tb³⁺ ions. The above results indicate that Ca₂Mg_0.25Al_1.5Si_1.25O₇:Ce³⁺,Eu²⁺/Tb³⁺ are promising single‐phase blue‐to‐green phosphors for application in phosphor conversion white‐light‐emitting diodes. Copyright © 2015 John Wiley & Sons, Ltd.     

Zur Substantivität von Tetrazoliumsalzen in der Histochemie

Zusammenfassung Die in der Literatur beschriebenen Beziehungen zwischen Substantivität und chemischem Bau der in der Histochemie verwendeten Tetrazoliumsalze wurden an weiteren Tetrazoliumsalzen überprüft. Die Untersuchungen ergaben, daß die Anzahl und die Stellung der Nitrogruppen im Molekül an Bedeutung für die Substantivität des Tetrazoliumsalzes hinter dem Einfluß einer linearen, aromatischen Substitution am N(₃) des Tetrazolringes bzw. einer Molekülverdoppelung zurücktreten. Es ist zwischen einer Substantivität der Tetrazoliumsalze und einer Substantivität der Formazane zu unterscheiden.

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On substantivity of tetrazolium salts in histochemistry

Summary The known correlations between substantivity and chemical constitution of tetrazolium salts used in histochemistry are further examined on several tetrazolium salts. The investigations are demonstrating that number and position of the nitro groups in the molecule are less important for substantivity of the salt than the influence of a linear, aromatic substitution on N(₃) of the tetrazol ring or of doubling the molecule. It is to differentiate between substantivity of tetrazolium salts and the substantivity of the formazans.

     

Assimilation of Phytate-phosphorus by the Extracellular Phytase Activity of Tobacco (Nicotiana tabacum) is Affected by the Availability of Soluble Phytate

Phytate, the major organic phosphorus in soil, is not readily available to plants as a source of phosphorus (P). It is either complexed with cations or adsorbed to various soil components. The present study was carried out to investigate the extracellular phytase activities of tobacco (Nicotiana tabacum variety GeXin No.1) and its ability to assimilate external phytate-P. Whereas phytase activities in roots, shoots and growth media of P_i-fed 14-day-old seedlings were only 1.3–4.9% of total acid phosphatase (APase) activities, P starvation triggered an increase in phytase secretion up to 914.9 mU mg⁻¹ protein, equivalent to 18.2% of total APase activities. Much of the extracellular phytase activities were found to be root-associated than root-released. The plants were not able to utilize phytate adsorbed to sand, except when insoluble phytate salts were preformed with Mg²⁺ and Ca²⁺ ions for supplementation. Tobacco grew better in sand supplemented with Mg-phytate salts (31.9 mg dry weight plant⁻¹; 0.68% w/w P concentration) than that with Ca-phytate salts (9.5 mg plant⁻¹; 0.42%), presumably due to its higher solubility. We conclude that insolubility of soil phytate is the major constrain for its assimilation. Improving solubility of soil phytate, for example, by enhancement of citrate secretion, may be a feasible approach to improve soil phytate assimilation.     

Energy transfer in M5(PO4)3 F:Eu2+,Ce3+ (M = Ca and Ba) phosphors

M₅(PO₄)₃ F:Eu²⁺ (M = Ca and Ba) co‐doped with Ce³⁺ phosphors were successfully prepared by the combustion synthesis method. The introduction of co‐dopant (Ce³⁺) into the host enhanced the luminescent intensity of the M₅(PO₄)₃ F:Eu²⁺ (M = Ca and Ba) efficiently. Previously, we have reported the synthesis and photoluminescence properties of same phosphors. The aim of this article is to report energy transfer mechanism between Ce³⁺?Eu²⁺ ions in M₅(PO₄)₃ F:Eu²⁺ (M = Ca and Ba) phosphors, where Ce³⁺ ions act as sensitizers and Eu²⁺ ions act as activators. The M₅(PO₄)₃ F:Eu²⁺ (M = Ca and Ba) co‐doped with Ce³⁺ phosphor exhibits great potential for use in white ultraviolet (UV) light‐emitting diode applications to serve as a single‐phased phosphor that can be pumped with near‐UV or UV light‐emitting diodes. Copyright © 2013 John Wiley & Sons, Ltd.     

The reaction of nitro-blue tetrazolium with d,l-L-tetrahydrofolate: The effect of pH,oxygen, formaldehyde and palladium(II)

d,l-L-Tetrahydrofolate (d,l-L-FH₄) transfers two electrons to nitro-blue tetrazolium (NBT) in oxygen-free buffers to form the highly coloured nitro-blue formazan and oxidized folate. Both the rate and extent of this reaction are affected by the pH, the nature of the buffer and the oxygen concentration. Inhibition of both the rate and extent of this reaction in air-saturated solutions by superoxide dismutase (SOD) indicates that the superoxide anion is an intermediate in the reaction so that formazan can be produced by both superoxide independent and superoxide dependent routes in air-saturated solutions.In oxygen-free solutions several lines of evidence can be interpreted to mean that the reduced pteridine ring of tetrahydrofolate is the electron donor in the reaction with NBT. Ionization of the amide hydrogen of the pteridine ring and subsequent increase in electron density of that ring might explain the large increases observed in the rate and extent of the reaction of tetrahydrofolate with NBT as the pH increases. Formaldehyde reacts non-enzymatically with tetrahydrofolate to form a methylene bridge between nitrogens 5 and 10 of methylenetetrahydrofolate. This molecule is much less reactive with nitro-blue tetrazolium than tetrahydrofolate. Complexes formed between tetrahydrofolate and palladium(II) ions are also less reactive with NBT than the tetrahydrofolate alone. This result provides added evidence that palladium(II) ions interact with tetrahydrofolate at the nitrogen 5, nitrogen 10 site of the molecule.     

The Mechanism of CeCl<Subscript>3</Subscript> on the Activiation of Alanine Aminotransferase from Mice

The activity of alanine aminotransferase (ALT; E.C. 2.6.1.2) is often changed upon inflammatory responses in animals. Rare earths was shown to provoke various inflammatory responses both in rats and mice; however, the molecular mechanism by which rare earths exert its toxicity has not been completely understood, especially, we know little about the mechanism of the interaction between CeCl₃ and ALT. In this report, we investigated the mechanisms of CeCl₃ on ALT activity in vivo and in vitro. Our results showed that Ce³⁺ could significantly activate ALT in vivo and in vitro; the kinetics constant (Km) and Vmax were 0.018 μM and 1,380 unit mg⁻¹ protein min⁻¹, respectively, at a low concentration of Ce³⁺, and 0.027 μM and 624 unit mg⁻¹ protein min⁻¹, respectively, at a high concentration of Ce³⁺. By UV absorption and fluorescence spectroscopy assays, the Ce³⁺ was determined to be directly bound to ALT; the binding site of Ce³⁺ to ALT was 1.72, and the binding constants of the binding site were 4.82 × 10⁸ and 9.05 × 10⁷ L mol⁻¹. Based on the analysis of the circular dichroism spectra, it was concluded that the binding of Ce³⁺ altered the secondary structure of ALT, suggesting that the observed enhancement of ALT activity was caused by a subtle structural change in the active site through the formation of the complex with Ce³⁺.     

Localized Tetrazolium Reduction in Relation to N2 Fixation, CO2 Fixation, and H2 Uptake in Aquatic Filamentous Cyanobacteria

The aquatic filamentous cyanobacteria Anabaena oscillarioides and Trichodesmium sp. reveal specific cellular regions of tetrazolium salt reduction. The effects of localized reduction of five tetrazolium salts on N₂ fixation (acetylene reduction), ¹⁴CO₂ fixation, and ³H₂ utilization were examined. During short-term (within 30 min) exposures in A. oscillarioides, salt reduction in heterocysts occurred simultaneously with inhibition of acetylene reduction. Conversely, when salts failed to either penetrate or be reduced in heterocysts, no inhibition of acetylene reduction occurred. When salts were rapidly reduced in vegetative cells, ¹⁴CO₂ fixation and ³H₂ utilization rates decreased, whereas salts exclusively reduced in heterocysts were not linked to blockage of these processes. In the nonheterocystous genus Trichodesmium, the deposition of reduced 2,3,5-triphenyl-2-tetrazolium chloride (TTC) in the internal cores of trichomes occurs simultaneously with a lowering of acetylene reduction rates. Since TTC deposition in heterocysts of A. oscillarioides occurs contemporaneously with inhibition of acetylene reduction, we conclude that the cellular reduction of this salt is of use in locating potential N₂-fixing sites in cyanobacteria. The possible applications and problems associated with interpreting localized reduction of tetrazolium salts in cyanobacteria are presented.     

Kinetic analysis of superoxide anion production by activated and resident murine peritoneal macrophages

Using a continuous spectrophotometric assay, we have monitored the formation of superoxide anion (O₂^?) by activated and resident murine peritoneal macrophages. Macrophages elicited by injection with Corynebacterium parvum, as well as resident macrophages from untreated mice, were kept in suspension culture overnight to eliminate short-lived, contaminating neutrophils. Cytochemical analysis of the cultured macrophages disclosed that essentially all of the activated macrophages reduced nitroblue tetrazolium (NBT) dye vigorously. In contrast, only 18% of the resident macrophages demonstrated vigorous NBT reduction; the remainder of the resident macrophages reduced NBT very weakly. Kinetic analysis of macrophage O₂^? formation revealed that activated macrophages exposed to phorbol myristate acetate (PMA) produced O₂^? at a 13-fold greater maximum rate than resident macrophages. The decline in the rate of O₂^? production with time by activated macrophages was also greater than that of resident macrophages. The data indicate that the greater O₂^? production by activated macrophage populations is due to (i) the presence of an increased percentage of macrophages that respond to PMA with vigorous O₂^? production, and (ii) an increased maximum rate of O₂^? formation by these macrophages.     

UDP-glucuronosyltransferases 1A6 and 1A10 catalyze reduced menadione glucuronidation

Menadione (2-methyl-1,4-naphthoquine), also known as vitamin K3, has been widely used as a model compound in the field of oxidative stress-related research. The metabolism of menadione has been studied, and it is known that menadione undergoes a two-electron reduction by NAD(P)H:Quinone oxidoreductase 1 (NQO1) after which the reduced form of menadione (2-methyl-1,4-naphthalenediol, menadiol) is glucuronidated and excreted in urine. To investigate which human UDP-glucuronosyltransferase (UGT) isoforms participate in the glucuronidation of menadiol reduced by NQO1 from menadione, we first constructed heterologously expressed NQO1 in Sf9 cells and tested the menadiol glucuronidating activity of 16 human recombinant UGT isoforms. Of the 16 UGT isoforms, UGTs 1A6, 1A7, 1A8, 1A9, and 1A10 catalyzed menadiol glucuronidation, and, of these, UGTs 1A6 and 1A10 catalyzed menadiol glucuronidation at much higher rates than the other UGTs. Menadiol was regioselectively glucuronidated in the manner of 4-position > 1-position by UGTs 1A7, 1A8, 1A9, and 1A10. In contrast to these UGTs, only UGT1A6 exhibited 1-menadiol-preferential glucuronidating activity. The results suggest possible detoxification pathways for quinones via NQO1 reduction followed by UGT glucuronidation.     

Synthesis and characterization of novel Na15(SO4)5F4Cl:Ce3+ halosulfate phosphors

A series of Na₁₅(SO₄)₅F₄Cl phosphors doped with Ce³⁺ ions was prepared using the wet chemical method. X‐Ray diffraction studies were used to determine their phase formation and purity. Fourier transform infrared spectroscopy effectively identified the chemical bonds present in the molecule. The photoluminescence properties of the as‐prepared phosphors were investigated and the Ce³⁺ ions in these hosts were found to give broadband emission in the UV range. For the thermoluminescence study, phosphors were irradiated with a 5 Gy dose of γ‐rays from a ⁶⁰Co source. Chen’s half‐width method was employed to calculate the trapping parameters from the thermoluminescence glow curve. Copyright © 2016 John Wiley & Sons, Ltd.     

Monovalent-ion carrier effects on transport of Rb86 and Cs137 into bush bean plants

Summary Bush bean plants were exposed to either Rb⁸⁶ or Cs¹³⁷ for 24 hours with different monovalent cations as carriers in single-salt solutions except for the presence of 10⁻⁴ M CaCl₂. Ratio of uptake of the radionuclides at 10⁻³ to 10⁻² M was used as an index of the carrier ability of various cations. Different monovalent cations decreased uptake of Cs¹³⁷ and its transport to shoots unequally when 10⁻² M salts were compared with 10⁻³ M salts. Rubidium and cesium salts decreased Cs¹³⁷ uptake equally but potassium salts were less effective in decreasing uptake when the ratios of the two concentrations were considered. All monovalent cations decreased uptake of Cs¹³⁷ at the 10⁻² M carrier concentration but some did not at 10⁻³ M. Nitrate nitrogen was a big factor in these results. Cesium and rubidium salts were most effective. Potassium appeared to increase Cs¹³⁷ transport to shoots particularly at 10⁻³ M KNO₃. Only cesium, rubidium, and potassium salts decreased uptake of Rb⁸⁶ when 10⁻² M salts were compared with 10⁻³ M. Rubidium and cesium salts decreased uptake essentially equally and potassium salts again were less effective. All nitrate salts tended to increase Rb⁸⁶ transport to shoots more consistently than with Cs¹³⁷. It is concluded that absorption and transport to shoots were not equivalent for potassium, rubidium, and cesium.