Natural Chlorinated Auxins Labelled with Radioactive Chloride in Immature Seeds

Immature seeds were harvested from 15 species grown in perlite/vermiculite containing ³⁶Cl^-, but with very low levels of cold Cl^-. Autoradiograms of one- and two-dimensional thin layer chromatograms of butanol extracts of lyophilized seeds indicated several radioactive compounds besides the ³⁶Cl^- in many species. In pea the radioactivity cochromatographed with 4-(or 6-)chloroindolyl-3-acetic acid and its methyl ester; in other species radioactivity was found near these chlorinated indolyl-acetic acid markers.     

Monomethyl-4-chloroindolyl-3-acetyl-L-aspartate and absence of indolyl-3-acetic acid in immature seeds of Pisum sativum

Summary A new auxin-related metabolite has been isolated from immature seeds of Pisum sativum and its structure has been determined as monomethyl-4-chloroindolyl-3-acetyl-L-aspartate. Neither indolyl-3-acetic acid nor its methyl ester have been detected in immature seeds by gas-liquid chromatographic analysis.     

The Role of Hormones in Controlling the Mechanically Induced Dormancy of Suaeda spp.

Seeds of several taxa in the genus Suaeda with a mechanically resistant testa were stimulated to germinate with applications: of 1 × 10^?4M gibberellic acid (GAg). The barley endosperm bioassay indicated that the non-dormant taxa, S. macrocarpa, had high initial gibberellin-like activity while the dormant varieties, S. flexilis and S. vulgaris, had not. Soaking for 2 days increased the gibberellin-like activity of the dormant taxa. At 20 days hormonal activity was repressed, and few seeds germinated. The barley endosperm bioassay also revealed an inhibitor activity in the dormant varieties. The wheat coleoptile bioassay and UV irradiation of thin layer chromatograms indicated that an inhibitor occurred at the Rf of cochromatographed ABA and that it had similar inhibitory characteristics.     

Effect of Auxin on Cell Wall Degrading Enzymes

The effect of auxin on the activities of amylase, cellulase, β-1, 3- and/or β-l, 6-glucanase and hemieellulase were observed using etiolated barley coleoptile and pea epicotyl internode segments. The activities of β-1, 3- and/or β-l, 6-glueanase and hemicellulase of barley were increased by indole-3-acetic acid in a 3 hours' treatment. Amylase activity was not influenced by the auxin. Cellulase activity was not detected under the experimental conditions. 2, 4-Dichlorophenoxyacetic acid increased hemicellulase activity, but not cellulase and amylase activities, in pea epicotyl segments in 3 hours. Fungal β-1, 3-glucanase exogenously applied induced the elongation of barley coleoptile segments. The elongation induced by the enzyme was as high as that induced by indole-3-acetic acid at least for the first 1 to 3 hours.     

A mutation affecting the synthesis of 4-chloroindole-3-acetic acid

Traditionally, schemes depicting auxin biosynthesis in plants have been notoriously complex. They have involved up to four possible pathways by which the amino acid tryptophan might be converted to the main active auxin, indole-3-acetic acid (IAA), while another pathway was suggested to bypass tryptophan altogether. It was also postulated that different plants use different pathways, further adding to the complexity. In 2011, however, it was suggested that one of the four tryptophan-dependent pathways, via indole-3-pyruvic acid (IPyA), is the main pathway in Arabidopsis thaliana,¹ although concurrent operation of one or more other pathways has not been excluded. We recently showed that, for seeds of Pisum sativum (pea), it is possible to go one step further.² Our new evidence indicates that the IPyA pathway is the only tryptophan-dependent IAA synthesis pathway operating in pea seeds. We also demonstrated that the main auxin in developing pea seeds, 4-chloroindole-3-acetic acid (4-Cl-IAA), which accumulates to levels far exceeding those of IAA, is synthesized via a chlorinated version of the IPyA pathway.     

The role of chloride ion in Photosystem II I. Effects of chloride ion on Photosystem II electron transport and on hydroxylamine inhibition

1. Chloroplasts washed with Cl^?-free, low-salt media (pH 8) containing EDTA, show virtually no DCMU-insensitive silicomolybdate reduction. The activity is readily restored when 10 mM Cl^? is added to the reaction mixture. Very similar results were obtained with the other Photosystem II electron acceptor 2,5-dimethylquinone (with dibromothymoquinone), with the Photosystem I electron acceptor FMN, and also with ferricyanide which accepts electrons from both photosystems.2. Strong Cl^?-dependence of Hill activity was observed invariably at all pH values tested (5.5–8.3) and in chloroplasts from three different plants: spinach, tobacco and corn (mesophyll).3. In the absence of added Cl^? the functionally Cl^?-depleted chloroplasts are able to oxidize, through Photosystem II, artificial reductants such as catechol, diphenylcarbazide, ascorbate and H₂O₂ at rates which are 4–12 times faster than the rate of the residual Hill reaction.4. The Cl^?-concentration dependence of Hill activity with dimethylquinone as an electron acceptor is kinetically consistent with the typical enzyme activation mechanism: E(inactive) + Cl^?ag E · Cl^? (active), and the apparent activation constant (0.9 mM at pH 7.2) is unchanged by chloroplast fragmentation.5. The initial phase of the development of inhibition of water oxidation in Cl^?-depleted chloroplasts during the dark incubation with NH₂OH ($\text{1}\text{2}$ H₂SO₄) is 5 times slower when the incubation medium contains Cl^? than when the medium contains NH₂OH alone or NH₂OH plus acetate ion. (Acetate is shown to be ineffective in stimulating O₂ evolution.)6. We conclude that the Cl^?-requiring step is one which is specifically associated with the water-splitting reaction, and suggests that Cl^? probably acts as a cofactor (ligand) of the NH₂OH-sensitive, Mn-containing O₂-evolving enzyme.     

The influence of ammonium and chloride on potassium and nitrate absorption by barley roots depends on time of exposure and cultivar

Net uptakes of K⁺ and NO₃⁻ were monitored simultaneously and continuously for two barley (Hordeum vulgare) cultivars, Prato and Olli. The cultivars had similar rates of net K⁺ and NO₃⁻ uptake in the absence of NH₄⁺ or Cl⁻. Long-term exposure (over 6 hours) to media which contained equimolar mixtures of NH₄⁺, K⁺, Cl⁻, or NO₃⁻ affected the cultivars very differently: (a) the presence of NH₄⁺ as NH₄Cl stimulated net NO₃⁻ uptake in Prato barley but inhibited net NO₃⁻ uptake in Olli barley; (b) Cl⁻ inhibited net NO₃⁻ uptake in Prato but had little effect in Olli; and (c) NH₄⁺ as (NH₄)₂SO₄ inhibited net K⁺ uptake in Prato but had little effect in Olli. Moreover, the immediate response to the addition of an ion often varied significantly from the long-term response; for example, the addition of Cl⁻ initially inhibited net K⁺ uptake in Olli barley but, after a 4 hour exposure, it was stimulatory. For both cultivars, net NH₄⁺ and Cl⁻ uptake did not change significantly with time after these ions were added to the nutrient medium. These data indicate that, even within one species, there is a high degree of genotypic variation in the control of nutrient absorption.     

Anion-Mediated Salinity Affecting Methane Production in a Flooded Alluvial Soil

In a laboratory incubation study, effects of amendment with sodium salts of SO₄ ^2?, Cl^? and HCO₃ ^? either singly or as a mixture on CH₄ production in a nonsaline alluvial soil under flooded condition were investigated. Methane production was considerable in the unamended alluvial soil, but was significantly inhibited following amendment with salts of different anions to raise the pore water EC to 8 dS·m^?1. SO₄ ^2? was the most inhibitory to CH₄ production and the degree of inhibition followed the order SO₄ ^2? > salt mixture > HCO₃ ^? > Cl^?. Salt amendment did not adversely affect soil microbial activities as expressed in terms of soil redox potential (Eh) and soil pH. However, readily mineralizable carbon content, an indicator of substrate availability for methanogenic bacteria, differed significantly among the treatments. Most probable number estimates indicated that acetotrophic methanogenic bacterial population was lowest in Cl^?-amended soils followed by SO₄ ^2?-amendment with little or no changes in HCO₃ ^?-amended soils. The data suggested that the inhibition in methanogenesis in saline soils rich in sulphate as in coastal saline soils could be due to competitive inhibition of methanogens, while in inland soils, Cl^? content could be a deciding factor.     

Microinjection of arginase into enzyme-deficient cells with the isolated glycoproteins of sendai virus as fusogen

Bumetanide is a potent diuretic drug which has some structural features in common with furosemide. The steady-state exchange of K⁺ and Cl^? was investigated in Ehrlich ascites tumor cells treated with bumetanide. This agent did not alter the cellular content of K⁺ or Cl^? but the self-exchange of both ions was depressed. K⁺ self-exchange was inhibited by 55% at bumetanide concentrations as low as 10^?6 M. Cl^? self-exchange was less sensitive to this drug but at low concentrations (between 10^?6 and 10^?3 M) bumetanide was a more effective inhibitor of Cl^? transfer than furosemide. The steady-state K⁺ flux of cells equilibrated in NO₃^? media was compared with the K⁺ flux in cells treated with 10^?4 or 10^?3 M bumetanide; the Cl^? -sensitive K⁺ exchange was equivalent to the bumetanide-sensitive K⁺ exchange. Since the results suggested that a bumetanide-sensitive (Cl^?, K⁺) cotransport could be operative in steady-state cells, the stoichiometry of the bumetanide-sensitive fluxes was determined by measuring Cl^? and K⁺ fluxes simultaneously in the same cell suspension. At $\text{5 · 10}{}^{\mathrm{?4}}$ and 10^?3 M bumetanide concentrations, the ratio of these fluxes was $\text{0.98 ? 0.07 (}\text{S.E.}\text{)}\text{and}\text{1.04 ? 0.06}$, respectively, consistent with the postulated cotransport mechanism. At 10^?4 and 10^?5 M, however, the ratio of the bumetanide-sensitive Cl^?/K⁺ flux was significantly less than 1.0. Since the magnitude of the bumetanide-sensitive K⁺ flux at 10^?4 M was close to that of the Cl^?-sensitive flux, a ratio of less than 1.0 at this drug level indicates that Cl^? sensitivity and drug sensitivity may not reflect inhibition of the same process under all circumstances.     

Photochemical study of a cyanobacterial chloride-ion pumping rhodopsin

Mastigocladopsis repens halorhodopsin (MrHR) is a Cl^?-pumping rhodopsin that belongs to a distinct cluster far from other Cl^? pumps. We investigated its pumping function by analyzing its photocycle and the effect of amino acid replacements. MrHR can bind I^? similar to Cl^? but cannot transport it. I^?-bound MrHR undergoes a photocycle but lacks the intermediates after L, suggesting that, in the Cl^?-pumping photocycle, Cl^? moves to the cytoplasmic (CP) channel during L decay. A photocycle similar to that of the I^?-bound form was also observed for a mutant of the Asp200 residue, which is superconserved and assumed to be deprotonated in most microbial rhodopsins. This residue is probably close to the Cl^?-binding site and the protonated Schiff base, in which a chromophore retinal binds to a specific Lys residue. However, the D200N mutation affected neither the Cl^?-binding affinity nor the absorption spectrum, but completely eliminated the Cl^?-pumping function. Thus, the Asp200 residue probably protonates in the dark state but deprotonates during the photocycle. Indeed, a H⁺ release was detected for photolyzed MrHR by using an indium?tin oxide electrode, which acts as a good time-resolved pH sensor. This H⁺ release disappeared in the I^?-bound form of the wild-type and Cl^?-bound form of the D200N mutant. Thus, Asp200 residue probably deprotonates during L decay and then drives the Cl^? movement to the CP channel.     

Grain yield, symbiotic N2 fixation and interspecific competition for inorganic N in pea-barley intercrops

The effect of mixed intercropping of field pea (Pisum sativum L.) and spring barley (Hordeum vulgare L.), compared to monocrop cultivation, on the yield and crop-N dynamics was studied in a 4-yr field experiment using ¹⁵N-isotope dilution technique. Crops were grown with or without the supply of 5 g ¹⁵N-labeled N m^-2. The effect of intercropping on the dry matter and N yields, competition for inorganic N among the intercrop components, symbiotic fixation in pea and N transfer from pea to barley were determined. As an average of four years the grain yields were similar in monocropped pea, monocropped and fertilized barley and the intercrop without N fertilizer supply. Nitrogen fertilization did not influence the intercrop yield, but decreased the proportion of pea in the yield. Relative yield totals (RYT) showed that the environmental sources for plant growth were used from 12 to 31% more efficiently by the intercrop than by the monocrops, and N fertilization decreased RYT-values. Intercrop yields were less stable than monocrop barley yields, but more stable than the yield of monocropped pea. Barley competed strongly for soil and fertilizer N in the intercrop, and was up to 30 times more competitive than pea for inorganic N. Consequently, barley obtained a more than proportionate share of the inorganic N in the intercrop. At maturity the total recovery of fertilizer N was not significantly different between crops, averaging 65% of the supplied N. The fertilizer N recovered in pea constituted only 9% of total fertilizer-N recovery in the intercrop. The amount of symbiotic N₂ fixation in the intercrop was less than expected from its composition and the fixation in monocrop. This indicates that the competition from barley had a negative effect on the fixation, perhaps via shading. At maturity, the average amount of N₂ fixation was 17.7 g N m^-2 in the monocrop and 5.1 g N m^-2 in the intercropped pea. A higher proportion of total N in pea was derived from N₂ fixation in the intercrop than in the monocrop, on average 82% and 62%, respectively. The ¹⁵N enrichment of intercropped barley tended to be slightly lower than of monocropped barley, although not significantly. Consequently, there was no evidence for pea N being transferred to barley. The intercropping advantage in the pea-barley intercrop is mainly due to the complimentary use of soil inorganic and atmospheric N sources by the intercrop components, resulting in reduced competition for inorganic N, rather than a facilitative effect, in which symbiotically fixed N₂ is made available to barley.Abbreviations MC monocrop - IC intercrop - PMC pea monocrop - BMC barley monocrop - PIC pea in intercrop - BIC barley in intercrop     

Activation of Excitatory Amino Acid Receptors in the Rat Hippocampal Slice Increases Intracellular Cl− and Cell Volume

Abstract: The effects of glutamatergic excitotoxins on intracellular Cl^? were investigated in the CA1 pyramidal cell layer of the hippocampal slice. Hippocampal slices from rats (14–19 days old) were loaded with 6-methoxy-N-ethylquinolinium chloride (MEQ), a Cl^?-sensitive fluorescent probe with a fluorescence intensity that correlates inversely with intracellular [Cl^?]. Slices were exposed for at least 10 min at 26–28°C to N-methyl-d -aspartate (NMDA; 100 µM) or α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA; 50 µM). A UV laser scanning confocal microscope was used to measure changes in MEQ fluorescence within area CA1 pyramidal cell soma. Both glutamate receptor agonists produced a rapid decrease in MEQ fluorescence that persisted after washout following a 10-min exposure. The effects of NMDA and AMPA were prevented by the competitive antagonists 2-amino-5-phosphonopentanoic acid and 6,7-dinitroquinoxaline-2,3-dione, respectively. Neither tetrodotoxin nor picrotoxin prevented the effect of NMDA or AMPA, indicating the lack of involvement of presynaptic mechanisms. The effects of NMDA and AMPA on MEQ fluorescence were dependent on the levels of extracellular Cl^?, but only NMDA responses were dependent on the levels of extracellular Na⁺. Removal of Ca²⁺ from the superfusion medium did not alter the effects of NMDA or AMPA on MEQ fluorescence. In addition, neither the Ca²⁺ ionophore ionomycin nor the L-type voltage-gated Ca²⁺ channel agonist (Bay K 8644) decreased MEQ fluorescence. The effects of NMDA and AMPA on cell (somal) volume were also assessed with the fluorescent probe calcein acetoxymethyl ester. Both NMDA and AMPA decreased calcein fluorescence (indicating an increased cell volume), but this was preceded by the decrease in MEQ fluorescence (equivalent to an intracellular accumulation of ～20 mM Cl^?). Thus, excitotoxins may cause Cl^? influx via an anion channel other than the GABA_A receptor and/or reduce Cl^? efflux mechanisms to produce cell swelling. Such anionic shifts may promote neuronal excitability and cell death following an excitotoxic insult to the hippocampal slice.     

The effect of divalent cations on Na+ tolerance in Charophytes. I: Char a buckellii

Abstract The comparative Na⁺ tolerance of Chora buckellii cultured in freshwater (FW) or artificial Waldsea water (AWW, which contains about 110 mol m^?3 each Na ⁺, Mg²⁺, Cl^? and SO^2-₄ was tested with respect to the external Na⁺ to Ca²⁺ ratio (Na: Ca). Fifty per cent of FW cells subjected to 70 mol m^?3 NaCl, which raised Na:Ca from 10: 1 to 700: 1 and the external osmotic pressure from 0.024 to 0.402 MPa, died within 6 d. Death was associated with the loss of Na/K selectivity, H⁺ -pump activity and turgor. Restoration of Na:Ca to 10:1 in high Na⁺ medium with CaCl₂ ensured 100% survival and maintained H⁺-pump activity and Na/K selectivity of FW cells. Turgor was regulated within 3 d with net uptake of Na ⁺, K⁺ and Cl^? in the vacuolc. Mg²⁺ was not as effective as Ca²⁺ in enhancing survival or maintaining H⁺ -pump activity and Na/K selectivity of FW cells in the presence of elevated Na⁺. However, turgor was regulated within 3 d by accumulation of Cl^? and an unknown cation in the vacuole. All AWW cells subjected to an increase of 70 mol m ^?3 NaCl, which raised Na: Ca from 16:1 to 25: 1 and the external osmotic pressure from 0.915 to 1.22 MPa, survived and maintained H ⁺ -pump activity. Turgor was regulated within 6d by accumulating Na ⁺, K⁺ and Cl^? in the vacuole. All AWW cells subjected to 70molm^?3 NaCl in a medium in which Na:Ca was equal to 700:1 survived and maintained H ⁺ -pump activity, but showed loss of Na/K selectivity. Turgor was regulated with an unknown osmoticum(a) within 6 d.     

The interaction of chloride with the sulfate transport system of ehrlich ascites tumor cells

The effect of Cl^? on SO₄^?2 efflux was studied in both Cl^?-containing and Cl^?-free ascites tumor cells loaded with ³⁵SO₄^?2 to test the hypothesis that Cl^?-SO₄^?2 exchange is mediated by the same mechanism responsible for SO₄^?2-self exchange. The addition of Cl^?-free, ³⁵SO₄^?2 loaded cells to a SO₄^?2-free, Cl^? medium results in: (1) SO₄^?2 efflux that is dependent on the extracellular Cl^? concentration (Km = 4.85 mM; k_e = 0.048 min^?1 at 50 mM Cl^?) and (2) net Cl^?-uptake that exceeds SO₄^?2 loss. Both SITS (4-acetamido-4′-isothiocyanostilbene-2,2′-disulfonate) and ANS (1-anilino-8-napthalene sulfonate) inhibit SO₄^?2 efflux but are without effect on Cl^? uptake. The addition of Cl^?-containing, ³⁵SO₄^?2 loaded cells to a SO₄^?2-free, C1^? medium results in: (1) a slight gain in cellular Cl^? and (2) k efor SO₄^?2 efflux identical to that for Cl^?-free cells. The results are compatible with the suggestion that: (1) Cl^? interacts with a membrane component responsible for transmembrane SO₄^?2 movement; (2) Cl^? interaction stimulates the rate of unidirectional SO₄^?2 efflux from cells initially free of Cl^? as well as the rate of SO₄^?2 turnover in cells maintained in the steady state with respect to Cl^? and SO₄^?2; and (3) in the case of cells initially free of Cl^?, the Cl^?-SO₄^?2 pathway represents only a small fraction of the total unidirectional Cl^?-influx the remainder being compatible with the electroneutral accumulation of NaCl and KCl.     

Changes in K+, Cl− and P contents in stomata of Zea mays leaves exposed to different light and CO2 levels

Maize plants (Zea mays L. hybrid INRA 508) were placed under controlled conditions of light and CO₂ partial pressure. The K⁺, Cl^? and P contents were then determined by X-ray microanalysis in the bulbous end of guard cells and in the center of subsidiary cells. The results were interpreted in connection with the stomatal conductance at the time of sampling. In normal air, the K⁺ and Cl^? contents in guard cells only rose from a light threshold of about 300 μmol m^?2 s^?1 at which stomata were already largely open. At 600 μmol m^?2 s^?1, the K⁺ and Cl^? levels in guard cells attained values that were 3- and 8-fold greater, respectively, than the values observed in darkness. The K⁺ and Cl^? contents in the subsidiary cells remained quite constant irrespective of the light conditions. CO₂-free air in darkness induced a significant K⁺ influx towards guard and subsidiary cells. Under light and in CO₂-free air, the K⁺ and Cl^? contents dramatically increased in the guard cells, but slightly decreased in the subsidiary cells. Thus, when subjected to strong light in CO₂-free air, the K⁺ and Cl^? contents in the subsidiary cells were approximately equal to those measured in normal air conditions. In the guard cells, stomatal opening was associated with a marked shift of the Cl^?/K⁺ ratio – from 0.3 for closed stomata to ca 1 for fully open stomata. This could imply a slow change in the nature of the principal counterion accompanying K⁺ during stomatal opening. The content of P in guard cells appeared, in contrast to that of K⁺ and Cl^?, to be practically independent of stomatal aperture.     

Kinetics of chloride transport in the cyanobacterium Synechococcus R-2 (Anacystis nidulans, S. leopoliensis) PCC 7942

The kinetics of the light-driven Cl^? uptake pump of Synechococcus R-2 (PCC 7942) were investigated. The kinetics of Cl^? uptake were measured in BG-11 medium (pH_o, 7·5; [K⁺]_o, 0·35 mol m^?3; [Na⁺]_o, 18 mol m^?3; [Cl^?]_o, 0·508 mol m^?3) or modified media based on the above. Net³⁶Cl^? fluxes (?Cl^?_o,i) followed Michaelis-Menten kinetics and were stimulated by Na⁺ [18 mol m^?3 Na⁺ BG-11 ?Cl^?_max= 3·29±0·60 (49) nmol m^?2 s^?1 versus Na⁺-free BG-11 ?Cl^?_max= 1·02±0·13 (54) nmol m^?2 s^?1] but the Km was not significantly different in the presence or absence of Na⁺ at pH_o 10; the Km was lower, but not affected by the presence or absence of Na⁺ [Km = 22·3±3·54 (20) mmol m^?3]. Na⁺ is a non-competitive activator of net ?Cl^?_o,i. High [K⁺]_o (18 mol m^?3) did not stimulate net ?Cl^?_o,i or change the Km in Na⁺-free medium. High [K⁺]_o (18 mol m^?3) added to Na⁺ BG-11 medium decreased net ?Cl^?_o,i [18 mol m^?3K⁺ BG-11; ?Cl^?_max= 2·50±0·32 (20) nmol m^?2 s^?1 versus BG-11 medium; ?Cl^?_max= 3·35±0·56 (20) nmol m^?2 s^?1] but did not affect the Km 55·8±8·100 (40) mmol m^?3]. Na⁺-stimulation of net ?Cl^?_o,i followed Michaelis-Menten kinetics up to 2–5 mol m^?3 [Na⁺]_o but higher concentrations were inhibitory. The Km for Na⁺-stimulation of net ?Cl^?_o,i [K_1/2(Na⁺)] was different at 47 mmol m^?3 [Cl^?]_o (K_1/2[Na⁺] = 123±27 (37) mmol m^?3]. Li⁺ was only about one-third as effective as Na⁺ in stimulating Cl^? uptake but the activation constant was similar [K_1/2(Li⁺) = 88±46 (16) mmol m^?3]. Br^? was a competitive inhibitor of Cl^? uptake. The inhibition constant (Ki) was not significantly different in the presence and absence of Na⁺. The overall Ki was 297±23 (45) mmol m^?3. The discrimination ratio of Cl^? over Br^? (δCl^?/δBr^?) was 6·38±0·92 (df = 147). Synechococcus has a single Na⁺-stimulated Cl^? pump because the Km of the Cl^? transporter and its discrimination between Cl^? and Br^? are not significantly different in the presence and absence of Na⁺. The Cl^? pump is probably driven by ATP.     

Selenium-containing tRNAs from Clostridium sticklandii. Cochromatography of seleno-tRNA I with l-valyl-tRNA

It has been previously shown that Clostridium sticklandii specifically synthesized three readily separable ⁷⁵Se-labeled tRNAs, designated seleno-tRNAs I, II and III, and the partially purified seleno-tRNA II cochromatographed with l-prolyl-tRNA on DEAE-Sephadex A-50 (Chen, C.S. and Stadtman, T.C. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 1403–1407). In the present study a highly purified ⁷⁵Se-labeled tRNA I was obtained by chromatography on benzoylated DEAE-cellulose, DEAE-Sephadex A-50 and Sepharose 4B. The ⁷⁵Se-labeled tRNA I cochromatographed with an l-valine-accepting species on DEAE-Sephadex A-50 and Sepharose 4B. Addition of a 285-fold molar excess of unlabeled l-valine to the l-valine acceptor activity assay mixture markedly decreased the amount of l-[¹⁴C]valine bound to seleno-tRNA I.     

The cyanobacterium Synechococcus R-2 (Anacystis nidulans, S. leopoliensis) PCC 7942 has a sodium-dependent chloride transporter

Synechococcus R-2 (PCC 7942) actively accumulated Cl^? in the light and dark, under control conditions (BG-11 media: pH_o, 7·5; [Na⁺]_o, 18 mol m^?3; [Cl^?]_o, 0·508 molm^?3). In BG-11 medium [Cl^?], was 17·2±0·848 mol m^?3 (light), electrochemical potential of Cl^? (ΔμCl^?_i,o) =+211±2mV; [Cl^?]_i= 1·24±0·11 mol m^?3(dark), ΔμCl^?_i,o=+133±4mV. Cl^? fluxes, but not permeabilities, were much higher in the light: ?Cl^?_i,o= 4·01±5·4 nmol m^?2 s^?1, ^PCl^?_i,o= 47±5pm s^?1 (light); ?Cl^?_i,o= 0·395±0·071 nmol m^?2 s^?1, _PCl^?_i,o= 69±14 pm s^?1 (dark). Chloride fluxes are inhibited by acid pH_o (pH_o 5; ?Cl^?_i,o= 0·14±0·04 nmol m^?2 s^?1); optimal at pH_o 7·5 and not strongly inhibited by alkaline pH_o (pH_o 10; ?Cl^?1_i,o= 1·7±0·14 nmol m^?2 s^?1). A Cl^?_in/2H⁺_in coporter could not account for the accumulation of Cl^? alkaline pH_o. Permeability of Cl^? is very low, below 100pm s^?1 under all conditions used, and appears to be maximal at pH_o 7·5 (50–70 pm s^?1) and minimal in acid pH_o (20pm s^?1). DCCD (dicyclohexyl-carbodiimide) inhibited ?Cl^?_i,o in the light about 75% and [Cl^?]_i fell to 2·2±0·26 (4) mol m^?3. Valinomycin had no effect but monensin severely inhibited Cl^? uptake ([Cl^?]_i= 1·02±0·32 mol m^?3; ?Cl^?_i,o= 0·20±0·1 nmol m^?2 s^?1). Vanadate (200 mmol m^?3) accelerated the Cl^? flux (?Cl^?_i,o= 5·28±0·64 nmol m^?2 s^?1) but slightly decreased accumulation of Cl^? ([Cl^?], = 13·9±1·3 mol m^?3) in BG-11 medium but had no significant effect in Na⁺-free media. DCMU (dichlorophenyldimethylurea) did not reduce [Cl^?], or ?Cl^?_i,o to that found in the dark ([Cl^?]_i= 8·41±0·76 mol m^?3; ?Cl^?_i,o= 2·06±0·36 nmol m^?2 s^?1). Synechococcus also actively accumulated Cl^? in Na⁺-free media, [Cl^?]_i was lower but ΔΨ_i,o hyperpolarized in Na⁺-free media and so the ΔμCl^?_i,o was little changed ([Cl^?]_i= 7·98±0·698 mol m^?3; ΔμCl^?_i,o=+203±3 mV). Net Cl^? uptake was stimulated by Na⁺; Li⁺ acted as a partial analogue for Na⁺. Synechococcus has a Na⁺ activated Cl^? transporter which is probably a primary 2Cl^?/ATP pump. The Cl^? pump is voltage sensitive. ΔμCl^?_i,o is directly proportional to ΔΨ_i,o(P»0·01%): ΔμCl^?_i,o= -1·487 (±0·102) ×ΔΨ_i,o, r= -0·983, n= 31. The ΔμCl^?_i,o increased (more positive) as the Δμ_i,o became more negative. The ΔμCl^?_i,o has no known function, but might provide a driving force for the uptake of micronutrients.     

Interactions between growth, Cl− and Na+ uptake, and water relations of plants in saline environments. I. Slightly vacuolated cells

Abstract. Slightly vacuolated cells, i.e. microalgae and meristematic cells of vascular plants, maintain low Cl^? and Na⁺ concentrations even when exposed to a highly saline environment. The factors regulating the internal ion concentration are the relative rate of volume expansion, the membrane permeability to ions, the electrical potential, and the active ion fluxes. For ion species which are not actively transported, a formula is developed which relates the internal concentration to the rate of expansion of cell volume, the permeability of membranes to that ion, and the electrical potential. For example, when the external concentration of Cl^? is high, and Cl^? influx is probably mainly passive, the formula predicts that rapid growth keeps the internal Cl^? concentration lower than that in a non-growing cell with the same electrical potential; this effect is substantial if the plasmalemma has a low permeability to Cl^?. For ion species which are actively transported, the rate of pumping must be considered. For instance Na⁺ concentrations are kept low mainly by an efficient Na⁺ extrusion pump which works against the electric field across the membrane. The requirement for Na⁺ extrusion is related to the external Na⁺ concentration, the rate of expansion of cell volume, the membrane permeability, and the electrical potential. It is possible that microalgae have a more positive electrical potential than many other plant cells; if so, requirements for high rates of active Na⁺ extrusion will be lower. The required rates of Na⁺ extrusion are lower during rapid growth, provided that the permeability of the plasmalemma to Na⁺ is low. The energy required for the regulation of Cl^? and Na⁺ concentrations is low, especially in rapidly expanding cells where Na⁺ extrusion requires only 1–2% of the energy normally produced in respiration. The exclusion of these ions, however, must be accompanied by the synthesis of enough organic compounds to provide adequate osmotic solutes for the increases in volume accompanying growth. This process reduces the substrates available for respiration and synthesis of cell constituents, but the reduction is not prohibitively large—even for cells growing in 750 mol m^?3 NaCl, the carbohydrate accumulated as osmotic solute is only 10% of that consumed in respiration.     

Identification of quantitative trait loci for ion homeostasis and salt tolerance in barley (Hordeum vulgare L.)

Ion homeostasis is considered to be one of the most important mechanisms underlying salt stress tolerance. We used the Steptoe × Morex barley doubled haploid population to screen for genetic variation in response to salinity stress at an early development stage in a hydroponics system, focusing on ion homeostasis. Salinity induced a strong adverse effect on growth of the parents and their derived population, with Steptoe as the more tolerant parent. Steptoe maintained higher concentrations of K⁺, Na⁺ and Cl^? in the roots and a similar shoot/root ion ratio (<1) under stress conditions compared to control conditions. In contrast, Morex had higher concentrations of these ions in the shoots under stress and a doubled shoot/root ion ratio relative to control conditions, indicating that salt exclusion might contribute to the higher tolerance of Steptoe. Correlation and path analysis demonstrated that shoot Cl^? contents most strongly affected salt tolerance and suggest that both Na⁺ and Cl^? contents are important for salinity stress tolerance in barley. We identified 11 chromosomal regions involved in the control of the variation observed for salt tolerance and various salt stress response traits, including Na⁺, Cl^? and K⁺ contents in shoots. Two specific regions on chromosomes 2H and 3H were found controlling ion contents and salt tolerance, pointing to genes involved in ion homeostasis that contribute to salt tolerance.