Basis of the Relationship between Ash Content in the Flag Leaf and Carbon Isotope Discrimination in Kernels of Durum Wheat

The relationship between ash content and carbon isotope discrimination () was studied in durum wheat (Triticum durum Desf.) grown in a Mediterranean region (Northwest Syria) under three different water regimes (hereafter referred to as environments). In two of these environments, 144 genotypes were cultivated under rain-fed conditions. In the third environment, 125 genotypes were cultivated under irrigation. Ash content was measured in the flag leaf about 3 weeks after anthesis, whereas was analysed in mature kernels. Total transpiration of the photosynthetic tissues of the culm contributing, from heading to maturity, to the filling of kernels was also estimated. Leaf ash content, expressed either on dry matter or leaf area basis or as total ash per blade, correlated positively (p< 0.001) with in the three environments. However, this relationship was not the result of a positive correlation across genotypes between and tissue water content. Moreover, only a small part of the variation in across genotypes was explained by concomitant changes in ash content. When all genotypes across the three environments were plotted, and ash content followed a non-linear relationship (r ² = 74), with tending to a plateau as the ash content increased. However, for the set of genotypes and environments combined, total ash content per leaf blade was positively and linearly related (r ² = 0.76) with the accumulated culm transpiration. The non-linear nature of the relationship between ash content and is sustained by the fact that culm transpiration also showed a non-linear relationship with kernel . Therefore, differences in leaf ash content between environments, and to a lesser extent between genotypes, seem to be brought about by variations in accumulated transpiration during grain formation.     

Comparative water-use efficiency of Sporobolus arabicus and Leptochloa fusca and its relation with carbon-isotope discrimination under semi-arid conditions

Water-use efficiency (WUE) of Leptochloa fusca (L.) Kunth (Kallar grass) and Sporobolus arabicus Boiss. was determined under different soil moisture regimes. Plants grown in lysimeters were subjected to three soil moisture regimes, viz. well-watered (100%), medium-watered (75%), and low-watered (50%) of total available water (TAW). The soil moisture was restored on alternate days by adding the required volume of water on the basis of neutron moisture meter readings taken from neutron access tubes installed in each lysimeter. The grasses were harvested after suitable intervals (4 months) to obtain maximum biomass. Leaf samples collected at each harvest were analyzed for carbon-isotope discrimination (¹³C) with an isotope ratio (¹³C/¹²C) mass spectrometer. Results indicated significant differences in WUE of both grasses subjected to different water regimes. Sporobolus arabicus showed higher WUE than Kallar grass. However, Kallar grass showed better value of yield response factor (k _y = 0.649) compared with Sporobolus (k _y = 1.06) over the entire season. The data confirm that these grasses can be grown successfully in water-limited environments by selecting an optimum soil moisture level for maximum biomass production. The mean carbon-isotope discrimination (¹³C) of Kallar grass (–14.4) and Sporobolus (–12.8) confirm that both are C₄ plants. The carbon-isotope discrimination () was significantly and negatively correlated with WUE of the two species studied. The results of the present study confirm that ¹³C or of leaves can be used as good predictor of WUE in some C₄ plants.     

Anaerobic biosynthesis of unsaturated fatty acids in the cyanobacterium,Oscillatoria limnetica

The mechanism for synthesis of monounsaturated fatty acids under aerobic and anaerobic conditions was studied in the facultative anaerobic cyanobacterium, Oscillatoria limnetica. The hexadecenoic acid (C161) of aerobically grown O. limnetica was shown to contain both the 7 (79%) and 9 (21%) isomers, while the octadecenoic (C181) acid was entirely the 9 acid. Incorporation of [2-¹⁴C] acetate into the fatty acids under aerobic conditions resulted in synthesis of the 7 and 9 C161 and the 9 C181. Synthesis of unsaturated fatty acids in the presence of DCMU required sulfide. Anaerobic incubations in the presence of DCMU and sulfide (less than 0.003% atmospheric oxygen) resulted in a two-fold increase in monounsaturated fatty acids of both 7 and 9 C161 and 9 and 11 C181. The synthesis of these isomers is characteristic of a bacterialtype, anaerobic pathway.Abbreviations DCMU 3(3,4-dichlorophenyl)-1,1-dimethylurea - MFA monounsaturated fatty acid     

The membrane potential in whole cells of Methanobacterium thermoautotrophicum

of whole cells of Methanobacterium thermoautotrophicum was estimated under varying conditions using an electrode sensitive to the lipophilic cation tetraphenylphosphonium chloride (TPP⁺). Since was found to be extremely sensitive to air, a special reaction vessel was developed to maintain strict anaerobiosis. The cells took up TPP⁺ under energization by H₂ and CO₂ thus allowing to calculate the from the distribution of TPP⁺ inside and outside the cells. The unspecific uptake of deenergized cells was around 10% of the total uptake of energized cells. TPP⁺ itself slightly diminished the , but had no effect on the formation of methane. Typical values of were in the range of-150 to-200 mV. showed a quantitative dependence on both the electron donor H₂ and the electron acceptor CO₂. NaCl stimulated the extent of the , whereas KCl slightly diminished it. Valinomycin resulted in a linear decline of , whereas the methane production rate was only slightly affected. In contrast, monensin reduced both methanogenesis and .Abbreviations pmf proton motive force - membrane potential - TPP⁺ tetraphenylphosphonium (chloride salt) - TPMP⁺ triphenylmethylphosphonium (chloride salt, if not otherwise indicated) - d.w. dry weight - t _d doubling time - PVC polyvinylchloride     

The electrochemical proton gradient and its influence on citrate uptake in tonoplast vesicles of Hevea brasiliensis

The relationship between the electrochemical proton gradient, _H+ ^– , and citrate transport has been studied in tonoplast vesicles from Hevea brasiliensis (the rubber tree). Vesicles were generated from lyophilized samples of fresh vacuoles obtained from the latex sap. Methylamine was used to measure intravesicular pH and lipophilic ions to determine the electrical potential difference () across the tonoplast. When incubated at pH 7.5 in the absence of ATP, the tonoplast vesicles showed a pH of 0.6 units (interior acid) and a of about-100 mV (interior negative). This potential is thought to be made up of contributions from an H⁺ diffusion potential, diffusion potentials from other cations and a Donnan potential arising from the presence of internal citrate. In the presence of 5 mol m^-3 MgATP the pH was increased to about 1.0 unit and the to about-10 mV. Under these conditions the proton-motive force ( _{p H+} ^– /F) became positive and reached +50 mV. These effects were specific to MgATP (ADP and Mg²⁺ having no significant effect) and were prevented by the protonophore p-trifluoromethoxycarbonylcyanidephenylhydrazone (FCCP). Citrate uptake by the vesicles was markedly stimulated by MgATP; ADP and Mg²⁺ again had no effect. Nigericin greatly increased pH and this was associated with a large increase in citrate accumulation. The results indicate that the vesicle membrane possesses a functional H⁺-translocating ATPase. The _H+ ^– generated by this ATPase can be used to drive citrate uptake into the vesicles. The properties of the tonoplast vesicles are compared with those of the fresh latex vacuoles.Abbreviations _H+ ^– electrochemical proton gradient - electrical potential difference across membrane - p proton-motive force ( _H+ ^– /F) - FCCP p-trifluoromethoxycarbonylcyanidephenylhydrazone - TPMP⁺ triphenylmethylphosphonium ion     

Estimation of Membrane Potential Δψ in Reconstituted Plasma Membrane Vesicles Using a Numerical Model of Oxonol VI Distribution

A model of membrane potential-dependent distribution of oxonol VI to estimate the electrical potential difference across Schizosaccharomyces pombe plasma membrane vesicles (PMV) has been developed. was generated by the H⁺-ATPase reconstituted in the PMV. The model treatment was necessary since the usual calibration of the dye fluorescence changes by diffusion potentials (K⁺ + valinomycin) failed. The model allows for fitting of fluorescence changes at different vesicle and dye concentrations, yielding in ATP-energized PMV of 80 mV. The described model treatment to estimate may be applicable for other reconstituted membrane systems.     

Regulation of proline catabolism in Pseudomonas aeruginosa PAO

Mutants of Pseudomonas aeruginosa deficient in the utilization of l-proline as the only carbon and nitrogen source have been found to be defective either in proline dehydrogenase activity or in both proline dehydrogenase and ¹-pyrroline-5-carboxylate dehydrogenase activities of the bifunctional proline degradative enzyme. The latter type of mutants was unable to utilize l-ornithine, indicating that a single ¹-pyrroline-5-carboxylate dehydrogenase activity is involved in the degradation of ornithine and proline. Proline dehydrogenase and ¹-pyrroline-5-carboxylate dehydrogenase activities were strongly and coordinately induced by proline. It was excluded that ¹-pyrroline-5-carboxylate acted as an inducer of the bifunctional enzyme and it was shown that the low level induction observed during growth on ornithine was due to the intracellular formation of proline. The formation of the proline degradative enzyme was shown to be subject to catabolite repression by citrate and nitrogen control.Abbreviations EMS Ethylmethane sulfonate - NG N-methyl-N-nitro-N-nitrosoguanidine - P Minimal medium P - Pro-DH Proline dehydro-genase - P5C ¹-Pyrroline-5-carboxylate - P5C-DH ¹-Pyrroline-5-carboxylate dehydrogenase     

Thermodynamics of Mn2+-binding to goat α-lactalbumin

By means of reaction calorimetry we measured the apparent enthalpy change, H^app, of the binding of Mn²⁺-ions to goat -lactalbumin as a function of temperature. The observed H^app can be written as the sum of contributions resulting from a conformational and a binding process. In combination with the thermal unfolding curve of goat -lactalbumin, we succeeded in separating the complete set of thermodynamic parameters (H, G, S, C_p) into the binding and conformational contributions. By circular dichroism we showed that NH ₄ ⁺ -ions, upon binding to bovine a-lactalbumin, induce the same conformational change as do Na⁺ and K⁺: the binding constant equals 98 ± 9 M^–1.Abbreviations BLA bovine -lactalbumin - GLA goat -lactalbumin - HLA human -lactalbumin - CD circular dichroism Offprint requests to: H. Van DaelDeceased     

Measurements of electrical potential differences across yeast plasma membranes with microelectrodes are consistent with values from steady-state distribution of tetraphenylphosphonium inPichia humboldtii

Summary Electrical potential differences across the plasma membrane () of the yeastPichia humboldtii were measured with microelectrodes (filled with 0.1m KCl) inserted into cells immobilized in microfunnels. The registered signals were reproducible and stable for several minutes. On attainment of stable reading for the specific membrane resistanceR _sp was determined by applying square-current pulses to the preparation. Both andR _sp were pH dependent and displayed equal but opposite deflection, reaching its maximal value of –88±9 mV (n=13) andR _sp its minimal value of 10 k·cm² (maximal conductance) at pH 6.5. Uncouplers and the polyene antibiotic nystatin depolarized the cells, decreasing to –21±15 mV (n=10) with concomitant decrease ofR _sp. Comparison of values from microelectrode measurements with those calculated from the steady-state distribution of tetraphenylphosphonium ions agreed within 10 mV under all physiological conditions tested, except at pH values above 7.0. During microelectrode insertion transient voltage signals (a few msec long) were detected by means of an oscilloscope. These voltage signals were superimposed on the stable recordings described above. These short voltage signals disappeared in uncoupled cells. The closely related values obtained by two independent methods (direct measurements with microelectrodes and calculation from steady-state distribution of a lipophilic cation) provide evidence that these values reffect the true membrane potential of intact cells.     

A nontoxicPseudomonas exotoxin a induces active immunity and passive protective antibody againstPseudomonas exotoxin a intoxication

Pseudomonas exotoxin A (PE) is one of the most potent cytotoxic agents produced byPseudomonas aeruginosa. In this study, we examined the possibility of using PE with a deletion of 38 carboxyl-terminal amino acid residues, designated PE(576–613), for active immunization against PE-mediated disease. We first examined the toxic effects of PE and PE(576–613) on 5- and 9-week-old ICR mice. The results show that the subcutaneous administration of PE(576–613) at a dose of 250 µg was still nontoxic to 5- and 9-week-old ICR mice, while native PE was lethal at a dose of 0.5 and 1 µg, respectively. PE(576–613) was then used to immunize ICR mice. The minimum dose of PE(576–613) that could effectively induce anti-PE antibodies in 5- and 9-week-old ICR mice was found to be 250 ng. However, immunization with 250 ng PE(576–613) failed to protect the immunized mice from a lethal dose of PE. The effective immunization dose of PE(576–613) that could protect mice against a 2 µg PE challenge was found to be 15 µg. In addition, sera obtained from PE(576–613)-immunized ICR mice were able to neutralize PE intoxication and effectively protect mice from PE. Thus, PE(576–613) may be used as an alternative route to new PE vaccine development.     

Protonmotive force driven 6-deoxyglucose uptake by the oral pathogen,Streptococcus mutans Ingbritt

Streptococcus mutans Ingbritt was grown in glucose-excess continuous culture to repress the glucose phosphoenolpyruvate phosphotransferase system (PTS) and allow investigation of the alternative glucose process using the non-PTS substrate, (³H) 6-deoxyglucose. After correcting for non-specific adsorption to inactivated cells, the radiolabelled glucose analogue was found to be concentrated approximately 4.3-fold intracellularly by bacteria incubated in 100 mM Tris-citrate buffer, pH 7.0. Mercaptoethanol or KCl enhanced 6-deoxyglucose uptake, enabling it to be concentrated internally by at least 8-fold, but NaCl was inhibitory to its transport. Initial uptake was antagonised by glucose but not 2-deoxyglucose. Evidence that 6-deoxyglucose transport was driven by protonmotive force (p) was obtained by inhibiting its uptake with the protonophores, 2,4-dinitrophenol, carbonylcyanide m-chlorophenylhydrazine, gramicidin and nigericin, and the electrical potential difference () dissipator, KSCN. The membrane ATPase inhibitor, N,N¹-dicyclohexyl carbodiimide, also reduced 6-deoxyglucose uptake as did 100 mM lactate. In combination, these two inhibitors completely abolished 6-deoxyglucose transport. This suggests that the driving force for 6-deoxyglucose uptake is electrogenic, involving both the transmembrane pH gradient (pH) and . ATP hydrolysis, catalysed by the ATPase, and lactate excretion might be important contributors to pH.Abbreviations DNP 2,4-dinitrophenol - CCCP carbonylcyanide m-chlorophenylhydrazone - DCCD N,N¹-dicyclohyxyl carbodiimide - p protonmotive force - pH transmembrane pH gradient - transmembrane electrical potential difference     

Preparation of a series of sulfated tetrasaccharides from shark cartilage chondroitin sulfate D using testicular hyaluronidase and structure determination by 500 MHz1H NMR spectroscopy

Six tetrasaccharide fractions were isolated from shark cartilage chondroitin sulfate D by gel filtration chromatography followed by HPLC on an amine-bound silica column after exhaustive digestion with testicular hyaluronidase. Their structures were determined unambiguously by one- and two-dimensional 500 MHz¹H NMR spectroscopy in conjunction with HPLC analysis of chondroitinase AC-II digests of the tetrasaccharides. One fraction was found to contain two tetrasaccharide components. All the seven tetrasaccharides shared the common core structure GlcA1-3GalNAc1-4GlcA1-3GalNAc with various sulfation profiles. Four were disulfated comprising of two monosulfated disaccharide units GlcA1-3GalNAc(4-sulfate) and/or GlcA1-3GalNAc(6-sulfate), whereas the other three were hitherto unreported trisulfated tetrasaccharides containing a disulfated disaccharide unit GlcA(2-sulfate)1-3GalNAc(6-sulfate) and a monosulfated disaccharide unit GlcA1-3GalNAc(4-or 6-sulfate). These sulfated tetrasaccharides were demonstrated to serve as appropriate acceptor substrates for serum -N-acetylgalactosaminyltransferase, indicating their usefulness as authentic oligosaccharide substrates or probes for the glycobiology of sulfated glycosaminoglycans.Abbreviations NFU National formulary unit - COSY correlation spectroscopy - HOHAHA homonuclear Hartmann-Hahn - 1D or 2D one- or two-dimensional - IdoA l-iduronic acid - GlcA d-gluco-4-enepyranosyluronic acid - Di-0S GlcA1-3GalNAc - Di-4S GlcA1-3GalNAc(4-sulfate) - Di-4S GlcA1-3GalNAc(4-sulfate) - Di-6S GlcA1-3GalNAc(6-sulfate) - Di-6S GlcA1-3GalNAc(6-sulfate) - Di-diS _d GlcA(2-sulfate)1-3GalNAc(6-sulfate) - Di-diS_E GlcA1-3GalNAc(4, 6-disulfate) - U G, U, 2S, 4S, and 6S represent GlcA, GalNAc, GlcA, 2-O-sulfate, 4-O-sulfate, and 6-O-sulfate, respectively     

Amino acid deletions in loop C of the chlorophyll a-binding protein CP47 alter the chloride requirement and/or prevent the assembly of photosystem II

The chlorophyll a-binding protein CP47 directs excitation energy to the reaction center of photosystem II (PSII) during oxygenic photosynthesis and has additional structural and functional roles associated with the PSII water-oxidizing complex. Oligonucleotide-directed mutagenesis was employed to study loop C of CP47 (approximately Trp-162 to Gly-197) which faces the thylakoid lumen. Five short amino acid deletion strains, (S169–P171), (Y172–G176), (G176–P180), (E184–A188) and (F190–N194), were created that span this domain. The deletion between Gly-176 and Pro-180, located around the middle of loop C, produced an obligate photoheterotroph that could not assemble functional PSII centers. The deletions in mutants (S169–P171) and (Y172–G176) reduced PSII levels to 20% of the control and thus impaired photoautotrophic growth. In contrast, mutants (E184-A188) and (F190–N194) were photoautotrophic even though the number of photosystems was decreased by 50%. All PSII complexes assembled in the deletion strains had an increased susceptibility to photoinactivation and deletion of Glu-184 to Ala-188 prevented photoautotrophic growth under chloride-limiting conditions. Furthermore, the removal of the extrinsic PSII-O, PSII-U and PSII-V proteins from mutants (E184–A188) and (F190–N194) reduced the rates of oxygen evolution and, in the strains lacking either the PSII-O or PSII-V proteins, also increased the photoautotrophic doubling times. These effects were greater in mutant (E184–A188) than in mutant (F190–N194) and the order of importance for the removal of the extrinsic proteins was found to be PSII-V PSII-O > PSII-U.     

D-Gluconate is an alternative growth substrate for cultivation of Schizosaccharomyces pombe mutants

Schizosaccharomyces pombe cells grow on d-gluconate as the sole carbon and energy source. d-Gluconate is taken up in symport with protons by a specific symporter, pH being the sole driving force. d-Gluconate uptake is independent of the sugar transporting system (e.g. for d-glucose) and of . The carrier is expressed constitutively, and its activity is not subject to glucose repression. Hence, d-gluconate is a suitable carbon and energy source for growth, when d-glucose or other hexoses have to be eliminated e.g. for selection of mutants deficient in hexose transport.Abbreviations 2-DG 2-deoxy-d-glucose - CCCP carbonylcyanide m-chlorophenylhydrazone - pH pH-gradient - electrical potential difference across the plasma membrane - SD standard deviation - SEM standard error of the mean - TPP⁺ tetraphenylphosphonium     

Energetic basis of cadmium toxicity in Staphylococcus aureus

In washed cells of cadmium-sensitive Staphylococcus aureus 17810S oxidizing glutamate, initial Cd²⁺⁺⁺ influx via the Mn²⁺ porter down membrane potential () was fast due to involvement of energy generated by two proton pumps—the respiratory chain and the ATP synthetase complex working in the hydrolytic direction. Such an unusual energy drain for rapid initial Cd²⁺ influx is suggested to be due to a series of toxic events elicited by Cd²⁺ accumulation down generated via the redox proton pump: (i) strong inhibition of glutamate oxidation accompanied by a decrease of electrochemical proton gradient ( _H ⁺) formation via the respiratory chain, (ii) automatic reversal of ATP synthetase from biosynthetic to hydrolytic mode, which was monitored by a decrease of _H ⁺-dependent ATP synthesis, (iii) acceleration of the initial Cd²⁺ influx down generated the reversed ATP synthetase, the alternative proton pump hydrolyzing endogenous ATP. The primary, cadmium-sensitive targets in strain 17810S seem to be dithiols located in the cytoplasmic glutamate oxidizing system, prior to the membrane-embedded NADH oxidation system. Inhibition by Cd²⁺ of _H ⁺-dependent ATP synthesis and of pH gradient (pH)-linked [¹⁴C]glutamate transport is a secondary effect due to cadmium-mediated inhibition of _H ⁺ generation at the cytoplasmic level. In washed cells of cadmium-resistant S. aureus 17810R oxidizing glutamate, Cd²⁺ accumulation was prevented due to activity of the plasmid-coded Cd²⁺ efflux system. Consequently, _H ⁺-producing and -requiring processes were not affected by Cd²⁺.     

Different Ionic Specificities of ATP Synthesis in Extremely Alkaliphilic Sulfate-Reducing and Acetogenic Bacteria

Ionic specificity of oxidative phosphorylation was studied in Natroniella acetigenaand Desulfonatronum lacustre, which are new alkaliphilic anaerobes that were isolated from soda lakes and have a pH growth optimum of 9.5–9.7. The ability of their cells to synthesize ATP in response to the imposition of artificial pH⁺and pNa⁺gradients was studied. As distinct from other marine and freshwater sulfate reducers and extremely alkaliphilic anaerobes, D. lacustreuses a Na⁺-translocating ATPase for ATP synthesis. The alkaliphilic acetogen N. acetigena, which develops at a much higher Na⁺concentration in the medium, generated primary pH⁺for ATP synthesis. Thus, the high Na⁺concentrations and alkaline pH values typical of soda lakes do not predetermine the type of bioenergetics of their inhabitants.     

Reverse genetic analysis of the glutathione metabolic pathway suggests a novel role of<Emphasis Type="Italic"> PHGPX</Emphasis> and<Emphasis Type="Italic"> URE2</Emphasis> genes in aluminum resistance in<Emphasis Type="Italic"> Saccharomyces cerevisiae</Emphasis>

We have taken a systematic genetic approach to study the potential role of glutathione metabolism in aluminum (Al) toxicity and resistance, using disruption mutants available in Saccharomyces cerevisiae. Yeast disruption mutants defective in phospholipid hydroperoxide glutathione peroxidases (PHGPX; phgpx1 , phgpx2 , and phgpx3), were tested for their sensitivity to Al. The triple mutant, phgpx1 /2/3, was more sensitive to Al (55% reduction in growth at 300 M Al) than any single phgpx mutant, indicating that the PHGPX genes may collectively contribute to Al resistance. The hypersensitivity of phgpx3 to Al was overcome by complementation with PHGPX3, and all PHGPX genes showed increased expression in response to Al in the wild-type strain (YPH250), with maximum induction of approximately 2.5-fold for PHGPX3. Both phgpx3 and phgpx1/2/3 mutants were sensitive to oxidative stress (exposure to H₂O₂ or diamide). Lipid peroxidation was also increased in the phgpx1/2/3 mutant compared to the parental strain. Disruption mutants defective in genes for glutathione S-transferases (GSTs) (gtt1 and gtt2), glutathione biosynthesis (gsh1 and gsh2), glutathione reductase (glr1) and a glutathione transporter (opt1) did not show hypersensitivity to Al relative to the parental strain BY4741. Interestingly, a strain deleted for URE2, a gene which encodes a prion precursor with homology to GSTs, also showed hypersensitivity to Al. The hypersensitivity of the ure2 mutant could be overcome by complementation with URE2. Expression of URE2 in the parental strain increased approximately 2-fold in response to exposure to 100 M Al. Intracellular oxidation levels in the ure2 mutant showed a 2-fold (non-stressed) and 3-fold (when exposed-to 2 mM H₂O₂) increase compared to BY4741; however, the ure2 mutant showed no change in lipid peroxidation compared to the control. The phgpx1/2/3 and ure2 mutants both showed increased accumulation of Al. These findings suggest the involvement of PHGPX genes and a novel role of URE2 in Al toxicity/resistance in S. cerevisiae.Communicated by D.Y. Thomas     

Evidence that plasma membrane electrical potential is required for vesicular stomatitis virus infection of MDCK cells: A study using fluorescence measurements through polycarbonate supports

Summary We used fluorescence microscopy of Madin-Darby Canine Kidney (MDCK) cells grown on polycarbonate filters to study a possible link between plasma membrane electrical potential (_pm) and infectivity of vesicular stomatitis virus (VSV). Complete substitution of K⁺ for extracellular Na⁺blocks VSV infection of MDCK cells as well as baby hamster kidney (BHK) cells. When we independently perfused the apical and basal-lateral surfaces of high resistance monolayers, high K⁺ inhibited VSV infection of MDCK cells only when applied to the basal-lateral side; high K⁺ applied apically had no effect on VSV infection. This morphological specificity correlates with a large decrease in _pm of MDCK cells when high K⁺ buffer is perfused across the basal-lateral surface. Depolarization of the plasma membrane by 130 mm basal K⁺ causes a sustained increase of cytosol pH in MDCK cells from 7.3 to 7.5 as reported by the fluorescent dye BCECF. Depolarization also causes a transient increase of cytosol Ca²⁺ from 70 to 300 nm as reported by the dye Fura-2. Neither increase could explain the block of VSV infectivity by plasma membrane depolarization. One alternative hypothesis is that _pm facilitates membrane translocation of viral macromolecules as previously described for colicins, mitochondrial import proteins, and proteins secreted by Escherichia coli.We thank Kenneth Spring for many helpful discussions concerning fluorescence digitized imaging systems, James Russell for his collaboration in the design of our imaging system, Herbert Chase for suggestions on dye loading into MDCK cells, and Manfred Schubert and George Harmison for providing expertise on VSV.     

Sodium ions are necessary for growth and energy transduction in the marine cyanobacterium Oscillatoria brevis

The maximal growth rate of the marine cyanobacterium Oscillatoria brevis was reached at 200–400 mM NaCl and pH 9.0–9.6. NaCl was found (i) to stimulate the rate of the light-supported generation across the cytoplasmic membrane of the cells and (ii) to decrease the sensitivity of level and motility of the O. brevis trichomes to protonophorous uncouplers. The Na⁺/H⁺ antiporter, monensin, increased both and the uncoupler sensitivity of the cells. The data obtained agree with the assumption that O. brevis possesses a primary Na⁺ pump in its cytoplasmic membrane.Abbreviations ATP adenosine-5-triphosphate - TTFB tetrachlortrifluoromethylimidazol - CCCP carbonyl cyanide m-chlorophenylhydrazone - Na⁺ transmembrane electrochemical potential differences of Na⁺ - transmembrane electric potential difference - pNa transmembrane pNa difference