The Partitioning of Nitrate Assimilation Between Root and Shoot of a Range of Temperate Cereals and Pasture Grasses

Nitrate reductase activity (NRA, in vivo assay) and nitrate(NO^-₃) content of root and shoot and NO^-₃ and reduced nitrogencontent of xylem sap were measured in five temperate cerealssupplied with a range of NO^-₃ concentrations (0·1–20mol m^–3) and three temperate pasture grasses suppliedwith 0·5 or 5 0 mol m^–3 NO^-₃ For one cereal (Hordeumvulgare L ), in vitro NRA was also determined The effect ofexternal NO^-₃ concentration on the partitioning of NO^-₃ assimilationbetween root and shoot was assessed All measurements indicatedthat the root was the major site of NO3 assimilation in Avenasatwa L, Hordeum vulgare L, Secale cereale L, Tnticum aestivumL and x Triticosecale Wittm supplied with 0·1 to 1·0mol m^–3 NO^-₃ and that for all cereals, shoot assimilationincreased in importance as applied NO^-₃ concentration increasedfrom 1.0 to 20 mol m^–3 At 5.0–20 mol m^–3 NO3,the data indicated that the shoot played an important if notmajor role in NO^-₃ assimilation in all cereals studied Measurementson Lolium multiflorum Lam and L perenne L indicated that theroot was the main site of NO^-₃ assimilation at 0.5 mol m^–3NO^-₃ but shoot assimilation was predominant at 5.0 mol m^–3NO^-₃ Both NRA distribution data and xylem sap analysis indicatedthat shoot assimilation was predominant in Dactylis glomerataL supplied with 0.5 or 5.0 mol m^–3 NO^-₃ Avena sativa L., oats, Hordeum vulgare L., barley, Secale cereale L., rye, x Triticosecale Wittm., triticale, Triticum aestivum L., wheat, Dactylis glomerata L., cocksfoot, Lolium multiflorum Lam., Italian ryegrass, Lolium perenne L., perennial ryegrass, nitrate, nitrate assimilation, nitrate reductase activity, xylem sap     

Allocation of Organ Biomass in Perfect and Imperfect Flowers

Perianth M_P, gynoecium M_G, and androecium M_A dry-weight biomass(in g) of 39 species of perfect flowers was measured. Thesedata were pooled with published data from an additional 51 speciesand used to determine size-dependent variations in (M_G and M_A)in terms of the hypothesis that the quotient of M_G and M_A exceeds1·0 for out-breeding (xenogamous) species and less than1·0 for in-breeding (autogamous) species. Ordinary leastsquare regression of the pooled data (n = 90) showed M_G = 0·118M^0·916_P (r² = 0·884) and M_A = 0·186 M^0·975_P(r² = 0·865), indicating that the biomass of the gynoeciumproportionally decrease as floral size increases. The exponentsof these regressions indicate that the ratio of gynoecial toandroecial biomass decreased with increasing floral size suchthat comparatively small flowers (M_P < 0·0021 g) hadM_G/M_A > 1·0 (predicted for 'out-breeders') while comparativelylarger flowers (M_P > 0·0021 g) had M_G /M_A < 1·0(predicted for 'in-breeders'). Thus, on average, the type ofbreeding system was a size-dependent phenomenon. To test whether the biomass of a floral organ-type is a legitimateindicator of gender reproductive effort, the biomass (in g)of stamen filaments M_m and anther sacs M_AS of 39 species wasdetermined. Least square regression of these data showed M_AS= 0·188 M^0·854_fil (r² = 0·967), indicatingthat species with larger stamen filaments, on the average, boreproportionally smaller anther sacs and thereby cautioning againstthe uncritical use of the allocation of biomass to floral organ-typeas a strict gauge of gender-function investment. To determine whether the loss of one gender-function resultsin proportional reallocation of biomass to the remaining gender-function,the size-dependency of androecial and gynoecial biomass wasdetermined for a total of 33 perfect and imperfect flowers ofCucumis melo. Regression of the data obtained from perfect flowersyielded M_A = 0·402 M^1·47_P (r² = 0·898)and M_G = 4·63 M^1·36_P (r² = 0·842). SinceM_G/M_A M^0·11_P , the biomass allocation to the gynoeciumrelative to the androecium decreased with increasing floralsize. This result was consistent with the broad interpecificcomparison based on 90 species with perfect flowers . Regressionof the data for imperfect flowers yielded M_A = 0·151M^1·02_P (r² = 0·675) and M_G = 4·68 M^1·47_P(r² = 0·996), indicating a near allometric relation forthe androecium and a strong positive anisometry for the gynoecium.Thus, for flowers of comparable size, a loss of female genderobtains a modest to significant again in androecial biomasswhereas the loss of male gender yields only a slight increasein gynoecial biomass. Collectively, the results of these studies indicate that biomassallocation patterns are size-dependent phenomena whose complexitieshave been largely ignored in the literature.Copyright 1993,1999 Academic Press Allometry, floral biomass, reproduction     

Temperature Response of Early Foliar Expansion of Potato and Wheat

We studied the course of early leaf area expansion and specificleaf area (S_LA) in potato (Solanum tuberosum L.) and wheat (Triticumaestivum L.) genotypes and tested whether air temperature explainsdifferences in these courses within different environments.Such knowledge can be used to improve crop growth modelling.The relative rate of leaf area expansion (R_L) of potato andwheat decreased with thermal time, but was nearly linear upto a leaf area index (L) of 1.0. TheR_L (L < 1; mean: 17.9x 10^-3°C^-1 d^-1) of potato showed an interaction betweengenotype and environment, and varied with year. TheR_L (L <1; mean: 7.1 x 10^-3°C^-1 d^-1) of winter wheat was lower thanthat of spring wheat (mean: 10.9 x 10^-3°C^-1 d^-1), and bothvaried with year. S_LAof potato increased nearly linearly withthermal time from 5 to 15 m² kg^-1at 50% emergence, to 20 to25 m² kg^-1at 155°Cd, and then decreased slightly. The S_LAofboth winter and spring wheat began at 16 to 23 m² kg^-1and inmost cases increased slightly with thermal time. In potato,regression parameters of S_LAwith thermal time were affectedby environment (management conditions and year) and genotype;in wheat they were affected by environment (year and site).Treatment effects on R_Lof potato were not correlated with thoseon S_LA , and were only partly correlated for wheat. Thereforewe conclude that the early foliar expansion of potato is associatedwith a strong increase in S_LA , and not so for wheat. For bothcrops the course of early leaf area expansion and ofS_LA withair temperature is not robust over environments and genotypes.The consequences of these results for modelling are discussed.Copyright 2000 Annals of Botany Company Triticum aestivum, spring wheat, winter wheat, Solanum tuberosum, leaf area expansion, specific leaf area, early growth, genotype, environment, modelling     

Sustained membrane depolarization and pulmonary artery smooth muscle cell proliferation

Pulmonary vasoconstriction and vascularmedial hypertrophy greatly contribute to the elevated pulmonaryvascular resistance in patients with pulmonary hypertension. A rise incytosolic free Ca²⁺ ([Ca²⁺]_cyt)in pulmonary artery smooth muscle cells (PASMC) triggers vasoconstriction and stimulates cell growth. Membrane potential (E_m) regulates[Ca²⁺]_cyt by governing Ca²⁺influx through voltage-dependent Ca²⁺ channels. Thusintracellular Ca²⁺ may serve as a shared signaltransduction element that leads to pulmonary vasoconstriction andvascular remodeling. In PASMC, activity of voltage-gated K⁺(Kv) channels regulates resting E_m. In thisstudy, we investigated whether changes of Kv currents[I_K(V)], E_m, and[Ca²⁺]_cyt affect cell growth by comparingthese parameters in proliferating and growth-arrested PASMC. Serumdeprivation induced growth arrest of PASMC, whereas chelation ofextracellular Ca²⁺ abolished PASMC growth. Resting[Ca²⁺]_cyt was significantly higher, andresting E_m was more depolarized, inproliferating PASMC than in growth-arrested cells. Consistently, wholecell I_K(V) was significantly attenuated in PASMCduring proliferation. Furthermore, E_mdepolarization significantly increased resting[Ca²⁺]_cyt and augmented agonist-mediatedrises in [Ca²⁺]_cyt in the absence ofextracellular Ca²⁺. These results demonstrate that reducedI_K(V), depolarized E_m, and elevated [Ca²⁺]_cyt may play a criticalrole in stimulating PASMC proliferation. Pulmonary vascular medialhypertrophy in patients with pulmonary hypertension may be partlycaused by a membrane depolarization-mediated increase in[Ca²⁺]_cyt in PASMC.

     

SH oxidation coordinates subunits of rat brain ryanodine receptor channels activated by calcium and ATP

We have reported that ryanodine receptor (RyR) channels display three different responses to cytoplasmic free Ca²⁺ concentration ([Ca²⁺]) depending on their redox state (Marengo JJ, Hidalgo C, and Bull R. Biophys J 74: 1263–1277, 1998), with low, moderate, and high maximal fractional open times (P_o). Activation by ATP of single RyR channels from rat brain cortex was tested in planar lipid bilayers with 10 or 0.1 µM cytoplasmic [Ca²⁺]. At 10 µM [Ca²⁺], low-P_o channels presented lower apparent affinity to activation by ATP [[ATP] for half-maximal activation (K_aATP) = 422 µM] than moderate-P_o channels (K_aATP = 82 µM). Oxidation of low-P_o channels with thimerosal or 2,2'-dithiodipyridine (DTDP) gave rise to moderate-P_o channels and decreased K_aATP from 422 to 82 µM. At 0.1 µM cytoplasmic [Ca²⁺], ATP induced an almost negligible activation of low-P_o channels. After oxidation to high-P_o behavior, activation by ATP was markedly increased. Noise analysis of single-channel fluctuations of low-P_o channels at 10 µM [Ca²⁺] plus ATP revealed the presence of subconductance states, suggesting a conduction mechanism that involves four independent subchannels. On oxidation the subchannels opened and closed in a concerted mode. subconductance states; calcium ion release channels; calcium ion regulation; thimerosal; 2,2'-dithiodipyridine     

Are Mistletoes Shade Plants? CO2Assimilation and Chlorophyll Fluorescence of Temperate Mistletoes and their Hosts

Mistletoes usually have slower rates of photosynthesis thantheir hosts. This study examines CO₂assimilation, chlorophyllfluorescence and the chlorophyll content of temperate host–parasitepairs (nine hosts parasitized by Ileostylus micranthus and Carpodetusserratus parasitized by Tupeia antarctica). The hosts of I.micranthus had higher mean annual CO₂assimilation (3.59 ±0.41 µmol m^-2 s^-1) than I. micranthus(2.42 ± 0.20µmol m^-2 s^-1), and C. serratus(2.41 ± 0.43 µmolm^-2 s^-1) showed higher CO₂assimilation than T. antarctica(0.67± 0.64 µmol m^-2 s^-1). Hosts saturated at significantlyhigher electron transport rates (ETR) and light levels thanmistletoes. The positive relationship between CO₂assimilationand electron transport suggests that the lower CO₂assimilationrates in mistletoes are a consequence of lower electron transportrates. When photosynthetic rates, ETR and chlorophyll a /b ratioswere adjusted for photosynthetically active radiation, hostsdid not have significantly higher CO₂assimilation (3.21 ±0.37 µmol m^-2 s^-1) than mistletoes (2.54 ± 0.41µmol m^-2 s^-1), but still had significantly higher ETRand chlorophyll a / b ratios. The electron transport rates,saturating light and chlorophyll a / b ratios of sun leavesfrom mistletoes were similar to host shade leaves. These responsesindicate that in comparison with their hosts, mistletoe leaveshave the photosynthetic characteristics of the leaves of shadeplants. Copyright 2000 Annals of Botany Company CO₂assimilation, photosynthetic active radiation (PAR), chlorophyll fluorescence, electron transport rate (ETR), photochemical quenching (q_p), non-photochemical quenching (q_n), sun and shade leaves, chlorophyll content, Ileostylus micranthus, Tupeia antarctica, New Zealand     

Photosynthesis of Stands of Tomato, Cucumber and Sweet Pepper Measured in Greenhouses under Various CO2-concentrations

The rate of net photosynthesis (P) of whole plant stands oftomato (Lycopersicon esculentum Mill.), cucumber (Cucumis sativusL.) and sweet pepper (Capsicum annuum L.) was measured in sixlong-term experiments in large greenhouses under normal operatingconditions and CO₂-concentrations between 200 and 1200 µmolmol^-1. The objective was to quantify the responses to lightand carbon dioxide and to obtain data sets for testing simulationmodels. The method of measuring canopy photosynthesis involvedan accurate estimation of the greenhouse CO₂ balance, usingnitrous oxide (N₂O) as tracer gas to determine, on-line, theexchange rate between greenhouse and outside air. The estimatedrelative error in the observed P was about ± 10%, exceptthat higher relative errors could occur under particular conditions. A regression equation relating P to the photosynthetically activeradiation, the CO₂ concentration and the leaf area index explained83-91% of the variance. The main canopy photosynthesis characteristicscalculated with the fitted regression equations were: canopyP_max 5-9 g m^-2 h^-1 CO₂ uptake; ratio P_max/LAI 1·5-3 gm^-2 h^-1; light compensation point 32-86 µmol s^-1 m^-2;light use efficiency (quantum yield) at low light 0·06-0·10µmol µmol^-1 and CO₂ compensation point 18-54 µmolmol^-1. The results were related to the prevailing conditions.Copyright1994, 1999 Academic Press Canopy photosynthesis, Capsicum annuum L., carbon dioxide, CO₂, CO₂ balance, CO₂ use efficiency, cucumber, _{Cucumis sativus} L., glasshouse, greenhouse, light use efficiency, Lycopersicon esculentum Mill., sweet pepper, tomato, tracer gas     

f-Ratio and its relationship to ambient nitrate concentration in coastal waters

The relationship between thef-ratio [NO₃^– uptake/(NO₃^–+ NH₄⁺) uptake] and ambient nitrate concentration was evaluatedfor eight data sets from coastal waters. The f-ratio increasedasymptotically with increase in nitrate concentration in mostdata sets. However, the rate at which f-ratio increased at lownitrate concentration (slope = m) and the maximum attained f-ratio(f_max) varied among regions; the initial slope varied most withvalues ranging in excess of an order of magnitude. The datawere analyzed in relation to environmental factors and methodologicalconsiderations known to influence the f-ratio. Ambient ammoniumconcentration was important in accounting for regional differencesin the f versus NO₃^– relationship. A further analysisof the data, relating f-ratio to the ratio of NO₃^–/(NO₃^–+ NH₄⁺) concentrations yielded a much more regionally consistentand approximately linear relationship; slopes varied by lessthan a factor of two in the extreme cases. Inclusion of knownalternative (aside from NH₄⁺) sources of reduced-N (e.g. urea)and correction for methodological/computational errors (isotopedilution) systematically reduce f-ratio estimates. Other factors,e.g. reduced-N uptake by microheterotrophs, may systematicallyincrease the f-ratio.     

Nitrogen utilization by plant species from acid heathland soils: II. Growth and shoot/root partitioning of NO3- assimilation at constant low pH and varying NO3-/NH4+ ratio

The growth of four heathland species, two grasses (D. flexuosa,M. caerulea) and two dwarf shrubs (C. vulgaris, E. tetralix),was tested in solution culture at pH 4.0 with 2 mol m^–3N, varying the N0₃^–/NH₄⁺ ratio up to 40% nitrate. In addition,measurements of NRA, plant chemical composition, and biomassallocation were carried out on a complete N0₃^–/NH₄⁺ replacementseries up to 100% nitrate. With the exception of M. caerulea, the partial replacement ofNH₄⁺ by NO₃^– tended to enhance the plant's growth ratewhen compared to NH₄⁺ only. In contrast to the other species,D. flexuosa showed a very flexible response in biomass allocation:a gradual increase in the root weight ratio (RWR) with NO₃^–increasing from 0 to 100%. In the presence of NH₄⁺, grassesreduced nitrate in the shoot only; roots did not become involvedin the reduction of nitrate until zero ambient NH₄⁺. The dwarfshrubs, being species that assimilate N exclusively in theirroots, displayed an enhanced root NRA in the presence of nitrate;in contrast to the steady increase with increasing NO₃^–in Calluna roots, enzyme activity in Erica roots followed arather irregular pattern. Free nitrate accumulated in the tissuesof grasses only, and particularly in D. flexuosa. The relative uptake ratio for NO₃^– [(proportion of nitratein N uptake)/(proportion of nitrate in N supply)] was lowestin M. caerulea and highest in D. flexuosa. Whereas M. caeruleaand the dwarf shrubs always absorbed ammonium highly preferentially(relative uptake ratio for NO₃^– <0.20), D. flexuosashowed a strong preference for NO₃^– at low external nitrate(the relative uptake ratio for N0₃^– reaching a value of2.0 at 10% NO₃^–). The ecological significance of thisprominent high preference for NO₃^– at low NO₃^–/NH₄⁺ratio by D. flexuosa and its consequences for soil acidificationare briefly discussed. Key words: Ammonium, heathland lants, N0₃^–/NH₄⁺ ratio, nitrate, nitrate reductase activity, soil acidification, specific absorption rate     

Intracellular pH shifts in cultured kidney (A6) cells: effects on apical Na+ transport

We report, for the epithelialNa⁺ channel (ENaC) in A6 cells,the modulation by cell pH (pH_c)of the transepithelial Na⁺ current(I_Na), thecurrent through the individual Na⁺channel (i), the openNa⁺ channel density(N_o), and thekinetic parameters of the relationship betweenI_Na and theapical Na⁺ concentration. Thei andN_o were evaluatedfrom the Lorentzian I_Na noise inducedby the apical Na⁺ channel blocker6-chloro-3,5-diaminopyrazine-2-carboxamide.pH_c shifts were induced, understrict and volume-controlled experimental conditions, byapical/basolateral NH₄Cl pulses orbasolateral arrest of theNa⁺/H⁺exchanger (Na⁺ removal; block byethylisopropylamiloride) and were measured with the pH-sensitive probe2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Thechanges in pH_c were positivelycorrelated to changes inI_Na and theapically dominated transepithelial conductance. The sole pH_c-sensitive parameter underlyingI_Na wasN_o. Only thesaturation value of theI_Na kinetics wassubject to changes in pH_c.pH_c-dependent changes inN_o may be causedby influencingP_o, the ENaC openprobability, or/and the total channel number,N_T = N_o/P_o.

     

Mechanism of shortened action potential duration in Na+-Ca2+ exchanger knockout mice

In cardiac-specific Na⁺-Ca²⁺ exchanger (NCX) knockout (KO) mice, the ventricular action potential (AP) is shortened. The shortening of the AP, as well as a decrease of the L-type Ca²⁺ current (I_Ca), provides a critical mechanism for the maintenance of Ca²⁺ homeostasis and contractility in the absence of NCX (Pott C, Philipson KD, Goldhaber JI. Excitation-contraction coupling in Na⁺-Ca²⁺ exchanger knockout mice: reduced transsarcolemmal Ca²⁺ flux. Circ Res 97: 1288–1295, 2005). To investigate the mechanism that underlies the accelerated AP repolarization, we recorded the transient outward current (I_to) in patch-clamped myocytes isolated from wild-type (WT) and NCX KO mice. Peak I_to was increased by 78% and decay kinetics were slowed in KO vs. WT. Consistent with increased I_to, ECGs from KO mice exhibited shortened QT intervals. Expression of the I_to-generating K⁺ channel subunit Kv4.2 and the K⁺ channel interacting protein was increased in KO. We used a computer model of the murine AP (Bondarenko VE, Szigeti GP, Bett GC, Kim SJ, and Rasmusson RL. Computer model of action potential of mouse ventricular myocytes. Am J Physiol Heart Circ Physiol 287: 1378–1403, 2004) to determine the relative contributions of increased I_to, reduced I_Ca, and reduced NCX current (I_NCX) on the shape and kinetics of the AP. Reduction of I_Ca and elimination of I_NCX had relatively small effects on the duration of the AP in the computer model. In contrast, AP repolarization was substantially accelerated when I_to was increased in the computer model. Thus, the increase in I_to, and not the reduction of I_Ca or I_NCX, is likely to be the major mechanism of AP shortening in KO myocytes. The upregulation of I_to may comprise an important regulatory mechanism to limit Ca²⁺ influx via a reduction of AP duration, thus preventing Ca²⁺ overload in situations of reduced myocyte Ca²⁺ extrusion capacity. genetically altered mice; cardiac myocytes; short QT interval; transient outward current     

Nitric oxide induces [Ca2+]i oscillations in pituitary GH3 cells: involvement of IDR and ERG K+ currents

The role of nitric oxide (NO) in the occurrence of intracellular Ca²⁺ concentration ([Ca²⁺]_i) oscillations in pituitary GH₃ cells was evaluated by studying the effect of increasing or decreasing endogenous NO synthesis with L-arginine and nitro-L-arginine methyl ester (L-NAME), respectively. When NO synthesis was blocked with L-NAME (1 mM) [Ca²⁺]_i, oscillations disappeared in 68% of spontaneously active cells, whereas 41% of the quiescent cells showed [Ca²⁺]_i oscillations in response to the NO synthase (NOS) substrate L-arginine (10 mM). This effect was reproduced by the NO donors NOC-18 and S-nitroso-N-acetylpenicillamine (SNAP). NOC-18 was ineffective in the presence of the L-type voltage-dependent Ca²⁺ channels (VDCC) blocker nimodipine (1 µM) or in Ca²⁺-free medium. Conversely, its effect was preserved when Ca²⁺ release from intracellular Ca²⁺ stores was inhibited either with the ryanodine-receptor blocker ryanodine (500 µM) or with the inositol 1,4,5-trisphosphate receptor blocker xestospongin C (3 µM). These results suggest that NO induces the appearance of [Ca²⁺]_i oscillations by determining Ca²⁺ influx. Patch-clamp experiments excluded that NO acted directly on VDCC but suggested that NO determined membrane depolarization because of the inhibition of voltage-gated K⁺ channels. NOC-18 and SNAP caused a decrease in the amplitude of slow-inactivating (I_DR) and ether-à-go-go-related gene (ERG) hyperpolarization-evoked, deactivating K⁺ currents. Similar results were obtained when GH₃ cells were treated with L-arginine. The present study suggests that in GH₃ cells, endogenous NO plays a permissive role for the occurrence of spontaneous [Ca²⁺]_i oscillations through an inhibitory effect on I_DR and on I_ERG. voltage-gated potassium channels; ether-à-go-go-related gene potassium channels; slow-inactivating outward currents; fast-inactivating outward currents     

Changes in the growth rates of saline-lake diatoms in response to variation in salinity, brine type and nitrogen form

The growth rates of four saline-lake diatom taxa were measuredunder varying conditions of salinity (5, 8 and 11), brine type(sulfate- versus bicarbonate-dominated) and nitrogen form (NH₄⁺versus NO₃^–), using a full factorial design. With NO₃^–as the nitrogen source, Cyclotella quillensis, Cymbella pusillaand Anomoeoneis costata exhibited lower growth rates in thesulfate versus bicarbonate media. The strain of Chaetoceroselmorei used in these experiments, isolated from a sulfate-dominatedlake, was unable to grow on NO₃^– alone. In the NH₄⁺ treatments,neither salinity nor brine type affected the growth rates ofC.quillensis or C.elmorei. When supplied with NH₄⁺, C.pusillaand A.costata had higher growth rates in the bicarbonate versussulfate media, although for C.pusilla the difference on NH₄⁺was not as great as on NO₃^–. The impact of brine typeon NO₃^– use is consistent with the theory that sulfateinhibits molybdate uptake, as molybdenum is required for NO₃^–use but not NH₄⁺. Cymbella pusilla was the only taxon affectedby changes in salinity. The four taxa used in these experimentsare frequently found in saline lakes and saline-lake sediments,hence they are used in paleoclimate reconstructions; the resultspresented here provide additional information that may enhancethese diatom-based reconstructions.     

The Biological Properties of Cyclopenin and Cyclopenol

Cyclopenin (C₁₇H₁₄O₃N₂) and cyclopenol (C₁₇H₁₄O₄N₂), isolatedfrom an abberent strain of Penicillium cyclopium (NRRL 6233),significantly inhibited the growth of etiolated wheat (Triticumaestivum) coleoptile segments. The former inhibited at 10^–3and 10^–4 M, the latter at 10^–3 M. Cyclopenin producedmalformation of the first set of trifoliate leaves in bean (Phaseolusvulgaris) at 10^–2 M and necrosis and stunting in corn(Zea mays) at 10^–2 M. Cyclopenol induced no apparent effectsin bean or corn plants. Neither compound changed the growthor morphology of tobacco (Nicotiana tabacum) plants. Cyclopenininduced intoxication, prostration and ataxia in day-old chicksat 500 mg/kg, but they recovered within 18 hours. Cyclopenolwas inactive against chicks when dosed at levels up to 500 mg/kg. (Received October 11, 1983; Accepted December 15, 1983)     

Effect of Sodium on Phosphate Uptake in Unicellular and Filamentous Cyanobacteria

The effect of Na⁺ on phosphate uptake was studied in four strainsof cyanobacteria: Synechococcus PCC 7942, Gloeothece PCC 6501,Phormidium sp. and Chlorogloeopsis PCC 6912. Phosphate uptakewas stimulated by Na⁺ in all cases. Li⁺ and K⁺ acted as partialanalogues for Na⁺. Half-saturation [K_1/2(Na⁺)] of phosphateuptake was reached with Na⁺ concentrations ranging from 317µM in Chlorogloeopsis to 659 µM in Phormidium. Theconcentration of phosphate required to reach half-saturationof phosphate uptake [K_1/2(P_i)]was not changed by the presenceof Na⁺. (Received April 11, 1994; Accepted July 5, 1994)     

Utilization Modes of Inorganic Carbon for Photosynthesis in Various Species of Chlorella

Rates of CO₂ and HCC₃^– fixation in cells of various Chlorellaspecies in suspension were compared from the amounts of ¹⁴Cfixed during the 5 s after the injection of a solution containingonly ¹⁴CO₂ or H¹⁴CO₃^–. Results indicated that irrespectiveof the CO₂ concentration during growth, Chlorella vulgaris 11h and C. miniata mainly utilized CO₂, whereas C. vulgaris C-3,C. sp. K. and C. ellipsoidea took up HCO₃^– in additionto CO₂. Cells of C. pyrenoidosa that had been grown with 1.5%CO₂ (high-CO₂ cells) mainly utilized CO₂, whereas those grownwith air (low-CO₂ cells) utilized HCO₃^– in addition toCO₂. Cells that utilized HCO₃^– had carbonic anhydrase(CA) on their surfaces. The effects of Diamox and CA on the rates of CO₂ and HCO₃^–fixation are in accord with the inference that HCO₃^– wasutilized after conversion to CO₂ via the CA located on the cellsurface. CA was found in both the soluble and insoluble fractions;the CA on the cell surface was insoluble. Independent of the modes of utilization, the apparent K_m (NaHCO₃)for photosynthesis was much lower in low-CO₂ cells than in high-CO₂ones. The fact that the CA in the soluble fraction in C. vulgarisC-3 was closely correlated with the K_m(NaHCO₃) indicates thatsoluble CA lowers the K_m. ¹ Dedicated to the late Professor Joji Ashida, one of the foundersand first president of the Japanese Society of Plant Physiologists. ⁴ On leave from Research and Production Laboratory of Algology,Bulgarian Academy of Sciences, Sofia. (Received September 14, 1982; Accepted March 1, 1983)     

Dependence of Na+-K+ pump current-voltage relationship on intracellular Na+, K+, and Cs+ in rabbit cardiac myocytes

To examine effects of cytosolicNa⁺, K⁺, and Cs⁺ on the voltagedependence of the Na⁺-K⁺ pump, we measuredNa⁺-K⁺ pump current (I_p)of ventricular myocytes voltage-clamped at potentials(V_m) from 100 to +60 mV. Superfusates weredesigned to eliminate voltage dependence at extracellular pump sites.The cytosolic compartment of myocytes was perfused with patch pipette solutions with a Na⁺ concentration ([Na]_pip)of 80 mM and a K⁺ concentration from 0 to 80 mM or withsolutions containing Na⁺ in concentrations from 0.1 to 100 mM and K⁺ in a concentration of either 0 or 80 mM. When[Na]_pip was 80 mM, K⁺ in pipette solutionshad a voltage-dependent inhibitory effect on I_pand induced a negative slope of theI_p-V_m relationship. Cs⁺ in pipette solutions had an effect onI_p qualitatively similar to that ofK⁺. Increases in I_p with increasesin [Na]_pip were voltage dependent. The dielectriccoefficient derived from[Na]_pip-I_p relationships at thedifferent test potentials was 0.15 when pipette solutions included 80 mM K⁺ and 0.06 when pipette solutions were K⁺ free.

     

Effects of Light and CO2 on Net Photosynthesis Rates of Stands of Aubergine and Amaranthus

Net photosynthetic rates per unit ground area for plant standsof Solanum melongena L. var. esculentum (aubergine) and Amaranthuscaudatus L. var. edulis (grain amaranth) were measured over10 min intervals in an airtight, glass, controlled-environmentcabinet for a range of light flux densities provided by thediurnal variation in daylight. Light response curves for photosynthesisof stands, grown at ambient CO₂ concentration, were definedat 400, 800 and 1200 vpm CO₂. Light compensation points for these stands were around 20-30J m^-2 s^-1 and decreased slightly at higher CO₂ concentrations.For aubergine, a C₃ species, the short-term effects of CO₂ enrichmentwere to increase the initial slope as well as the asymptoteof the light response curve, reducing light saturation at moderateto high light flux densities; but for amaranthus, a C₄ species,saturation was less apparent and CO₂ enrichment scarcely increasedphotosynthesis except at light flux densities above 150 J m^-2s^-1. The canopies intercepted 93-98% of incident light. The efficiencyof utilization of intercepted light in photosynthesis (µgCO₂ J^-1) increased from zero at the light compensation pointto a maximum at an optimum light flux density of about 100 Jm^-2 s^-1 (the optimum rose a little with CO₂ enrichment) anddecreased slightly with further increase in light. Maximum utilizationefficiencies at 400 vpm CO₂ were 8-9 µg CO₂ J^-1. Enrichmentto 1200 vpm did not affect the peak utilization efficiency ofthe C₄ amaranthus, but increased that aubergine to 12·2µg CO₂ J^-1 (equivalent to some 14% when using the heatof combustion of plant dry matter to convert to the dimensionlessform). This is among the highest recorded efficiencies of lightutilization for stands, and relates to the exceptionally favourableenvironment, with optimal control of CO₂ concentration, humidity,temperature, water supply and mineral nutrition.Copyright 1993,1999 Academic Press Amaranthus caudatus L. var. edulis, Solanum melongena L. var. esculentum, canopy photosynthesis, CO₂ enrichment, light interception, light utilization, photosynthetic efficiency     

The Influence of NO-3 and NH+4 Nutrition on the Gas Exchange Characteristics of the Roots of Wheat (Triticum aestivum) and Maize (Zea mays) Plants

Respiratory oxygen consumption by roots was 1·4- and1·6-fold larger in NH⁺₄-fed than in NO^-₃-fed wheat (Triticumaestivum L.) and maize (Zea mays L.) plants respectively. Higherroot oxygen consumption in NH⁺₄-fed plants than in NO^-₃-fedplants was associated with higher total nitrogen contents inNH⁺4-fed plants. Root oxygen consumption was, however, not correlatedwith growth rates or shoot:root ratios. Carbon dioxide releasewas 1·4- and 1·2-fold larger in NO⁺3-fed thanin NH⁺₄-fed wheat and maize plants respectively. Differencesin oxygen and carbon dioxide gas exchange rates resulted inthe gas exchange quotients of NH^-₄-fed plants (wheat, 0·5;maize, 0·6) being greatly reduced compared with thoseof NO^-₃-fed plants (wheat, 1·0; maize, 1·1). Measuredrates of HCO^-₃ assimilation by PEPc in roots were considerablylarger in 4 mM NH⁺₄-fed than in 4 NO^-₃ plants (wheat, 2·6-fold;maize, 8·3-fold). These differences were, however, insufficientto account for the observed differences in root carbon dioxideflux and it is probable that HCO^-₃ uptake is also importantin determining carbon dioxide fluxes. Thus reduced root extension in NH⁺₄-fed compared with NO^-₃-fedwheat plants could not be ascribed to differences in carbondioxide losses from roots.Copyright 1993, 1999 Academic Press Triticum aestivum, wheat, Zea mays, maize assimilation, ammonium assimilation, root respiration     

Presence of the distinct systems responsible for superoxide anion and hydrogen peroxide generation in red tide phytoplankton Chattonella marina and Chattonella ovata

Raphidophycean flagellates, Chattonella marina and C. ovata,are harmful red tide phytoplankters; blooms of these phytoplanktersoften cause severe damage to fish farming. Previous studieshave demonstrated that C. marina and C. ovata continuously producereactive oxygen species (ROS) such as superoxide anion (O₂^–)hydrogen peroxide (H₂O₂) under normal growth conditions, andan ROS-mediated toxic mechanism against fish and other marineorganisms has been proposed. Although the exact mechanism ofROS generation in these phytoplankters still remains to be clarified,our previous study suggested that NADPH oxidase-like enzymelocated on the cell surface of C. marina may be involved inO₂^– generation. To investigate the localization of O₂^–and H₂O₂ generation in C. marina and C. ovata, we employed 2-methyl-6(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazin-3-oneand 5-(and-6)-carboxy-2',7'-dichlorodihydrodihydrofluoresceindictate, acetyl ester, which are specific fluorescent probefor detecting O₂^– and H₂O₂, respectively. Observationby fluorescence microscopy of live phytoplankters incubatedwith each probe revealed that O₂^– is mainly generatedon the cell surface, whereas H₂O₂ is generated in the intracellularcompartment in these phytoplankters. When the cells were rupturedby ultrasonic treatment, O₂^– levels of C. marina and C.ovata decreased significantly, whereas a few times higher levelsof H₂O₂ were detected in the ruptured cell suspensions whencompared with the levels of the live cell suspension. In immunoblottinganalysis, the protein recognized by anti-human gp91 phox wasdetected in both species. These results suggest that, in bothphytoplankters, the underlying mechanisms of O₂^– and H₂O₂generation may be distinct and such systems are independentlyoperating in the cells.