Compartmentation and flux characteristics of ammonium in spruce

Using ¹³NH ₄ ⁺ as a tracer, compartmental analyses for NH ₄ ⁺ were performed in non-mycorrhizal roots of intact Picea glauca (Moench) Voss. seedlings at four different concentration regimes of external NH ₄ ⁺ ([NH ₄ ⁺ ]_o), i.e. 0, 10, 100, and 1500 M. Three kinetically distinct compartments were identified, with half-lives of exchange of approximately 2 s, 30 s, and 14 min, assumed to represent surface adsorption, Donnan free space, and cytoplasm, respectively. No significant differences were found in half-lives of exchange with changes in [NH ₄ ⁺ ]_o. Influx was calculated to be 0.96 mol·g^–1·h^–1 in N-deprived plants (measured at 10 M [NH ₄ ⁺ ]_o), while under steady-state conditions it was 0.21 mol·g^–1h^–1 at 10 M [NH ₄ ⁺ ]_o, 1.96 mol·g^–1h·^–1 at 100 M [NH ₄ ⁺ ]_o, and 6.45 mol·g^–1·h^–1 at 1.5 mM [NH ₄ ⁺ ]_o. Efflux measured over the same range constituted approximately 9% of influx in N-deprived plants, 10% at 10 M, 28% at 100 M, and 35% at 1.5 mM [NH ₄ ⁺ ]_o. Cytoplasmic [NH ₄ ⁺ ] was estimated at 6 m M in N-deprived plants, 2 mM at 10 M [NH ₄ ⁺ ]_o, 14 mM at 100 M, and 33 mM at 1.5 mM. Free-space [NH ₄ ⁺ ] was 84 M, 50 M, 700 M, and 8 mM, respectively. In comparison with previously published data on fluxes and compartmentation of NO ₃ ^– in white-spruce seedlings, results of this study identify a pronounced physiological preference of this species for NH ₄ ⁺ over NO ₃ ^– as an inorganic N source in terms of uptake and intracellular accumulation. The significant ecological importance of this N-source preference is discussed.The research was supported by a Natural Sciences and Engineering Research Council, Canada, grant to Dr. A.D.M. Glass and a University of British Columbia Graduate Fellowship to Herbert J. Kronzucker. Our thanks go to Dr. M. Adam and Mr. P. Culbert at the particle accelerator facility TRIUMF on the University of British Columbia campus for providing ¹³N, to Drs. R.D. Guy and S. Silim for providing plant material, and to Dr. M.Y. Wang, Mr. J. Bailey, Mr. J. Mehroke and Mr. P. Poon for essential assistance in experiments.     

Compartmentation and flux characteristics of nitrate in spruce

The radiotracer¹³N was used to undertake compartmental analyses for NO ₃ ^– in intact non-mycorrhizal roots ofPicea glauca (Moench) Voss. seedlings. Three compartments were defined, with half-lives of exchange of 2.5 s, 20 s, and 7 min. These were identified as representing surface adsorption, apparent free space, and cytoplasm, respectively. Influx, efflux, and net flux as well as cytoplasmic and apparent-free-space nitrate concentrations were estimated for three different concentration regimes of external nitrate. After exposure to external NO ₃ ^– for 3 d, influx was calculated to be 0.09 mol·g^–1·h^–1 (at 10 M [NO ₃ ^– ]_o), 0.5mol·g^–1·h^–1 (at 100 M [NO _inf3 ^sup– ]_o), and 1.2 mol · g^–1· h^–1 (at 1.5 mM [NO ₃ ^– ]_o). Efflux increased with increasing [NO ₃ ^– ]_o, constituting 4% of influx at 10 M, 6% at 100 M, and 21% at 1.5 mM. Cytoplasmic [NO ₃ ^– ] was estimated to be 0.3 mM at 10 uM [NO ₃ ^– ]_o, 2mM at 100 M [NO ₃ ^– ]_o, and 4mM at 1.5 mM [NO ₃ ^– ]_o, while free-space [NO ₃ ^– ] was 16 M, 173 M, and 2.2 mM, respectively. A series of experiments was carried out to confirm the identity of the compartments resolved by efflux analysis. Pretreatment at high temperature or application of 2-chloro-ethanol, sodium dodecyl sulphate or hydrogen peroxide made it possible to distinguish the metabolic (cytoplasmic) phase from the remaining two (physical) phases. Likewise, varying [Pi] of the medium altered efflux and thereby [NO ₃ ^– ]_cyt, but did not affect [NO ₃ ^– ]_{free space}.Abbreviations and Symbols [NO ₃ ^– ]_cyt cytoplasmic NO ₃ ^– concentration - [NO ₃ ^– ]_{free space} apparent-free-space NO ₃ ^– concentration - [NO ₃ ^– ]_o concentration of NO ₃ ^– in the external solution - NO ₃ ^– flux - _co efflux from the cytoplasm - _oc influx to the cytoplasm - _net net flux - _xylem flux to the xylem - _red/vac combined flux to reduction and the vacuole The research was supported by a Natural Sciences and Engineering Research Council, Canada, grant to Dr. A.D.M. Glass and by a University of British Columbia Graduate Fellowship to Herbert J. Kronzucker. Our thanks go to Dr. M. Adam and Mr. P. Culbert at the particle accelerator facility TRIUMF on the University of British Columbia Campus for providing¹³NO ₃ ^– , Drs. R.D. Guy and S. Silim for providing plant material, and Dr. M.Y. Wang, Mr. J. Mehroke and Mr. P. Poon for assistance in experiments and for helpful discussions.     

Effects of constitutive expression of nitrate reductase in transgenic Nicotiana plumbaginifolia L. in response to varying nitrogen supply

Transformed Nicotiana plumbaginifolia plants with constitutive expression of nitrate reductase (NR) activity were grown at different levels of nitrogen nutrition. The gradients in foliar NO ₃ ^– content and maximum extractable NR activity observed with leaf order on the shoot, from base to apex, were much decreased as a result of N-deficiency in both the transformed plants and wild type controls grown under identical conditions. Constitutive expression of NR did not influence the foliar protein and chlorophyll contents under any circumstances. A reciprocal relationship between the observed maximal extractable NR activity of the leaves and their NO ₃ ^– content was observed in plants grown in nitrogen replete conditions at low irradiance (170 mol photons·m^–2 ·s^–1). This relationship disappeared at higher irradiance (450 mol photons·m^–2·S^–1) because the maximal extractable NR activity in the leaves of the wild type plants in these conditions increased to a level that was similar to, or greater than that found in constitutive NR-expressors. Much more NO ₃ ^– accumulated in the leaves of plants grown at 450 mol photons·m^–2·s^–1 than in those grown at 170 mol photons·m^–2·s^–1 in N-replete conditions. The foliar NO ₃ ^– level and maximal NR activity decreased with the imposition of N-deficiency in all plant types such that after prolonged exposure to nitrogen depletion very little NO ₃ ^– was found in the leaves and NR activity had decreased to almost zero. The activity of NR decreased under conditions of nitrogen deficiency. This regulation is multifactoral since there is no regulation of NR gene expression by NO ₃ ^– in the constitutive NR-expressors. We conclude that the NR protein is specifically targetted for destruction under nitrogen deficiency. Consequently, constitutive expression of NR activity does not benefit the plant in terms of increased biomass production in conditions of limiting nitrogen.Abbreviations Chl chlorophyll - N nitrogen - NR NADH-nitrate reductase - WT wild type     

Ammonium and nitrate uptake in gap,generalist and understory species of the genus Piper

Summary We studied root net uptake of ammonium (NH ₄ ⁺ ) and nitrate (NO ₃ ^– ) in species of the genus Piper (Piperaceae) under high, intermediate and low photosynthetically active photon flux densities (PFD). Plants were grown hydroponically, and then transferred to temperature controlled (25° C) root cuvettes for nutrient uptake determinations. Uptake solutions provided NH ₄ ⁺ and NO ₃ ^– simultaneously (both) or separately (single). In the first experiment, seven species of Piper, from a broad range of rainforest light habitats ranging from gap to understory, were screened for mineral nitrogen preference (100 M NH ₄ ⁺ and/or 100 M NO ₃ ^– ) at intermediate PFD (100 mol m^–2 s^–1). Preference for NH ₄ ⁺ relative to NO ₃ ^– , defined as the ratio of NH ₄ ⁺ (both):NO ₃ ^– (both) net uptake, was higher in understory species than in gap species. Ammonium repression of NO ₃ ^– uptake, defined as the ratio of NO ₃ ^– (single): NO ₃ ^– (both) net uptake, was also higher in understory species as compared to gap species. In a second set of experiments, we examined the effect of nitrogen concentration (equimolar, 10 to 1000 M) on NH ₄ ⁺ preference and NH ₄ ⁺ repression of NO ₃ ^– net uptake at high (500 mol m^–2 s^–1) and low (50 mol m^–2 s^–1) PFD in a gap (P. auritum), generalist (P. hispidum) and understory species (P. aequale). All species exhibited negligible NH ₄ ⁺ repression of NO ₃ ^– net uptake at high PFD. At low PFD, NH ₄ ⁺ preference and repression of NO ₃ ^– net uptake occurred in all species (understory > generalist > gap), but only at intermediate nitrogen concentrations, i.e. between 10 and 200 M. Ammonium repression of net NO ₃ ^– uptake decreased or increased rapidly (in < 48 h) after transitions from low to high or from high to low PFD respectively. No significant diurnal patterns in NO ₃ ^– or NH ₄ ⁺ net uptake were observed.CIWDPB publication # 1130     

Light response of D1 turnover and photosystem II efficiency in the seagrassZostera capricorni

Biochemical and biophysical parameters, including D1-protein turnover, chlorophyll fluorescence, oxygen evolution activity and zeaxanthin formation were measured in the marine seagrassZostera capricorni (Aschers) in response to limiting (100 mol·m^–2·^–1), saturating (350 mol·m^–2·s^–1) or photoinhibitory (1100 mol·m^–2·s^–1) irradiances. Synthesis of D1 was maximal at 350 mol·m^–2·s^–1 which was also the irradiance at which the rate of photosynthetic O₂ evolution was maximal. Degradation of D1 was saturated at 350 mol·m^–2·s^–1. The rate of D1 synthesis at 1100 mol·m^–2·s^–1 was very similar to that at 350 mol·m^–2·s^–1 for the first 90 min but then declined. At limiting or saturating irradiance little change was observed in the ratio of variable to maximal fluorescence (Fv/Fm) measured after dark adaptation of the leaves, while significant photoinhibition occurred at 1100 mol·m^–2·s^–1. The proportion of zeaxanthin in the total xanthophyll pool increased with increasing irradiance, indicative of the presence of a photoprotective xanthophyll cycle in this seagrass. These results are consistent with a high level of regulatory D1 turnover inZostera under non-photoinhibitory irradiance conditions, as has been found previously for terrestrial plants.We would like to thank Professor Peter Böger (Department of Plant Biochemistry, University of Konstanz, Germany) for the kind gift of D1 antibodies. This work was partly supported by a University of Queensland Enabling Grant to CC.     

Influence of inorganic microelements on the production of camptothecin with suspension cultures of <Emphasis Type="Italic">Camptotheca acuminata</Emphasis>

The effects of eight microelements (I^–, BO₃ ^3–, MoO₄ ^2–, Co²⁺, Cu²⁺, Mn²⁺, Fe²⁺, Zn²⁺) on the biosynthesis of camptothecin and the growth of suspension cultures of Camptotheca acuminata were studied. The increase of I^– to 25 M l^–1, Cu²⁺ to 1 M l^–1, Co²⁺ to 2 M l^–1 and MoO₄ ^2– to 10 M l^–1 in Murashige and Skoog (MS) medium resulted in 1.66, 2.84, 2.53 and 2.04 times higher of camptothecin yield than that in standard MS medium respectively. Combined treatment of I^– (25 M l^–1), Cu²⁺ (1 M l^–1), Co²⁺ (2 M l^–1) and MoO₄ ^2– (10 M l^–1) lead to improve cell dry weight, camptothecin content, and camptothecin yield to 30.56 g l^–1, 0.0299%, and 9.15 mg l^–1, respectively, which were 20.2, 208.9 and 273.8% increment respectively when compared with those of control.     

Evidence for the involvement of plasma-membrane-bound nitrate reductase in signal transduction during blue-light stimulation of nitrate uptake in Chlorella saccharophila

Nitrate uptake in Chlorella saccharophila (Krüger) Nadson was found to be stimulated by blue light, leading to a doubling of the rate. In the presence of background red light (300 mol photons · m^-2 · s^-1), only 15–20 mol photons · m^-2 · s^-1 of blue light was sufficient to saturate this increased uptake rate. Incubation of Chlorella cells with anti-nitrate-reductase immunoglobulin-G fragments inhibited blue-light stimulation. However, ferricyanide (10 M) doubled and dithiothreitol (100 M) inhibited the stimulatory effect of blue light. Among the protein-kinase inhibitors used, only staurosporine (10 M) prevented the blue-light stimulation. Phosphatase inhibitors were without effect and sodium vanadate totally inhibited nitrate uptake, pointing to an involvement of the plasma-membrane ATPase. Preincubation of the cells with calmodulin antagonists or calcium ionophores did not significantly reduce blue-light stimulation of nitrate uptake. The data are discussed with regard to transduction of the signal for blue-light stimulation of nitrate uptake and the possibility that the plasma-membrane-bound nitrate reductase is the blue-light receptor.Abbreviations Chl chlorophyll - DMSO dimethylsulfoxide - 1,2-DHG 1,2-dihexanoylglycerol - ML-9 1-(5-chloronaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine - NR nitrate reductase - H-7 1-(5-isoquinolinyl-sulfonyl)-2-methylpiperazine - IgG immunoglobulin G - PFD photon flux density - PM plasma membrane - W-7 N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide This work was supported by a grant from the Deutsche Forschungs-gemeinschaft to R.T.     

Comparison of the growth rates of dinitrogen fixing subterranean clover swards with those assimilating nitrate ions

Summary Subterranean clover plants were grown as swards (about 2000 plants/m²) under controlled conditions with N provided either by N₂-fixation (NO ₃ ^– withheld) or by assimilation of NO ₃ ^– (NO ₃ ^– supplied). Crop growth rates were measured by dry matter sampling over periods of up to 70 days at PPFD values of 400–1000 mole quanta/m²/s. When NO ₃ ^– was supplied from sowing the swards grew more rapidly than when the swards were not supplied with NO ₃ ^– and plants had to establish an N₂-fixing apparatus. When inter-plant competition was reduced within the sward, a difference in growth rate in favour of NO ₃ ^– -fed plants continued for at least 50 days. When however, a closed canopy was allowed to form, the NO ₃ ^– -fed swards had more dry weight than the N₂-fed swards at the time of canopy closure but thereafter the two swards grew at similar rates at light flux densities of above about 800 mole quanta/m²/s. At light flux densities of about 400 mole quanta/m²/s N₂-fed swards had a growth rate 70–80% of that of NO ₃ ^– -fed plants. NO ₃ ^– -fed plants had a higher organic N content than did N₂-fed plants under all conditions.     

Short-term studies of NO 3 − uptake in Pisum using 13NO 3 −

Influx, efflux and net uptake of NO ₃ ^– was studied in Pisum sativum L. cv. Marma in short-term experiments where ¹³NO ₃ ^– was used to trace influx. The influx rate in N-limited plants was similar both during net uptake at external concentrations of around 50 M, and at low external NO ₃ ^– concentrations (4–6 M) when net uptake was practically zero. Efflux could be inferred from discrepancies between influx and net uptake but was never very high in the N-limited plants during net uptake. Close to the threshold concentration for not NO ₃ ^– uptake, efflux was high and equalled influx. Thus, the threshold concentration can be regarded as a NO ₃ ^– compensation point. The inclusion of NH ₄ ⁺ in the outer medium decreased influx by about 40% but did not significantly affect efflux. The roles of NO ₃ ^– fluxes and nitrate-reductase activity in regulating/limiting NO ₃ ^– utilization are discussed.Abbreviations DW dry weight - FW fresh weight - R_N relative nitrogen addition rate     

Auxin activity of phenylacetic acid in tissue culture

The ability of phenylacetic acid (PAA), a naturally occurring auxin, to initiate and support growth of callus and suspension cultures of several species is reported. Callus tissue of tobacco (Nicotiana tabacum L. var. WI-38), initiated and maintained on a medium with 2,4-dichlorophenoxyacetic acid (2,4-D), was transferred to and maintained on media supplemented with 25–500 M PAA as the only plant growth regulator (PGR). Optimal concentrations of PAA were determined for tobacco callus proliferation in the dark (250 M PAA) and with a 16-h light/8-h dark photoperiod (500 M PAA). Tobacco suspension cultures were maintained for over 28 transfers in media containing 20–40 M PAA as the sole PGR. When tobacco callus tissue maintained on PAA-supplemented media for over 18 months was transferred to liquid media containing kinetin, plantlets were regenerated. Callus of sunflower (Helianthus annuus L. var. Russian Mammoth) proliferated on media containing PAA at 5–250 M as the sole PGR. Similar PAA concentrations inhibited normal development and promoted callus formation in tobacco and pea (Pisum sativum L. vars. common, Frogel, and Frimas) epicotyl tissue. PAA as the sole PGR did not support the growth of soybean (Glycine max (L.) Merrill var. Fiskeby) callus or suspension cultures. Chickpea (Cicer arietinum L. var. UC-5) and lentil (Lens culinaris Medic. var. Laird) callus cultures proliferated on media containing 25–500 M PAA, but habituation of the cultures was common. PAA was not toxic to tobacco, chickpea, and lentil tissues at levels as high as 500 M.Paper No. 88514 of the Journal Series of the Idaho Agricultural Experiment Station, Moscow, Idaho, USA.     

The effect of endogenous and externally supplied nitrate on nitrate uptake and reduction in sugarbeet seedlings

The pericarp of the dormant sugarbeet fruit acts as a storage reservoir for nitrate, ammonium and -amino-N. These N-reserves enable an autonomous development of the seedling for 8–10 d after imbibition. The nitrate content of the seed (1% of the whole fruit) probably induces nitrate-reductase activity in the embryo enclosed in the pericarp. Nitrate that leaks out of the pericarp is reabsorbed by the emerging radicle. Seedlings germinated from seeds (pericarp was removed) without external N-supply are able to take up nitrate immediately upon exposure via a low-capacity uptake system (v_max = 0.8 mol NO ₃ ^- ·(g root FW)^–1·h^–1; K_s = 0.12 mM). We assume that this uptake system is induced by the seed nitrate (10 nmol/seed) during germination. Induction of a high-capacity nitrate-uptake system (v_max = 3.4 mol NO ₃ ^- ·(g root FW)^–1·h^–1; K_s = 0.08 mM) by externally supplied nitrate occurs after a 20-min lag and requires protein synthesis. Seedlings germinated from whole fruits absorb nitrate via a highcapacity uptake mechanism induced by the pericarp nitrate (748 nmol/pericarp) during germination. The uptake rates of the high-capacity system depend only on the actual nitrate concentration of the uptake medium and not on prior nitrate pretreatments. Nitrate deprivation results in a decline of the nitrate-uptake capacity (t_1/2 of v_max = 5 d) probably caused by the decay of carrier molecules. Small differences in K_s but significant differences in v_max indicate that the low- and high-capacity nitrate-uptake systems differ only in the number of identical carrier molecules.Abbreviations NR nitrate reductase - pFPA para-fluorophenylalanine This work was supported by a grant from Bundesministerium für Forschung und Technologie and by Kleinwanzlebener Saatzucht AG, Einbeck.     

Tissue culture ofKarwinskia humboldtiana—a plant producing toxins with antitumoural effects

Isolated embryos ofKarwinskia humboldtiana were cultured in vitro. The growth of embryos and development to plantlets on woody plant medium supplemented with indole-3-acetic acid 6.10^-2 mol l^–1, gibberellic acid (GA₃) 3.10^-2 mol l^–1, and 6-benzylaminopurine (BA) 2 mol l^–1 was obtained. Multiplication of shoots and rooting of excised shoots has been achieved. Callus formation on modified Murashige-Skoog medium supplemented with 1-naphthaleneacetic acid 10 mol l^–1, GA₃ 14 mol l^–1, and kinetin 5 mol l^–1 on hypocotyls, or on root cultures on medium supplemented with 2.4-dichlorophenoxyacetic acid 10 mol l^–1 and BA 10 mol l^–1 was induced.Abbreviations BA 6-benzylaminopurine - 2,4-d 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - NAA 1-naphthaleneacetic acid - TEM transmission electron microscopy     

Some effects of long-term ozone fumigations on Norway spruce

Summary Potted cuttings of a 12-year-old, and grafts of an 80-year-old, Norway spruce (Picea abies (L.) Karst.) were subjected to 100 or 300 g O₃·m^–3 for 1215 h (45 h of daylight per week) during the growing season of 1985. At the end of the fumigation the plants did not exhibit any visible signs of injury. Whereas in the fumigation with 100g O₃·m^–3 we did not detect any significant change in gas exchange, 300 g O₃·m^–3 did alter the CO₂ uptake after 27 weeks, and in one clone transpiration was also altered. Stomatal reaction to a change of light suggested sluggishness, but the change was not statistically significant.     

A lyophilized aqueous extract of<Emphasis Type="Italic"> Maytenus ilicifolia</Emphasis> leaves inhibits histamine-mediated acid secretion in isolated frog gastric mucosa

Lyophilized aqueous extract of Maytenus ilicifolia leaves (LAEMIL) is commonly used in Brazilian folk medicine in the treatment of dyspepsia as well as gastric ulcers. We have investigated the effect and the possible mechanism of action of the LAEMIL on acid secretion in isolated frog gastric mucosa incubated in an Ussing chamber. It was observed that LAEMIL (7–28 mg%) as well as cimetidine (125–4,000 M), a well-known histamine H₂ receptor antagonist, decreased basal acid secretion in a concentration-dependent manner. Similarly to cimetidine (190 M), LAEMIL (21 mg%) also inhibited gastric acid secretion induced by increasing concentrations of histamine (50–800 M). The EC₅₀ values for histamine alone and histamine in the presence of LAEMIL or cimetidine were 94.6 M (71.1–125.9 M), 244.9 M (209.4–286.4 M) and 142.2 M (23.6–855.0 M), respectively. LAEMIL, histamine and cimetidine were effective on acid secretion only when added to the serosal surface of the mucosa. Furthermore, simultaneous addition of LAEMIL and cimetidine at concentrations, per se, ineffective, caused a 16% reduction in the basal acid secretion [from 8.3±0.3 to 6.9±0.2 Eq g^–1 (15 min)^–1, n=4]. Although effects such as inhibition of histamine biosynthesis and/or histamine release can not be ruled out, our data suggest that LAEMIL, like cimetidine, reduces acid secretion in the isolated frog gastric mucosa by antagonising histamine H₂ receptors.Abbreviations LAEMIL Lyophilized aqueous extract of Maytenus ilicifolia leaves - Hist Histamine - Cim Cimetidine     

Arsenic concentrations in water and fish from Chautauqua Lake,New York

Synopsis Arsenic persists in Chautauqua Lake, New York waters 13 years after cessation of herbicide (sodium arsenite) application and continues to cycle within the lake. Arsenic concentrations in lake water ranged from 22.4–114.81 g l^–1, = 49.0 ag l^–1. Well water samples generally contained less than 10 g l^–1 arsenic. Arsenic concentrations in lake water exceeded U.S. Public Health Service recommended maximum concentrations (10 g l^–1) and many samples exceeded the maximum permissible limit (50 g l^–1). Fish accumulated arsenic from water but did not magnify it. Fish to water arsenic ratios ranged from 0.4–41.6. Black crappie (Pomoxis nigromaculatus) contained the highest arsenic concentrations (0.14–2.04 g g^–1 ), X = 0.7 g g^–1) while perch (Perca flavescens), muskellunge (Esox masquinongy) and largemouth bass (Micropterus salmoides) contained the lowest concentrations (0.02–0.13 g g^–1). Arsenic concentrations in fish do not appear to pose a health hazard for human consumers.     

Purification and characterization of membrane-bound hydrogenase from Methanosarcina barkeri MS

Hydrogenase was solubilized from the membrane of acetate-grown Methanosarcina barkeri MS and purification was carried out under aerobic conditions. The enzyme was reactivated under reducing conditions in the presence of H₂. The enzyme showed a maximal activity of 120±40 mol H₂ oxidized · min^–1 · min^–1 with methyl viologen as an electron acceptor, a maximal hydrogen production rate of 45±4 mol H₂ · min^–1 · mg^–1 with methyl viologen as electron donor, and an apparent K _m for hydrogen oxidation of 5.6±1.7 M. The molecular weight estimated by gel filtration was 98,000. SDS-PAGE showed the enzyme to consist of two polypeptides of 57,000 and 35,000 present in a 1:1 ratio. The native protein contained 8±2 mol Fe, 8±2 mol S^2–, and 0.5 mol Ni/mol enzyme. Cytochrome b was reduced by hydrogen in a solubilized membrane preparation. The hydrogenase did not couple with autologous F₄₂₀ or ferredoxin, nor with FAD, FMN, or NAD(P)⁺. The physiological function of the membrane-bound hydrogenase in hydrogen consumption is discussed.Abbreviation CoM-S-S-HTP the heterodisulfide of 7-mercaptoheptanoylthrconine phosphate and coenzyme M (mercaptoethanesulfonic acid)     

Sodium influx in isolated gills of the freshwater mussel,Ligumia subrostrata

Summary Isolated gills of the freshwater mussel,Ligumia subrostrata, accumulate Na from a pondwater bathing medium. The rate of Na transport by the isolated gill is 13.2±1.1 mol (g dry gill·10 min)^–1 which equals or exceeds the estimated Na transport rate of intact animals. Sodium influx is saturable with aV _max of 13.6±1.2 mol (g dry gill·10 min)^–1 and an affinity (K _s) of 0.17 mM Na/l. The isolated gills survive prolonged exposure to pondwater with a constant of 890 l O₂ (g dry gill·h)^–1 over a 4 h period. Sodium transport in the isolated gills is stimulated 80% above control values by 10^–4 M serotonin, 60% by 0.5 mM cAMP and 60% by 12.5 g/ml nystatin. Sodium influx is inhibited by 0.5 mM amiloride and 1 mM lithium.     

Ammonium and nitrate uptake rates and rhizosphere pH in non-mycorrhizal roots of Norway spruce [Picea abies (L.) Karst.]

Summary Relationships between root zone temperature, concentrations and uptake rates of NH ₄ ⁺ and NO ₃ ^– were studied in non-mycorrhizal roots of 4-year-old Norway spruce under controlled environmental conditions. Additionally, in a forest stand NH ₄ ⁺ and NO ₃ ^– uptake rates along the root axis and changes in the rhizosphere pH were measured. In the concentration (C_min) range of 100–150 M uptake rates of NH ₄ ⁺ were 3–4 times higher than those of NO ₃ ^– The preference for NH ₄ ⁺ uptake was also reflected in the minimum concentration (C_min) values. Supplying NH₄NO₃, the rate of NO ₃ ^– uptake was very low until the NH ₄ ⁺ concentrations had fallen below about 100 M. The shift from NH ₄ ⁺ to NO ₃ ^– uptake was correlated with a corresponding shift from net H⁺ production to net H⁺ consumption in the external solution. The uptake rates of NH ₄ ⁺ were correlated with equimolar net production of H⁺. With NO ₃ ^– nutrition net consumption of H⁺ was approximately twice as high as uptake rates of NO ₃ ^– In the forest stand the NO ₃ ^– concentration in the soil solution was more than 10 times higher than the NH ₄ ⁺ concentration (<100 M), and the rhizosphere pH of non-mycorrhizal roots considerably higher than the bulk soil pH. The rhizosphere pH increase was particularly evident in apical root zones where the rates of water and NO ₃ ^– uptake and nitrate reductase activity were also higher. The results are summarized in a model of water and nutrient transport to, and uptake by, non-mycorrhizal roots of Norway spruce in a forest stand. Model calculations indicate that delivery to the roots by mass flow may meet most of the plant demand of nitrogen and calcium, and that non-mycorrhizal root tips have the potential to take up most of the delivered nitrate and calcium.