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     

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.     

Effect of ammonium on the regulation of nitrate and nitrite transport systems in roots of intact barley (Hordeum vulgare L.) seedlings

The effect of NH ₄ ⁺ on the regulation of NO ₃ ^– and NO ₂ ^– transport systems in roots of intact barley (Hordeum vulgareL.) seedlings grown in NO ₃ ^– or NO ₂ ^– was studied. Ammonium partially inhibited induction of both transport systems. The inhibition was less severe in NO ₂ ^– -fed than in NO ₃ ^– -fed seedlings, presumably due to lower uptake of NH ₄ ⁺ in the presence of NO ₂ ^– . In seedlings pretreated with NH ₄ ⁺ subsequent induction was inhibited only when NH ₄ ⁺ was also present during induction, even though pretreated roots accumulated high levels of NH ₄ ⁺ . This indicates that inhibition may be regulated by NH ₄ ⁺ concentration in the cytoplasm rather than its total accumulation in roots. L-Methionine sulfoximine did not relieve the inhibition by NH ₄ ⁺ , suggesting that inhibition is caused by NH ₄ ⁺ itself rather than by its assimilation product(s). Ammonium inhibited subsequent expression of NO ₃ ^– transport activity similarly in roots grown in 0.1, 1.0, or 10 mM NO ₃ ^– for 24 h (steady-state phase) or 4 d (decline phase), indicating that it has a direct, rather than general feedback effect. Induction of the NO ₃ ^– transport system was about twice as sensitive to NH ₄ ⁺ as compared to the NO ₂ ^– transport system. This may relate to higher turnover rates of membraneassociated NO ₃ ^– -transport proteins.Abbreviations Mes 2(N-morpholino)ethanesulfonic acid - MSO L-methionine sulfoximine     

Interspecies differences in the preference of ammonium and nitrate in vascular plants

Three solution experiments were performed to test the importance of NH ₄ ⁺ versus NO ₃ ^- +NH ₄ ⁺ to growth of 23 wild-forest and open-land species, using field-relevant soil solution concentrations at pH 4.5. At N concentrations of 1–200 M growth increased with increasing N supply in Carex pilulifera, Deschampsia flexuosa, Elymus caninus and Bromus benekenii. Geum urbanum was the most N demanding species and had little growth below 200 M. The preference for NH ₄ ⁺ or NO ₃ ^- +NH ₄ ⁺ was tested also at pH 4.0; no antagonism was found between NH ₄ ⁺ and H⁺, as indicated by similar relative growth in both of the N treatments at both pH levels. Growth in solution with NH ₄ ⁺ relative to NO ₃ ^- +NH ₄ ⁺ , 200 M, was negatively related to the mean pH of the field occurrence of the species tested; acid-tolerant species grew equally well with only NH ₄ ⁺ as with NO ₃ ^- +NH ₄ ⁺ (Oxalis acetosella, Carex pilulifera, Festuca gigantea, Poa nemoralis, Deschampsia flexuosa, Stellaria holostea, Rumex acetosella), while species of less acid soils were favoured by NO ₃ ^- +NH ₄ ⁺ (Urtica dioica, Ficaria verna, Melandrium rubrum, Aegopodium podagraria, Geum urbanum, Bromus benekenii, Sanguisorba minor, Melica ciliata, Silene rupestris, Viscaria vulgaris, Plantago lanceolata). Intermediate species were Convallaria majalis, Elymus caninus, Hordelymus europaeus and Milium effusum. No antagonism between NH ₄ ⁺ and Ca²⁺, Mg²⁺ and K⁺ was indicated by the total uptake of the elements during the experiment.     

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.     

Nitrate induction in spruce: an approach using compartmental analysis

Using ¹³NO ₃ ^– -efflux analysis, the induction of nitrate uptake by externally supplied nitrate was monitored in roots of intact Picea glauca (Moench) Voss. seedlings over a 5-d period. In agreement with our earlier studies, efflux analysis revealed three compartments, which have been identified as surface adsorption, apparent free space, and cytoplasm. While induction of nitrate uptake was pronounced, NO ₃ ^– fluxes in induced plants were decidedly lower and the induction response was slower than in other species. Influx rose from 0.1 mol·g^–1·h^–1 (measured at 100 M [NO ₃ ^– _o) in uninduced plants to a maximum of 0.5 mol·g^–1h^–1 after 3 d of exposure to 100 M [NO ₃ ^– _o and declined to 0.3–0.4 mol·g^–1h^–1 at the end of the 5-d period. Efflux remained relatively constant around 0.02-0.04 mol·g^–1h^–1, but its percentage with respect to influx declined from initially high values (around 30%) to steady-state values of 4–7%. Cytoplasmic [NO ₃ ^– ] ranged from the low micromolar in uninduced plants to a maximum of 2 mM in plants fully induced at 100 M [NO ₃ ^– ]_o. In-vivo root nitrate reductase activity (NRA) was measured over the same time period, and was found to follow a similar pattern of induction as influx. The maximum response in NRA slightly preceded that of influx. It increased from 25 nmol·g^–1·h^–1 without prior exposure to NO ₃ ^– to peak values around 150 nmol· g^–1h^–1 after 2 d of exposure to 100 M [NO ₃ ^– ]_o. Subsequently, NRA declined by about 50%. The dynamics of flux partitioning to reduction, to the vacuole, the xylem, and to efflux during the induction process are discussed.The research was supported by an 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 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. J. Vidmar for essential assistance in experiments.     

Laminaria culture for reduction of dissolved inorganic nitrogen in salmon farm effluent

Finfish culture is a growing industry, and it causes a nutrient loading problem. To investigate the feasibility of an integrated culture of kelp and salmon, 15-cm long kelp (Laminaria saccharina) was grown in salmon culture effluent. The objectives were to test the effects of flow rate and kelp density on dissolved inorganic nitrogen removal (DIN), and DIN uptake and growth by the kelp. NH ₄ ⁺ , NO ₃ ^– and DIN (NH ₄ ⁺ + NO ₃ ^– ) loadings were in the ranges 6.2–25.4, 12.9–40.0, 19.7–52.7 mol 1^–1, respectively, over the experimental period.Surplus uptake of nitrogen was not evident, because the C:N ratio (10–11) was constant in all experiments. During light periods, the kelp removed from 170–339 mol 1^–1 h^–1, and approximately 26–40% of the incoming DIN. The DIN uptake rate, based on daylight sampling periods, ranged between 6.1–22.5 mol g^–1 dry mass h^–1. The highest-flow rate, lowest-density tank had the highest DIN uptake rate. Debris from the fish effluent settling on the kelp thalli in the low-flow rate tanks affected uptake. Mean DIN uptake rate based on 3 days of growth for all flow-density combinations ranged between 5.4–8.3 mol g^–1 dry mass h^–1. The kelp utilized NH ₄ ⁺ and NO ₃ ^– equally.The growth ranged between 6.5–9% d^–1. The biomass production ranged from 1–2 g per sampling period. The highest growth rate and biomass production were achieved by kelp in the highest-flow rate, lowest-density tank. Lower DIN concentrations due to higher DIN removal rates in the other tanks and light limitation due to self-shading in the high-density tanks were probably responsible for the reduced growth rate in these tanks.Author for correspondence     

Nitrate deposition in northern hardwood forests and the nitrogen metabolism of Acer saccharum marsh

It is generally assumed that plant assimilation constitutes the major sink for anthropogenic Nitrate NO ₃ ^– deposited in temperate forests because plant growth is usually limited by nitrogen (N) availability. Nevertheless, plants are known to vary widely in their capacity for NO ₃ ^– uptake and assimilation, and few studies have directly measured these parameters for overstory trees. Using a combination of field and greenhouse experiments, we studied the N nutrition of Acer saccharum Marsh. in four northern hardwood forests receiving experimental NO ₃ ^– additions equivalent to 30 kg N ha^–1 year^–1. We measured leaf and fine-root nitrate reductase activity (NRA) of overstory trees using an in vivo assay and used ¹⁵N to determine the kinetic parameters of NO ₃ ^– uptake by excised fine roots. In two greenhouse experiments, we measured leaf and root NRA in A. saccharum seedlings fertilized with 0–3.5 g NO ₃ ^– –N m^–2 and determined the kinetic parameters of NO ₃ ^– and NH ₄ ⁺ uptake in excised roots of seedlings. In both overstory trees and seedlings, rates of leaf and fine root NRA were substantially lower than previously reported rates for most woody plants and showed no response to NO ₃ ^– fertilization (range = non-detectable to 33 nmol NO ₂ ^– g^–1 h^–1). Maximal rates of NO ₃ ^– uptake in overstory trees also were low, ranging from 0.2 to 1.0 mol g^–1 h^–1. In seedlings, the mean V _max for NO ₃ ^– uptake in fine roots (1 mol g^–1 h^–1) was approximately 30 times lower than the V _max for NH ₄ ⁺ uptake (33 mol g^–1 h^–1). Our results suggest that A. saccharum satisfies its N demand through rapid NH ₄ ⁺ uptake and may have a limited capacity to serve as a direct sink for atmospheric additions of NO ₃ ^– .     

Indices of plant N availability in an alpine grassland under elevated atmospheric CO2

The objective of this study was to estimate whether elevated atmospheric [CO₂] alters plant N availability in a native high-elevation grassland in the Swiss Alps using two integrative, relatively non-disruptive methods. Estimates based on seasonal net plant N uptake, and those based on the amounts of NH ₄ ⁺ -N plus NO ₃ ^– -N captured by ion exchange resin (IER) bags, did not differ in plots treated with ambient (355 L L^–1) and elevated (680 L L^–1) [CO₂] in either the second (1993) or third (1994) growing season under treatment with elevated [CO₂]. The results of this study suggest that the effects of rising atmospheric [CO₂] on plant N availability may be negligible in this grassland. The results also contrast the relatively large effects of elevated atmospheric [CO₂] (increases and decreases) reported for highly disturbed artificial systems.     

Characteristics of transient photosynthesis in Quercus serrata seedlings grown under lightfleck and constant light regimes

Photosynthetic-induction response and light-fleck utilization were investigated for the current-year seedlings of Quercus serrata, a deciduous tree found in temperate regions of Japan. The tree seedlings were grown under three light regimes: a constant low photosynthetic photon flux density (PFD) regime of 50 mol m^–2 s^–1, a constant high PFD regime of 500 mol m^–2 s^–1, and a lightfleck regime with alternated low (lasting 5 s) and high (lasting 35 s) PFD. The photosynthetic-induction response following a sudden increase of PFD from 50 to 500 mol m^–2 s^–1 exhibited two phases: an initial fast increase complete within 3–5 s, and a second slow increase lasting for 15–20 min. Induction times required to reach 50% and 90% of steady-state assimilation rates were significantly shorter in leaves from the constant low PFD than those from the high PFD regime. During the first 60–100 s, the ratio of observed integrated CO₂ uptake to that predicted by assuming that a steady-state assimilation would be achieved instantaneously after the light increase was significantly higher for leaves from the low PFD regime than from the high PFD regime. Lightfleck utilization was examined for various durations of PFD of 500 mol m^–2 s^–1 on a background PFD of 50 mol m^–2 s^–1. Lightfleck utilization efficiency was significantly higher in low PFD leaves than in the high PFD leaves for 5-s and 10-s lightflecks, but showed no difference among different light regimes for 100-s lightflecks. The contribution of post-illumination CO₂ fixation to total carbon gain decreased markedly with increasing lightfleck durations, but exhibited no significant difference among growth regimes. Photosynthetic performances of induction response and lightfleck utilization in leaves from the lightfleck regime were more similar to those in leaves from the low PFD regime. It may be the total daily PFD rather than PFD dynamics in light regimes that affects the characteristics of transient photosynthesis in Q. serrata seedlings.     

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.     

Photosynthetic gas exchange response of poplars to steady-state and dynamic light environments

The steady-state and dynamic photosynthetic response of two poplar species (Populus tremuloides and P. fremontii) to variations in photon flux density (PFD) were observed with a field portable gas exchange system. These poplars were shown to be very shade intolerant with high light saturation (800 to 1300 mol photons m^–2 s^–1) and light compensation (70 to 100 mol m^–2 s^–1) points. Understory poplar leaves showed no physiological acclimation to understory light environments. These plants become photosynthetically induced quickly (10 min). Activation of Rubisco was the primary limitation for induction, with stomatal opening playing only a minor role. Leaves maintained high stomatal conductances and stomata were unresponsive to variations in PFD. Leaves were very efficient at utilizing rapidly fluctuating light environments similar to those naturally occurring in canopies. Post-illumination CO₂ fixation contributed proportionally more to the carbon gain of leaves during short frequent lightflecks than longer less frequent ones. The benefits of a more dynamic understory light environment for the carbon economy of these species are discussed.     

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.     

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.     

Concentration and flux of solutes from snow and forest floor during snowmelt in the West-Central Adirondack region of New York

Decreases in pH and increases in the concentration of Al and NO ₃ ^– have been observed in surface waters draining acid-sensitive regions in the northeastern U.S. during spring snowmelt. To assess the source of this acidity, we evaluated solute concentrations in snowpack, and in meltwater collected from snow and forest floor lysimeters in the west-central Adirondack Mountains of New York during the spring snowmelt period, 29 March through 15 April 1984.During the initial phase of snowmelt, ions were preferentially leached from the snowpack resulting in elevated concentrations in snowmelt water (e.g. H⁺ = 140 eq.l^–1; NO ₄ ^2– = 123 eq.l^–1; SO ₃ ^– = 160 eq.l^–1). Solute concentrations decreased dramatically within a few days of the initial melt (< 50 eq.l^–1). The concentrations of SO ₄ ^2– and NO ₃ ^– in snowpack and snowmelt water were similar, whereas NO^– ₃ in the forest floor leachate was at least two times the concentration of SO ₄ ^2– .Study results suggest that the forest floor was a sink for snowmelt inputs of alkalinity, and a net source of H⁺, NO ₃ ^– , dissolved organic carbon, K⁺ and Al inputs to the mineral soil. The forest floor was relatively conservative with respect to snowmelt inputs of Ca²⁺, SO ₄ ^2– and Cl^–. These results indicate that mineralization of N, followed by nitrification in the forest floor may be an important process contributing to elevated concentrations of H⁺ and NO ₃ ^– in streams during the snowmelt period.     

Ecotoxicity of lead to the zebra musselDreissena Polymorpha,Pallas

The effect of lead on the filtration rate of the zebra musselDreissena polymorpha was investigated, together with the accumulation of Pb in the soft tissues of the mussels. The NOEC-filtration was 116 g.l^–1 (0,56 mol.l^–1) and the EC₅₀-filtration was 370 g.l^–1 (1.79 mol.l^–1). The NOEC-accumulation was the concentration found in the control water (1.4g.l^–1). These experiments show that the EC₅₀-filtration for Pb is similar to that for Cd, higher than that for Cu and lower than that for Zn. The water quality criteria for lead allow 25 g Pb.l^–1 in surface water. This will not cause short-term effects. Long-term effects may, however, occur, since an accumulation of Pb as low as 16 g.l^–1 was recorded in this study.     

Ammonium uptake in Rhodopseudomonas capsulata

Investigations of the uptake of ammonium (NH ₄ ⁺ ) by Rhodopseudomonas capsulata B100 supported the presence of an NH ₄ ⁺ transport system. Experimentally NH ₄ ⁺ was determined by electrode or indophenol assay and saturation kinetics were observed with two apparent K _m's of 1.7 M and 11.1 M (pH 6.8, 30°) and a V _max at saturation of 50–60 nmol/min·mg protein. The optimum pH and temperature were 7.0 and 33° C, respectively. The Q₁₀ quotient was calculated to be 1.9 at 100 M NH ₄ ⁺ , indicating enzymatic involvement. In contrast to the wild type, B100, excretion of NH ₄ ⁺ , not uptake, was observed in a glutamine auxotroph, R. capsulata G29, which is derepressed for nitrogenase and lacks glutamine synthetase activity. G29R1, a revertant of G29, also took up NH ₄ ⁺ at the same rate as wild type and had fully restored glutamine synthetase activity. Partially restored derivatives, G29R5 and G29R6, grew more slowly than wild type on NH ₄ ⁺ as the nitrogen source, remained derepressed for nitrogenase in the presence of NH ₄ ⁺ , and displayed rates of NH ₄ ⁺ uptake in proportion to their glutamine synthetase activity. Ammonium uptake and glutamine synthetase activity were also restored in R. capsulata G29 exconjugants which had received the plasmid pPS25, containing the R. capsulata glutamine synthetase structural gene. These data suggest that NH ₄ ⁺ transport is tightly coupled to assimilation.Abbreviations used CHES cyclohexylaminoethanesulfonic acid - GS glutamine synthetase - SDS sodium dodecylsulfate     

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.     

Effects of cadmium on the uptake,distribution and assimilation of nitrate in Pisum sativum

The net uptake, distribution and assimilation of NO ₃ ^– were studied in pea plants subjected to either long-term continuous Cd treatment for 10 d (10 or 50 M Cd) or short-term treatment (72 h) with 50 M Cd. In the latter treatment, the effects of transferring the plants to a Cd-free nutrient solution for a 'recovery period' of 96 h were also studied. All these treatments were compared with 'controls', plants which received no Cd. In both experiments, the reduction in fresh weight was associated with a decrease in the content (%) of shoot and root water and in transpiration rate as Cd concentration increased. The concentration of ₃ ^– in the shoots and sap decreased dramatically and net ₃ ^– uptake was severely inhibited, effects associated with a loss of shoot nitrate reductase (NR) activity. In the short-term Cd treatment, net ₃ ^– uptake was almost completely inhibited after 24 h, but recovered after the transfer of plants to a Cd-free nutrient solution. Similarly, a dramatic decrease in the shoot NR activity was observed. The uptake, distribution and tissue partitioning of K was also studied, which is considered to be the major counterion of ₃ ^– . Potassium uptake was similarly affected by Cd, as inferred from the ratio ₃ ^– /K uptake, which was ca. 10. The ratio K/ ₃ ^– tissue content increased in the shoot concomitantly to Cd in both long-term and short-term metal supply. These parameters showed a tendency of K similar to that observed for ₃ ^– , although its relative tissue distribution was not affected by Cd.     

Fate of 15N labelled urine on four soil types

A field lysimeter experiment was conducted over a 406 day period to determine the effect of different soil types on the fate of synthetic urinary nitrogen (N). Soil types included a sandy loam, silty loam, clay and peat. Synthetic urine was applied at 1000 kg N ha^-1, during a winter season, to intact soil cores in lysimeters. Leaching losses, nitrous oxide (N₂O) emissions, and plant uptake of N were monitored, with soil ¹⁵N content determined upon destructive sampling of the lysimeters. Plant uptake of urine-N ranged from 21.6 to 31.4%. Soil type influenced timing and form of inorganic-N leaching. Macropore flow occurred in the structured silt and clay soils resulting in the leaching of urea. Ammonium (NH ₄ ⁺ –N), nitrite (NO ₂ ^- –N) and nitrate (NO₃ ^-–N) all occurred in the leachates with maximum concentrations, varying with soil type and ranging from 2.3–31.4 g NH ₄ ⁺ –N mL^-1, 2.4–35.6 g NO ₂ ^- –N mL^-1, and 62–102 g NO ₃ ^- –N mL^-1, respectively. Leachates from the peat and clay soils contained high concentrations of NO ₂ ^- –N. Gaseous losses of N₂O were low (<2% of N applied) over a 112 day measurement period. An associated experiment showed the ratio of N₂–N:N₂O–N ranged from 6.2 to 33.2. Unrecovered ¹⁵N was presumed to have been lost predominantly as gaseous N₂. It is postulated that the high levels of NO ₂ ^- –N could have contributed to chemodenitrification mechanisms in the peat soil.