Nitrate Reductase Activity In Plants Research Articles

Elevated Nitrate Preference Over Ammonium in Aquatic Plants by Nitrogen Loadings in a City River

AbstractAquatic plants are the dominant biota in retaining nitrogen (N) pollutants discharged into river ecosystems, but the sensitivity of plant N pools and N assimilation to riverine N loadings, which is essential for evaluating river biogeochemistry and functions, remains poorly understood. Here, concentrations and stable isotopes of N in river water and aquatic plants were measured along the Nanming River in Guiyang of southwestern China. Total N (TN) contents of aquatic plants increased, but the increments decreased with river N concentrations. The δ15N of plant TN decreased with sewage N loadings along the river, which revealed a distinct shift of plant N preference from ammonium to nitrate. Higher levels of nitrate reductase activity in plants at the downstream river section supported the elevated nitrate preference and assimilation, which might explain the decreased nitrate concentrations observed in the river water of the downstream section. These findings contributed to understanding riverine N biogeochemical processes and their response to N loadings, which can help trace sewage N pollution and its ecological effects on river ecosystems.

Nitrate accumulation and physicochemical characteristics of lettuce as affected by sodium selenite and synthesized selenium nanoparticles

ABSTRACT Exogenous selenium (SE) application during lettuce (Lactuca sativa L.) production may prevent Se deficiency. Low concentrations of Se have beneficial effects on plant cell metabolism and application of Se can increase growth, yield, and quality and reduce nitrate concentration in lettuce. In the present study, biosynthetic synthesis of selenium (Se) nanoparticles (NPs) was carried out via Se ions reduction during exposure to rosemary (Salvia rosmarinus Spenn.) extract. Using scanning electron microscopy (SEM), the shape and size of the Se NPs were determined. To investigate effects of concentrations of sodium selenite (1, 2, and 4 mg∙L−1) and Se NPs (1, 2, and 4 mg∙L−1) on morphological and physiochemical traits of lettuce. Most nutrient solutions, especially 2 mg∙L−1 Se NPs, increased plant height, leaf number, fresh weight, chlorophyll a, total chlorophyll, and nitrate reductase activity of plants. Application of 2 and 1 mg∙L−1 Se NPs, caused a decrease in the level of nitrate accumulation. Under nutrient treatments, concentrations of P, K, Fe, Zn, and Se, and concentration of N decreased. Foliar application of biosynthetic synthesized Se NPs, may have potential for improved quantity and reduced nitrate accumulation in lettuce.

Effects of excessive nitrogen fertilizer and soil moisture deficiency on antioxidant enzyme system and osmotic adjustment in tomato seedlings

Long-term excessive application of nitrogen fertilizer induces secondary salinization of soil, which results in inhibiting plant growth. In addition, soil moisture deficiency also affects plant growth. To investigate the effects of excessive nitrogen fertilizer and soil moisture deficiency on the antioxidant enzyme system, plant water relations were analyzed through pressure-volume (P-V) curve, and photosynthetic light response parameters in tomato (Solanum lycopersicum L. Myoko) seedlings, an indoor experiment about 50 d was conducted using two irrigation water amounts based on field capacity (soil moisture deficiency: 50%-80%; adequate water: 70%-80%), two nitrogen fertilizer rates (moderate nitrogen; excessive nitrogen fertilizer: 0.585 g/pot) and two types of irrigation water (tap water and microbial diluent). The results showed that excessive nitrogen fertilizer (N) and soil moisture deficiency (W) reduced the biomass of tomato seedlings. In comparison to CK (combination of adequate water and tap water quality), microbial dilution (EM) increased plant biomass by 5.2%. Also, the nitrogen application increased chlorophyll relative contents (SPAD). The maximum net photosynthetic rate (Pc) decreased with nitrogen application and increased with EM application and irrigation amount. Excessive nitrogen application increased the plant nitrate reductase activity (NR). The plant NR in the N treatment showed a 13.0% increase compared to CK, and the plant NR in the treatment of nitrogen application with water deficiency (WN) increased 34.0% compared to water deficiency (W). After applying excessive nitrogen, N, EM-N, WN, EM-WN respectively increased the plant nitrate reductase activity by 13.0%, 22.9%, 34.0% and 28.6%, compared with the corresponding treatment with moderate nitrogen (i.e., CK, EM, W and EM-W). In addition, the activities of antioxidant enzymes [superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT)] in four treatments of nitrogen application (N, EM-N, WN, EM-WN) also increased significantly. Both soil moisture and nitrogen fertilizer significantly affect the parameters of osmotic adjustment, which is manifested in the reduction of osmotic potential (πFT), and the increase in the osmotic concentration (Cosm) and concentration difference (ΔCosm). But the decrease in the relative water content of apoplast (ζap), indicating that water deficiency and excessive nitrogen reduced the water absorption and water retention capacity of tomatoes to a certain extent. In conclusion, excessive nitrogen application and soil moisture deficiency inhibit plant growth significantly in this experiment. Meanwhile, microbial dilution can alleviate excessive nitrogen fertilizer and water stress to some extent, but the effect was not significant. Keywords: antioxidant enzyme, nitrogen, osmotic adjustment, pressure-volume curve, stress, tomato, water DOI: 10.25165/j.ijabe.20221502.5555 Citation: Zhang Y J, Yu S E, Li Z J, Chang T T, Xu Q C, Xu H L, et al. Effects of excessive nitrogen fertilizer and soil moisture deficiency on antioxidant enzyme system and osmotic adjustment in tomato seedlings. Int J Agric & Biol Eng, 2022; 15(2): 127–134.

Nitrate reductase activities in plants from different ecological and taxonomic groups grown in Japan

AbstractPlants generally use soil inorganic nitrogen, ammonium (NH4+–N), and nitrate (NO3−–N) as sources of nitrogen, an essential nutrient. The assimilation processes after uptake differ considerably from ammonium to nitrate. Nitrate must be reduced to ammonium in plant tissue before it is synthesized to amino acids, while ammonium is directly and immediately synthesized to amino acids after its uptake. Nitrate reductase is an enzyme that catalyzes the first and rate‐limiting step of nitrate assimilation, reducing nitrate to nitrite. It is a substrate‐inducible enzyme, and the capacity to induce nitrate reductase varies greatly among plant species. In vivo nitrate reductase activity (NRA) is generally measured as a nitrite production rate during incubation using fine cut pieces of plant tissue, and it is applicable as an indicator on plant nitrate use. Here we present in vivo NRA of leaves from a total of 108 species including arboreal trees, small trees, shrubs, herbs, a vine and a moss. For 75 of the species, NRA in fine roots was also determined. At least 20 species in sampled plants were imported and planted for scientific or industrial purposes, but most sampled species were native to Japan. Several inventory studies of plant NRA have been conducted, mainly in Europe, and they provided information on the species‐specific capacity of nitrate use by plants in Europe. However, to our best knowledge, there has been hitherto no published inventory of the NRA of plants in Japan where many endemic species are distributed. Our dataset contains plant NRA with species, family name, life form, leaf lifespan (evergreen or deciduous), growth stage, the season of sample collection, growth conditions (natural or cultivated) and other treatments/conditions when applicable. The data provided by this study may contribute to future works that require information regarding the plant species characteristics for nitrate use capacity or nitrate preference.The complete data set for this abstract published in the Data Paper section of the journal is available in electronic format in MetaCat in JaLTER at http://db.cger.nies.go.jp/JaLTER/metacat/metacat/ERDP-2019-06.1/jalter-en. [Correction added on 7 September 2020, after first online publication: JaLTER URL has been updated.]

Exploitation of new endophytic bacteria and their ability to promote sugarcane growth and nitrogen nutrition.

Few studies have evaluated endophytic bacteria in relation to plant growth promotion, nitrogen uptake and biological control. The aim of this study was to molecularly and physiologically characterize thirteen endophytic bacteria strains, evaluate their biological control properties and their ability to promote plant growth and plant N nutrition. All the strains produced indole acetic acid and promoted increase of plant biomass, N accumulative amount and N-use efficiency index. None of the strains carries the nifH gene. Four strains stimulated plant nitrate reductase activity, four solubilized phosphate, nine produced siderophores and none produced HCN. Seven strains inhibited Bipolaris sacchari growth and one was antagonistic to Ceratocystis paradoxa. The pathogens were inhibited by the production of diffusible and volatile metabolites by the bacterial strains. Moreover, this is the first study to demonstrate the effect of Delftia acidovorans on sugarcane plant growth, nitrogen metabolism improvement and antagonism to B. sacchari. The most efficient strains in promoting plant growth and exhibiting antagonistic activities towards fungal pathogens were Herbaspirillum frinsingense (IAC-BECa-152) and three Pantoea dispersa strains (IAC-BECa-128, IAC-BECa-129, and IAC-BECa-132). These bacteria show potential to be used as inoculants for sustainable agricultural management, mainly at the seedling production phase.

In situ assay of nitrate reductase activity using portable water bath.

In environmental research (i.e., plant ecophysiology, environmental microbiology, and environmental chemistry), some assays require incubation of samples at controlled temperature and darkness. Until now, due to a lack of equipment providing such possibility in situ, researchers had to move collected samples to the laboratory for incubation. Obviously, a delayed incubation and the ex situ conditions could seriously affect the assays' results. A good example of analysis where water bath use is needed is the nitrate reductase activity (NRA) in vivo assay where plant tissue samples are incubated in buffer solution at a predetermined temperature. We designed a transportable water bath with a temperature control which enables in situ measurements in many types of environmental studies. The presented device is small in size featuring a thermally insulated chamber and an electronically controlled thermostat system powered by a 12-V battery. Due to its modular design, it can be transported comfortably in difficult terrain. The incubation process can be carried out continuously in stable temperature and darkness. In order to examine the field usability of the presented device, we conducted measurements of plant nitrate reductase activity in difficult field conditions. The in situ assays were carried out at high altitudes in the Karkonosze mountains, SW Poland. The NRA was studied in two alpine species (Deschampsia caespitosa and Homogyne alpina). Our results showed low NR activity in H. alpina (mean 0.31μM NO2 g-1 DW h-1) and higher NRA in D. caespitosa (mean 2.7μM NO2 g-1 DW h-1). The obtained results were highly reproducible and had small variability (low standard error values).

The effector AWR5 from the plant pathogen Ralstonia solanacearum is an inhibitor of the TOR signalling pathway.

Bacterial pathogens possess complex type III effector (T3E) repertoires that are translocated inside the host cells to cause disease. However, only a minor proportion of these effectors have been assigned a function. Here, we show that the T3E AWR5 from the phytopathogen Ralstonia solanacearum is an inhibitor of TOR, a central regulator in eukaryotes that controls the switch between cell growth and stress responses in response to nutrient availability. Heterologous expression of AWR5 in yeast caused growth inhibition and autophagy induction coupled to massive transcriptomic changes, unmistakably reminiscent of TOR inhibition by rapamycin or nitrogen starvation. Detailed genetic analysis of these phenotypes in yeast, including suppression of AWR5-induced toxicity by mutation of CDC55 and TPD3, encoding regulatory subunits of the PP2A phosphatase, indicated that AWR5 might exert its function by directly or indirectly inhibiting the TOR pathway upstream PP2A. We present evidence in planta that this T3E caused a decrease in TOR-regulated plant nitrate reductase activity and also that normal levels of TOR and the Cdc55 homologues in plants are required for R. solanacearum virulence. Our results suggest that the TOR pathway is a bona fide T3E target and further prove that yeast is a useful platform for T3E function characterisation.

Effect of elevated carbon dioxide on nitrogen assimilation and mobilization in wheat and rye genotypes of different ploidy levels

Two wheat genotypes differing in ploidy level viz. PBW 343 (hexaploid) and PDW 274 (tetraploid), and rye genotype WSP 540-2 (diploid) were grown under elevated CO2 (EC: 550 ± 50 ppm) and ambient CO2 (AC: 380 ppm) to study the changes in nitrogen assimilatory pathway enzymes. Elevated CO2 increased nitrate reductase (NR) activity in flag leaves of the three genotypes at milk stage, and activity was highest in rye (diploid). At dough stage, hexaploid and tetraploid genotypes showed higher NR activity in plants grown under EC. Elevated CO2 resulted in higher expression of NR gene (NIA1). Activity of glutamine synthetase (GS) in flag leaves was higher in all the three genotypes under EC at milk stage but the activity declined at dough stage. The expression of GS1 increased in flag leaves of plants grown under EC at both milk and dough stages, while the expression of GS2 declined during the reproductive stages, especially in ears of EC grown plants. Nitrate content decreased in leaf tissues of all the three genotypes by 90 DAS in EC grown plants. This indicated enhanced nitrate assimilation in leaves by NR under EC at reproductive stage. However, lower GS2 expression and lower GS activity during late reproductive phase (dough stage) indicated inhibition of consequent steps.

Response of Different Brassica Vegetables to Manure Source , NO3-N Accumulation and Nitrate Reductase Activity in Plant

Response of Different Brassica Vegetables to Manure Source , NO3-N Accumulation and Nitrate Reductase Activity in Plant

The effect of used engine oil on carbohydrate, mineral content and nitrate reductase activity of leafy vegetable (<i>Amaranthus hybridus</i> L.)

The effects of used engine oil on carbohydrate, mineral elements and nitrate reductase activity of Amaranthus hybridus were investigated. Seedlings were grown for 8 weeks in soil containing 0-5 % v/w usedengine oil. There was a significant (p=0.05) low level of mineral elements in plants grown in oil treated soils. The carbohydrate content of the control plants was significantly higher than the values observed for plants grown in oil treated soils. The control plants had a mean value of 48.3 ± 0.5 ìg g-1 dry wt, while 42.0 ± 1.0 and 30.9 ± 0.4 ìg g-1 dry wt were observed for plants treated with 1 and 5 % oil. There was significant inhibitory effect on nitrate reductase activity in plants that were exposed to engine oil. Therefore, the potential risk of used engine oil as potent environmental pollutant has been established from the results of this study

Nitrogen Dioxide-Induced Responses in Brassica campestris Seedlings: The Role of Hydrogen Peroxide in the Modulation of Antioxidative Level and Induced Resistance

This article investigates the responses of Brassica campestris seedlings to an acute level of nitrogen dioxide (NO 2) exposure in a plant growth chamber, and examines whether pretreating plants with hydrogen peroxide (H 2O 2) will alleviate NO 2-caused injury. Twenty-eight-day-old B. campestris plants sprayed with 10 mmol L −1 H 2O 2 aqueous solution (corresponding to approximate 1.0 mg H 2O 2 per single plant) were exposed to different concentrations of NO 2 (0.25, 0.5, 1.0, and 2.0 μL L −1, respectively) for 24 h under controlled environment. To measure the plant biomass, the plants were fumigated with the same NO 2 concentrations as mentioned above for 7 h per day (8.00-15.00) for 7 days. As a control, charcoal filtered air alone was applied. Data were collected on plant biomass, total chlorophyll, photosynthetic rate, stomatal conductance, nitrate and nitrate reductase (NR), antioxidative enzymes, ascorbate (ASA), and malondialdehyde (MDA), immediately after exposure. The results showed that exposure to a moderate dose of NO 2 (e.g., 0.25 μL L −1) had a favorable effect on plants, and the dry weight of the above-ground part increased, whereas the exposure to high NO 2 concentrations (e.g., 0.5 μL L −1 or higher) caused a reduction in the plant biomass and the total chlorophyll, when compared with the control. In addition, at 0.5 μL L −1 or higher NO 2 concentrations, prominent increases in the MDA level and superoxide dismutase (SOD) and NR activities were observed. Exposure to 1 μL L −1 and higher NO 2 resulted in necroses appearing on older leaves, and an increase in catalase (CAT) activity, decrease in ASA content, increased accumulation of NO 3, and reduction in photosynthesis, when compared with the controls. No changes were detected in stomatal conductance under NO 2 fumigation. The pretreatment with 10 mmol L −1 H 2O 2 alleviated significantly NO 2-caused biomass decrease and photosynthetic inhibition when compared with H 2O 2-untreated plants. Under NO 2 fumigation, further induction in SOD and CAT activities occurred in H 2O 2 treated plants when compared with H 2O 2-untreated plants. The effect of NO 2 on the ASA and MDA contents was also absent in H 2O 2-treated plants. However, the H 2O 2 treatment did not alter the nitrate content and NR activity in plants under NO 2 fumigation. The H 2O 2 treatment caused a lower rate of stomatal conductance. Taken together, these data suggest that fumigation with an acute level of NO 2 causes oxidative damage to B. campestris seedlings. The H 2O 2 pretreatment markedly protects plants against NO 2 stress and this may be associated with inducible antioxidative level. NO 2 fumigation contributes, at least in part, to the enhanced levels of nitrate in B. campestris leaves.

A study on nitrate reductase activity (NRA) of geophytes from Mediterranean environment

Nitrate reductase activity (NRA) in different compartments of 14 Mediterranean geophytes (bulbous, tuberous and rhizomatous) and actual mineral nitrogen (NO 3 − and NH 4 +) in their soils were investigated. The nitrate reduction capacities of each species were determined as NRA per total plant material. Differences among compartments for NRA were significant in all species. The highest NRA was found in leaves of tuberous species ( Anemone coronaria, Cyclamen coum) and of most bulbous species ( Allium flavum, Allium guttatum, Bellevelia sarmatica, Galanthus plicatus, Leucojum aestivum, Ornithogalum nutans, Tulipa sylvestris). Therefore, in this group of species the contribution of the leaves to total plant NRA was the highest. The other bulbous species ( Allium scorodoprasum, Crocus chrysanthus, Fritillaria bithynica, Muscari neglectum) and one rhizomatous taxon ( Iris suaveolens) have a different NRA distribution within the plants. In these species the highest values of NRA were found in different organs. For example, in Allium scorodoprasum the highest NRA was in tunics, and in flowers in M. neglectum. Although leaves are the main compartments reducing nitrate in most of the studied geophytes, other compartments also contribute to total plant nitrate reduction. Our results show that the nitrate reduction capacity is different among geophyte species. Even if it roughly reflects the nitrogen supply in a habitat, differences in nitrate reduction capacities of different species collected from same sites indicate that the nitrate reducing capacity is species-specific.

Activity of nitrate reductase and glutamine synthetase in shoot and root of mycorrhizal Allium cepa: Effect of drought stress

The effect of arbuscular-mycorrhizal (AM) fungus Glomus fasciculatum on growth and N form assimilation was measured on onion ( Allium cepa) grown under well-watered (−0.04 MPa) or drought conditions (−0.17 MPa). Two uninoculated control treatments, one provided with phosphate, were also addressed. These three treatments were supplemented with 2.0 mM nitrogen as nitrate and ammonium in a 1/1 ratio. Shoots and root weights, percentage of root colonized and glutamine synthetase (GS) (EC 6.3.1.2.) and nitrate reductase (NR) (EC 1.6.6.1) activity in shoot and root tissue were determined when water was maintained at (−0.04 MPa) or (−0.17 MPa) in the growth medium. The growth of G. fasciculatum-colonized plants was comparable to that of uncolonized P-supplemented plants under well-watered or drought conditions but mycorrhizal plants reached a higher specific and total GS activity in shoots and roots than P-fertilized plants growth at −0.04 MPa. The mycorrhizal effect on GS activity under water stress (−0.17 mPa) was evident only in roots being comparable to that found in P-fertilized plants. The proportion of GS in roots was increased in AM plants under whatever soil water conditions. The most marked increasing effect of AM-colonization on NR activity was in root tissue. Under water limitations the effectiveness of G. fasciculatum increasing NR activity in plant was enhanced. The proportion of nitrate assimilation into root was increased in AM plants particularly under well-watered conditions. Mycorrhizal modifications in the GS and NR distribution into root and shoot compartments may account for some physiological effect from mycorrhizal colonization. These results are further evidence of a direct effect on absorption, translocation and assimilation of both N forms by the endomycorrhizal system. That mycorrhizal plants can utilize nitrate form more efficiently than ammonium under drought conditions is consistent with more recent studies on the AM effect on N uptake from a neutral-alkaline soil. Results here presented suggest that either AM fungi increase the nitrogen forms assimilation in the host plant (regardless of P content) or the AM fungi have such enzymatic activities per se. This last assumption is supported by the relative high increase of NR and GS activities found in the roots of mycorrhizal plants. Nevertheless while NR was maintained increased in mycorrhizal roots under water stress the GS activity was not affected. This suggests the AM ability to provide an active nitrate acquisition in particular in water stressed environment. The different proportion of nitrate and ammonium assimilation into shoot and root compartments may account to modify physiological mycorrhizal responses related to plant sensitivity to drought.

Changes in nitrate reductase activity and the protective effect of molybdenum during cold stress in winter wheat grown on acid soil

Summary Two cultivars (frost resistant Sadovo 1 and frost susceptible San Pastore) of winter wheat (Triticum aestivum L.) were used to study the protective effect of molybdenum during freezing of plants grown on acid soil. We followed the effect of cold acclimation (2°C for 7 days) and freezing (−5 °C for 16 h) on the activities of nitrate reductase (NR), nitrite reductase (NiR) and glutamine synthetase (GS) in the leaves of both wheat cultivars grown on soil with pH 6.0 and pH 4.5. No difference was observed between the cultivars in the temperature induced changes of enzyme activities. During cold acclimation the activities of the three enzymes increased irrespective of the soil's pH; this increase, which was most pronounced for NADH: NR activity, was paralleled by an increase in NR protein. Freezing affected only NR activity in plants grown on acid soil; the sharpest decline was found for NADH : NR activity and FADH : NR partial activity. Molybdenum supplied to winter wheat cv. Sadovo 1 grown on soil with pH 4.5 prevented the frost-induced decline of NADH : NR activity. The possible mechanism of the protective effect is discussed.

Effects of Nitrate Withdrawal and Resupply on the Assimilation of Nitrate in Leaves of Tomato

The aim of this work was to establish the relationships between the concentration of nitrate in the medium and nitrate reductase activity (NRA) per gram of leaf material, NRA in the whole leaf system, and the concentration of nitrate in the leaves of tomatoes. Differences in NRA in plants growing continuously in different concentrations of nitrate, and also in plants growing in changing concentrations of nitrate, were studied

Redução de nitrato em plantas jovens de café cultivadas em diferentes níveis de luz e de nitrogênio

Foi estudado o efeito de níveis de luz e de nitrogênio na atividade da enzima redutase de nitrato e nos teores de nitrato e de açúcares nas folhas de plantas jovens de café (Coffea arabica L), assim como as possíveis relações entre a disponibilidade desses compostos e a atividade enzimática. Foram utilizadas plantas de dez meses de idade cultivadas em vasos contendo uma mistura de terra mais composto, e mantidas em condições ambientais em pleno sol e em 50% da luz solar. Metade das plantas de cada tratamento de luz foi suplementada semanalmente com nitrogênio. Os resultados mostraram que a atividade da redutase de nitrato, nos dois tratamentos de luz, foi maior nas plantas suplementadas com nitrogênio. Para um mesmo nível de nitrogênio, as plantas cultivadas em pleno sol apresentaram menor atividade da redutase de nitrato, maiores teores de nitrato e de açúcares e maiores taxas de transpiração, do que as cultivadas na sombra. Tais resultados indicam que a menor atividade da redutase de nitrato nas plantas cultivadas em pleno sol aparentemente não foi devida a limitações na disponibilidade de nitrato e de açúcares para fornecer a energia necessária para a redução de nitrato.

Nitrate Reductase Activity and Nitrate Concentration in Cotton Plant Leaf Blades and Petioles

AbstractGreenhouse studies were conducted to determine the potential of nitrate reductase activity (NRA) as an indicator of the change of N concentration of cotton (Gossypium hirsutum L.) shoots. The results showed that cotton petiole in vivo NRA was not significantly different from NRA in leaf blades during vegetative growth. Nitrate reductase activity (in vivo) in cotton petioles was significantly higher than in leaf blades during reproductive growth. When plants were in the three‐mature‐leaf stage, petiole NRA contributed 16% of total cotton shoot NRA. The petiole biomass was 14% of total shoot fresh weight and 8% of total shoot dry weight. Petiole NRA of plants in the vegetative growth stage increased from 39 to 68 pmol NO−2 g1− FW (fresh weight) s−1 when supplemented with nitrate‐N. These results indicate that cotton petiole NRA is significant and its assay has potential for incorporation into monitoring systems that determine the change of N concentration in cotton shoots.

The effect of temperature and nitrogen interactions on growth and nitrogen assimilation of white clover

White clover plants were grown for 97 days under two temperature regimes (20/15°C and 8/5°C day/night temperatures) and were supplied with either small amounts (a total of 80 mg N pot−1) of ammonium (NH 4 + ) or nitrate (NO 3 − ) nitrogen, or received no mineral N and relied on N2 fixation. Greatest growth and total leaf area of clover plants occurred in N2 fixing and NO 3 − -fed plants grown at 20/15°C and poorest growth occurred in NH 4 + -fed plants grown at 8/5°C. Nodule mass per plant was greater at 8/5°C due to increased nodule numbers rather than increased dry weight per nodule. This compensated to some extent for the reduced N2-fixing activity per unit dry weight of nodule tissue found at the low growth temperature up to 116 d after sowing, but thereafter both activity per nodule dry weight and activity per plant were greater at the low temperature. Highest nitrate reductase activity (NRA) per g fresh weight and total activity per leaf, petiole or root occurred in NO 3 − -fed plants at 8/5°C. Low growth temperature resulted in a greater partitioning of total plant NRA to the roots of NO 3 − -fed plants. The results are considered in relation to the use of N fertiliser in the spring under field conditions.

Effects of time of nitrate application on nitrate reductase activity, nitrate uptake, and symbiotic dinitrogen fixation in faba bean and pea

The effects of increasing concentrations of [Formula: see text] (0, 5, 10, or 15 mol∙m−3) supplied at planting or 7 or 14 days after planting were studied in faba bean (Vicia faba L.) and pea (Pisum sativum L.) inoculated with Rhizobium leguminosarum biovar viceae isolate 175F19. Averaged over all times of [Formula: see text] application, N2 fixation (acetylene reduction) was inhibited significantly more in pea than in faba bean. Times of [Formula: see text] application had little effect on N2 fixation for faba bean. In contrast, N2 fixation in pea was most strongly inhibited when [Formula: see text] was applied at planting and showed a decreasing sensitivity as [Formula: see text] applications were delayed to 7 and 14 days after planting. At all times of [Formula: see text] application, as the levels of [Formula: see text] increased, the proportion of total plant nitrate reductase activity contributed by leaves and roots remained relatively constant in faba bean, but these proportions increased and decreased, respectively, in pea. Nitrate was taken up at higher levels and at a greater rate in pea than in faba bean. The lower capacity for [Formula: see text] uptake in faba bean could contribute to the greater tolerance of the symbiosis to [Formula: see text] compared with that in pea.

In situ nitrate reductase activity as an indicator of nitrate availability

The effect of external nitrate concentration in the nutrient solution on nitrate reduction by 7-day-old barley seedlings was investigated using anin situ nitrate reductase activity (NRA) assay, performed with or without exogenous nitrate during the incubation. The difference between plus and minus nitrate NRA of the leaves related to plus nitrate NRA decreased with increasing nitrate concentration in the nutrient solution. Furthermore, the root contribution to the whole plant NRA became predominant at low external nitrate levels. It is proposed that plus and minus nitrate NRA should be used together as an indicator of nitrate availability in the medium and of root contribution to whole plant nitrate reduction.