Higher Nitrate Reductase Activity Research Articles

The Determination of Nitrate Reductase Activity of Leaves to the Dominant Species in Forest Community of Northern Aspect of Changbai Mountains

This paper addresses the application of improvement in vivo of traditional method for determination of nitrate reductase (NR) activity of leaves to dominant tree species in forest community of northern aspect of Changbai Mountains. It describes the NR activity of tree species related to the shade-endurance and shows that the intolerance tree species has higher NR activity. The NR of a species is also related to the ecological situation of the sites. Tree species with higher NR activities should be selected for breeding of fast growing and high yield tree species.

Efeito fisiológico do fungicida boscalida na atividade da nitrato redutase e nas características fitotécnias de pepineiro japonês enxertado e não enxertado.

The present study aimed to evaluate physiological effect of the fungicide boscalida in the activity of nitrate reductase in the plant parameters characteristics of Japonese cucumber grafted and non grafted. The experiment was carried out under protected cultivation at Sao Manuel Experimental Farm, Faculty of Agronomical Sciences (FCA), Sao Paulo State University (UNESP), Botucatu Campus, Sao Paulo State, Brazil. Both the cucumber hybrid ‘Tsuyataro’ grafted onto the pumpkin ‘Excite Ikky’ and ungrafted plants were subjected to different levels (0, 25, 50, 75 and 100 g a.i. ha-1) of the boscalida fungicide through leaf application at weekly intervals. Experimental design was in randomized blocks, in a 5x2 factorial arrangement, with four replicates and six plants per plot, so that the four central plants were considered in the evaluation. Higher activity of nitrate reductase was observed in grafted plants and a linear response according to the fungicide level was detected at 81 D.A.T. There was also a linear effect according to the fungicide level for leaf area and plant dry matter and there was no difference between plant types. On the other hand, the two highest levels led to increased number of commercial, non-commercial and total fruits. Grafted plants had higher non-commercial production, but with no difference relative to commercial and total production. The lowest levels together with the treatment without boscalida had the lowest productivities. Conversely, the two highest levels led to an increase in commercial, with increases of 15.90 and 62.37% relative to the treatment without boscalida. In conclusion, the physiological effect of boscalida was obtained by using the levels 75 and 100 g a.i. ha-1 in both grafted and ungrafted cucumber plants.

FHANT‐AC genes of the ectomycorrhizal fungus Laccaria bicolor are not repressed by l‐glutamine allowing simultaneous utilization of nitrate and organic nitrogen sources

In boreal and temperate forest ectomycorrhizal fungi play a crucial role in nitrogen cycling by assimilating nitrogenous compounds from soil and transferring them to tree hosts. The expression profile of fHANT-AC genes, nitrate transporter (Lbnrt), nitrate reductase (Lbnr) and nitrite reductase (Lbnir), responsible for nitrate utilization in the ectomycorrhizal fungus Laccaria bicolor, was studied on variable N regimens. The three genes were shown to be under a common regulation: repressed in the presence of ammonium while growth on nitrate resulted in high transcripts accumulation. The presence of nitrate was shown not to be indispensable for activation of Laccaria fHANT-AC as also N starvation and growth on urea and l-asparagine resulted in high transcript levels. Equally high expression of Laccaria fHANT-AC genes was detected in mycelia grown on variable concentrations of l-glutamine. This finding shows that in L. bicolor N metabolite repression of fHANT-AC is not signalled via l-glutamine like described in ascomycetes. The expression patterns of Lbnrt and Lbnir were also studied in an Lbnr RNA-silenced Laccaria strain. No differences were observed on the N source regulation or the degree of transcript accumulation of these genes, indicating that the presence of high nitrate reductase activity is not a core regulator of L. bicolor fHANT-AC expression. The simultaneous utilization of nitrate and organic N sources, already suggested by high transcript levels of Laccaria fHANT-AC genes on organic N, was supported by the increase of culture medium pH as a result of nitrate transporter activity. The possible ecological and evolutionary significance of the herein reported high regulatory flexibility of Laccaria nitrate utilization pathway for ectomycorrizal fungi and the ectomycorrhizal symbiosis is discussed.

STUDIES ON DIFFERENCES OF NITROGEN EFFICIENCY AND ROOT CHARACTERISTICS OF OILSEED RAPE (BRASSICA NAPUS L.) CULTIVARS IN RELATION TO NITROGEN FERTILIZATION

Differences of nitrogen efficiency of oilseed rape (Brassica napus L.) cultivars and their physiological properties were studied in a pot experiment, and the ratio of seed yield with no nitrogen supplied to that with normal nitrogen supply was adopted as a nitrogen efficiency coefficient. Results showed that the nitrogen efficiency coefficient determined for eight oilseed rape cultivars varied from 0.37 to 0.69, the ratio of nitrogen uptake amounts per plant, nitrogen transfer velocity from stems and leaves to seeds, and nitrogen physiological efficiency of oilseed rape cultivars under nitrogen stressed condition differed from with normal nitrogen supply. The higher the nitrogen efficiency of a cultivar, the higher the ratio of N uptake in no nitrogen to with N supplied. Under low nitrogen-supplying conditions, high nitrogen efficiency cultivars had longer roots, more lateral roots, higher amounts of reuse of nitrate from stem and leaves, and higher nitrate reductase activities in leaves.

Improving Nitrogen Use Efficiency in Melon by Grafting

Identification of rootstocks capable of improving the nitrogen use efficiency (NUE) of the scion could reduce N fertilization and nitrate leaching; however, screening different graft combinations under field conditions can be costly and time-consuming. This study evaluated a rapid and economical methodology for screening of melon rootstocks for NUE. Two experiments were designed. In the first, melon plants (Cucumis melo L. cv. Proteo) either ungrafted or grafted onto four commercial rootstocks: ‘Dinero’ and ‘Jador’ (Cucumis melo L.), ‘P360’, and ‘PS1313’ (Cucurbita maxima Duchesne × Cucurbita moschata Duchesne) grown in hydroponics were compared in terms of shoot dry biomass, leaf area, root-to-shoot ratio, SPAD index, shoot N uptake, and nitrate reductase (NR) activity at the early developmental stage in response to nitrate availability (0.5, 2.5, 5, 10, or 15 mm of NO3–). The second experiment was aimed to confirm whether the use of a selected rootstock with high NUE (‘P360’) could improve crop performance and NUE of grafted melon plants under field conditions. In the first experiment, carried out under greenhouse conditions, melon plants grafted onto ‘Dinero’, ‘Jador’, and ‘P360’ rootstocks needed 5.7, 5.2, and 6.1 mm of NO3–, respectively, to reach half-maximum shoot dry weight, whereas plants grafted onto ‘PS1313’ rootstock and the control treatment (ungrafted plants) needed 9.1 and 13.1 mm of NO3–, respectively. Total leaf area, SPAD index, and shoot N uptake increased linearly and quadratically in response to an increase of the N concentration in the nutrient solution. At 2.5 mm of NO3–, melon plants grafted onto both C. melo and Cucurbita maxima × Cucurbita moschata rootstocks had the highest NR activity, whereas no significant difference was observed at 10 mm of NO3–. In the second experiment, carried out under open field conditions, increasing the N fertilization rates from 0 to 120 kg·ha−1 increased the total and marketable yields of melon plants, whereas the NUE decreased. When averaged over N levels, the marketable yield, NUE, and N uptake efficiency were higher by 9%, 11.8%, and 16.3%, respectively, in ‘Proteo’ grafted onto ‘P360’ than in ungrafted ‘Proteo’ plants.

Metabolismo de nitrogênio em dois sistemas de cultivo de café sob veranico da estação úmida

Com o objetivo de avaliar o efeito do veranico ocorrido na estação úmida sobre o metabolismo de nitrogênio em cafeeiros em sistema a pleno sol e associados com abacateiro (Persea americana Mill.) e ingazeiro (Inga edulis Mart.), foi realizado este experimento. O estudo foi conduzido em propriedade situada no município de Barra do Choça, BA, composto por plantas de café (Coffea arabica L.), variedade Catuaí, sendo caracterizados dois campos experimentais (sistema sombreado x sistema a pleno sol). As avaliações foram realizadas em janeiro (período de veranico) e março (final da estação úmida), em cinco repetições por campo experimental. Os dados foram submetidos ao teste t por meio do programa SAEG, versão 9.1. Maior teor de NO3 - foi verificado no sistema a pleno sol, tanto no período de veranico como no final da estação úmida. Em março foi observado maior acúmulo de N-orgânico no terço superior do cafeeiro a pleno sol e no terço médio do cafeeiro sombreado. Maiores teores de nitrogênio total e a tendência de maior atividade enzimática da redutase do nitrato foram verificados nos sistemas arborizados, quando avaliados dentro do mesmo terço do cafeeiro nas duas estações.

Nitrate reductase activity (NRA) in Asphodelus aestivus Brot. (Liliaceae): distribution among organs, seasonal variation and differences among populations

Nitrate reductase activity (NRA) in different compartments (leaves, inflorescence stalks, flowers and tuberous roots) of Asphodelus aestivus Brot. (Liliaceae) and actual mineral nitrogen (NO 3 −-N and NH 4 +-N) in soil surrounding the roots were investigated over one year. Although the highest NRA was found in the leaves, the other plant compartments, such as flowers and tuberous roots, also have nitrate assimilation capacity. High nitrate assimilation capacity under suitable conditions is considered to be a good strategy for development and dominance of this species in Mediterranean environments. There was a seasonal variation in nitrate assimilation in leaves and actual NO 3 −-N content of soils. Depending on actual nitrate content of soils, nitrate assimilation increased in winter.

Soybean seed protein, oil, fatty acids, N, and S partitioning as affected by node position and cultivar differences

The mechanisms controlling the partitioning of seed composition constituents along the main stem in soybean are still controversial. Therefore, the objective of this study was to investigate seed protein, oil, and fatty acids partitioning in soybean cultivars along the main stem. The cultivars were DT97-4290, maturity group (MG) IV; Stressland, MG IV; Hutcheson, MG V; TracyM, MG VI. Seeds were harvested based on position on the plant (top nodes, middle nodes, and bottom nodes). At R8 (physiological maturity stage), DT97-4290, Hutcheson, and Stressland had higher percentage of protein and oleic acid and lower percentage of oil and linolenic acid in top node seed compared with bottom node seed. The increase of protein in top node compared with the bottom node across the two experiments ranged from 15.5 to 19.5%, 7.0 to 10.5%, 14.2 to 15.8%, 11.2 to 16.5%, respectively for DT97-4290, Hutcheson, Stressland, and TracyM. Except for TracyM, the increase of oleic acid in the top node ranged from 45.4 to 93%, depending on the cultivar. Conversely, the decrease in the top node seed ranged from 14.4 to 26.8% for oil and from 5.7 to 34.4% for linolenic acid, depending on the cultivar. The partitioning trend of seed composition constituents at R6 (seed - fill stage) was inconsistent. Except for Stressland, seed oleic acid was higher at R6 than at R8. The higher protein and oleic acid concentrations in the top node seed was accom- panied by higher activity of nitrate reductase activity, higher chlorophyll concentration, higher nitrogen (N) and sulfur (S) percentages in the fully expanded leaves at R5-R6 growth stage, and higher seed nitrogen (N) and sulfur (S) percentages in DT 97-4290 and Stressland. The current research suggests that the partitioning of seed protein, oil, and fatty acids in nodes along the plant depended on the position of node on the main stem, cultivar differences, seed N and S status, and tissue N and S partitioning. The higher nitrate reductase activity at the top nodes, accompanied higher protein and oleic acid, and the changes of oleic acid at R6 and R8 along the stem, were not previously reported, and need further investigation. The current knowledge is useful for soybean germplasm selection for desirable traits such protein and oleic acid, and for accurate measurements of seed composition constituents in breeding lines.

Nitrogen nutrition of Canna indica: Effects of ammonium versus nitrate on growth, biomass allocation, photosynthesis, nitrate reductase activity and N uptake rates

The effects of inorganic nitrogen (N) source (NH 4 +, NO 3 − or both) on growth, biomass allocation, photosynthesis, N uptake rate, nitrate reductase activity and mineral composition of Canna indica were studied in hydroponic culture. The relative growth rates (0.05–0.06 g g −1 d −1), biomass allocation and plant morphology of C. indica were indifferent to N nutrition. However, NH 4 + fed plants had higher concentrations of N in the tissues, lower concentrations of mineral cations and higher contents of chlorophylls in the leaves compared to NO 3 − fed plants suggesting a slight advantage of NH 4 + nutrition. The NO 3 − fed plants had lower light-saturated rates of photosynthesis (22.5 μmol m −2 s −1) than NH 4 + and NH 4 +/NO 3 − fed plants (24.4–25.6 μmol m −2 s −1) when expressed per unit leaf area, but similar rates when expressed on a chlorophyll basis. Maximum uptake rates ( V max) of NO 3 − did not differ between treatments (24–35 μmol N g −1 root DW h −1), but V max for NH 4 + was highest in NH 4 + fed plants (81 μmol N g −1 root DW h −1), intermediate in the NH 4NO 3 fed plants (52 μmol N g −1 root DW h −1), and lowest in the NO 3 − fed plants (28 μmol N g −1 root DW h −1). Nitrate reductase activity (NRA) was highest in leaves and was induced by NO 3 − in the culture solutions corresponding to the pattern seen in fast growing terrestrial species. Plants fed with only NO 3 − had high NRA (22 and 8 μmol NO 2 − g −1 DW h −1 in leaves and roots, respectively) whereas NRA in NH 4 + fed plants was close to zero. Plants supplied with both forms of N had intermediate NRA suggesting that C. indica takes up and assimilate NO 3 − in the presence of NH 4 +. Our results show that C. indica is relatively indifferent to inorganic N source, which together with its high growth rate contributes to explain the occurrence of this species in flooded wetland soils as well as on terrestrial soils. Furthermore, it is concluded that C. indica is suitable for use in different types of constructed wetlands.

Biostimulant activity of two protein hydrolyzates in the growth and nitrogen metabolism of maize seedlings

AbstractTwo protein hydrolyzate–based fertilizers (PHFs), one from alfalfa (AH) and one from meat flour (MFH), were studied chemically and biologically. AH and MFH revealed a different degree of hydrolysis and a different amino acid composition. The biostimulant activity was investigated using two specific and sensitive bioassays of auxins and gibberellins. Extracts of AH and MFH elicited a gibberellin‐like activity and a weak auxin‐like one. To improve our understanding of the biostimulant activity, AH and MFH were supplied to maize plants and their effect on growth and nitrate metabolism was studied. Both PHFs increased root and leaf growth and induced morphological changes in root architecture. Besides, the treatments increased nitrate reductase (NR) and glutamine synthetase (GS) activities, suggesting a positive role of the two hydrolyzates in the induction of nitrate conversion into organic nitrogen. Moreover, treatments enhanced GS1 and GS2 isoforms in maize leaves. The latter isoform, amounting to 5‐ to 7‐fold the level of the former, appears to be a superior form in the assimilation of ammonia. The high NR and GS activities together with the high induction of GS isoforms indicate a stimulatory effect of the two PHFs on the assimilation of nitrate. In addition, a role of amino acids and small peptides of the two PHFs is suggested in the regulation of the hormone‐like activity and nitrogen pathway.

Nitrate accumulation, growth and leaf quality of spinach beet (Beta vulgaris Linn.) as affected by NPK fertilization with special reference to potassium

The present study was carried out at the Herbal Garden of Jamia Hamdard, New Delhi on Pusa Bharti variety of Spinach Beet ( Beta vulgari s Linn.) to understand the effect of potassium with other fertilizers on nitrate accumulation, growth and quality of the leaves. Potassium application along with other fertilizers increased leaf area, per cent dry weight, Chlorophyll Content Index (CCI) and Nitrate Reductase Activity (NRA), but decreased nitrate content. Effect of 2:1 ratio of N and K was found statistically at par with 1:1 ratio of N and K. Fertilizer treatments without potassium had lower level of NRA and higher nitrate content in the leaves as compared to other applications. Application of FYM along with NPK fertilizers increased leaf area, per cent dry weight, CCI and NRA, whereas it decreases nitrate content. As higher NRA and lower nitrate content was recorded in treatments with potassium, application of K is desirable to reduce health hazards related with nitrate toxicity. Based on the results of the study, application of 1:1 ratio of N and K fertilizer and FYM is recommended.

Nitrate accumulation, growth and leaf quality of spinach beet (Beta vulgaris Linn.) as affected by NPK fertilization with special reference to potassium

The present study was carried out at the Herbal Garden of Jamia Hamdard, New Delhi on Pusa Bharti variety of Spinach Beet (Beta vulgaris Linn.) to understand the effect of potassium with other fertilizers on nitrate accumulation, growth and quality of the leaves. Potassium application along with other fertilizers increased leaf area, per cent dry weight, Chlorophyll Content Index (CCI) and Nitrate Reductase Activity (NRA), but decreased nitrate content. Effect of 2:1 ratio of N and K was found statistically at par with 1:1 ratio of N and K. Fertilizer treatments without potassium had lower level of NRA and higher nitrate content in the leaves as compared to other applications. Application of FYM along with NPK fertilizers increased leaf area, per cent dry weight, CCI and NRA, whereas it decreases nitrate content. As higher NRA and lower nitrate content was recorded in treatments with potassium, application of K is desirable to reduce health hazards related with nitrate toxicity. Based on the results of the study, application of 1:1 ratio of N and K fertilizer and FYM is recommended. Keywords: Spinach beet, potassium, nitrate toxicity, nitrate reductase, manure; fertilizers, NPK.

High nitrate reductase activity in sprouts of Phyllostachys pubescens

We investigated the distribution of nitrate reductase activity (NRA) among leaves, roots, culms, twigs, sprouts, culm sheaths, and new leaves of Phyllostachys pubescens Mazel in May, when many sprouts emerge above ground and new leaves of adult culms expand. We found that the NRA differed among parts, and that sprouts showed high NRA. These results indicate that different tissues of P. pubescens vary in nitrate reduction, and sprouts possess high nitrate reduction capacity. We also found that culm sheaths showed high NRA, indicating that they have a high potential for nitrate reduction, even though they are shed in the way of sprout growth.

Nitrogen nutrition of Salvinia natans: Effects of inorganic nitrogen form on growth, morphology, nitrate reductase activity and uptake kinetics of ammonium and nitrate

In this study we assessed the growth, morphological responses, and N uptake kinetics of Salvinia natans when supplied with nitrogen as NO 3 −, NH 4 +, or both at equimolar concentrations (500 μM). Plants supplied with only NO 3 − had lower growth rates (0.17 ± 0.01 g g −1 d −1), shorter roots, smaller leaves with less chlorophyll than plants supplied with NH 4 + alone or in combination with NO 3 − (RGR = 0.28 ± 0.01 g g −1 d −1). Ammonium was the preferred form of N taken up. The maximal rate of NH 4 + uptake ( V max) was 6–14 times higher than the maximal uptake rate of NO 3 − and the minimum concentration for uptake ( C min) was lower for NH 4 + than for NO 3 −. Plants supplied with NO 3 − had elevated nitrate reductase activity (NRA) particularly in the roots showing that NO 3 − was primarily reduced in the roots, but NRA levels were generally low (<4 μmol NO 2 − g −1 DW h −1). Under natural growth conditions NH 4 + is probably the main N source for S. natans, but plants probably also exploit NO 3 − when NH 4 + concentrations are low. This is suggested based on the observation that the plants maintain high NRA in the roots at relatively high NH 4 + levels in the water, even though the uptake capacity for NO 3 − is reduced under these conditions.

Interactive Effect of Sulfur and Nitrogen on Nitrogen Accumulation and Harvest in Oilseed Crops Differing in Nitrogen Assimilation Potential

ABSTRACT Field experiments were conducted to determine the interactive effect of sulfur (S) and nitrogen (N) on nitrogen accumulation, its distribution in various plant parts, and nitrogen harvest of oilseed crops viz. rapeseed (Brassica campestris L. cv. ‘Pusa Gold’) and taramira (Eruca sativa Mill.) differing in their N-assimilation potential. Two combinations of S and N (in Kg/ha): 0S + 100N (−S+N) and 40S + 100N (+S+N) were used. The results showed that combined application of S and N (+S+N) significantly (P < 0.05) increased the nitrogen accumulation in both the genotypes at all the growth stages compared with N applied alone (−S+N). This increase in nitrogen accumulation was due to the improvement in the reduction of nitrate into reduced nitrogen as evident from higher nitrate reductase (NR) activity in the leaves of plants grown with both S and N, compared with N alone. Nitrate-N content in the leaves of plants grown with only N (−S+N) was higher compared to those grown with both S and N (+S+N), showing that combined application of S along with N (+S+N) appreciably reduced the nitrate content in the leaves due to higher NR activity. This decline in nitrate (NO3 −) was followed by an overall increase in N-accumulation in the plants. Consequently, the nitrogen content in the plant was increased by 29–148% in rapeseed and 38-166% in taramira with +S+N treatment. Combined application of S along with N (+S+N) also increased seed protein content and nitrogen harvest index of both the genotypes. It is concluded that combined application of S along with N (+S+N) not only increased the N-accumulation, but also its mobilization towards economic sinks.

Colour formation in fermented sausages by meat-associated staphylococci with different nitrite- and nitrate-reductase activities

Three Staphylococcus strains, S. carnosus, S. simulans and S. saprophyticus, selected due to their varying nitrite and/or nitrate-reductase activities, were used to initiate colour formation during sausage fermentation. During fermentation of sausages with either nitrite or nitrate added, colour was followed by L ∗ a ∗ b measurements and the content of nitrosylmyoglobin (MbFe IINO) quantified by electron spin resonance (ESR). MbFe IINO was rapidly formed in sausages with added nitrite independent of the presence of nitrite reducing bacteria, whereas the rate of MbFe IINO formation in sausages with added nitrate depended on the specific Staphylococcus strain. Strains with high nitrate-reductase activity showed a significantly faster rate of pigment formation, but other factors were of influence as well. Product stability for the sliced, packaged sausage was evaluated as surface colour and oxidation by autofluorescence and hexanal content, respectively. No significant direct effect of the Staphylococcus addition was observed, however, there was a clear correspondence between high initial amount of MbFe IINO in the different sausages and the colour stability during storage. Autofluorescence data correlated well with hexanal content, and may be used as predictive tools. Overall, nitrite- and nitrate-reductase activities of Staphylococcus strains in nitrite-cured sausages were of limited importance regarding colour development, while in nitrate-cured sausages strains with higher nitrate reductase activity were crucial for ensuring optimal colour formation during initial fermentation stages.

Purification and Characterization of Nitrate Reductase from the Halotolerant Cyanobacterium Aphanothece halophytica

Factors affecting the activity of nitrate reductase (E.C.1.7.7.2) from the halotolerant cyanobacterium Aphanothece halophytica were investigated. Cells grown in nitrate-containing medium exhibited higher nitrate reductase activity than cells grown in medium in which nitrate was replaced by glutamine. When ammonium was present in the medium instead of nitrate, the activity of nitrate reductase was virtually non-detectable, albeit with normal cell growth. The enzyme was localized mainly in the cytoplasm. The enzyme was purified 406-fold with a specific activity of 40.6 µmol/min/mg protein. SDS-PAGE revealed a subunit molecular mass of 58 kDa. Gel filtration experiments revealed a native molecular mass of 61 kDa. The Km value for nitrate was 0.46 mM. Both methyl viologen and ferredoxin could serve as electron donor with Km values of 4.3 mM and 5.2 µM, respectively. The enzyme was strongly inhibited by sulfhydryl-reactive agents and cyanide. Nitrite, the product of the enzyme reaction, showed little inhibition. Chlorate, the substrate analog, could moderately inhibit the enzyme activity. NaCl up to 200 mM stimulated the activity of the enzyme whereas enzyme inhibition was observed at ≥300 mM NaCl.

Grafting to improve nitrogen‐use efficiency traits in tobacco plants

AbstractNitrate plays a major role in the yield and quality of tobacco plants. This work explored the nitrogen‐use efficiency (NUE) and how it can be affected by grafting. Two experiments were designed: in the first, using six commercial tobacco cultivars, the best cultivar for the NUE was selected and analysed for foliar NO3− content, total N, nicotine and nitrate reductase (NR) activity. The results showed the cultivar H‐20 to have the best performance on NUE. It was further featured by the highest NR activity and total N and by the lowest NO3− and nicotine content, resulting in the highest foliar leaf biomass production and quality. In the second experiment it was tested whether the cultivar H‐20 could be used as rootstock to improve the NUE of the other cultivars under study. The results showed that the grafted plants had improved the NO3− assimilation with respect to non‐grafted plants. Hence grafting tobacco plants can be used as a quick and effective method to improve NUE, which has beneficial implications for human health and for a reduction in environmental pollution. Copyright © 2006 Society of Chemical Industry

Impact of genotype and micronutrient applications on nitrate reductase activity of tea leaves

Abstract:Teaflushshootscomprisingthreeleavesandabudwerecollectedfromvariousclones(cultivars)from different experimental fields and analysed for nitrate reductase (NR) activity. Most of the cultivarsof Assam type had higher NR activity, followed by Cambod and China types. NR activity was maximum inthe clone UPASI-9. It was found that NR activity could be used as a biochemical tool to predict the yieldpotential of cultivars at the initial stage of selection for a breeding programme. The activity was higher inthe youngest part of the tea plant. With the existing methodology it was not possible to measure the NRactivity in stem portions of the tea plant. There was a strong positive correlation between NR activity andamino acid contents of tea shoots. Inclusion of molybdenum in the foliar applied micronutrient mixturewas found helpful in triggering the NR activity in a few clones and seedlings.  2004 Society of Chemical Industry Keywords: tea shoots; NR activity; micronutrients; amino acids; leaf N

Nitrogen Metabolism in Rice Cultivated Under Seasonal Flush of Nitrate

Two rice varieties, a land race (Piaui) and an improved variety (IAC-47), were cultivated in pots in a system that simulates the seasonal nitrate flushes in tropical soils. Piaui plants did accumulate more in the shoots than IAC-47, especially in the sheaths. Piaui plants have also shown a low nitrate reductase activity (NRA) at the early stages of growth, what may be and advantage for the accumulation of . Piaui plants showed a higher content and a lower NRA in the flag leaves at anthesis, while IAC-47 on the contrary showed lower content and higher NRA at anthesis. The data indicated that Piaui plants have apparently a higher N-use efficiency than IAC-47 plants do. This ability results in higher content of grain protein, even when growing in poor soils. These results suggest this to be related to a superior capacity of Piaui plants to take up from low nutrient soils, and store it in the reserve pools during the early stages of growth and development.