Effects of nitrogen dioxide and nitrate nutrition on nodulation, nitrogenase activity, growth, and nitrogen content of bean

The influence of nutrient nitrate level (0-20 millimolar) on the effects of NO₂ (0-0.5 parts per million) on nodulation and in vivo acetylene reduction activity of the roots and on growth and nitrate and Kjeldahl N concentration in shoots was studied in bean (Phaseolus vulgaris L. cv Kinghorn Wax) plants. Exposing 8-day old seedlings for 6 hours each day, for 15 days, to 0.02 to 0.5 parts per million NO₂ decreased total nodule weight at 0 and 1 millimolar nitrate, and nitrogenase (acetylene reduction) activity at all concentrations of nitrate. The pollutant had little effect on root fresh or dry weights. Shoot growth was inhibited by NO₂. The NO₂ exposure increased nitrate concentration in roots only at 20 millimolar nutrient nitrate. Exposure to NO₂ markedly increased Kjeldahl N concentration in roots but generally decreased that in shoots. The experiments demonstrated that nutrient N level and NO₂ concentration act jointly in affecting nodulation and N fixing capability, plant growth and composition, and root/shoot relationships of bean plants.     

Comparison of nitrogen uptake in the roots and rhizomes of <Emphasis Type="Italic">Leymus chinensis</Emphasis>

Leymus chinensis (Trin.) Tzvel is a rhizomatous grass species in the Eastern Eurasian steppe zone that is often limited by low soil nitrogen availability. Although a previous study showed that the rhizomes of L. chinensis have the capacity to take up nitrogen, the importance of such uptake for nitrogen nutrition is unclear. Moreover, little is known regarding the inorganic nitrogen uptake kinetics of roots and rhizomes in response to nitrogen status. Here, we first found that ammonium is preferred over nitrate and glycine for L. chinensis growth. Using the ¹⁵N-labelling method, we found that the rate of ion influx into roots was approximately five-fold higher than into rhizomes under the same nitrogen content, and the ion influxes into roots and rhizomes under 0.05 mM N were greater than in the presence of 3 mM N, especially in the form of NH₄⁺. Using a non-invasive micro-test technique, we characterised the patterns of NH₄⁺ and NO₃^– fluxes in the root mature zone, root tip, rhizome mature zone, and rhizome tip following incubation in the solution with different N compounds and different N concentrations. These results suggest a dynamic balance between the uptake, utilisation, and excretion of nitrogen in L. chinensis.     

Involvement of phosphoenolpyruvate carboxylase and antioxydants enzymes in nitrogen nutrition tolerance in <Emphasis Type="Italic">Sorghum bicolor</Emphasis> plants

Plants of Sorghum bicolor (C₄ species) were grown at different nitrate or ammonium concentrations (0.5, 5, 20 and 50 mM) in order to examine the effect of nitrogen nutrition on growth, phosphoenolpyruvate carboxylase (PEPC) and antioxidant enzymes activities in both roots and leaves of 30-day-old plants. At high NO₃^? levels (20 and 50 mM) the fresh weight was significantly higher. When the nitrogen source was in ammonium form, the leaf and root mass increased drastically at low concentration 5 mM and significantly at 20 mM, however similar fresh weight was found at high level of ammonium (50 mM). The leaves catalase (CAT), guaiacol peroxidase (POD), glutathione reductase (GR), and glutathione S-transferase (GST) activities and the roots glutathione reductase and glutathione S-transferase activities were significantly higher in the NH₄⁺-fed plants than those grown in the nitrate medium. Activity and proteins levels of phosphoenolpyruvate carboxylase in both leaves and roots of sorghum plants were increased progressively with increasing external nitrogen concentration. This increase was more pronounced at high level of ammonium (50 mM), being 2-fold at 50 mM of NO₃^? and 3-fold at 50 mM of NH₄⁺. Our results suggested that antioxidant enzymes activities and PEPC play a key role in ammonium detoxification and tolerance in sorghum plants.     

Effects of varied soil nitrogen supply on Norway spruce (Picea abies [L.] Karst.)

During a seven-month period the effect of different nitrogen (N) availability in soil on growth and nutrient uptake was studied in three-year-old Norway spruce (Picea abies [L.] Karst.) trees. The plants were grown in pots on N-poor forest soil supplied with various amounts and forms (inorganic and organic) of N. Increasing supply of inorganic N (as NH₄NO₃) increased the formation of new shoots and shoot dry weight. The root/shoot dry weight ratio of new growth was drastically decreased from 1.6 in plants without N supply to 0.5 in plants supplied with high levels of NH₄NO₃. This decrease in root/shoot dry weight ratio was associated with distinct changes in root morphology in favour of shorter and thicker roots. The addition of keratin as organic N source did neither affect growth nor root morphology of the trees. The amount of N taken up by plants was closely related to the supply of inorganic N, and trees supplied with highest levels of NH₄NO₃ also had the highest N contents in the dry matter of needles and roots. In contrast, N contents in needles of trees grown without additional N, or with keratin supply, were in the deficiency range. Supply of NH₄NO₃ decreased the contents of phosphate (P) and potassium (K) and therefore markedly increased N/P and N/K ratios in the needles. On the other hand, the contents of calcium (Ca), magnesium (Mg), and manganese (Mn) in the needles were increased in the plants supplied with inorganic N, suggesting high soil availability and promotion of uptake of these divalent cations by high nitrate uptake. The observed effects on root/shoot dry weight ratio, root morphology, and mineral nutrient composition of the needles indicated that high inorganic N supply may increase above-ground productivity but at the same time decrease the tolerance of trees against soil-borne (e.g. deficiency of other mineral nutrients) stress factors. Deceased 21 September 1996 Deceased 21 September 1996     

Elevated CO2 plus chronic warming reduce nitrogen uptake and levels or activities of nitrogen‐uptake and ‐assimilatory proteins in tomato roots

Atmospheric CO₂ enrichment is expected to often benefit plant growth, despite causing global warming and nitrogen (N) dilution in plants. Most plants primarily procure N as inorganic nitrate (NO₃^?) or ammonium (NH₄⁺), using membrane‐localized transport proteins in roots, which are key targets for improving N use. Although interactive effects of elevated CO₂, chronic warming and N form on N relations are expected, these have not been studied. In this study, tomato (Solanum lycopersicum) plants were grown at two levels of CO₂ (400 or 700 ppm) and two temperature regimes (30 or 37°C), with NO₃^? or NH₄⁺ as the N source. Elevated CO₂ plus chronic warming severely inhibited plant growth, regardless of N form, while individually they had smaller effects on growth. Although %N in roots was similar among all treatments, elevated CO₂ plus warming decreased (1) N‐uptake rate by roots, (2) total protein concentration in roots, indicating an inhibition of N assimilation and (3) shoot %N, indicating a potential inhibition of N translocation from roots to shoots. Under elevated CO₂ plus warming, reduced NO₃^?‐uptake rate per g root was correlated with a decrease in the concentration of NO₃^?‐uptake proteins per g root, reduced NH₄⁺ uptake was correlated with decreased activity of NH₄⁺‐uptake proteins and reduced N assimilation was correlated with decreased concentration of N‐assimilatory proteins. These results indicate that elevated CO₂ and chronic warming can act synergistically to decrease plant N uptake and assimilation; hence, future global warming may decrease both plant growth and food quality (%N).     

Nitrate reductase activity and nitrogen compounds in xylem exudate of Juglans nigra seedlings: relation to nitrogen source and supply

Nitrogen (N) limits plant productivity and its uptake and assimilation may be regulated by N source, N availability, and nitrate reductase activity (NRA). Knowledge of how these factors interact to affect N uptake and assimilation processes in woody angiosperms is limited. We fertilized 1-year-old, half-sib black walnut (Juglans nigra L.) seedlings with ammonium (NH₄ ⁺) [as (NH₄)₂SO₄], nitrate (NO₃ ⁻) (as NaNO₃), or a mixed N source (NH₄NO₃) at 0, 800, or 1,600 mg N plant⁻¹ season⁻¹. Two months following final fertilization, growth, in vivo NRA, plant N status, and xylem exudate N composition were assessed. Specific leaf NRA was higher in NO₃ ⁻-fed and NH₄NO₃-fed plants compared to observed responses in NH₄ ⁺-fed seedlings. Regardless of N source, N addition increased the proportion of amino acids (AA) in xylem exudate, inferring greater NRA in roots, which suggests higher energy cost to plants. Root total NRA was 37% higher in NO₃ ⁻-fed than in NH₄ ⁺-fed plants. Exogenous NO₃ ⁻ was assimilated in roots or stored, so no difference was observed in NO₃ ⁻ levels transported in xylem. Black walnut seedling growth and physiology were generally favored by the mixed N source over NO₃ ⁻ or NH₄ ⁺ alone, suggesting NH₄NO₃ is required to maximize productivity in black walnut. Our findings indicate that black walnut seedling responses to N source and level contrast markedly with results noted for woody gymnosperms or herbaceous angiosperms.     

Nitrate reductase activity of two leafy vegetables as affected by nickel and different nitrogen forms

The author studied the effect of different nickel concentrations (0, 0.4, 40 and 80 μM Ni) on the nitrate reductase (NR) activity of New Zealand spinach (Tetragonia expansa Murr.) and lettuce (Lactuca sativa L. cv. Justyna) plants supplied with different nitrogen forms (NO₃ ⁻–N, NH₄ ⁺–N, NH₄NO₃). A low concentration of Ni (0.4 μM) did not cause statistically significant changes of the nitrate reductase activity in lettuce plants supplied with nitrate nitrogen (NO₃ ⁻–N) or mixed (NH₄NO₃) nitrogen form, but in New Zealand spinach leaves the enzyme activity decreased and increased, respectively. The introduction of 0.4 μM Ni in the medium containing ammonium ions as a sole source of nitrogen resulted in significantly increased NR activity in lettuce roots, and did not cause statistically significant changes of the enzyme activity in New Zealand spinach plants. At a high nickel level (Ni 40 or 80 μM), a significant decrease in the NR activity was observed in New Zealand spinach plants treated with nitrate or mixed nitrogen form, but it was much more marked in leaves than in roots. An exception was lack of significant changes of the enzyme activity in spinach leaves when plants were treated with 40 μM Ni and supplied with mixed nitrogen form, which resulted in the stronger reduction of the enzyme activity in roots than in leaves. The statistically significant drop in the NR activity was recorded in the aboveground parts of nickel-stressed lettuce plants supplied with NO₃ ⁻–N or NH₄NO₃. At the same time, there were no statistically significant changes recorded in lettuce roots, except for the drop of the enzyme activity in the roots of NO₃ ⁻-fed plants grown in the nutrient solution containing 80 μM Ni. An addition of high nickel doses to the nutrient solution contained ammonium nitrogen (NH₄ ⁺–N) did not affect the NR activity in New Zealand spinach plants and caused a high increase of this enzyme in lettuce organs, especially in roots. It should be stressed that, independently of nickel dose in New Zealand spinach plants supplied with ammonium form, NR activity in roots was dramatically higher than that in leaves. Moreover, in New Zealand spinach plants treated with NH₄ ⁺–N the enzyme activity in roots was even higher than in those supplied with NO₃ ⁻–N.     

Manganese tolerance in subterranean clover (Trifolium subterraneum L.) genotypes grown with ammonium nitrate or symbiotic nitrogen

Summary A wide range of clover accessions were screened for reaction to manganese (Mn) in solution culture. Growth was supported with ammonium nitrate (NH₄NO₃) or symbiotic nitrogen to assess Mn effects on symbiosis and the suitability of NH₄NO₃ dependent growth for assessing Mn tolerance in clover. Reduction of dry matter at Mn 45 ppm varied 0–70%, at Mn 90 ppm, 38–92%, the extent depending on genotype. Tolerant clovers tended to restrict the movement of Mn from roots to shoots. Several previously untested lines were the most tolerant while some commercial lines possessed poor tolerance. Ranks of tolerance for the two nitrogen (N) sources at Mn 45 ppm were correlated suggesting no dominant, discriminatory effects of N source on Mn tolerance; but inclusion of symbiotic effectiveness in a multiple correlation improved the relation between relative tolerances of genotypes under different N sources. Mn affected some aspects of symbiosis. Total nodule nitrogenase activity mainly reflected effects of Mn on nodule number but nitrogenase activity per nodule also contributed. To establish relative tolerances of subterranean clover to Mn growth with NH₄NO₃ is suitable and useful when symbiotic effectiveness is unknown.     

Expression of OsAMT1 (1.1-1.3) in rice varieties differing in nitrogen accumulation

OsAMT is a high-affinity ammonium transporter responsible for NH ₄ ⁺ uptake by rice plants. To investigate the expression patterns of OsAMT in different genotypes in relation to nitrogen accumulation, we measured the expression of OsAMT1.1, OsAMT1.2, and OsAMT1.3 using Real-Time PCR (RT-PCR) in GD (higher N accumulation) and NG (lower N accumulation) seedlings of the Oryza sativa L. cultivar treated with 0.1 mM NH₄NO₃ and 2 mM NH₄NO₃. We found that the expression level of OsAMT1.1 was significantly higher than those of OsAMT1.2 and OsAMT1.3 in the roots treated with 0.1 mM NH₄NO₃, suggesting that OsAMT1.1 contributed the most to N accumulation among the three genes. In GD root, OsAMT1.1 had significantly higher expression levels when it was up-regulated by 0.1 mM NH₄NO₃ than when down-regulated by 2 mM NH₄NO₃. OsAMT1.1 was mainly found in GD roots treated with 0.1 mM NH₄NO₃. We conclude that the OsAMT1.1 in GD roots, which was significantly up-regulated by low N and down-regulated by high N, was the dominating factor in determining the higher N acquisition in GD than in NG at 0.1 mM NH₄NO₃.     

Effect of nitrogen forms on growth and chemical changes in the rhizosphere of strawberry plants

The experiment was set up to examine the influence of different nitrogen forms: (NH₄)₂SO₄, Ca(NO₃)₂ or NH₄NO₃ on growth response, root induced pH changes in the rhizosphere, root-borne acid phosphatase activity in strawberry plants cv. Senga Sengana. The plants grown on sandy mineral soil were fertilized with 3 forms of nitrogen, in concentrations of 46 mg N·kg⁻¹ soil. The plants were grown in rhizoboxes with removable plexiglass lids. To ensure the root growth along the plexiglass lids, the rhizoboxes were placed at an angle of about 50° with the lid on the lower side. In case of ammonium supply, the nitrification inhibitor DIDIN was added (10 mg·kg⁻¹ of moist soil) to prevent conversion of ammonium into nitrate. The growth response (roots and shoots) of strawberry plants were determined after 11 weeks of treatment with different N forms. The best development of the root system and shoots (root and shoot dry weight and root length) was obtained, when ammonium nitrate was supplied. It is suggested therefore, that NH₄NO₃ stimulates vegetative growth of strawberry plants cv. Senga Sengana. However, there were no statistical differences in a leaf and flower number of the plants grown under different forms of N-fertilization. Determination of rhizosphere pH, and acid phosphatase activity were executed using non-destructive techniques, which enabled weekly measurement of chemical changes in the rhizosphere. The results revealed that the form of nitrogen supplied had a predominant effect on chemical changes in the rhizosphere of strawberry plants. The highest pH values (average pH 6.8) were measured in the rhizosphere of individual plants supplied with Ca(NO₃)₂. Whereas the lowest pH values (average pH 5.8) were detected in the presence of (NH₄)₂SO₄. The curve of rhizosphere pH measured along individual roots of the plants treated with Ca(NO₃)₂ represents the highest pH values whereas the curve of rhizosphere pH under (NH₄)₂SO₄ treatment had the lowest pH values. The highest activity of acid phosphatase were observed in the rhizosphere of strawberry plants grown in the presence of (NH₄)₂SO₄, at pH 5.8.     

Response of Douglas fir seedlings to nitrate and ammonium nitrogen sources at different levels of pH and iron supply

Douglas fir seedlings were grown for two to three months in sand and soil cultures in a greenhouse to examine their growth response to nitrogen (N) source at different levels of pH and iron (Fe) supply. In the first two experiments nutrient solutions of known pH were automatically applied to the top of the sand cultures and allowed to run to waste from the bottom. Under these conditions seedlings made most growth on nitrate (NO₃–N) under acid (pH4) conditions, but most growth on ammonium (NH₄–N) under neutral (pH7) conditions. Calcium carbonate (CaCO₃) was used to create a range of pH conditions (from 4.0 to 7.2) in a peat and sand artificial soil. Over the pH range 4 to 6 NH₄–N or NO₃+NH₄–N produced larger seedlings than NO₃–N alone, but above pH6 growth on all N sources was depressed. Chemical analysis showed that seedling Ca concentration had increased and Fe concentration had decreased with increase in CaCO₃ application. Both Ca and Fe concentrations were higher in seedlings receiving NO₃–N than in those receiving NH₄ or NO₃+NH₄.In sub-irrigated sand cultures, Doughlas fir seedlings receiving NO₃–N were shown to respond to additions of Fe chelate, but seedlings receiving NH₄–N responded little to Fe chelate. At pH5 seedlings receiving NO₃–N did not grow as big as seedlings receiving NH₄–N in the absence of Fe chelate, but addition of Fe chelate resulted in NO₃-fed seedlings growing larger than NH₄-fed seedlings. The relationship between seedling Fe concentration and N nutrition is discussed.The relatively larger root dry weight and surface area of seedlings grown on NO₃–N, as compared to NH₄–N, in sand culture, was noted.     

The effect of ammonium and nitrate nitrogen sources on copper uptake and amino acid status of cereals

Summary The effects of different nitrogen sources (NH₄, NO₃, and NH₄ NO₃) on the uptake of copper by wheat and barley growing in solution culture were compared in three experiments. Both the copper concentration and weight gain of shoots and roots were found to decrease in the order NO₃>NH₄ NO₃>NH₄ irrespective of the solution copper concentration. Ammonium nitrogen was also found to decrease the copper concentration of wheat grown on a copper deficient soil compared with a nitrate source of nitrogen. Increasing concentrations of ammonium ions in solution culture caused ammonium toxicity and reduced both plant copper concentrations and vegetative yield. Biochemical investigations using paper chromatography revealed that the amino acid asparagine was the major detoxification product of ammonia in wheat. Copper deficient plants were found to have elevated levels of amino acids compared with controls, irrespective of the nitrogen source.     

Biological role of mycorrhizal fungi on the assimilation and transportation of carbon and nitrogen to Anacamptis palustris and Anacamptis laxiflor

Fungal is a physiological trail and its understanding in the assimilation with the transfer of carbon (C) cum nitrogen (N) or (C/N) to orchid-seedlings have not been determined. Labelled stable isotopes ¹³C and ¹⁵N were used to plan the flow of C and N between orchid plants and mycorrhizal connotations in-terms of bulk transfer for C/N. This study attends to comprehend the mechanism, supporting mycorrhizal fungi which influences on orchid-seedling growth. Determined integration and transfer of C/N from amino acids (AA), ammonium nitrate (NH₄NO₃) and sugar for orchid-plant may lead to understand these mechanisms. This current study tries to estimate the importance of organic compounds as a source for C/N over the inorganic-NH₄NO₃. Generally, after begging of germination and when it is found to be associated to the nutrient resource, organic compound enhance the biomass accumulation of two orchid species. AA significantly increase the mass of ¹³C assimilated by two species. With amino acids the concentration of ¹³C in two species was greater than with NH₄NO₃ and sugar. At another phase, amount of ¹⁵N content shoots was a higher value in Anacamptis laxiflora shoots assimilated substantially additional of ¹⁵N with NH₄NO₃ plus sugar compared with ammonium nitrate only. This study showed that two terrestrial orchids species are reliant on organic compounds as a source of carbon and nitrogen more than inorganic compounds.     

Nitrogen uptake,assimilation and transport in barley in the presence of atmospheric nitrogen dioxide

Summary Exposure of the leaves of young barley plants to nitrogen dioxide (NO₂) was shown to affect the rate of translocation of N, the form in which it is transported in the xylem stream and the partitioning of N between roots and shoots. Following its entry through the leaves, NO₂ is assimilated by the plant into reduced nitrogenous compounds which accounted for the major increases in plant N content and growth. The various effects of atmospheric NO₂ upon barley seedlings were strongly influenced by nitrate supply to the roots.     

Relationships among nitrogen accumulation, nitrogen assimilation and plant growth in chrysanthemums

Relationships among growth, N accumulation and assimilation were investigated in Chrysanthemum morifolium Ramat cv. Fiesta in experiments testing the effects of varying levels of NO^–3₃supply and of increasing NH⁺₄ added to a constant level of NO^–3₃ Flowing solution culture systems were used to provide NO^?₃at concentrations of 0.03 to 5.0 mol m^–3 and NH⁺₄ levels from 0.05 to 0.3 mmol m^–3 added to 0.1 mol m^–3NO^?₃. Rates of growth, N absorption, accumulation, distribution and utilization were estimated by regression analysis of data obtained from sequential plant harvests, and rates of NO^?₃ and NH^?₄ net uptake were estimated from solution depletion. A sustained ambient NO^?₃ concentration of 0.03 mol m^–3 was evidently adequate to support growth, since relative growth rates were not affected by increasing NO^?₃ supply from 0.03 to 1.0 mol m^–3, nor from 0.25 to 5.0 mol m^–3, in separate experiments. Shoot growth rates were stimulated by NH₄ added to NO^?₃ one experiment, but not when the experiment was repeated under ambient conditions less favorable to growth. Relative accumulation rates for total N increased with increasing NO^?₃ and with NH⁺₄added to NO^?₃ A constant proportion of NO^?₃ taken up was reduced when NO^?₃ alone was supplied. Both the proportion of total N taken up as NO^?₃ and the proportion of NO^?₃ reduced decreased with increasing NH⁺₃ added to NO^?₃ NH⁺₄ uptake apparently must exceed a threshold of about 30% of the total uptake to inhibit NO^?₃ uptake. Utilization of N in chrysanthemum was apparently limited by redistribution since relative accumulation rates for total N were equal to or greater than relative growth rates, in contrast to results reported for several other species. Results of this study and other information support the postulate that NH⁺₄ added to NO^?₃might stimulate growth by increasing transport of reduced N from roots to shoots, thus increasing the supply of reduced N available to support growth of shoot meristems.     

桧叶白发藓对不同氮源胁迫的形态和生理响应

桧叶白发藓(Leucobryum juniperoideum)在我国东南部常见,被认为是一种理想的、适用于庭院栽培的苔藓植物,而氮是植物必需的矿质元素,但过量摄入会对其造成伤害,近年来氮沉降水平的提高对苔藓植物的多样性造成了严重影响。该研究为揭示氮沉降加剧对桧叶白发藓的影响,以经6个月断茎培养的桧叶白发藓配子体为材料,用Ca(NO3)2、NH4HCO3和NH4NO3代表三种氮源,设置2、4、8、16gN·m-2 4个水平,以喷洒去离子水为对照,进行不同氮源的胁迫试验。结果表明:氮处理浓度的增加引起组织氮含量的显著提高,增加幅度分别为69.1%、25.7%和43.1%;同时引起植株坏死率显著上升,增加幅度分别为16.5%、12.5%和13.9%。三种氮源处理对株高和净重的影响有显著差异,低浓度的铵态氮(4gN·m-2)引起株高和净重的显著增加,而硝态氮和混合态氮处理差异不显著;加氮浓度的进一步提高,引起株高和净重的减低,硝态氮处理的减低幅度最大,铵态氮的降低幅度最小。三种氮源处理均引起叶绿素含量先上升后下降,但同一水平铵态氮处理的叶绿素含量要高于其它两种氮处理,而且引起叶绿素含量下降的处理浓度要高于其它两种氮源;三种氮源均引起SOD活性显著增加、可溶性蛋白和脯氨酸含量先升后降,但不同氮源间生理指标的变化不同步。这说明桧叶白发藓对硝态氮胁迫的响应比铵态氮敏感,硝态氮的增加对桧叶白发藓造成严重危害,而少量的铵态氮(4gN·m-2)则能促进桧叶白发藓的生长。研究结果可作为桧叶白发藓繁殖与生产的氮源。     

Effect of form and level of applied nitrogen on nitrogenase and nitrate reductase activities in faba beans

The effects of nitrogen applied at increasing levels of 0, 4, 8, 16 and 32 mM N (KNO₃ or NH₄Cl) were studied in faba bean (Vicia faba) nodulated byRhizobium leguminosarum bv.viceae RCR lool. Nitrogenase activity was higher at 4 and 8 mM N than the zero N treatment (control), but 16 and 32 mM N significantly reduced the efficiency of nodule functions. Nitrate reductase activities (NRA) of leaves, stems, roots, nodules and nodule fractions (bacteroid and cytosol) were increased with rising the NO₃ ^? or NH₄ ⁺ levels. NRA decreased in the order of nodules>leaves>stems>roots. Cytosolic NR was markedly higher than that recorded in the bacteroid fractions. Nitrate levels were linearly correlated to NRA of nodules. Accumulation of NO₂ ^? within nodules suggests that NO₂ ^? inhibits nodule’s activity after feeding plants with NO₃ ^? or NH₄ ⁺.     

Genetic engineering of sunflower (<Emphasis Type="Italic">Helianthus annuus</Emphasis> L.) for resistance to necrosis disease through deployment of the TSV coat protein gene

Nitrogen is a major driver of plant growth and the nitrogen source can be critical to good growth in vitro. A response surface methodology mixture-component design and a data mining algorithm were applied to nitrogen (N) nutrition for improving the micropropagation of Prunus armeniaca Lam. Data taken on shoot cultures included a subjective quality rating, shoot number, shoot length, leaf characteristics and physiological disorders. Data were analyzed using the Classification and Regression Tree data mining algorithm. The best overall shoot quality as well as leaf color were on medium with NO₃^??>?25 mM and NH₄⁺/Ca⁺ >?0.8. Improving shoot length to15 mm required 25?<?NO₃^? ≤?35 mM with NH₄⁺/Ca²⁺ ≤?2.33. The most shoots (11.6) were produced with NO₃^? >?25 mM and NH₄⁺/Ca²⁺ ≤ 0.8, but there were 5–10 shoots at other NO₃^? concentrations regardless of NH₄⁺/Ca²⁺ proportion. Leaves increased in size with higher NO₃^? concentrations (>?55 mM). Physiological disorders were also influenced by the nitrogen components. Shoot tip necrosis was rarely present with NO₃^? > 45 mM. Callus production decreased somewhat with NH₄⁺/Ca²⁺ >?2.33. Suggested concentrations for an improved medium considering all of these growth characteristics would be 25?<?NO₃^? ≤?35 mM and NH₄⁺/Ca⁺ ≤ 0.8. Validation experiments comparing WPM and three trial media showed improvements in several shoot growth parameters on medium with optimized mesos and optimized nitrogen components.     

Metabolic regulation and gene expression of root phosphoenolpyruvate carboxylase by different nitrogen sources

Alfalfa (Medicago sativa L.) N-sufficient plants were fed 1·5 mM N in the form of NO₃⁻, NH₄⁺ or NO₃⁻ in conjunction with NH₄⁺, or were N-deprived for 2 weeks. The specific activity of phosphoenolpyruvate carboxylase (PEPC) from the non-nodulated roots of N-sufficient plants was increased in comparison with that of N-deprived plants. The PEPC value was highest with NO₃⁻ nutrition, lowest with NH₄⁺ and intermediate in plants that were fed mixed salts. The protein was more abundant in NO₃⁻-fed plants than in either NH₄⁺- or N mixed-fed plants. Nitrogen starvation decreased the level of PEPC mRNA, and nitrate was the N form that most stimulated PEPC gene expression. The malate content was significantly lower in NO₃⁻-deprived than in NO₃⁻-sufficient plants. Root malate accumulation was high in NO₃⁻-fed plants, but decreased significantly in plants that were fed with NH₄⁺. The effect of malate on the desalted enzyme was also investigated. Root PEPC was not very sensitive to malate and PEPC activity was inhibited only by very high concentrations of malate. Asparagine and glutamine enhanced PEPC activity markedly in NO₃⁻-fed plants, but failed to affect plants that were either treated with other N types or N starved. Glutamate and citrate inhibited PEPC activity only at optimal pH. N-nutrition also influenced root nitrate and ammonium accumulation. Nitrate accumulated in the roots of NO₃⁻- and (NO₃⁻ + NH₄⁺)-fed plants, but was undetectable in those administered NH₄⁺. Both the nitrate and the ammonium contents were significantly reduced in NO₃⁻- and (NO₃⁻ + NH₄⁺)-starved plants. Root accumulation of free amino acids was strongly influenced by the type of N administered. It was highest in NH₄⁺-fed plants and the most abundant amides were asparagine and glutamine. It was concluded that root PEPC from alfalfa plants is N regulated and that nitrate exerts a strong influence on the PEPC enzyme by enhancing both PEPC gene expression and activity.