Leaf Nitrate Reductase Activity Research Articles

Nitrate reductase regulation in wheat seedlings by exogenous nitrate: A possible role in tolerance to salt stress

AbstractBackgroundSoil salinity is a major abiotic stress causing severe damage to plants. Thus, proper management approaches need to be developed to lessen the detrimental effect of salinity on crop growth and productivity.AimsThis study was conducted to investigate the putative role of nitrate (NO3−) and nitrate reductase (NR) in mitigating the adverse effects of salt stress on the growth of durum wheat seedlings.MethodsNitrogen nutrition has been modified, in the presence of 100 mM NaCl, either by increasing the NO3− availability, the deprivation of NO3− or by the addition of sodium tungstate—an inhibitor of NR—in the culture medium.ResultsObtained results showed that, in the presence of 2.5 mM NO3−, salt stress significantly decreased all studied growth traits (biomass production, relative growth rate, and water content). This was associated with a noteworthy reduction in total chlorophyll pigment, total carbohydrates, and protein contents. Concomitantly, NR activity was remarkably decreased. However, proline and malondialdehyde (MDA) were significantly accumulated. In the absence of NO3− as well as in the presence of tungstate, NR activities were noticeably reduced, and wheat seedling growth was further disturbed in comparison to salt‐stressed seedlings grown under 2.5 mM NO3−. Increasing the NO3− availability to 7.5 mM significantly restricted Cl− uptake, markedly increased root and leaf NR activities, and alleviated salt stress–induced seedling growth inhibition as compared to salt‐stressed seedlings grown under 2.5 mM NO3−. Such effects were associated with an increase in leaf chlorophyll and protein concentrations and in root and leaf carbohydrate concentrations. Nevertheless, MDA concentrations were sharply decreased.ConclusionsThis study provides strong arguments highlighting the potential role of NO3− reduction in mitigating the adverse effects of salt stress on the growth of wheat plants at the early seedling stage. The enhancement of the NR activity through increasing the NO3− availability may, therefore, represent a potential strategy to overcome the salinity‐mediated impairment of wheat seedlings to some extent.

Biological nitrification inhibitor-trait enhances nitrogen uptake by suppressing nitrifier activity and improves ammonium assimilation in two elite wheat varieties.

Synthetic nitrification inhibitors (SNI) and biological nitrification inhibitors (BNI) are promising tools to limit nitrogen (N) pollution derived from agriculture. Modern wheat cultivars lack sufficient capacity to exude BNIs, but, fortunately, the chromosome region (Lr#n-SA) controlling BNI production in Leymus racemosus, a wild relative of wheat, was introduced into two elite wheat cultivars, ROELFS and MUNAL. Using BNI-isogenic-lines could become a cost-effective, farmer-friendly, and globally scalable technology that incentivizes more sustainable and environmentally friendly agronomic practices. We studied how BNI-trait improves N-uptake, and N-use, both with ammonium and nitrate fertilization, analysing representative indicators of soil nitrification inhibition, and plant metabolism. Synthesizing BNI molecules did not mean a metabolic cost since Control and BNI-isogenic-lines from ROELFS and MUNAL presented similar agronomic performance and plant development. In the soil, ROELFS-BNI and MUNAL-BNI plants decreased ammonia-oxidizing bacteria (AOB) abundance by 60% and 45% respectively, delaying ammonium oxidation without reducing the total abundance of bacteria or archaea. Interestingly, BNI-trait presented a synergistic effect with SNIs since made it also possible to decrease the AOA abundance. ROELFS-BNI and MUNAL-BNI plants showed a reduced leaf nitrate reductase (NR) activity as a consequence of lower soil formation and a higher amino acid content compared to BNI-trait lacking lines, indicating that the transfer of Lr#-SA was able to induce a higher capacity to assimilate ammonium. Moreover, the impact of the BNI-trait in wheat cultivars was also noticeable for nitrate fertilization, with improved N absorption, and therefore, reducing soil nitrate content.

Effects of Trichoderma on nitrogen absorption and use efficiency in Lycium chinense roots under saline stress

To clarify the mechanisms underlying the improvement of Trichoderma on Chinese wolfberry (Lycium chinense) growth under saline stress, we analyzed the effects of application of organic fertilizer, Trichoderma agent and fertilizer on nitrogen uptake, assimilation, accumulation and use efficiency in Chinese wolfberry, based on a pot experiment with coastal saline soil. The organic fertilizer was the sterilization substance of Trichoderma fertilizer without viable Trichoderma, without any difference in the content of nutrients (such as nitrogen, phosphorus and potassium) between them. The results showed that the application of organic fertilizer, Trichoderma agent and ferti-lizer significantly increased NO3- and NH4+ influx rate in meristematic zone and NO3- influx rate in maturation zone of roots. The magnitude of such enhancement was greater in the application with Trichoderma fertilizer than organic fertilizer. Compared with the control, the application of Trichoderma agent and fertilizer significantly increased root, stem and leaf biomass and nitrogen content as well as plant nitrogen accumulation, strengthened root and leaf nitrate reductase, nitrite reductase and glutamine synthetase activities, and elevated nitrogen uptake efficiency, photosynthetic rate, stable carbon isotope abundance and photosynthetic nitrogen use efficiency. For all those variables, the beneficial effect was obviously stronger in the application with Trichoderma fertilizer than organic fertilizer. Therefore, Trichoderma facilitated nitrogen uptake, assimilation and accumulation in Chinese wolfberry under saline stress, improved photosynthetic carbon fixation ability and nitrogen use efficiency, and ultimately promoted plant growth.

Community-specific patterns of nitrogen transformations along an elevational gradient in alpine and subalpine ecosystems

AimsThe aim of the study was to investigate N biogeochemistry of four neighboring, high mountain plant communities and to identify main factors which drive variability among them. We hypothesized that the vegetation types differ in terms of N transformations, and that spatial differentiation of the communities and dominant growth form can reflect an existence of several N-environments along an elevational gradient.MethodsPlant and soil N characteristics were studied in four vegetation types: heathland, scrub, sward and tall forb. Leaf nitrate reductase activity and total N were measured in the dominant species. Soil pH, total C, N, inorganic and dissolved organic N concentrations were measured. The soil net N mineralization rate was examined.ResultsThe DistLM and PERMANOVA analyses revealed that variability among the vegetation types was driven primarily by elevation, soil N–NH4+, soil pH and soil total C. We identified three distinct N-environments along an elevational gradient. The “N-poor alpine” located at the highest altitudes, strongly N-limited and dominated by dwarf-shrub. The "N-mixed subalpine" located in the middle of the gradient and covered by scrub and sward. It was characterized by moderate N turnover rate. The "N-rich subalpine" occurred at lowest locations and was covered by subalpine tall forb community. It exhibited the highest dynamics of N transformations and was rich in inorganic N.ConclusionThree main N-environments were identified: N-poor alpine, N-mixed subalpine, N-rich subalpine. Variability among the vegetation types was driven primarily by elevation, soil N–NH4+, soil pH and soil total C.

Molybdenum Foliar Fertilization Improves Photosynthetic Metabolism and Grain Yields of Field-Grown Soybean and Maize.

Foliar fertilization has been used as a supplemental strategy to plant nutrition especially in crops with high yield potential. Applying nutrients in small doses stimulates photosynthesis and increases yield performance. The aim of this study was to evaluate the efficiency of foliar application of molybdenum (Mo) to soybean and maize. The treatments consisted of the presence (+Mo) and absence (-Mo) of supplementation. Plant nutritional status, nitrate reductase (NR) activity, gas exchange parameters, photosynthetic enzyme activity (Rubisco in soybean and maize and PEPcase in maize), total soluble sugar concentration, leaf protein content, shoot dry matter, shoot nitrogen accumulated, number of grains per plant, mass of 100 grains, and grain yield were evaluated. For soybean and maize, application of Mo increased leaf NR activity, nitrogen and protein content, Rubisco activity, net photosynthesis, and grain yield. These results indicate that foliar fertilization with Mo can efficiently enhance nitrogen metabolism and the plant’s response to carbon fixation, resulting in improved crop yields.

Use of Piriformospora indica to Promote Growth of Strawberry Daughter Plants

As an endophytic fungus, the growth-promoting effects of Piriformospora indica have been widely confirmed in many of its host plants. In this study, we investigated the influences of P. indica colonization on the growth of the daughter plants of two strawberry cultivars, ‘Benihoppe’ and ‘Sweet Charlie.’ The results showed that the fungus colonization significantly promoted the growth of the daughter plants of both of the two strawberry varieties. Its colonization greatly improved almost all of the growth parameters of the ‘Benihoppe’ daughter plants, including the above-ground fresh weight, above-ground dry weight, root fresh weight, root dry weight, plant height, petiole length, leaf area, number of roots and chlorophyll content. However, the fungus colonization showed significant improving effects on only the above-ground fresh weight, root fresh weight and root dry weight of ‘Sweet Charlie.’ Surprisingly, the average root length of ‘Benihoppe’ and ‘Sweet Charlie’ was suppressed by about 14.3% and 24.6%, respectively, by P. indica. Moreover, after P. indica colonization, the leaf nitrate reductase activity and root activity upregulated by 30.12% and 12.74%, and 21.85% and 21.16%, respectively, for the ‘Benihoppe’ and ‘Sweet Charlie’ daughter plants. Our study indicated that P. indica could promote the growth of strawberry daughter plants by improving rooting, strengthening photosynthetic pigments production and nutrient absorption and accelerating biomass accumulation. The fungus shows great potential to be used in the strawberry industry, especially in the breeding of daughter plants.

Comparison of nitrogen assimilation components among Agrostis species and cultivars

AbstractEnhanced nitrogen use efficiency (NUE) in turfgrass systems comprises several factors, including more efficient uptake and assimilation of applied nitrogen (N), as well as reduced N losses to the environment. The objectives of the current research were to evaluate the inter‐ and intraspecific variation in N use parameters in two Agrostis species, creeping bentgrass (Agrostis stolonifera L.) and velvet bentgrass (Agrostis canina L.), under field and controlled environmental conditions. Measurements included leaf NUE (g dry matter mg–1 N), leaf N content (mg g–1 dry matter), leaf and root nitrate reductase activity (NRA)(μmol NO2– g–1 fresh weight h–1), and root nitrate uptake rate (NUR). Velvet bentgrass cultivars exhibited higher leaf N content and therefore lower leaf NUE than creeping bentgrass cultivars in the field and in a nutrient solution. Differences in leaf NRA were only observed in Agrostis species and cultivars in the field, with higher NRA observed in creeping bentgrass. Velvet bentgrass cultivars grown in a nutrient solution exhibited a 50% higher root NUR than creeping bentgrass, with leaf NRA and N content increasing and leaf NUE decreasing in Agrostis under higher NO3– supply.

Effects of Nitrogen Application Rate on Protein Components and Yield of Low-Gluten Rice

Low-gluten rice cultivar D105 was grown in the field under five nitrogen (N) treatments (N0: 0, N90: 90, N135: 135, N180: 180, and N225: 225 kg·hm−2) to investigate the effect of N application rate on the yield and the resulting dynamic changes in protein content, grain processing quality, and relative content of each component protein. The results indicated that the number of effective panicles, seed setting rate, the number of solid grains, dry matter, leaf nitrate reductase and glutamine synthetase activities, and yield increased with N application rate ranging from 0 to 180 kg·hm−2. However, the seed setting rate and the number of solid grains decreased under N225 treatment, leading to a decline in yield. At maturity, 35 days after flowering, no significant differences between albumin and gliadin in the rice grain were found among the N treatments, while globulin and gluten differed among treatments, indicating that the effect of N application rate on the former was slightly the opposite to that observed on the latter. Further, the N application rates did not change the proportions of component proteins relative to the total protein content in the grain. Processing and taste qualities of D105 low-gluten rice were optimal in the N135 and N180 treatments, and the overall rice quality decreased under the N225 treatment. Therefore, the optimal N application rate for yield and processing quality of D105 low-gluten rice is N180: 180 kg·hm−2.

Rice productivity and profitability with slow-release urea containing organic-inorganic matrix materials

Applying slow-release fertilizers is possible means for reducing nitrogen (N) loss in rice production. Matrix-based fertilizers represent novel slow-release fertilizers. To date, there is little consensus about the effect of combined addition of organic and inorganic matrix materials on rice production. We developed a slow-release urea fertilizer with selected organic and inorganic matrix materials. The study aimed to: i) determine the effect of the slow-release urea on rice yield, profit, and agronomic efficiency and ii) elucidate its possible mechanisms. A two-year field experiment was conducted during 2015–2016. Besides, laboratory experiments were conducted to determine the potential N loss risk. Three treatments were set up: control without N application (CK), regular urea treatment (RU, 150 kg N ha–1), and slow-release urea treatment (SU, 150 kg N ha–1). The results showed that rice biomass and grain yield were significantly higher in SU than in RU (P < 0.05). The higher panicle density in SU was largely responsible for the greater grain yield. Net profit in SU was ≥ US$450 ha–1, higher than in RU. Agronomic efficiency was significantly greater in SU than in RU (P < 0.05). Rice height, root area, leaf chlorophyll, leaf nitrate reductase activity, and leaf glutamine synthetase activity were larger in SU than in RU. Less N loss and greater soil N availability were partly responsible for the improvements in rice growth traits and physiological parameters in SU. Overall, the slow-release urea is a promising fertilizer for rice production.

Nitrogen partitioning traits and expression patterns of N metabolism‐associated genes in maize hybrids with contrasting N utilization efficiencies

AbstractThe nitrogen (N) uptake and utilization in maize (Zea mays L.) plants are accomplished through a series of biochemical reactions and transformations involving the N assimilation enzymes. Nitrate reductase (NR) and glutamine synthetase (GS) exert important functions in the N assimilation and remobilization processes. The mechanisms underlying plant N partitioning and the associated expression patterns of NR and GS genes in maize hybrids with different N utilization efficiencies were still not clear. In this study, the expression of ZmNR and ZmGS genes that are related to N partitioning were analyzed in two maize hybrids (XY335 and HN138). Results showed that XY335 displayed higher grain yield, kernel numbers, shoot N uptake, and physiological N utilization efficiency (NUtE) than those shown in HN138 under low‐N conditions. The higher post‐silking N uptake and N remobilization in vegetative organs in XY335 were associated with the enhanced net photosynthetic rate (Pn), the NR and GS activities in ear‐leaf. Additionally, the expression levels of ZmGS1.3 and ZmGS1.4 were up‐regulated when exposed to low‐N stress, showing higher values in XY335 than those in HN138. Correlation analysis showed that the expression levels of ZmNR, ZmGS1.3, and ZmGS1.4 are correlated with leaf NR and GS activities, N remobilization, and grain yield. Our investigation suggested the critical roles of the N metabolism‐associated genes in the modulation of internal N translocation and plant productivity in maize. Future transgene analysis on ZmNR and ZmGS can provide insights into the molecular mechanisms underlying plant tolerance to low N stress in maize.

Transcriptome Analysis for Fraxinus mandshurica Rupr. Seedlings from Different Carbon Sequestration Provenances in Response to Nitrogen Deficiency

To explore the molecular regulatory mechanism of high-carbon (C) sequestration Fraxinus mandshurica Rupr. (F. mandshurica) provenance and the expression profile of F. mandshurica during nitrogen (N) starvation, the foliage and roots of the annual Wuchang (WC) seedlings with greater C amount and Hailin (HL) seedlings with smaller C amount, which were grown in N-deficient nutrition and complete N, were used for RNA-seq and physiological determination, respectively. One thousand and fifty-seven differentially expressed genes (DEGs) between WC and HL and 8173 DEGs related to N deficiency were identified, respectively. The root of F. mandshurica responded to N deficiency more strongly than foliar. The target genes that responded to N deficiency in roots were mainly regulatory genes (transcription factors, hormones and protein kinases), and their response patterns were upregulated. The growth and N concentration in both WC and HL were reduced by the N deficiency, which might result from the decrease of the leaf Nitrate reductase (NR) and glutamine synthetase (GS) enzyme activity and ABA content, although the root-to-shoot ratio; lateral root number; lignin content; endogenous hormones content (GA, IAA and ZR); root GS and glutamate synthetase activity and transcriptional level of most of the regulatory genes were increased. The C sequestration capacity in WC was greater than that in HL, which related to the higher GS enzymes activity and transcriptional levels of regulatory genes and metabolic genes (terpenes, carbohydrates, and lipid energy). However, the C sequestration advantage of WC was significantly reduced by the N deficiency, which was due to the smaller response to N deficiency compared to HL.

TIBA and nitrogen incorporation, senescense and yield in a symbiotically grown vining dry bean (Phaseolus vulgaris L.) genotype

The growth regulator 2, 3, 5 triiodobenzoic add (TIBA) was applied foliarly at the beginning of flowering (R1 stage) to a vining dry bean (Phaseolus vulgaris L.) genotype, grown symbiotically in a low nitrogen containing soil. Profiles of root nodule nitrogenase and leaf nitrate reductase activities, as well as of leaf chlorophyll content throughout the postflowering period, indicate that TIBA reduced the duration of nitrogen incorporation and caused early senescence. An increase in the number of pods per plant as well as in dry matter harvest index, supports the theory that TIBA causes bean plants to shift from vegetative to reproductive growth. No seed yield increase occurred as a result of TIBA application. Symbiotic nitrogen fixation alone may not provide sufficient nitrogen to allow optimal development of an increased number of pods. Further trials under higher soil nitrogen levels are suggested.

Responses of CO2 and N2O emissions from soil-plant systems to simulated warming and acid rain in cropland

Climate warming is anticipated to change the terrestrial carbon/nitrogen cycle through its impact on the fluxes of greenhouse gases such as CO2 and N2O. This study investigated the effect of diurnal warming and acid rain on CO2 and N2O emissions from soil-plant systems in a winter wheat–soybean rotation cropland. Field rotational experiments of winter wheat and soybean were conducted by simulating diurnal warming and acid rain. Manipulated experiments included the control (CK), diurnal warming (T, + 2 °C), acid rain (AR, pH = 2.5), and the combined treatment (TAR, + 2 °C and acid rain). CO2 and N2O fluxes from soil-plant systems were measured using a static chamber-gas technique. The results showed that in the winter wheat and soybean growing seasons, compared with CK treatment, T, AR, and TAR treatments did not change the accumulative amount of CO2 emission (AAC) across the full growth period (p ˃ 0.05), although T treatment significantly increased soil AAC (p < 0.05) at the grain filling-maturity stage. On the contrary, T and AR treatments significantly increased the accumulative amount of N2O emission (AAN) in winter wheat and soybean croplands (p < 0.05), which was attributed to leaf nitrate reductase activity, total biomass, and soil NO3−–N content. In addition, there was a significant interaction between warming and acid rain on N2O flux. The AAN from the winter wheat cropland under treatments was in the order: TAR ˃ AR ˃ T ˃ CK. Our findings suggest that diurnal warming and acid rain had no significant effect on CO2 emissions from soil-plant systems, but significantly increase N2O emissions in winter wheat and soybean growing seasons. Moreover, diurnal warming would strengthen the positive effect of acid rain on N2O emissions from soil-plant systems in winter wheat farmland.

Elevated CO2 alters tissue balance of nitrogen metabolism and downregulates nitrogen assimilation and signalling gene expression in wheat seedlings receiving high nitrate supply.

Tissue and canopy-level evidence suggests that elevated carbon dioxide (EC) inhibits shoot nitrate assimilation in plants and thereby affects nitrogen (N) and protein content of the economic produce. It is speculated that species or genotypes relying more on root nitrate assimilation can adapt better under EC due to the improved/steady supply of reductants required for nitrate assimilation. A study was conducted to examine the effect of EC on N assimilation and associated gene expression in wheat seedlings. Wheat genotypes, BT-Schomburgk (BTS) with comparatively high leaf nitrate reductase (NR) activity and Gluyas Early (GE) with high root NR activity were grown in hydroponic culture for 30days with two different nitrate levels (0.05mM and 5mM) in the climate controlled growth chambers maintained at either ambient (400 ± 10μmolmol-1) or EC (700 ± 10μmolmol-1) conditions. Exposure to EC downregulated the activity of enzyme NR and glutamate synthase (GOGAT) in leaf tissues, whereas in roots, activities of both the enzymes were upregulated by exposure to EC. In addition, EC downregulated N assimilation and signalling gene expression under high N availability. Root N assimilation was less affected in comparison with shoot N assimilation; thereby, the proportion of root contribution towards total assimilation was higher. The results suggest that EC could alter and re-programme N assimilation and signalling in wheat seedlings. The genotype and tissue-specific effects of EC on N assimilation also warrants the need for identification of suitable genotypes and revision of fertiliser regime for tapping the beneficial effects of EC conditions.

Nitrogen metabolism enzymes activity in flag leaf and roots of pearl millet during grain development stage

Nitrate reductase (NR), Glutamine synthatase (GS), Glutamate dehydrogenase (GDH) and Aspartate aminotransaminase (AspAT) were assayed in flag leaves and roots of four pearl millet genotypes, started from ear emergence till grain maturity at four days intervals. All enzymes showed higher activities in flag leaf than that of roots irrespective of growth stage and genotypes. A slight increase in flag leaf NR, GS and AspAT activity till anthesis started decreasing while GDH increased till 12 days after anthesis (DAA) and almost constant till 18 DAA and then started decreasing. While in roots a steep declining trend was observed in NR, GS and AspAT and reached to almost non-detectable level till maturity while GDH increased up to 6 DAA and then decreased sharply irrespective of the genotypes. The almost stable GDH activity and decreasing trend in NR, GS and AspAT suggested that re-assimilation of amino nitrogen takes place in flag leaf instead of direct assimilation from the roots for nitrogen deposition in pearl millet developing grains.

Weakened carbon and nitrogen metabolisms under post-silking heat stress reduce the yield and dry matter accumulation in waxy maize

Post-silking high temperature is one of the abiotic factors that affects waxy maize (Zea mays L. sinensis Kulesh) growth in southern China. We conducted a pot trial in 2016–2017 to study the effects of post-silking daytime heat stress (35°C) on the activities of enzymes involved in leaf carbon and nitrogen metabolisms and leaf reactive oxygen species (ROS) and water contents. This study could improve our understanding on dry matter accumulation and translocation and grain yield production. Results indicated that decreased grain number and weight under heat stress led to yield loss, which decreased by 20.8 and 20.0% in 2016 and 2017, respectively. High temperature reduced post-silking dry matter accumulation (16.1 and 29.5% in 2016 and 2017, respectively) and promoted translocation of pre-silking photoassimilates stored in vegetative organs, especially in leaf. The lower leaf water content and chlorophyll SPAD value, and higher ROS (H2O2 and O2−·) content under heat stress conditions indicated accelerated senescent rate. The weak activities of phosphoenolpyruvate carboxylase (PEPCase), Ribulose-1,5-bisphosphate carboxylase (RuBPCase), nitrate reductase (NR), and glutamine synthase (GS) indicated that leaf carbon and nitrogen metabolisms were suppressed when the plants suffered from a high temperature during grain filling. Correlation analysis results indicated that the reduced grain yield was mainly caused by the decreased leaf water content, weakened NR activity, and increased H2O2 content. The increased accumulation of grain weight and post-silking dry matter and the reduced translocation amount in leaf was mainly due to the increased chlorophyll SPAD value and NR activity. Reduced PEPCase and RuBPCase activities did not affect dry matter accumulation and translocation and grain yield. In conclusion, post-silking heat stress down-regulated the leaf NR and GS activities, increased the leaf water loss rate, increased ROS generation, and induced pre-silking carbohydrate translocation. However, it reduced the post-silking direct photoassimilate deposition, ultimately, leading to grain yield loss.

Characterization of nitrate reductase activity (NR) in foliar and radicular tissues of Physalis angulata L.: diurnal variations and protocol optimization

Nitrate reductase (NR) is the first enzyme in the nitrogen assimilation pathway. The determination of its activity requires modifications for each plant species. The goal of this work was to evaluate the variation of NR activity throughout the day and the optimization of assay conditions in foliar and radicular tissues of Physalis angulata. The analysis was done in plants cultivated in a hydroponic system at two months of age. The NR activity was based on the in vivo assay method. Enzyme activity was observed on leaf and root, indicating two sites of nitrate assimilation with a higher activity in the daylight in leaf. The NR activity in leaf was increased after 4h of luminosity. In the root, we observed a high activity during most of the day, especially in periods of higher solar radiation and temperature. To obtain the highest activity of NR in both tissues we suggest 1% n-propanol, 50mM of KNO3- in pH=7 phosphate buffer for 75 min incubation in water bath.

Nitrate reductase activity in leaves as a plant physiological indicator of in vivo biological nitrification inhibition by Brachiaria humidicola

The tropical forage grass Brachiaria humidicola (Bh) controls soil microbial nitrification via biological nitrification inhibition (BNI). The aim of our study was to verify if nitrate reductase activity (NRA) in Bh roots or leaves reflects in vivo performance of BNI in soils. NRA was measured in roots and leaves of contrasting accessions and apomictic hybrids of Bh grown under controlled greenhouse and natural field conditions. Nitrate (NO3−) contents were measured in soil solution and in Bh stem sap to validate NRA data. Potential soil nitrification rates (NRs) and leaf δ15N values were used to verify in vivo BNI by the NRA assay in the field study. NRA was detected in Bh leaves rather than roots, regardless of NO3− availability. NRA correlated with NO3− contents in soils and stem sap of contrasting Bh genotypes substantiating its reflectance of in vivo BNI performance. Additionally, leaf NRA data from the field study significantly correlated with simultaneously collected NRs and leaf δ15N data. The leaf NRA assay facilitated a rapid screening of contrasting Bh genotypes for their differences in in vivo performance of BNI under field and greenhouse conditions, but inconsistency of the BNI potential by Bh germplasm was observed. Among Bh genotypes tested, leaf NRA was closely linked with nitrification activity, and consequently with actual BNI performance. It was concluded that NRA in leaves of Bh can serve as an indicator of in vivo BNI activity when complemented with established BNI methodologies (δ15N, NRs) under greenhouse and field conditions.

Characterization of nutrients uptake and enzymes activity in Khatouni melon (Cucumis melo var. inodorus) seedlings under different concentrations of nitrogen, potassium and phosphorus of nutrient solution

A nutrient solution experiment was done to evaluate effects of different concentrations of nitrogen (N), phosphorus (P) and potassium (K) on leaf mineral concentrations and some enzymes activity of melon seedlings (Cucumismelo var. inodorus subvar. Khatouni). Different levels of these nutrients including 0, 53, 105, 158 and 210 mg L−1 N; 0, 8, 16, 23 and 31 mg L−1 P; 0, 59, 118, 176 and 235 mg L−1 K, all corresponding to 0, 25, 50, 75 and 100% of their concentrations in Hoagland nutrient solution, were applied to plants. The results showed that the highest leaf nitrate reductase (NR) activity was observed at highest N and P levels, whereas the three highest K levels showed the highest NR activity. The highest leaf peroxidase activity was observed at 8 mg L−1 P, 59 mg L−1 K and 158 mg L−1 N. The leaf catalase activity was highest at zero concentration of P, 158 mg L−1 N and 176 mg L−1 K; however, catalase activity was decreased by increasing P levels. Leaf protein content showed an increasing trend with increasing N, P and K levels of nutrient solution, while there was no significant difference between 158 and 210 mg L−1 N. The highest leaf concentrations of N, P, K and Mg were observed at highest nitrogen, potassium and phosphorus levels of nutrient solution, whereas the highest leaf concentration of Ca were obtained at 53 or 105 mg L−1 N, 176 mg L−1 K and 23–31 mg L−1 P. The highest iron concentration of leaves was obtained from 23 to 31 mg L−1 P, 176 mg L−1 K and 210 mg L−1 N.

LeNRT1.1 Improves Nitrate Uptake in Grafted Tomato Plants under High Nitrogen Demand.

Grafting has become a common practice among tomato growers to obtain vigorous plants. These plants present a substantial increase in nitrogen (N) uptake from the root zone. However, the mechanisms involved in this higher uptake capacity have not been investigated. To elucidate whether the increase in N uptake in grafted tomato plants under high N demand conditions is related to the functioning of low- (high capacity) or high-affinity (low capacity) root plasma membrane transporters, a series of experiments were conducted. Plants grafted onto a vigorous rootstock, as well as ungrafted and homograft plants, were exposed to two radiation levels (400 and 800 µmol m−2 s−1). We assessed root plasma membrane nitrate transporters (LeNRT1.1, LeNRT1.2, LeNRT2.1, LeNRT2.2 and LeNRT2.3) expression, Michaelis‒Menten kinetics parameters (Vmax and Km), root and leaf nitrate reductase activity, and root respiration rates. The majority of nitrate uptake is mediated by LeNRT1.1 and LeNRT1.2 in grafted and ungrafted plants. Under high N demand conditions, vigorous rootstocks show similar levels of expression for LeNRT1.1 and LeNRT1.2, whereas ungrafted plants present a higher expression of LeNRT1.2. No differences in the uptake capacity (evaluated as Vmax), root respiration rates, or root nitrate assimilation capacity were found among treatments.