Nitrate Reductase Activity In Roots Research Articles

Pre-Sowing Irrigation Plus Surface Fertilization Improves Morpho-Physiological Traits and Sustaining Water-Nitrogen Productivity of Cotton

The changing climatic conditions are causing erratic rains and frequent episodes of moisture stress; these impose a great challenge to cotton productivity by negatively affecting plant physiological, biochemical and molecular processes. This situation requires an efficient management of water-nutrient to achieve optimal crop production. Wise use of water-nutrient in cotton production and improved water use-efficiency may help to produce more crop per drop. We hypothesized that the application of nitrogen into deep soil layers can improve water-nitrogen productivity by promoting root growth and functional attributes of cotton crop. To test this hypothesis, a two-year pot experiment under field conditions was conducted to explore the effects of two irrigation levels (i.e., pre-sowing irrigation (W80) and no pre-sowing irrigation (W0)) combined with different fertilization methods (i.e., surface application (F10) and deep application (F30)) on soil water content, soil available nitrogen, roots morpho-physiological attributes, dry mass and water-nitrogen productivity of cotton. W80 treatment increased root length by 3.1%–17.5% in the 0–40 cm soil layer compared with W0. W80 had 11.3%–52.9% higher root nitrate reductase activity in the 10–30 cm soil layer and 18.8%–67.9% in the 60–80 cm soil layer compared with W0. The W80F10 resulted in 4.3%–44.1% greater root nitrate reductase activity compared with other treatments in the 0–30 cm soil layer at 54–84 days after emergence. Water-nitrogen productivity was positively associated with dry mass, water consumption, root length and root nitrate reductase activity. Our data highlighted that pre-sowing irrigation coupled with basal surface fertilization is a promising option in terms of improved cotton root growth. Functioning in the surface soil profile led to a higher reproductive organ biomass production and water-nitrogen productivity.

Nitrogen use-inefficient oilseed rape genotypes exhibit stronger growth potency during the vegetative growth stage

There is significant genetic diversity within a species in terms of nitrogen utilization efficiency (NUtE), and genotypes with higher NUtE can help reduce nitrogen (N) fertilization rates and therefore mitigate ecological problems. Determining various characteristic differences in the NUtE of crops is helpful for dissecting the mechanisms of N use efficiency within crop species. In this study, a pot experiment, as well as a hydroponic experiment, was conducted to investigate the differences in oilseed rape biomass, N nutrition traits, N metabolism enzyme activity, root exudates and root RNA expression levels at the vegetative stage between the high and low NUtE genotypes. NUtE was negatively correlated with leaf SPAD values (− 0.341**), N accumulation (− 0.362*) and total biomass (− 0.395**), while there was no significant correlation between NUtE and N content (− 0.150 ns). The root biomass; primary root length and root activity; root N content and accumulation; transpiration rate, and stomatal conductance; root nitrate reductase, glutamine synthetase, and glutamate synthetase activity; the number of alkanes; expression levels of BnNRT1.1 and BnNRT2.1 of the low NUtE genotypes were higher than those of the high NUtE ones. It was concluded that during the vegetative growth stage, compared with the high NUtE oilseed genotypes, low NUtE oilseed genotypes demonstrate higher physiological activity or stronger growth potency at the vegetative growth stage.

Long-term rice-rice-rape rotation optimizes 1,2-benzenediol concentration in rhizosphere soil and improves nitrogen-use efficiency and rice growth

We examined differences in soil metabolites from the rice root rhizosphere of long-term rice-rice-fallow (RRF) and rice-rice-rape (RRR) rotations, and examined the effects of 1,2-benzenediol on nitrogen-use efficiency (NUE) and rice growth. The metabolite composition of rice rhizospheres was analyzed using the gas chromatography-mass spectrometry (GC-MS). A range of 0.2, 2.0 and 200 μmol L−1 concentrations of external 1,2-benzenediol were applied to examine their effects on rice growth, nitrate reductase (NR) and glutamine synthetase (GS) activities, and physiological nitrogen-use efficiency (PNUE). The metabolite composition of rhizospheres differed significantly between RRR and RRF. Soil total N and 1,2-benzenediol concentrations during the early rice season were significantly lower under RRR than RRF. Rice growth and NUE significantly enhanced at 0.20 μmol 1,2-benzenediol L−1, but inhibited at 2.0 μmol L−1 or higher. Changes in root morphology and uptake associated with 1,2-benzenediol possibly had contributed to a higher NUE of the early season rice under RRR. The NR and GS activities in rice roots were significantly higher with 0.2 μmol L−1 1,2-benzenediol than without 1,2-benzenediol treatment. Crop rotation significantly affected rice rhizosphere metabolites. An optimal soil 1,2-benzenediol concentration under long-term RRR rotation may be associated with an enhanced NUE and root N uptake and assimilation, resulting in an increased rice growth and yield.

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.

Biological Effects of Seed Irradiation by Synchrotron X Ray Beam in Young Bean Seedlings

Irradiated seeds of Phaseolus vulgaris cv. Rajmah using Synchrotron X Ray Beam (BL-07) in RRCAT, Indore at doses of 1, 10 and 20 Gy were used to raise the seedling and the effects on growth and biochemical constituents in 4 - 8 days, old seedlings were analyzed. The seed irradiation effect on seedling development up to about 4 - 5 days, % germination, seedling length and seedling vigor are significantly decreased at 10 and 20 Gy doses with strong -ve correlation. Other parameters, like relative water content, electrical conductivity and acid phosphatase activity are also decreased. Decrease in various biochemical constituents, like, protein and proline has shown significant reduction at 10 and 20 Gy and phenol at 1 - 20 Gy. However, peroxidase activity is increased at 1 and 10 Gy. Amongst the antioxidant enzymes, only superoxide dismutase activity has shown significant increase at 10 and 20 Gy. For seed irradiation (1 and 10 Gy) effect on seedling development up to 8 days involving transfer to hydroponic culture after 4 days, in shoot tissue, decrease in nitrate reductase activity and pigment content is observed, while nitrate reductase activity in root tissue is increased. The results demonstrate adverse effects on growth as well as biochemical constituents along with increased antioxidant effect in bean seedlings with irradiation of seeds at high dose of synchrotron X radiations. Also the nitrate assimilation and photosynthetic activity are reduced in shoot tissue with seed irradiation, however, increased nitrate reductase activity in roots suggests the involvement of NO signaling.

Biochar can increase nitrogen use efficiency of Malus hupehensis by modulating nitrate reduction of soil and root

A surplus of nitrogen (N) fertilizer can reduce plant nitrogen use efficiency (NUE), however, biochar can improve nutrient uptake by altering soil properties and root growth. Therefore, the objective was to determine how biochar alter soil nitrate (NO3−-N) availability and root development, and then to affect the plant NUE. The biochar was prepared by heating the apple branches at 700 °C and low oxygen. The effects of biochar on NO3−-N leaching and nitrogen oxides fluxes in orchard soil treated with five biochar rates (0, 0.5%, 1%, 2% and 4%) were investigated, the nitrate reduction in the soil and roots, and the NUE of Hupeh Crabapple (Malus hupehensis Rehd.) were measured in two soils amended (or not) with biochar, at six N fertilizer rates, using the solution culture, amino benzene sulfonate and subtraction method, respectively. The results showed that 0.5–4% (w/w) biochar decreased the leaching ratio of NO3−-N (9.9–68.7%) and nitrogen oxides flux (6.3–19.2%) in the soil. Soil denitrification intensity were most significantly decreased in the presence of 1% biochar when N fertilizer was applied at 0–450 mg NO3−-N kg−1; the soil nitrate reductase (NR) activity decreased at the application of 0–50 mg NO3−-N kg−1 in the presence of biochar, The root NR activity and root activity of M. hupehensis were significantly increased in the presence of 1% biochar at the application of 0–300 mg NO3−-N kg−1. In the biochar-amended soil, when the highest root activity and NR activity were obtained, N fertilizer application rate were reduced by 33.3% and 66.7%, compared to the non-amended soil, respectively. The NUE of M. hupehensis was increased by biochar-amended from 6.77% to 261.53%, comparied with the non-amended soils. These results indicated that biochar amendment could decrease nitrate leaching and nitrate reduction in soil, and promote nitrate absorption and reduction by root, thereby increasing the biomass and NUE of M. hupehensis when the input of N fertilizer was reduced from 450 to 300 mg NO3−-N kg−1.

Ammonium uptake and metabolism alleviate PEG-induced water stress in rice seedlings

Ammonium (NH4+) can enhance the water stress induced drought tolerance of rice seedlings in comparison to nitrate (NO3−) nutrition. To investigate the mechanism involved in nitrogen (N) uptake, N metabolism and transcript abundance of associated genes, a hydroponic experiment was conducted in which different N sources were supplied to seedlings growing under water stress. Compared to nitrate, ammonium prevented water stress-induced biomass, leaf SPAD and photosynthesis reduction to a significantly larger extent. Water stress significantly increased root nitrate reductase (NR) and nitrite reductase (NiR) activities, but decreased leaf NiR and glutamate synthetase (GS) activities under NO3− supply, causing lower nitrate content in roots and higher in leaves. In contrast, under NH4+ supply root GS and glutamine oxoglutarate aminotransferase (GOGAT) activities were significantly decreased under water stress, but remained higher in leaves, compared to NO3− treatment, which was beneficial for the transport and assimilation of ammonium in leaves. 15N tracing assays demonstrated that rice 15N uptake rate and accumulation were significant reduced under water stress, but were higher in plants supplied with NH4+ than with NO3−. Therefore, the formers showed higher leaf soluble sugar, proline and amino acids contents, and in turn, associated with a higher photosynthesis rate and biomass accumulation. Most genes related to NO3− uptake and reduction in roots and leaves were down-regulated; however, two ammonium transporter genes closely related to NH4+ uptake (AMT1;2 and AMT1;3) were up-regulated in response to water stress. Overall, our findings suggest that ammonium supply alleviated waters tress in rice seedlings, mainly by increasing root NH4+ uptake and leaf N metabolism.

Biomass Accumulation, Photosynthetic Traits and Root Development of Cotton as Affected by Irrigation and Nitrogen-Fertilization.

Limitations of soil water and nitrogen (N) are factors which cause a substantial reduction in cotton (Gossypium hirsutum L.) yield, especially in an arid environment. Suitable management decisions like irrigation method and nitrogen fertilization are the key yield improvement technologies in cotton production systems. Therefore, we hypothesized that optimal water-N supply can increase cotton plant biomass accumulation by maintaining leaf photosynthetic capacity and improving root growth. An outdoor polyvinyl chloride (PVC) tube study was conducted to investigate the effects of two water-N application depths, i.e., 20 cm (H20) or 40 cm (H40) from soil surface and four water-N combinations [deficit irrigation (W55) and no N (N0) (W55N0), W55 and moderate N (N1) (W55N1), moderate irrigation (W75) and N0 (W75N0), W75N1] on the roots growth, leaf photosynthetic traits and dry mass accumulation of cotton crops. H20W55N1 combination increased total dry mass production by 29–82% and reproductive organs biomass by 47–101% compared with other counterparts. Root protective enzyme and nitrate reductase (NR) activity, potential quantum yield of photosystem (PS) II (Fv/Fm), PSII quantum yield in the light [Y(II)] and electron transport rate of PSII were significantly higher in H20W55N1 prior to 82 days after emergence. Root NR activity and protective enzyme were significantly correlated with chlorophyll, Fv/Fm, Y(II) and stomatal conductance. Hence, shallow irrigation (20 cm) with moderate irrigation and N-fertilization application could increase cotton root NR activity and protective enzyme leading to enhance light capture and photochemical energy conversion of PSII before the full flowering stage. This enhanced photoassimilate to reproductive organs.

Evidence towards the involvement of nitric oxide in drought tolerance of sugarcane

Exogenous supply of nitric oxide (NO) increases drought tolerance in sugarcane plants. However, little is known about the role of NO produced by plants under water deficit. The aim of this study was to test the hypothesis that drought-tolerance in sugarcane is associated with NO production and metabolism, with the more drought-tolerant genotype presenting higher NO accumulation in plant tissues. The sugarcane genotypes IACSP95-5000 (drought-tolerant) and IACSP97-7065 (drought-sensitive) were submitted to water deficit by adding polyethylene glycol (PEG-8000) in nutrient solution to reduce the osmotic potential to −0.4 MPa. To evaluate short-time responses to water deficit, leaf and root samples were taken after 24 h under water deficit. The drought-tolerant genotype presented higher root extracellular NO content, which was accompanied by higher root nitrate reductase (NR) activity as compared to the drought-sensitive genotype under water deficit. In addition, the drought-tolerant genotype had higher leaf intracellular NO content than the drought-sensitive one. IACSP95-5000 exhibited decreases in root S-nitrosoglutathione reductase (GSNOR) activity under water deficit, suggesting that S-nitrosoglutathione (GSNO) is less degraded and that the drought-tolerant genotype has a higher natural reservoir of NO than the drought-sensitive one. Those differences in intracellular and extracellular NO contents and enzymatic activities were associated with higher leaf hydration in the drought-tolerant genotype as compared to the sensitive one under water deficit.

Cyanogen Metabolism in Cassava Roots: Impact on Protein Synthesis and Root Development.

Cassava (Manihot esculenta Crantz), a staple crop for millions of sub-Saharan Africans, contains high levels of cyanogenic glycosides which protect it against herbivory. However, cyanogens have also been proposed to play a role in nitrogen transport from leaves to roots. Consistent with this hypothesis, analyses of the distribution and activities of enzymes involved in cyanide metabolism provides evidence for cyanide assimilation, derived from linamarin, into amino acids in cassava roots. Both β-cyanoalanine synthase (CAS) and nitrilase (NIT), two enzymes involved in cyanide assimilation to produce asparagine, were observed to have higher activities in roots compared to leaves, consistent with their proposed role in reduced nitrogen assimilation. In addition, rhodanese activity was not detected in cassava roots, indicating that this competing means for cyanide metabolism was not a factor in cyanide detoxification. In contrast, leaves had sufficient rhodanese activity to compete with cyanide assimilation into amino acids. Using transgenic low cyanogen plants, it was shown that reducing root cyanogen levels is associated with elevated root nitrate reductase activity, presumably to compensate for the loss of reduced nitrogen from cyanogens. Finally, we overexpressed Arabidopsis CAS and NIT4 genes in cassava roots to study the feasibility of enhancing root cyanide assimilation into protein. Optimal overexpression of CAS and NIT4 resulted in up to a 50% increase in root total amino acids and a 9% increase in root protein accumulation. However, plant growth and morphology was altered in plants overexpressing these enzymes, demonstrating a complex interaction between cyanide metabolism and hormonal regulation of plant growth.

An estimation of the effects of synthetic auxin and cytokinin and the time of their application on some morphological and physiological characteristics of Medicago x varia T. Martyn.

The aim of the experiment was to determine the effects of synthetic auxin and cytokinin and the time of their application on some morphological and physiological characteristics of Medicago x varia T. Martyn grown under controlled conditions. The experiment was to check whether an application of exogenous hormones during vegetative and generative stages of the plant had an effect on above-ground mass development, on nitrate reductase activity and on plastid pigments content. Experiment factor was synthetic auxin and cytokinin and the date of their application. Auxin was applied in the form of a synthetic indole-3-butyric acid, while cytokinin was sprayed as synthetic 6-benzylaminopurine. The control plants were treated with distilled water. Depending on the experimental variant, spraying was applied at the sixth true leaf stage and at the first flower bud stage. The research showed that the response of the alfalfa plants to the application of cytokinin and auxin was not uniform. It seems that the most effective was the application of a mixture of them both but only during the vegetative stage.Additionally, cytokinin caused an increase in plastid pigments content in alfalfa leaves. On the other hand, a mixture of auxin and cytokinin triggered the highest nitrate reductase activity in alfalfa roots and raised the ratio of total chlorophyll content to carotenoids. Synthetic auxin caused the decrease of the levels of most parameters compared to the control.

Exogenous proline significantly affects the plant growth and nitrogen assimilation enzymes activities in rice (Oryza sativa) under salt stress

Salinity has been shown to be a major factor contributing to low nitrogen availability in plants. To verify the changes in nitrogen metabolism activity as affected by the exogenous application of proline under salt stress and its relation to salt tolerance, in vitro rice shoot apices were used as a model to study the growth performance and changes in nitrogen assimilation activities in two Malaysian rice cultivars MR 220 and MR 253. Results revealed that salt stress greatly reduced the plant height, shoot nitrate (NO3 −) content, shoot glutamine synthetase (GS), and root nitrate reductase (NR) activities in both cultivars. Supplementation of proline significantly increased the plant height, number of roots, root NO3 − content, root NR, and root GS activities under salt stress in both cultivars with greater enhancement in MR 253 than MR 220. The results also indicated that MR 253 possessed higher nitrite reductase (NiR) and glutamate synthase (NADH–GOGAT) activities as compared with MR 220 in all tested treatments. It was suggested that the NO3 − content, NR, and GS activities played important roles in regulating nitrogen metabolism under salt stress. Taken together, it was concluded that the ability of proline in mitigating salt stress-induced damages was correlated with the changes in nitrogen assimilation activities.

Positive effects of night warming on physiology of coniferous trees in late growing season: Leaf and root

Previous studies about the effects of experimental warming on tree species have focused primarily on response of morphology and physiology in leaf and biomass allocation in the growing season, and a few studies considered the importance of roots. Based on the available evidence, it is unclear whether photosynthesis rate is enhanced by night warming in late autumn an issue that deserves further investigation. Thus, we exposed two coniferous species, Picea asperata and Abies faxoniana, to night warming continued throughout the year to investigate morphological and physiological responses of roots and leaves in the autumn. The results showed that night warming caused significant increases in net influxes of NH4+ and NO3− in P. asperata seedlings corresponding well with net H+ efflux and net influx of O2. Meanwhile, night warming had a positive effect on foliar gas exchange such as net photosynthesis rate, apparent quantum efficiency, dark respiration rate and maximum quantum efficiency of PS II, and nitrate reductase activity of roots. Additionally, root morphology such as total roots length, surface area, specific root area and specific root length was also stimulated by night warming. In contrast, night warming decreased concentrations of non-structural carbohydrate in leaves and roots of both species in autumn. The present study demonstrates that night warming would enhance late autumn leaf photosynthetic rate, and increase N uptake capacity of roots.

Short-term water stress affecting NO3− absorption by almond plants

Identifying the rates of nitrate absorption by almond plants under water stress is important for improving nitrogen use efficiency in almond orchards. This study aimed to determine the rates of nitrate absorption by almond plants subjected to short-term water stress and no water stress, and the kinetic NO3− absorption parameters in well-watered three-year-old almond plants. Two assays were performed. In the first, fourteen plants arranged in completely randomized design received nutrient solutions with water potentials (Ψw) of 0.0, −0.2, −0.4 and −0.7MPa and containing 1.2mmoll−1 KNO3. We accessed the NO3− depletion in these solutions over an 8-h interval and estimated regression curves of the quantity of nitrate in the nutrient solution (Q) as a function of time (t). Subsequently nitrate uptake rates were calculated. Water loss; nitrate reductase activity; nitrate and total N of the sap; nitrate concentration of leaf dry matter; and nitrate and nitrite concentration of root dry matter were, either, evaluated. The second assay was performed the same way of the first one, with four well-watered plants submitted to 0.3mmoll−1 KNO3 as initial concentration, and allowed estimating NO3− absorption parameters Vmax, Km and Cmin. We observed a linear decrease in the nitrate content of the containers receiving 1.2mmoll−1 of NO3− over a period of 8h. In this concentration, the rates of NO3− uptake ranged from 1.11 to 3.43μmolg−1h−1 and decreased in low water potentials at the root medium. Root nitrate reductase activity followed the same trend of nitrate absorption. In the low NO3− concentration range, the absorption showed a Michaelis–Menten pattern, being the kinetic parameters of NO3− absorption 1.15±0.27μmolg−1h−1, 28.81±4.12μmoll−1 and 17.93±1.1μmoll−1 for Vmax, Km, and Cmin, respectively. We concluded that NO3− uptake of almonds is affected by short periods of water stress, with harmful effects occurring at Ψw below −0.18MPa.

The difference in responses to nitrogen deprivation and re-supply at seedling stage between two barley genotypes differing nitrogen use efficiency

Understanding how crops respond to limited nitrogen supply is essential to develop new ways of manipulating genes for breeding new crop cultivars or lines with high nitrogen use efficiency (NUE). However, little is known about the differences among barley (Hordeum vulgare L.) genotypes in their responses to N starvation and subsequent N re-supply. In this study, two barley genotypes, BI-04 (higher NUE) and BI-45 (lower NUE) were used to investigate N uptake and assimilation at seedling stage in response to N deprivation and re-supply at low (3.75 mM) and normal (7.5 mM) levels. Compared to the continues normal N supply, under N deprivation, both genotypes exhibited less total biomass and N accumulation, but had higher N uptake efficiency, with BI-04 having more biomass, N accumulation and nitrate reductase activity than BI-45. The higher nitrate reductase activity in roots of BI-04 versus BI-45 was associated with up-regulated HvNar1 gene expression under N deprivation condition. NUE of both genotypes was higher under low N re-supply than under normal N re-supply after N deprivation. In addition, glutamine synthetase activity in the two barley roots was higher under low N re-supply than under normal N re-supply, which was associated with the expression of HvGS1_1 and HvGS1_2 genes. Compared to the lower NUE genotype (BI-45), the higher NUE genotype (BI-04) under low N re-supply performed better in response to N stress, and may require relatively less N fertilizer application in production.

Aluminum effect on starch, soluble sugar, and phytohormone in roots of Quercus serrata Thunb. seedlings

Glucose was a key substance as an energy source in the root growth promotion by Al, and ABA may relate to metabolism involved with its process. Generally, excess aluminum (Al) ions in soil solution are toxic to many cultivated plant species, but beneficial effects of Al for plant growth have been reported. Previously, we reported stimulation of root growth and nitrate reductase (NR) activity by Al. In this study, we focused on sugars, such as sucrose, glucose, and fructose, as energy sources and also signaling substances to regulate root growth. To understand the mechanism of root growth stimulation by Al, we investigated the change in concentration of sugars and phytohormones, and the activity of NR in roots using Quercus serrata seedlings. Ten-week-old Q. serrata seedlings were hydroponically cultured with nutrient solution containing 2.5 mM Al (pH 4.0) or 3.25 mM calcium (Ca) (pH 4.0) for 3 and 15 days. The growth of first lateral root and NR activity was stimulated for 3 and 15 days of Al treatment. The concentration of starch and sucrose decreased, while the concentration of glucose increased in the Al-treated roots. The concentration of abscisic acid (ABA) in Al-treated roots increased gradually throughout the experiment. From the present study, the mechanism of root growth promotion by Al involves a complex signaling network. We suggest that glucose is a key substance as an energy source and a signaling substance to promote root growth induced by Al and ABA may relate to nitrogen (N) and carbon (C) metabolism involved with the signaling network to promote root growth induced by Al.

Influence of rhizosphere ventilation on soil nutrient status, root architecture and the growth of young peach trees

The peach tree root respiration rate is high, which requires large amounts of oxygen. When the rhizosphere oxygen content is poor, the root respiration and energy metabolism are restrained which will have negative impacts on peach trees growth, fruit quality and yield, especially during high temperature and rainy season. Our objectives were to investigate the relationship between rhizosphere ventilation and orchard soil enzyme activity, nutrient status, root architecture and growth of young peach trees. Two-year-old ‘Chunmei’ peach (Prunus persica L. Batsch) was subjected to various treatments (Treatment 1 [T1]: ventilation every three days; T2: ventilation every six days; T3: natural ventilation; Control: no ventilation) under field cultivation conditions. The soil oxygen content decreased and subsequently increased during the growth period, reaching a minimum in August. The rhizosphere soil oxygen content was higher under ventilation treatment than control, and T1 markedly increased the rhizosphere soil oxygen content. The rhizosphere soil available K and organic matter decreased while the rhizosphere soil available N and available P content increased and the soil enzyme activity was improved under ventilation treatments. The root activity and root nitrate reductase activity increased under ventilation treatments. Under T1, the total root surface area, total root length and number of first lateral root and second lateral root were increased significantly, but the average root diameter and the average length of first lateral root was reduced significantly, the branching angle between first lateral root and vertically downward direction was decreased, the number of small angle was increased. T1improved leaf functions and increased the net photosynthetic rate. Under T1, the leaf chlorophyll content and leaf protective enzyme activity (Superoxide dismutase, Guaiacol peroxidase and Catalase) increased markedly in the middle- and late-growth period and leaf senescence was postponed. The total nitrogen, phosphorus and potassium contents of young peach roots, shoots and leaves, as well as shoot growth, leaf weight and leaf area, increased under T1.

The role of light in the inducation of nitrate reductase and nitrite reductase in cucumber seedlings

The activity of nitrate reductase (NR) and nitrite reductase (NiR) was investigated in vivo and in vitro in the roots and NR activity in 3-day-old cotyledons of cucumber seedlings. NR activity in the roots appears almost immediately after addition of nitrate ions to the induction medium, whereas, in the cotyledones NR induction is delayed. In general light enhances NR activity in the cotyledons and depresses it in the roots in experiments of short duration. Etiolation of the cotyledons reduces NR activity in the roots and leads to disappearance of the activity of this enzyme in the cotyledons, whereas the NR activity of roots kept in darkness, after transfer of the etiolated plants to light, increases threefold. In roots growing in darkness a delay in NiR induction is observed, while in those growing in ligth it occurs at the same time as NR induction. Chlormaphenicol (CAP), cycloheximide (CHI) and actinomycin D (ACM) applied at the beginning of the period of seedling induction with initrates inhibit NR activity in the cotyledons, whereas in the roots only CHI and ACM exert such an effect. To sum up, NR is synthesized in cucumber roots and cotyledons de novo on the cytoplasmic polyribosomes, and light per se is not indispensable for this synthesis, but it has an indirect influence on the activity level of NR and NiR both in the roots and the cotyledons.

Ammonium and potassium effect on nitrate assimilation in cucumber seedlings

The effect of ammonium present in the induction medium toghether with nitrate on the activity of nitrate reductase (NR), nitrite reductase (NiR), glutamic acid dehydrogenase (GDH) and absorption and accumulation of NO<sub>3</sub><sup>-</sup> in cucumber seedlings were investigated. Maximum NR and NiR activity in the cotyledons was observed when seedlings were supplied with KNO<sub>3</sub> as the sole source of nitrogen. When plants were supplied with NH<sub>4</sub>NO<sub>3</sub> the presence of NH<sub>4</sub><sup>+</sup> in the induction medium repressed by about 50 per cent the activity of both reductases in the cotyledons. Addition of K<sup>+</sup> to this medium abolished completely the inhibitory effect of NH<sub>4</sub><sup>+</sup>. The effect of K<sup>+</sup> cannot be replaced by that Na+ ions. On the other hand, ammonium has no effect on the level of NR activity in roots, while NiR was almost completely repressed. Under the experimental conditions ammonium, in the presence of nitrates, decreased the activity of GDH, but this diminution did not occur when the plants were supplied with K<sup>+</sup> simultaneously. It has found that NH<sub>4</sub><sup>+</sup> ions reduced NO<sub>3</sub><sup>-</sup> absorption but at the same time, the ratio of NO<sub>3</sub>- absorbed to that reduced was increased more than twice. The presumable mechanism of these phenomena is discussed.

Response of nitrate reductase activity and NIA genes expression in roots of Arabidopsis hxk1 mutant treated with selected carbon and nitrogen metabolites

In plants sugar sensing and signal transduction involves pathways dependent or independent on HXK1 as a glucose sensor. Research was conducted to determine which pathway is responsible for regulation of the nitrate reduction. The effect of selected carbon and nitrogen metabolites on nitrate reductase (NR) activity in Arabidopsis thaliana wild type (WT) and hxk1 mutant roots was studied. Exogenously supplied sugar, sucrose (Suc) and organic acid, 2-oxoglutarate (2-OG) led to an increase in the total and actual activity of NR. It was due to both the increase in expression of NIA genes and NR activation state. The stimulatory effect of Suc and 2-OG on nitrate reduction was less pronounced in hxk1 mutant roots with T-DNA insertion in the AtHXK1 gene encoding hexokinase1 (HXK1) and characterized by reduced hexokinase activity and root level of G6P and F6P. On the other hand, it was shown that exogenous glucose did not mimic Suc-mediated NR activation in Arabidopsis roots. Taken together, this data suggest that the Suc signaling pathway might be independent from hexose's sensor dependent mechanism.