Changes In Nitrate Reductase Activity Research Articles

Bronchopulmonary dysplasia is associated with reduced oral nitrate reductase activity in extremely preterm infants

Oral microbiome mediated nitrate reductase (NR) activity regulates nitric oxide (NO) bioavailability and signaling. While deficits in NO-bioavailability impact several morbidities of extreme prematurity including bronchopulmonary dysplasia (BPD), whether oral NR activity is associated with morbidities of prematurity is not known. We characterized NR activity in extremely preterm infants from birth until 34 weeks' post menstrual age (PMA), determined whether changes in the oral microbiome contribute to changes in NR activity, and determined whether changes in NR activity correlated with disease. In this single center prospective cohort study (n = 28), we observed two surprising findings: (1) NR activity unexpectedly peaked at 29 weeks' PMA (p < 0.05) and (2) when infants were stratified for BPD status, infants who developed BPD had significantly less NR activity at 29 weeks’ PMA compared to infants who did not develop BPD. Oral microbiota and NR activity may play a role in BPD development in extremely preterm infants, indicating potential for disease prediction and therapeutic targeting.

Omeprazole Treatment Enhances Nitrogen Use Efficiency Through Increased Nitrogen Uptake and Assimilation in Corn.

Omeprazole is a selective proton pump inhibitor in humans that inhibits the H+/K+-ATPase of gastric parietal cells. Omeprazole has been recently shown to act as a plant growth regulator and enhancer of salt stress tolerance. Here, we report that omeprazole treatment in hydroponically grown maize improves nitrogen uptake and assimilation. The presence of micromolar concentrations of omeprazole in the nutrient solution alleviates the chlorosis and growth inhibition induced by low nitrogen availability. Nitrate uptake and assimilation is enhanced in omeprazole treated plants through changes in nitrate reductase activity, primary metabolism, and gene expression. Omeprazole enhances nitrate assimilation through an interaction with nitrate reductase, altering its activation state and affinity for nitrate as a substrate. Omeprazole and its targets represent a novel method for enhancing nitrogen use efficiency in plants.

植物によるNO_3-N利用に関する研究(第8報) : 大豆各着位葉の硝酸還元酵素活性の消長について

植物によるNO_3-N利用に関する研究(第8報) : 大豆各着位葉の硝酸還元酵素活性の消長について

Effect of Nitrate Reductase (NR) Inhibitor on NR Activity in Oilseed Rape ( Brassica napus L．) and Its Relation to Nitrate Content

为进一步揭示硝酸还原酶（nitratereductase，NR）活性的调控机制及其与植株体内硝酸盐含量的关系。本试验在正常供氮（15mmolL—N03-）和缺氮（7．5mmolL—N03-）条件下，以氮高效（H1：742和H2：Xiangyou15）和氮低效（L1：814和L2：H8）油菜基因型为研究材料，通过NR活性的专性抑制剂处理，研究NR活性和硝酸盐含量的基因型和氮水平差异。结果表明，NR专性抑制剂处理可以显著降低叶片NR活性，正常供氮和缺氮条件下分别降低53．0％和57．6％，但对叶片硝酸盐的含量没有显著影响。正常供氮条件下的NR活性和硝酸盐含量比缺氮条件下分别高46．9％和16．4％。氮高效油菜基因型的硝酸盐含量显著低于氮低效基因型。H2的NR活性（NRA。。。）显著高于氮低效基因型的本质原因是其主效基因（＂f以）的相对表达量高于氮低效基因型。本研究充分表明NR活性和硝酸盐含量存在明显的基因型和氮水平差异，一定程度的NR活性变化对植株体内硝酸盐的含量并没有显著的影响。

Nitrate reductase activity in soil under shelterbelt and an adjoining cultivated field

Laboratory studies were conducted to evaluate the effect of moisture (field-moist and 15% moisture) and nitrogen concentrations (field content and after the addition of nitrogen in the form of 0.25 and 0.5% urea, respectively), pH and organic matter on the changes in nitrate reductase activity in soils under shelterbelt and an adjoining cultivated field. Shelterbelt consists mainly of Robinia pseudoaccacia. A first-order kinetics reaction model was fitted to the experimental changes in nitrate reductase activity over time data at different moisture and nitrogen content. Under shelterbelt, an increase in the soil moisture content from field-moist to 15% led to a 1.13-fold increase in the first-order reaction rate constant. However, under the adjoining cultivated field, an increase in the soil moisture content from field-moist to 15% increased the first-order reaction rate constant significantly more than in soil under shelterbelt. Changes in nitrate reductase activity for a 15% moisture content in soil under shelterbelt and in field-moist soil in the adjoining cultivated field were similar. Moreover, the addition of 0.25% nitrogen to the adjoining cultivated field with field-moist soil led to a 3.65-fold increase in the first-order reaction rate constant.

RELATIONSHIP BETWEEN FLORAL BUD INDUCTION BY APPLICATION OF KCLO3 AND NITRATE REDUCTASE ACTIVITY OF LEAVES ON LONGAN

Longan (Dimocarpus longan Lour.) trees were treated with potassium chlorate (KClO 3 ) in soil in June. The changes of nitrate reductase activity, C/N and the main nutrient elements in the leaves were determined in a period of floral bud formation. Results showed that the trees were induced to form floral bud and bloom 30 days after the trees were treated with KClO 3 . Floral bud differentiation began after the trees were treated for 75 days with both KClO 3 and Padobutrazol (PP 333 ). The content of nitrate reductase in the leaves was reduced on a period of time after treatment began after. It began to increase at the floral physiological phase and reached the peaks at the morphological differentiation, then fell down. The content of nitrate reductase of control (CK) was kept on a lower level. Otherwise, relationship between flower bud formation induced and changes of the content of chlorate in the leaves were undefined.

Changes of Nitrate Reductase Activity in Cucumber Seedlings in Response to Nitrate Stress

In China, nitrogen fertilizer application rates in intensive agricultural systems have increased dramatically in recent years, especially in protected vegetable production systems. This excessive use of nitrogen fertilizer has resulted in soil secondary salinization, which has become a significant environmental stress for crops such as cucumber, in the protected farmland of China. So it is necessary to illuminate how crops respond to nitrate stress. The objective of this work was to examine the effects of increased nitrate concentration [14 (CK) and 140 mmol L −1 (T)] on NO 3 − concentration, and in vitro and in vivo nitrate reductase activities in the roots and leaves of cucumber ( Cucumis sativus L. cv. Xintaimici) seedlings with hydroponic culture. The results showed that the NO 3 − concentration in the roots and leaves of T seedlings significantly increased over treatment course, and at 12 d increased by 1.08 and 1.72 times with respect to CK seedlings, respectively; in vitro nitrate reductase activity of T was increased dramatically to 1.74 times of CK in the roots at 2 d and 1.56 times of CK in the leaves at 6 d, and then decreased. At 12 d, in vitro activity was still 24.3% higher in the roots and only 9.9% lower in the leaves than CK. Compared with in vitro nitrate reductase activity, in vivo activity responded differently to the increase of treatment time. At the beginning, in vivo nitrate reductase activity in the roots and leaves of T had no significant difference from CK, whereas with the increase of treatment duration, the activity decreased. At 12 d, in vivo activity in the roots and leaves of T lowered by 20.1 and 52.8% with respect to CK, respectively. This evidence suggests that posttranslational activation of nitrate reductase in cucumber seedlings may be seriously inhibited by nitrate stress.

Effect of different N application modes in the first cropping rice on the physiobiochemistry of the first cropping rice and its ratoon rice

In order to determine physiobiochemical mechanisms of the first cropping rice and its ratoon rice under different N application modes in the first cropping rice, the different ratios of N supply for basal-tillering fertilizer to that for spike fertilizer in the first cropping rice were designed under total N supply of 225 kg·hm-2, which were N1 (8︰2), N2 (7︰3), N3 (6︰4), and zero N supply (N0) was the control. Changes in nitrate reductase activity, chlorophyll content, net photosynthetic rate, and root activity were analyzed and their effect on dry-matter accumulation and grain yield formation determined. The results show that the changing tendency in nitrate reductase activity, chlorophyll content and net photosynthetic rate in different treatments is similar under different N application modes in different developmental stages of the first cropping rice and its ratoon rice, showing increasing at the early stage, peaking at the booting stage, then gradually declining in the first cropping rice. It rapidly ascends again at full- heading stage, and then rapidly declines at the ripening stage of the ratoon rice. It is also found that bleeding rate continuously declines after the booting stage of the first cropping rice, however, during the ratooning cropping, it gradually increases at budding and tillering stages, reaches a peak at full-heading stage, then gradually declines at maturity. The result indicates that nitrogen supply enhances nitrate reductase activity, chlorophyll content, net photosynthetic rate and root activity. This therefore suggests that the proportion of N supply should be increased to enhance these parameters during the middle and late growth stages of the first cropping rice. The good pratoce in N application can also enhance root activity, especially at the booting stage of the first cropping rice. This, in turn, can result in increased dry-matter accumulation of the first cropping rice, consequently, high grain output of the ratoon rice .

Virus-induced gene silencing of 14-3-3 genes abrogates dark repression of nitrate reductase activity in Nicotiana benthamiana

In order to study the effect of repression of 14-3-3 genes on actual activity of the nitrate reductase (NR) in Nicotiana benthamiana leaves, Nb14-3-3a gene was silenced by virus-induced gene silencing (VIGS) method using potato virus X (PVX). Expression of Nb14-3-3a as well as Nb14-3-3b genes was altogether repressed in the leaves of PVX-14-3a-infected plants. Furthermore, two-dimensional gel electrophoresis and immunoblot analysis with anti-14-3-3 antiserum suggested that the expressions of Nb14-3-3a and Nb14-3-3b proteins are accordingly repressed in PVX-14-3a-infected plants. It is well known that binding of 14-3-3 proteins to phosphorylated NR leads to substantial decrease in NR activity of leaves under darkness. Therefore, we studied the changes in NR activity in response to light/dark transitions in the leaves of PVX-14-3a-infected plants. NR activation state was kept at a high level under darkness in PVX-14-3a-infected plants, but not in PVX-green fluorescent protein (GFP)-infected and control plants. This result suggests that Nb14-3-3a and/or Nb14-3-3b proteins are indeed involved in the inactivation of NR activity under darkness in N. benthamiana.

Changes in nitrate reductase activity and oxidative stress response in the moss Polytrichum commune subjected to chromium, copper and zinc phytotoxicity

The main aim of this paper was to investigate the effect of chromium (Cr), copper (Cu) and zinc (Zn) on nitrate reductase (NR) activity and oxidative stress responses in the moss Polytrichum commune. Cr, Cu and Zn resulted in the inhibition of NR activity. A decline in total chlorophyll content was observed after 24 and 48 h of metal treatment. Accumulation of the metals showed a dose and time dependent increase. High accumulation of Cu, Cr and Zn were seen in moss shoots after 24 and 48 h of treatment. Treatment of Cr, Cu and Zn for 24 or 48 h resulted in the increase of malondialdehyde (MDA) content in moss shoots. The highest increase was observed in shoots under Cu treatment followed by Cr and Zn. The MDA content was significantly higher after 48h. Antioxidant enzymes viz., catalase (CAT), guaiacol peroxidase (GPx), glutathione reductase (GR) and superoxide dismutase (SOD) were affected by elevated concentrations of the three metals. Increase in the activity of CAT, GR and SOD was seen after 24 and 48 h of treatment. GPx activity declined under Cr treatment. However, under Cu and Zn, an increase in GPx was seen after 24 h and 48 h of treatment. For Zn, the antioxidant efficiency was less affected as compared to Cr and Cu. The response of Polytrichum commune to toxic concentrations of Cr, Cu and Zn appears to induce oxidative damage as observed by the increase in MDA content and antioxidant metabolism.

Post-translational regulation of nitrate reductase: mechanism, physiological relevance and environmental triggers.

Assimilatory nitrate reductase (NR) of higher plants is a most interesting enzyme, both from its central function in plant primary metabolism and from the complex regulation of its expression and control of catalytic activity and degradation. Here, present knowledge about the mechanism of post-translational regulation of NR is summarized and the properties of the regulatory enzymes involved (protein kinases, protein phosphatases and 14-3-3-binding proteins) are described. It is shown that light and oxygen availability are the major external triggers for the rapid and reversible modulation of NR activity, and that sugars and/or sugar phosphates are the internal signals which regulate the protein kinase(s) and phosphatase. It is also demonstrated that stress factors like nitrate deficiency and salinity have remarkably little direct influence on the NR activation state. Further, changes in NR activity measured in vitro are not always associated with changes in nitrate reduction rates in vivo, suggesting that NR can be under strong substrate limitation. The degradation and half-life of the NR protein also appear to be affected by NR phosphorylation and 14-3-3 binding, as NR activation always correlates positively with its stability. However, it is not known whether the molecular form of NR in vivo affects its susceptibility to proteolytic degradation, or whether factors that affect the NR activation state also independently affect the activity or induction of the NR protease(s). A second and potentially important function of NR, the production of nitric oxide (NO) from nitrite is briefly described, but it remains to be determined whether NR produces NO for pathogen/stress signalling in vivo.

Regulation of plant NR activity by reversible phosphorylation, 14-3-3 proteins and proteolysis.

This review highlights progress in dissecting how plant nitrate reductase (NR) activity is regulated by Ca2+, protein kinases, protein kinase kinases, protein phosphatases, 14-3-3 proteins and protease(s). The signalling components that regulate NR have also been discovered to target other enzymes of metabolism, vesicle trafficking and cellular signalling. Extracellular sugars exert a major impact on the 14-3-3-binding status and stability of many target proteins, including NR in plants, whereas other stimuli affect the regulation of some targets and not others. We thus begin to see how selective or global switches in cellular behaviour are triggered by regulatory networks in response to different environmental stimuli. Surprisingly, the question of how changes in NR activity actually affect the rate of nitrate assimilation is turning out to be a tough problem.

Nitrate reductase activity of radish cotyledons as affected by phytohormones and different nitrogen sources

Radish (Raphanus sativus L.) seedlings pretreated with different hormones viz. kinetin, gibberellic acid and abscisic acid were subjected to different N-forms. The seedlings were treated with different concentrations of KNO3, NH4Cl and NH4NO3 and the changes in nitrate reductase activity were seen in light and dark conditions in the cotyledons. Nitrate reductase activity was affected differently by hormone application. Nitrate increased and ammonia decreased nitrate reductase activity; in both light and dark-grown seedlings KNO3 induced more in vitro nitrate reductase activity. NH 4 + when combined with NO 3 − , however, could level up to some extent, with KNO3 in light, except in kinetin. A transient response of induction of NR activity was evident with decreased levels after a certain specific ambient N-concentration, despite the presence of high N in the medium. However, the pattern of transition varied with the hormones applied. Further, hormones are found to affect induction of different isoforms of nitrate reductase by NH 4 + and NO 3 − . NH 4 + induced isoform was prominently promoted by kinetin treatment in dark. The data documents a particular kind of interaction between controlling factors (light, N-source and phytohormones) which affect nitrate reductase levels.

Growth of tobacco in short-day conditions leads to high starch, low sugars, altered diurnal changes in the Nia transcript and low nitrate reductase activity, and inhibition of amino acid synthesis.

Diurnal changes in carbohydrates and nitrate reductase (NR) activity were compared in tobacco (Nicotiana tabacum. L.cv. Gatersleben) plants growing in a long (18 h light/6 h dark) and a short (6 h light/18 h dark) day growth regime, or after short-term changes in the light regime. In long-day-grown plants, source leaves contained high levels of sugars throughout the light and dark periods. In short-day-grown plants, levels of sucrose and reducing sugars were very low at the end of the night and, although they rose during the light period, remained much lower than in long days and declined to very low levels again by the middle of the night. Starch accumulated more rapidly in short-day-than long-day-grown plants. Starch was completely remobilised during the night in short days, but not in long days. A single short day/long night cycle sufficed to stimulate starch accumulation during the following light period. In long-day-grown plants, the Nia transcript level was high at the end of the night, decreased during the day, and recovered gradually during the night. In short-day-grown plants, the Nia transcript level was relatively low at the end of the night, decreased to very low levels at the end of the light period, increased to a marked maximum in the middle of the night, and decreased during the last 5 h of the dark period. In long-day-grown plants, NR activity in source leaves rose by 2- to 3-fold in the first part of the light period and decreased in the second part of the light period. In short-day-grown plants, NR activity was low at the end of the night, and only increased slightly after illumination. Dark inactivation of source-leaf NR was partially reversed in long-day-grown plants, but not in short day-grown plants. In both growth regimes, mutants with one instead of four functional copies of the Nia gene had a 60% reduction in maximum NR activity in the source leaves, compared to wild-type plants. The diurnal changes in NR activity were almost completely suppressed in the mutants in long days, whereas the mutants showed similar or slightly larger diurnal changes than wild-type plants in short days. When short-day-grown plants were transferred to long-day conditions for 3 d, NR activity and the diurnal changes in NR activity resembled those in long-day-grown plants. Phloem export from source leaves of short-day-grown plants was partially inhibited by applying a cold-girdle for one light and dark cycle. The resulting increase in leaf sugar was accompanied by an marked increase in the Nia transcript level and a 2-fold increase in NR activity at the end of the dark period. When wild-type plants were subjected to a single short day/long night cycle of increasing severity, NR activity in source leaves at the end of the night decreased when the endogenous sugars declined below about 3 mumol hexose (g FW)-1. In sink leaves in short-day conditions, sugars were higher and the light-induced rise in NR activity was much larger than in source leaves on the same plants. The source leaves of wild-type plants in short-day conditions contained very high levels of nitrate, very low levels of glutamine, low levels of total amino acids, and lower protein and chlorophyll, compared to long-day-grown plants. Plants grown in short days had relatively high levels of glutamate and aspartate, and extremely low levels of most of the minor amino acids in their source leaves at the end of the night. Illumination led to a decrease in glutamate and an increase in the minor amino acids. A single short day/long night cycle led to an increase in glutamate, and a large decrease in the minor acids at the end of the dark period, and reillumination led to a decrease in glutamate and an increase in the minor amino acids. It is proposed that sugar-mediated control of Nia expression and NR activity overrides regulation by nitrogenous compounds when sugars are in short supply, resulting in a severe inhibition of nitrate assimilation. It is also proposed that su

Enhanced carbon dioxide leads to a modified diurnal rhythm of nitrate reductase activity in older plants, and a large stimulation of nitrate reductase activity and higher levels of amino acids in young tobacco plants

Higher rates of nitrate assimilation are required to support faster growth in enhanced carbon dioxide. To investigate how this is achieved, tobacco plants were grown on high nitrate and high light in ambient and enhanced (700 μmol mol–1) carbon dioxide. Surprisingly, enhanced carbon dioxide did not increase leaf nitrate reductase (NR) activity in the middle of the photoperiod. Possible reasons for this anomalous result were investigated. (a) Measurements of biomass, nitrate, amino acids and glutamine in plants fertilized once and twice daily with 12 mol m–3 nitrate showed that enhanced carbon dioxide did not lead to a nitrate limitation in these plants. (b) Enhanced carbon dioxide modified the diurnal regulation of NR activity in source leaves. The transcript for nia declined during the light period in a similar manner in ambient and enhanced carbon dioxide. The decline of the transcript correlated with a decrease of nitrate in the leaf, and was temporarily reversed after re‐irrigating with nitrate in the second part of the photoperiod. The decline of the transcript was not correlated with changes of sugars or glutamine. NR activity and protein decline in the second part of the photoperiod, and NR is inactivated in the dark in ambient carbon dioxide. The decline of NR activity was smaller and dark inactivation was partially reversed in enhanced carbon dioxide, indicating that post‐transcriptional or post‐translational regulation of NR has been modified. The increased activation and stability of NR in enhanced carbon dioxide was correlated with higher sugars and lower glutamine in the leaves. (c) Enhanced carbon dioxide led to increased levels of the minor amino acids in leaves. (d) Enhanced carbon dioxide led to a large decrease of glycine and a small decrease of serine in leaves of mature plants. The glycine:serine ratio decreased in source leaves of older plants and seedlings. The consequences of a lower rate of photorespiration for the levels of glutamine and the regulation of nitrogen metabolism are discussed. (e) Enhanced carbon dioxide also modified the diurnal regulation of NR in roots. The nia transcript increased after nitrate fertilization in the early and the second part of the photoperiod. The response of the transcript was not accentuated in enhanced carbon dioxide. NR activity declined slightly during the photoperiod in ambient carbon dioxide, whereas it increased 2‐fold in enhanced carbon dioxide. The increase of root NR activity in enhanced carbon dioxide was preceded by a transient increase of sugars, and was followed by a decline of sugars, a faster decrease of nitrate than in ambient carbon dioxide, and an increase of nitrite in the roots. (f) To interpret the physiological significance of these changes in nitrate metabolism, they were compared with the current growth rate of the plants. (g) In 4–5‐week‐old plants, the current rate of growth was similar in ambient and enhanced carbon dioxide (≈ 0·4 g–1 d–1). Enhanced carbon dioxide only led to small changes of NR activity, nitrate decreased, and overall amino acids were not significantly increased. (h) Young seedlings had a high growth rate (0·5 g–1 d–1) in ambient carbon dioxide, that was increased by another 20% in enhanced carbon dioxide. Enhanced carbon dioxide led to larger increases of NR activity and NR activation, a 2–3‐fold increase of glutamine, a 50% increase of glutamate, and a 2–3‐fold increase in minor amino acids. It also led to a higher nitrate level. It is argued that enhanced carbon dioxide leads to a very effective stimulation of nitrate uptake, nitrate assimilation and amino acid synthesis in seedlings. This will play an important role in allowing faster growth rates in enhanced carbon dioxide at this stage.

Changes in Nitrate Reductase Activity of Leaf and Nitrogen Distribution with Growth in Potato Plants.

Four field-grown potato cultivars, Irish Cobbler, May Queen, Dejima and Nishiyutaka, were subjected to measurements of leaf nitrate reductase (NR) activity (in vivo assay) and the distribution of nitrogen during growth and development. Varietal differences in NR-activity averaged over a season were observed : Highest activity was Nishiyutaka (6.08 NO2- μmol h-1 g-1 fresh weight) and lowest was May Queen (4.92 NO2- μmol h-1 g-1 fresh weight). Slightly high NR-activities were observed during the 30 days of early growth in all cultivars, and as growth proceeded, they tended to fall. The NR-activity was positively correlated with the percentage total leaf nitrogen, and with nitrogen accumulated in the leaf. The NR-activity had no correlation with total dry matter or tuber dry matter. The accumulation of nitrogen in the leaves declined with age, whereas it increased in the tubers regardless of the cultivar. At the end of the season, all cultivars except Nishiyutaka accumulated almost the same level of nitrogen in the tubers. A significant linear correlation (r=0.749***) was found between the natural logarithm of SPAD reading (relative chlorophyll content) and NR. Harvest indices for nitrogen showed that the partitioning of nitrogen to the tubers was higher in Irish Cobbler and May Queen than in Dejima and Nishiyutaka. There was no evidence to conclude that NR-activity has a direct effect on dry matter production in potato.

Short-term modulation of nitrate reductase activity by exogenous nitrate in Nicotiana plumbaginifolia and Zea mays leaves

Maize (Zea mays L.) grown on low (0.8 mM) NO 3 - , as well as untransformed and transformed Nicotiana plumbaginifolia constitutively expressing nitrate reductase (NR), was used to study the effects of NO 3 - on the NR activation state. The NR activation state was determined from the relationship of total activity extracted in the presence of ethylenediaminetetracetic acid to that extracted in the presence of Mg2+. Light activation was observed in both maize and tobacco leaves. In the tobacco lines, NO 3 - did not influence the NR activation state. In excised maize leaves, no correlation was found between the foliar NO 3 - content and the NR activation state. Similarly, the NR activation state did not respond to NO 3 - . Since the NR activation state determined from the degree of Mg2+-induced inhibition of NR activity is considered to reflect the phosphorylation state of the NR protein, the protein phosphatase inhibitor microcystin LR was used to test the importance of protein phosphorylation in the NO 3 - -induced changes in NR activity. In-vivo inhibition of endogenous protein phosphatase activity by microcystin-LR decreased the level of NR activation in the light. This occurred to the same extent in the presence or absence of exogenous NO 3 - . We conclude that NO 3 - does not effect the NR activation state, as modulated by protein phosphorylation in either tobacco (a C3 species) or maize (a C4 species). The short-term regulation of NR therefore differs from the NO 3 - -mediated responses observed for phosphoenolpyruvate carboxylase and sucrose phosphate synthase.

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

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

Adaptations of Photosynthetic Electron Transport, Carbon Assimilation, and Carbon Partitioning in Transgenic Nicotiana plumbaginifolia Plants to Changes in Nitrate Reductase Activity.

Transgenic Nicotiana plumbaginifolia plants that express either a 5-fold increase or a 20-fold decrease in nitrate reductase (NR) activity were used to study the relationships between carbon and nitrogen metabolism in leaves. Under saturating irradiance the maximum rate of photosynthesis, per unit surface area, was decreased in the low NR expressors but was relatively unchanged in the high NR expressors compared with the wild-type controls. However, when photosynthesis was expressed on a chlorophyll (Chl) basis the low NR plants had comparable or even higher values than the wild-type plants. Surprisingly, the high NR expressors showed very similar rates of photosynthesis and respiration to the wild-type plants and contained identical amounts of leaf Chl, carbohydrate, and protein. These plants were provided with a saturating supply of nitrate plus a basal level of ammonium during all phases of growth. Under these conditions overexpression of NR had little impact on leaf metabolism and did not stimulate growth or biomass production. Large differences in photochemical quenching and nonphotochemical quenching components of Chl a fluorescence, as well as the ratio of variable to maximum fluorescence, (FV/FM), were apparent in the low NR expressors in comparison with the wild-type controls. Light intensity-dependent increases in nonphotochemical quenching and decreases in FV/FM were greatest in the low NR expressors, whereas photochemical quenching decreased uniformly with increasing irradiance in all plant types. Nonphotochemical quenching was increased at all except the lowest irradiances in the low NR expressors, allowing photosystem II to remain oxidized on its acceptor side. The relative contributions of photochemical and nonphotochemical quenching of Chl a fluorescence with changing irradiance were virtually identical in the high NR expressors and the wild-type controls. Zeaxanthin was present in all leaves at high irradiances; however, at high irradiance leaves from the low NR expressors contained considerably more zeaxanthin and less violaxanthin than wild-type controls or high NR expressors. The leaves of the low NR expressors contained less Chl, protein, and amino acids than controls but retained more carbohydrate (starch and sucrose) than the wild type or high NR expressors. Sucrose phosphate synthase activities were remarkably similar in all plant types regardless of the NR activity. In contrast phosphoenolpyruvate carboxylase activities were increased on a Chl or protein basis in the low NR expressors compared with the wild-type controls or high NR expressors. We conclude that large decreases in NR have profound repercussions for photosynthesis and carbon partitioning within the leaf but that increases in NR have negligible effects.

Changes in nitrate reductase activity, plastid pigment content, and plant mineral composition of wheat, rye, and triticale grown in the presence of aluminum

Abstract The effects of aluminum (Al) on nitrate reductase activity, plastid pigment content, and mineral element composition in wheat, rye, and triticale seedlings were studied. Different responses of the plant species to Al content in the growth solution were observed. Under conditions of different Al concentrations (from 1 to 10 ppm), nitrate reductase (NR) activity increased in wheat and triticale, while in rye an interference with nitrate reductase by Al was observed. A definite tendency in plastid pigment content changes independent on Al levels was not found. The chlorophyll “a”;, chlorophyll “b”;, and carotenoid contents were influenced in a different way in wheat, rye, and triticale seedlings. A positive effect of 1, 5, and 10 ppm Al on the nitrogen (N) content in the shoots of wheat and rye was observed. The N content in the shoots of triticale was not affected by the presence of Al. The presence of Al in the nutrient solution led to a tendency toward reduction of potassium (K), calcium (Ca), an...