Increase In Nitrate Reductase Activity Research Articles

Red Light Is Effective in Reducing Nitrate Concentration in Rocket by Increasing Nitrate Reductase Activity, and Contributes to Increased Total Glucosinolates Content.

Rocket cultivation is increasing to supply the expanding ready-to-eat market because of its unique taste, but crops are often over fertilized to avoid nitrogen deficiencies. This leads to nitrate accumulation in leaves, and the products of their degradation (nitrites and nitrosamines) have been related to several health problems. Nitrate concentrations in rocket and other leafy vegetables are subject to limits by the EU legislation, yet rocket holds a great nutritional value. Degradation products of glucosinolates (isothiocyanates) have been consistently linked with benefits to human health. We investigated the influence of nitrogen application (1 and 8 mM), species [Eruca sativa (L.) Cav. and Diplotaxis tenuifolia (L.) DC.] and light spectrum (full spectrum, red, blue and red + blue) on the nitrate concentration, nitrate reductase activity and glucosinolate content of rocket grown in a soil-less system. Red light decreased the nitrate concentration with respect to the blue spectrum (4,270 vs. 7,100 mg⋅kg–1 of fresh weight, respectively), but such reduction was influenced by the species and the nitrogen level (significantly higher in D. tenuifolia and with the higher concentration of N). The nitrate reductase activity increased under red light in D. tenuifolia, with the lower N concentration. Rocket is known to contain several health-promoting compounds mainly antioxidants and glucosinolates, as secondary metabolites that act as part of plant defense mechanisms. The total content of glucosinolates was mainly affected by the species (D. tenuifolia showed the highest concentrations). Our results will help growers to tailor light spectra with the aim of reducing nitrate concentration and to remain within EU legislative limits, without any detrimental influence on other qualitative parameters in rocket.

Biochemical Response of Hybrid Maize (Zea mays L.) to NPK Fertilization Based on Spent Bleaching Earth in Field Scale

Indonesia is one of the largest crude palm oil (CPO) producing countries in the world. To improve oil quality, CPO purification is carried out including bleaching earth. The process produced spent bleaching earth (SBE) and deoiled spent bleaching earth (DSBE) classified as hazardous and toxic materials waste. SBE and DSBE have the potential as an adhesive material in the manufacture of NPK fertilizers. This study aimed to compare the effects of SBE and DSBE on replacing clay minerals in terms of biochemical response. The study was arranged in randomized completly block design with three treatments and blocks. The treatment consisted of NPK fertilizer containing 10% brown clay (control), NPK fertilizer containing 5% pure clay minerals + 5% SBE, and NPK fertilizer containing 5% pure clay minerals + 5% DSBE. Data were analyzed using ANOVA and tested using LSD test at a 95% confidence level. The results showed that NPK containing DSBE was able to increase nitrate reductase activity (NRA) (41.9%), chlorophyll b content (4.7%), glycine betaine (GB) (2.5%), decreasing electrolite leakage (19%), malondialdehyde (MDA) (23%) compared NPK containing brown clay. Thus the use of NPK containing DSBE and NPK containing SBE to be able to replace NPK containing brown clay.

Physiological, biochemical activities of cherelle wilt on three cocoa clones (Theobroma cacao) under two levels of soil fertilities

Abstract. Dewi HS ES, Ydono P, Putra ETS, Purwanto BH. 2020. Physiological, biochemical activities of cherelle wilt on three cocoa clones (Theobroma cacao) under two levels of soil fertilities. Biodiversitas 21: 187-194. Cherelle wilt is one of the diseases caused by physiological disorders. It results in loss of young pods by 70-90%. This study aims to reveal the correlation of physiological, biochemical activities of several cocoa clones with two soil fertility status. The study was conducted using a nested design with two blocks as replications. The soil fertility status was classified based on soil chemical status. This obtained two clusters of soil fertility, namely low soil fertility, high soil fertility. The second factor was cocoa clone, consisting of three clones, namely RCC 70, RCC 71, KKM 22. Variables measured were soil character, biochemistry of fresh, wilting cherelles, physiological activities, cherelle wilt, biochemical activities including sucrose content, reducing sugar, invertase activity. The data obtained were analyzed for their variance (ANOVA) with a 95% confidence level, tested using Tukey’s HSD there were significant differences between treatments. The results showed that high soil fertility status could increase contents of N, P, K, boron in leaves, increase nitrate reductase activity, chlorophyll contents, increase photosynthesis rate, suppress transpiration rate, increase assimilate transport from leaves to cherelle, increase enzyme invertase activity. RCC 70 clone indicated better physiological, biochemical activity, had the smallest percentage of cherelle wilt. Soil fertility status can suppress cherelle wilt by up to 60% through increasing physiological, biochemical activity. The RCC 70 clone shows the lowest cherelle wilt values ​​compared to RCC 71, KKM 22 clones.

Transformation of nitrogenous compounds in the water-sediment-microbiological system from the Yangtze River

The water-sediment-microbiological system was constructed by flow-through technique in the laboratory using the undisturbed sediment cores collected from Nanjing section of Yangtze River to determine nitrification, denitrification and anaerobic ammonium oxidation (anammox) processes of nitrogenous compounds. The nitrification rates ranged from 11.95 to 19.29 μmol N m−2 h−1 in the sediments and the rates of denitrification and anammox ranged from 11.98 to 65.86 μmol N m−2 h−1 and 0.40 to 8.04 μmol N m−2 h−1, respectively. Denitrification dominated nitrogen removal process, especially non-coupling nitrification process. The decrease of total organic carbon (TOC) and electrical conductivity (EC) in sediments increased the activity of ammonia monooxygenase and promoted the rate of nitrification. The denitrification rates were related to NO3−-N concentrations in the overlying water, and TOC, pH and EC affected the activity of the nitrate reductase. The increase of TOC and clay content and the decrease of EC corresponded to the increase of nitrate reductase activity and anaerobic ammonia oxidation rate. The optimum temperature was 35°C for denitrification and 25°C for nitrification. The pH values influenced nitrogen conversion, denitrification occurred more easily in neutral environment, and the nitrogen conversion rates in the light were higher than in the dark.

Effect of green synthesized molybdenum nanoparticles on nitrate accumulation and nitrate reductase activity in spinach

In the present study, the green synthesized Mo nanoparticles (NPs) were firstly prepared using vermicompost extracts and, then, two experiments were separately carried out in a completely randomized design. The first experiment was conducted to investigate the effects of ammonium nitrate (AN) on nitrate (NO3−) accumulation rates as well as some other vegetative traits in spinach in four treatments and three replicates and the second experiment was done to investigate the effects of elemental Mo and green synthesized Mo NPs on NO3− accumulation, nitrate reductase (NR) activity and some morphological parameters in seven treatments with three replicates. The results of the first experiment indicated that the greatest accumulation of NO3− in the aerial parts of the plants was observed in the 3 M AN treatment. That is why the same concentration was utilized in the second experiment to study the effects of elemental Mo and green synthesized Mo NPs on the NR activity, NO3− accumulation and the other traits. The results of the second experiment indicated that various concentrations of elemental Mo and green synthesized Mo NPs have significant effects on all measured traits including the fresh and dry weights of the plant, NO3− concentration, NR activity, chlorophyll a (Chl a) and chlorophyll b (Chl b) rates, total chlorophyll (Chl a + b) and the plant height. Moreover, it was found that the green synthesized Mo NPs, as compared to elemental Mo, have a greater effect on the increase of NR activity and, consequently, significant reduction of NO3− accumulation.AbbreviationsANammonium nitrateChl achlorophyll aChl bchlorophyll bChl a + bthe total chlorophyllsMMolarMomolybdenumNPsnanoparticlesNRnitrate reductaseNnitrogenNO3−nitrate

Acute salt stress differentially modulates nitrate reductase expression in contrasting salt responsive rice cultivars

Salt stress response includes alteration in the activity of various important enzymes in plants. Nitrate reductase (NR) is one of the known enzyme affected by salt stress. In this study, contrasting salt responsive cultivars (CVS) (IR64-sensitive and CSR 36-tolerant) were considered to study the regulation of NR genes under salt stress conditions. Using Arabidopsis genes Nia1 and Nia2, three different NR genes were identified in rice and their expression study was conducted. Under stress condition, salt-sensitive CVS (IR64) showed a decrease in NR activity under in vitro and in vivo conditions, whereas tolerant CVS showed an increase in NR activity. Different trends for NR activity in contrasting genotype are explained by the variable number of GATA element in the upstream region of the NR gene. This variation of NR activity in contrasting CVS further co-relates with the transcript level of NR genes. The transcript level of three different NR genes also evidenced the effect of CREs in gene regulation. Promoter (1-kb upstream region) of different NR genes contained different abiotic stress-responsive CREs, which explain the differential behavior of these genes towards the abiotic stress. Overall, this study concludes the role of CREs in the regulation of NR gene and indicates the importance of transcriptional control of NR activity under stress condition. This is the first type of report that highlights the role of the regulatory mechanism of NR genes under salt stress condition.

Effects of surface-modified biochars and activated carbon on the transformation of soil inorganic nitrogen and growth of maize under chromium stress

Elevated chromium (Cr) level is challenging agricultural production and affecting soil biochemical process. This study evaluated the effect of amendments including surface-modified biochars (HBC: acid washing, Fe(III)-HBC: ferric iron loading, nZVI-HBC: nanoscale zero-valent iron loading) and activated carbon on hexavalent chromium (Cr(VI)) removal in soil and on N cycling enzyme activities, transformation of soil inorganic nitrogen, and growth of maize under Cr stress. The results showed that amendments increased Cr(VI) removal by 72.9%–96.34% at three levels of spiked Cr(VI) (low: 125 mg kg−1, moderate: 250 mg kg−1, high: 500 mg kg−1). Under low Cr stress, amendments generally significantly decreased urease and nitrite reductase activities but increased nitrate reductase activity (p < 0.05). The NH4+-N content had a significant positive correlation with urease activity (p < 0.01), while both NO2−-N and NO3−-N were absent correlations with N cycling enzyme studied. Amendments decreased NH4+-N/NO3−-N ratio under low Cr stress but increased it under moderate Cr stress, although the difference was not significant. Under high Cr stress, only Fe(III)-HBC significantly increased NH4+-N/NO3−-N ratio (p < 0.05). The decrease and increase of NH4+-N/NO3−-N ratios indicate the enhancement of nitrification and denitrification, respectively. The increase in Cr(VI) removal by amendments contributed to the increase in the migration of NO3−-N from roots to shoots. Amendments (except for nZVI-HBC in soil under low Cr stress) increased maize height by 20%–59%. Under low Cr stress, however, nZVI-HBC significantly decreased maize height by 65% (p < 0.05), indicating the toxic effect of nZVI on maize growth overwhelmed low Cr stress.

Early events following phosphorus restriction involve changes in proteome and affects nitric oxide metabolism in soybean leaves

Phosphorus (P) is a macronutrient with structural and regulatory functions, essential for energy transfer. Under limited P availability, plant cells respond to internal signals, adjusting their metabolic pathways in order to reorganize physiological priorities. This work was conducted with the aim to explore the initial changes following P deprivation, before neither growth nor photosynthesis was strongly affected. The first unifoliate leaves of nine-day-old soybean plants (Glycine max, cv. Williams 82) were analyzed. Plants grown hydroponically under control conditions (+P, nutrient solution with 500 μM H2PO4−) were compared with those restricted in phosphate (-P, without H2PO4− in the nutrient solution). No visible symptoms of P-deficiency, such as changes in pigment intensity and leaf number or size, were observed up to 48 h of P deprivation. Neither fresh weight nor shoot/root FW ratio was affected in plants as a consequence of early P-restriction. Shotgun proteomic analyses of leaves from plants exposed to 24 h of P-deprivation, revealed that a total of 202 proteins were exclusively detected and 232 increased their relative abundance under –P conditions. The proteins affected belong mainly to the catalytic activity group according to Gene Ontology Consortium including proteins like 6-phosphogluconate dehydrogenase (from pentose phosphate pathway), pyrophosphate-fructose 6-phosphate 1-phosphotransferase subunit alpha, alpha-1,4 glucan phosphorylases (from carbohydrate metabolic processes), and other enzymes involved in metabolic processes such as glyceraldehyde-3-phosphate dehydrogenase, pyruvate kinase and fructose-bisphosphate aldolase (from gycolisis), and nitrate reductase (from nitrogen assimilation). Early events in leaves also involve higher levels of the bioactive molecule nitric oxide (NO), detected employing confocal laser microscopy, accompanied with a parallel increase in nitrate reductase activity. Furthermore, the presence of nitrated proteins was detected using shotgun liquid chromatography–mass spectrometry (LCMS/MS). This post-translational protein modification, affected proteins mainly related to photosynthesis (chlorophyll a–b binding protein, ribulose bisphosphate carboxylase), and some other metabolic processes (glutamine synthetase, methionine synthase, lipoxygenase). This methodology allowed the confirmation of nitration sites in proteins previously described as putatively nitrated. Taken together the data presented suggest important metabolic changes, including nitric oxide metabolism, during the first hours of P deprivation.

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.

Municipal Waste and Poultry Manure Compost Affect Biomass Production, Nitrate Reductase Activity and Heavy Metals in Tomato Plants

Organic wastes can be usefully recovered to produce organic amendments, for example, compost, to be used for crop production, thus reducing impacts through efficient waste management. The aim of this work was to study the effects of compost obtained from municipal waste in combination with poultry manure on plant growth, nitrate reductase (NR) activity and absorption and distribution of heavy metals (HM) in plant tissues of tomatoes, grown in pots in greenhouses. Two compost types obtained from municipal waste mixed with poultry manure (C1 = 3:2 and C2 = 2:3) were used at two different ages (105 d and 173 d) and at two mix rates with soil (32.5 g pot−1 and 65 g pot−1); soil with no compost amendment was used as control. The experiment was conducted using tomato plants in pots and plant growth and nutrient plant uptake was determined after 65 days from plant transplanting. Results obtained indicated that compost type and compost rate affected biomass production. However, compost age did not influence the development of plants. Nutrient status of tomato plants was also investigated with reference to the N cycle. Nitrite accumulation in the leaves increased with the increase in compost doses. The accumulation of NO2− was associated with a significant increase in NR activity. HM content in leaves decreased with compost use. HM accumulated preferentially in roots and leaves and the soil to root metals transfer was in this order: Fe (1.08–2.14)> Co (0.53–4.10)>Cu (0.28–2.28) >Mn (0.3–1.34) >Zn (0.87–1.21)>Cr (0.12–1.64). The highest and lowest dynamic bioaccumulation factors (BAFdyn) were observed in roots and stems, respectively. The root system acted as a barrier for Cd and Pb. It was concluded that compost use is beneficial for tomato plants, with particular reference to the compost obtained by using a higher amount of poultry manure (C2) in the mix.

Nitrate nutrition influences multiple factors in order to increase energy efficiency under hypoxia in Arabidopsis.

Nitrogen (N) levels vary between ecosystems, while the form of available N has a substantial impact on growth, development and perception of stress. Plants have the capacity to assimilate N in the form of either nitrate (NO3-) or ammonium (NH4+). Recent studies revealed that NO3- nutrition increases nitric oxide (NO) levels under hypoxia. When oxygen availability changes, plants need to generate energy to protect themselves against hypoxia-induced damage. As the effects of NO3- or NH4+ nutrition on energy production remain unresolved, this study was conducted to investigate the role of N source on group VII transcription factors, fermentative genes, energy metabolism and respiration under normoxic and hypoxic conditions. We used Arabidopsis plants grown on Hoagland medium with either NO3- or NH4+ as a source of N and exposed to 0.8 % oxygen environment. In both roots and seedlings, we investigated the phytoglobin-nitric oxide cycle and the pathways of fermentation and respiration; furthermore, NO levels were tested using a combination of techniques including diaminofluorescein fluorescence, the gas phase Griess reagent assay, respiration by using an oxygen sensor and gene expression analysis by real-time quantitative reverse transcription-PCR methods. Under NO3- nutrition, hypoxic stress leads to increases in nitrate reductase activity, NO production, class 1 phytoglobin transcript abundance and metphytoglobin reductase activity. In contrast, none of these processes responded to hypoxia under NH4+ nutrition. Under NO3- nutrition, a decreased total respiratory rate and increased alternative oxidase capacity and expression were observed during hypoxia. Data correlated with decreased reactive oxygen species and lipid peroxidation levels. Moreover, increased fermentation and NAD+ recycling as well as increased ATP production concomitant with the increased expression of transcription factor genes HRE1, HRE2, RAP2.2 and RAP2.12 were observed during hypoxia under NO3- nutrition. The results of this study collectively indicate that nitrate nutrition influences multiple factors in order to increase energy efficiency under hypoxia.

Ocean acidification and nutrient limitation synergistically reduce growth and photosynthetic performances of a green tide alga &amp;lt;i&amp;gt;Ulva linza&amp;lt;/i&amp;gt;

Abstract. Large-scale green tides have been invading the coastal zones of the western Yellow Sea annually since 2008. Meanwhile, oceans are becoming more acidic due to continuous absorption of anthropogenic carbon dioxide, and intensive seaweed cultivation in Chinese coastal areas is leading to severe regional nutrient limitation. However, little is known about the combined effects of global and local stressors on the eco-physiology of bloom-forming algae. We cultured Ulva linza for 9–16 days under two levels of pCO2 (400 and 1000 µatm) and four treatments of nutrients (nutrient repletion, N limitation, P limitation, and N–P limitation) to investigate the physiological responses of this green tide alga to the combination of ocean acidification and nutrient limitation. For both sporelings and adult plants, elevated pCO2 did not affect the growth rate when cultured under nutrient-replete conditions but reduced it under P limitation; N or P limitations by themselves reduced growth rate. P limitation resulted in a larger inhibition in growth for sporelings compared to adult plants. Sporelings under P limitation did not reach the mature stage after 16 days of culture while those under P repletion became mature by day 11. Elevated pCO2 reduced net photosynthetic rate for all nutrient treatments but increased nitrate reductase activity and soluble protein content under P-replete conditions. N or P limitation reduced nitrate reductase activity and soluble protein content. These findings indicate that ocean acidification and nutrient limitation would synergistically reduce the growth of Ulva species and may thus hinder the occurrence of green tides in a future ocean environment.

Leaf nitrogen assimilation and partitioning differ among subtropical forest plants in response to canopy addition of nitrogen treatments

Global increases in nitrogen deposition may alter forest structure and function by interfering with plant nitrogen metabolism (e.g., assimilation and partitioning) and subsequent carbon assimilation, but it is unclear how these responses to nitrogen deposition differ among species. In this study, we conducted a 2-year experiment to investigate the effects of canopy addition of nitrogen (CAN) on leaf nitrogen assimilation and partitioning in three subtropical forest plants (Castanea henryi, Ardisia quinquegona, and Blastus cochinchinensis). We hypothesized that responses of leaf nitrogen assimilation and partitioning to CAN differ among subtropical forest plants. CAN increased leaf nitrate reductase (NR) activity, and leaf nitrogen and chlorophyll contents but reduced leaf maximum photosynthetic rate (Amax), photosynthetic nitrogen use efficiency (PNUE), ribulose-1,5-bisphosphate carboxylase (Rubisco) activity, and metabolic protein content of an overstory tree species C. henryi. In an understory tree A. quinquegona, CAN increased NR activity and glutamine synthetase activity and therefore increased metabolic protein synthesis (e.g., Rubisco) in leaves. In the shrub B. cochinchinensis, CAN increased Amax, PNUE, Rubisco content, metabolic protein content, and Rubisco activity in leaves. Leaf nitrogen assimilation and partitioning results indicated that A. quinquegona and B. cochinchinensis may better acclimate to CAN than C. henryi and that the acclimation mechanism differs among the species. Results from this study suggest that long-term elevated atmospheric nitrogen deposition has contributed to the ongoing transformation of subtropical forests into communities dominated by small trees and shrubs.

Involvement of NR and PM-NR in NO biosynthesis in cucumber plants subjected to salt stress

Nitrate reductase (NR) mainly reduces nitrate to nitrite. However, in certain conditions it can reduce nitrite to NO. In plants, a plasma membrane-associated form of NR (PM-NR) is present. It produces NO2− for nitrite NO/reductase (Ni-NOR), which can release NO into the apoplastic space. The effect of 50 mM NaCl on NO formation and the involvement of NR in NO biosynthesis were studied in cucumber seedling roots under salt stress. In salt-stressed roots, the amount of NO was higher than in control. The application of tungstate abolished the increase of NO level in stressed roots, indicating that NR was responsible for NO biosynthesis under the test conditions. The involvement of other molybdoenzymes was excluded using specific inhibitors. Furthermore, higher cNR and PM-NR activities were observed in NaCl-treated roots. The increase in NR activity was due to the stimulation of CsNR genes expression and posttranslational modifications, such as enzyme dephosphorylation. This was confirmed by Western blot analysis. Moreover, the increase of nitrite tissue level in short-term stressed roots and the nitrite/nitrate ratio, with a simultaneous decrease of nitrite reductase (NiR) activity, in both short- and long-term stressed roots, could promote the production of NO by NR in roots under salt stress.

Recombination between DEP1 and NRT1.1B under japonica and indica genetic backgrounds to improve grain yield in rice

DEP1 and NRT1.1B genes for improving nitrogen utilization efficiency (NUE) have been widely used in japonica and indica rice (Oryza sativa L.) breeding, respectively. The aim of this study was to determine the effect of the non-allelic recombination of two genes on agronomic traits, grain yield and NUE under japonica and indica genetic backgrounds. One hundred and fifty-one recombinant inbred lines were derived from a cross between japonica variety SN265 with dep1/NRT1.1B alleles and indica variety R99 with DEP1/nrt1.1b alleles. Among these, we found four genotypes (DEP1/NRT1.1B, DEP1/nrt1.1b, dep1/NRT1.1B and dep1/nrt1.1b) under japonica and indica genetic backgrounds. Results showed a significant increase in nitrate reductase activity, N uptake and grain yield under low N growth condition, after the nrt1.1b allele was introduced into japonica lines with dep1. Whereas, the introduction of dep1 allele into indica lines with nrt1.1b increased glutamine synthetase activity, N transfer and grain yield under both low and high N growth conditions. Our results showed diverse physiological pathway between dep1 and nrt1.1b alleles in the N metabolism of rice, providing new strategies in flexible application of dep1 and nrt1.1b alleles for improvement of NUE in japonica and indica rice breeding.

Transgenic Centipedegrass (Eremochloa ophiuroides [Munro] Hack.) Overexpressing S-Adenosylmethionine Decarboxylase (SAMDC) Gene for Improved Cold Tolerance Through Involvement of H2O2 and NO Signaling.

Centipedegrass (Eremochloa ophiuroides [Munro] Hack.) is an important warm-season turfgrass species. Transgenic centipedgrass plants overexpressing S-adenosylmethionine decarboxylase from bermudagrass (CdSAMDC1) that was induced in response to cold were generated in this study. Higher levels of CdSAMDC1 transcript and sperimidine (Spd) and spermin (Spm) concentrations and enhanced freezing and chilling tolerance were observed in transgenic plants as compared with the wild type (WT). Transgenic plants had higher levels of polyamine oxidase (PAO) activity and H2O2 than WT, which were blocked by pretreatment with methylglyoxal bis (guanylhydrazone) or MGBG, inhibitor of SAMDC, indicating that the increased PAO and H2O2 were a result of expression of CdSAMDC1. In addition, transgenic plants had higher levels of nitrate reductase (NR) activity and nitric oxide (NO) concentration. The increased NR activity were blocked by pretreatment with MGBG and ascorbic acid (AsA), scavenger of H2O2, while the increased NO level was blocked by MGBG, AsA, and inhibitors of NR, indicating that the enhanced NR-derived NO was dependent upon H2O2, as a result of expression CdSAMDC1. Elevated superoxide dismutase (SOD) and catalase (CAT) activities were observed in transgenic plants than in WT, which were blocked by pretreatment with MGBG, AsA, inhibitors of NR and scavenger of NO, indicating that the increased activities of SOD and CAT depends on expression of CdSAMDC1, H2O2, and NR-derived NO. Our results suggest that the elevated cold tolerance was associated with PAO catalyzed production of H2O2, which in turn led to NR-derived NO production and induced antioxidant enzyme activities in transgenic plants.

Nitric Oxide Mediates Molybdenum-Induced Antioxidant Defense in Wheat under Drought Stress.

Molybdenum (Mo) has been reported to alleviate drought stress by enhancing antioxidant defense in plants, but the underlying mechanism remains unclear. Here, we hypothesized that Mo mediates nitric oxide (NO)-induced antioxidant defense through Mo-enzymes, particularly by nitrate reductase (NR) in wheat under drought stress. The 30-day-old wheat seedlings cultivated in -Mo (0 μM Mo) and +Mo (1 μM Mo) Hoagland solutions were detached and then pretreated with Mo-enzyme inhibitors, NO scavengers, NO donors or their combinations according to demands of complementary experiment under 10% polyethylene glycol 6000 (PEG)-stimulated drought stress (PSD). Mo supplementation increased the activities and transcripts of antioxidant enzymes, decreased H2O2 and MDA contents, and elevated NO production, implying that Mo-induced antioxidant defense may be related to NO signal. Complementary experiment showed that NO production was induced by Mo, while suppressed by Mo-enzyme inhibitors and NO scavengers, but restored by NO donors, suggesting that Mo-induced increase of NO production may be due to the regulation by Mo-enzymes. Further experiment indicated that the increased activities and transcripts of antioxidant enzymes induced by Mo were suppressed by Mo-enzyme inhibitors and NO scavengers, and NO donors could eliminate their suppressing effects. Moreover, Mo application increased NR activity and inhibitors of Mo-enzymes inhibited NR activity in wheat leaves under PSD, suggesting that NR might involve in the regulation of Mo-induced NO production. These results clearly indicate that NO mediates Mo-induced antioxidant defense at least partially through the regulation of NR.

The bZIP transcription factor MdHY5 regulates anthocyanin accumulation and nitrate assimilation in apple

The basic leucine zipper (bZIP) transcription factor HY5 plays a multifaceted role in plant growth and development. Here the apple MdHY5 gene was cloned based on its homology with Arabidopsis HY5. Expression analysis demonstrated that MdHY5 transcription was induced by light and abscisic acid treatments. Electrophoretic mobility shift assays and transient expression assays subsequently showed that MdHY5 positively regulated both its own transcription and that of MdMYB10 by binding to E-box and G-box motifs, respectively. Furthermore, we obtained transgenic apple calli that overexpressed the MdHY5 gene, and apple calli coloration assays showed that MdHY5 promoted anthocyanin accumulation by regulating expression of the MdMYB10 gene and downstream anthocyanin biosynthesis genes. In addition, the transcript levels of a series of nitrate reductase genes and nitrate uptake genes in both wild-type and transgenic apple calli were detected. In association with increased nitrate reductase activities and nitrate contents, the results indicated that MdHY5 might be an important regulator in nutrient assimilation. Taken together, these results indicate that MdHY5 plays a vital role in anthocyanin accumulation and nitrate assimilation in apple.

Nitrogen-source preference in blueberry (Vaccinium sp.): Enhanced shoot nitrogen assimilation in response to direct supply of nitrate

Blueberry (Vaccinium sp.) is thought to display a preference for the ammonium (NH4+) form over the nitrate (NO3−) form of inorganic nitrogen (N). This N-source preference has been associated with a generally low capacity to assimilate the NO3− form of N, especially within the shoot tissues. Nitrate assimilation is mediated by nitrate reductase (NR), a rate limiting enzyme that converts NO3− to nitrite (NO2−). We investigated potential limitations of NO3− assimilation in two blueberry species, rabbiteye (Vaccinium ashei) and southern highbush (Vaccinium corymbosum) by supplying NO3− to the roots, leaf surface, or through the cut stem. Both species displayed relatively low but similar root uptake rates for both forms of inorganic N. Nitrate uptake through the roots transiently increased NR activity by up to 3.3-fold and root NR gene expression by up to 4-fold. However, supplying NO3− to the roots did not increase its transport in the xylem, nor did it increase NR activity in the leaves, indicating that the acquired N was largely assimilated or stored within the roots. Foliar application of NO3− increased leaf NR activity by up to 3.5-fold, but did not alter NO3− metabolism-related gene expression, suggesting that blueberries are capable of post translational regulation of NR activity in the shoots. Additionally, supplying NO3− to the cut ends of stems resulted in around a 5-fold increase in NR activity, a 10-fold increase in NR transcript accumulation, and up to a 195-fold increase in transcript accumulation of NITRITE REDUCTASE (NiR1) which codes for the enzyme catalyzing the conversion of NO2− to NH4+. These data indicate that blueberry shoots are capable of assimilating NO3− when it is directly supplied to these tissues. Together, these data suggest that limitations in the uptake and translocation of NO3− to the shoots may limit overall NO3− assimilation capacity in blueberry.

Changes in morphological plasticity of Ulva prolifera under different environmental conditions: A laboratory experiment

The large-scale green tides, consisting mainly of Ulva prolifera, have invaded the coastal zones of western Yellow Sea each year since 2008, resulting in tremendous impacts on the local environment and economy. A large number of studies have been conducted to investigate the physiological traits of U. prolifera to explain its dominance in the green tides. However, little has been reported regarding the response of U. prolifera to changing environmental factors via morphological variation. In our experiments, we found remarkable morphological acclimation of U. prolifera to various temperature (20 and 25°C) and salinity (10, 20, and 30) conditions. U. prolifera had more, but shorter branches when they were cultured at lower temperature and salinity conditions. To investigate the significance of these morphological variations in its acclimation to changes of environmental factors, physiological and biochemical traits of U. prolifera grown under different conditions were measured. Higher temperature increased the relative growth rate while salinity did not affect it. On the other hand, higher temperature did not enhance the net photosynthetic rate whilst lower salinity did. The increased net photosynthetic rate at lower salinity conditions could be attributed to more photosynthetic pigments—chlorophyll a, chlorophyll b, and carotenoids—in thalli due to there being more branches at lower salinity conditions. Increased numbers of branches and thus an increased intensity of thalli may be helpful to protect thalli from increased osmotic pressure caused by lower salinity, but it led to more shading. In order to capture enough light when being shaded, thalli of U. prolifera synthesized more photosynthetic pigments at lower salinity levels. In addition, higher temperature increased nitrate reductase activity and soluble protein content but variations in salinity did not impose any effect on them. Our results demonstrate conclusively that U. prolifera can acclimatize in the laboratory to the changes of environmental factors (salinity and temperature) by morphology-driven physiological and biochemical variation. We suggest that the morphological plasticity of U. prolifera may be an important factor for it to outcompete other algal species in a changing ocean.