硫和6-苄氨基腺嘌呤对水稻幼苗硝酸还原酶活性的影响

缺硫培养6天的水稻幼苗,其叶片和根中的硝酸还原酶(NR)活性明显下降。用1pPm 的6-苄氨基腺嘌呤(6-BA)处理培养了10天的水稻幼苗根系,24小时后缺硫培养的水稻幼苗叶片和根系的 NR 活性升高,加硫培养的水稻幼苗叶片和根中的 NR 活性下降。用~(35)S示踪发现,6-BA 可降低加硫幼苗对~(35)S 的吸收和转化,但促进缺硫幼苗对~(35)S 的转化。     

Interaction of sulfur and nitrogen nutrition in tobacco (Nicotiana tabacum) plants: significance of nitrogen source and root nitrate reductase

Abstract: The significance of root nitrate reductase for sulfur assimilation was studied in tobacco (Nicotiana tabacum) plants. For this purpose, uptake, assimilation, and long-distance transport of sulfur were compared between wild-type tobacco and transformants lacking root nitrate reductase, cultivated either with nitrate or with ammonium nitrate. A recently developed empirical model of plant internal nitrogen cycling was adapted to sulfur and applied to characterise whole plant sulfur relations in wild-type tobacco and the transformant. Both transformation and nitrogen nutrition strongly affected sulfur pools and sulfur fluxes. Transformation decreased the rate of sulfate uptake in nitrate-grown plants and root sulfate and total sulfur contents in root biomass, irrespective of N nutrition. Nevertheless, glutathione levels were enhanced in the roots of transformed plants. This may be a consequence of enhanced APR activity in the leaves that also resulted in enhanced organic sulfur content in the leaves of the tranformants. The lack of nitrate reductase in the roots in the transformants caused regulatory changes in sulfur metabolism that resembled those observed under nitrogen deficiency. Nitrate nutrition reduced total sulfur content and all the major fractions analysed in the leaves, but not in the roots, compared to ammonium nitrate supply. The enhanced organic sulfur and glutathione levels in ammonium nitrate-fed plants corresponded well to elevated APR activity. But foliar sulfate contents also increased due to decreased re-allocation of sulfate into the phloem of ammonium nitrate-fed plants. Further studies will elucidate whether this decrease is achieved by downregulation of a specific sulfate transporter in vascular tissues.     

Nitrate uptake by bean (Phaseolus vulgaris L.) roots under phosphate deficiency

Bean (Phaseolus vulgaris L.) plants were cultured for 19 d on complete or on phosphate deficient culture media. Low inorganic phosphate concentration in the roots decreased ATP level and nitrate uptake rate. The mechanisms which may control nitrate uptake rate during phosphate deficiency were examined. Plasma membrane enriched fractions from phosphate sufficient and phosphate deficient plants were isolated and compared. The decrease in total phospholipid content was observed in plasma membranes from phosphate deficient roots, but phospholipid composition was similar. No changes in ATPase and proton pumping activities measured in isolated plasma membrane of phosphate sufficient and phosphate deficient bean roots were noted. The electron microscope observations carried out on cortical meristematic cells of the roots showed that active ATPases were found in plasma membrane of both phosphate sufficient and phosphate deficient plants. The decrease in inorganic phosphate concentration in roots led to increased nitrate accumulation in roots, accompanied by a corresponding alterations in NO₃ distribution between shoots and roots. Nitrate reductase activity in roots of phosphate deficient plants estimated in vivo and in vitro was reduced to 50–60% of the control. The increased NO₃ concentration in root tissue may be explained by decreased NR activity and lower transport of nitrate from roots to shoots. Therefore, the reduction of nitrate uptake during phosphate starvation is mainly a consequence of nitrate accumulation in the roots.     

Cadmium phytoextraction potential of poplar clones (Populus spp.)

Biomass production, leaf number and area, photosynthetic and dark respiration rates, leaf concentration of photosynthetic pigments, nitrate reductase activity, as well as cadmium concentrations in leaves, stem, and roots were measured in poplar clones PE 4/68, B-229, 665, and 45/51. Plants were grown hydroponically under controlled conditions and treated with two different cadmium (Cd) concentrations (10(-5) and 10(-7) M) in the same background solution (Hoagland's solution). The presence of Cd did not cause serious disturbance of growth and physiological parameters in the studied poplar clones. Cd concentrations in plant tissues reflected external concentrations. In treated plants, root contents increased from 38.57 to 511.51 ppm, leaf contents from 0.91 to 7.50, while stem contents ranged from 1.37 to 9.50 ppm.     

Effect of ammonium nutrition on the activity of nitrate reductase in the roots of apple seedlings

Active extracts of nitrate reductase were prepared from theroots of apple seedlings c.v. Granny Smith which were grownin nutrient solution under controlled enviromental conditions.The nutrient solutions contained various ratios of nitrate andammonium ions but all the treatments contained a total of 112ppm nitrogen. Maximum nitrate reductase activity in the roots was obtainedwhen plants were supplied with nitrate as the sole source ofnitrogen. Roots grown in solution containing only ammonium nitrogenhad little or no activity. When plants were supplied with bothforms of nitrogen in the nutrient solution, the presence ofammonium ions markedly lowered the activity of nitrate reductasein the roots. Plants supplied with 98 ppm nitrate nitrogen plus14 ppm ammonium nitrogen had activities only half those of plantsgrown in nitrate alone. Plants supplied with equal amounts ofammonium and nitrate nitrogen had activities less than one sixththose of plants grown in nitrate alone. (Received June 3, 1972; )     

Zinc-Induced Changes in Morpho-Physiological and Biochemical Parameters in Artemisia annua

Responses of Artemisia annua to different concentrations of zinc [50, 100, 200, 300 and 400 μg g⁻¹(soil dry mass)] were studied during plant ontogeny. Total leaf area, dry mass of leaves, length and dry mass of shoots and roots increased with the age of the plant but the magnitude of increase declined significantly under the influence of Zn treatment. Net photosynthetic rate, intercellular carbon dioxide concentration and stomatal conductance were highest at flowering stage in control and treated plants and decreased at post flowering stage. Contents of chlorophyll a, chlorophyll b, carotenoids, proteins and nitrate reductase activity in leaves increased from pre-flowering to maximum level at flowering stage and decreased thereafter in both control and treated plants. Presence of Zn in the soil drastically decreased/inhibited all the parameters, and the magnitude of decline increased with increasing Zn concentration. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of nodulation on the nitrate assimilation in vegetative soybean plants

Summary Nitrate assimilation in the first trifoliate leaf of vegetative soybean plants (Glycine max L. Merr, cv Hodgson) was studied in relation to nodulation. Nodulated and non-nodulated plants were grown in a nitrate medium (4 mM). As a control nodulated plants were grown in a nutrient medium without combined nitrogen. This study included measurements of the acetylene reduction activity of the whole plant and of thein vitro nitrate reductase, glutamine synthetase and glutamate dehydrogenase activities in the first leaf and of the nitrate concentration. Nitrate accumulation and nitrate reductase activity were depressed in nodulated plants; root growth was decreased in the presence of nitrate. The relationships between nitrate assimilation and nodulation are discussed.     

Triadimenol Increases Nitrate Levels and Nitrate Reductase Activity in Canola Leaves

Nitrate reductase activity in the first true leaves of canola(Brassica napus L.) seedlings grown in one-quarter strengthHoagland's solution from seeds pretreated with triadimenol (0.3or 30 g (a.i.) kg^–1 of seed) was higher than controlsduring the growth period of 15 to 25 d after planting. Triadimenolalso increased chlorophyll levels, the increase being more pronouncedat its lower concentration. The treatment also increased theweight and nitrate content of the leaves. When seedlings weregrown in nutrient solution containing 1 to 20 mM nitrate, theincrease in nitrate reductase activity by triadimenol was higherat lower rather than at higher nitrate concentrations. The nitratelevels and Kjeldahl nitrogen in the triadimenol-treated leaveswas higher than the controls at concentrations of added nitrateabove 2 mM. Addition of nitrate to plants grown in ammonium,increased nitrate reductase activity more in plants grown fromtriadimenol-treated seeds than controls. However, addition of10µM triadimenol for 24 h to ammonium-grown plants hadlittle effect on enzyme activity, both in the absence as wellas the presence of nitrate. This study demonstrates that triadimenolincreases nitrate reductase activity and nitrate accumulationin the leaves and at least part of the increased enzyme activityis independent of nitrate accumulation. Key words: Triazoles, nitrate content, nitrate reductase activity     

Nicotinamide Adenine Dinucleotide Phosphate Phosphatase Facilitates Dark Reduction of Nitrate: Regulation by Nitrate and Ammonia

Leaves of 15 - 30-d-old plants of sunflower and jute were harvested at 10.00 or 23.00 (local time) and measured immediately, or those harvested at 10.00 were incubated for one hour in sunlight either in water or 5 mM methionine sulfoximine (MSX) solution and then for three hours in dark either in water or 15 mM KNO3 solution. Nitrate feeding during dark incubation, in general, increased nitrate reductase (NR) and nitrite reductase (NiR) activities, and NADH and soluble sugar contents. Increase in tissue nitrate concentration in MSX fed but not in control samples suggested reduction of nitrate in dark. NADPH-dependent NR activity increased considerably upon feeding with nitrate in dark. Concomitantly, NADPH phosphatase activity was also increased in nitrate treated, dark incubated leaves. It is proposed that nitrate regulates dark nitrate reduction by facilitating generation of NADH from NADPH by NADPH phosphatase. High amounts of ammonia accumulated in MSX treated, but not in control leaves, upon dark incubation. Relative activities of NR and NADPH phosphatase, and amounts of soluble sugar and NADH were low in MSX fed samples compared to that of control. So, high amount of ammonia might partially repress NADPH phosphatase and consequently deprive NR of reducing equivalents. This revised version was published online in July 2006 with corrections to the Cover Date.     

Relationships between Nitrate Reductase Activity, Plant Weight and Nitrogen Content in Seedlings of Triticum, Aegilops and Triticale

Seedlings of 12 genotypes were grown in pots and watered withnutrient solutions providing 0, 1, 6 and 20 mg equivalents ofnitrate per I. Increasing the external nitrate supply broughtabout increases in plant weight, nitrate, reduced nitrogen concentrationsand in vivo nitrate reductase activity. When given solutioncontaining 6 mg equivalents of nitrate per litre, the plantscontained approximately 0.1 per cent nitrate, a concentrationsimilarto that found in field-grown plantsat thesamestage of growth.At the 6 mg equivalent level nitrate supply, nitrate reductaseactivity was strongly positively correlated with the concentrationsof nitrate and reduced nitrogen and negatively correlated withplant weight. Similar, though weaker, correlations were foundat the lower and higher levels of nitrate supply. The two Triticalegenotypes however, had higher than average plant weights andnitrate reductase activities, while plants of the two Aegilopsspecies weighed much less, especially at the higher levels ofnitrate supply, than the average of all 12 genotypes and generallyhad correspondingly greater nitrate and reduced nitrogen concentrationsand nitrate reductase activities. For individual genotypes,plant weight at a given level of nitrate supply was stronglycorrelated with weight at all other levels. In a second experiment seedlings of 150 genotypes were grownin compost watered with 10 mM Ca(NO₃)₂ Nitrate and reduced nitrogenconcentrations were negatively correlated with plant weightbut there was no significant correlation between nitrate reductaseactivityand either plant weight, nitrate or reduced nitrogen concentration. The results are taken to indicate that genetic factors, otherthan those determining the supply of reduced nitrogen, werelimiting growth and that as a consequence small plants accumulatednitrate and reduced nitrogen compounds in greater concentrationsthan large ones. The greater nitrate concentrations in smallplants may have induced the increased nitrate reductase activityfound in these, as compared with larger plants. Because plantweight varied more than did reduced nitrogen concentration,variation in reduced nitrogen per plant was more highly correlatedwith plant weight than with per cent reduced nitrogen.     

Ontogenetic Variation of Nitrogenase, Nitrate Reductase, and Glutamine Synthetase Activities in Oryza sativa

The relationship between the rates of nitrogenase, nitrate reductase, and glutamine synthetase activities, and plant ontogeny in rice (Oryza sativa L.), cultivar `M9', grown in salt marsh sediment with and without nitrate treatment was studied. In both treatments, nitrogenase activity measured as the immediate linear rate of acetylene reduction by bacteria associated with the roots varied with plant age. In control plants, the nitrogenase activity developed during the vegetative stage, peaked during early reproductive growth and then declined. The application of 10 kilograms N per hectare as KNO₃ once every 2 weeks delayed the development of and decreased the nitrogenase activity. The nitrogenase activity in both treatments developed as leaf nitrate reductase activity declined. The per cent nitrogen of roots was negatively correlated with the rates of acetylene reduction during the life cycles of control and nitrate-treated plants. This suggests that the concentration of combined nitrogen in the plants controlled the development and rate of root-associated nitrogenase activity. During reproductive growth, no nitrate reductase activity was detected in the roots from either treatment. In control plants, the patterns of nitrogenase activity and glutamine synthetase activity in the roots were similar. Thus, rice roots have the potential to assimilate ammonia while fixing N₂. During the vegetative and early reproductive stages of growth, the development of maximal rates of nitrogenase activity coincided with an increase of total nitrogen of the plants in both treatments.     

Phytochrome, nitrate movement, and induction of nitrate reductase in etiolated pea terminal buds

The role of phytochrome in the induction of nitrate reductase of etiolated field peas (Pisum arvense L.) was examined. Terminal bud nitrate concentration increased in darkness, and the increase correlated with induction of nitrate reductase following brief exposure of intact plants to red, blue, far red, and white lights. Brief light exposure of intact plants stimulated nitrate uptake and induction of nitrate reductase by terminal buds subsequently excised and incubated on nitrate solution in darkness; exposure of excised buds in contact with nitrate led to less uptake but more induction. Nitrate and nitrate reductase activity both declined during incubation with water, irrespective of light treatment. Nitrate enrichment of intact terminal buds and uptake into excised buds and increases in nitrate reductase activity were all red/far red reversible. Dimethyl sulfoxide (1%, v/v) and sugars (sucrose 0.5%, glucose 1, w/v), although stimulating nitrate uptake into excised tissue in darkness, failed to enhance nitrate reductase activity over dark controls. Phytochrome may regulate nitrate reductase via both nitrate movement and a general mechanism such as enhancement of protein synthesis.     

Reduction of root iron in Plantago lanceolata during recovery from Fe deficiency

Changes in root-associated Fe(III) reductase activity and Fe concentration during recovery from temporary iron starvation were investigated in hydroponically grown Plantago lanceolata L. Within two days, interruption of the Fe supply resulted in enhanced rates of reduction by intact plant roots. Transfer of iron deficient plants to a solution containing various amounts of chelated Fe caused a transient increase in reduction activity before the rates declined to a level determined by the amount of Fe added. Repression of root-associated redox activity was independent of the Fe concentration in the preculture. When iron deficient plants were submitted to a supply of Fe localized to a part of the root system (split-root plants), the decrease in reduction rates was much more pronounced in the Fe-deprived portion of the roots than in the Fe-supplied one. No correlation was observed between root Fe concentration and Fe(III) reductase activity. Continued growth of split-root plants in the +Fe/-Fe regime increased the reduction rates of the +Fe-grown portion of the root system over the rates in iron sufficient plants with non-divided roots. The results are discussed in relation to putative factors mediating intra- and interorgan regulation of iron nutrition.     

Reduction of root iron in Plantago lanceolata during recovery from Fe deficiency

Changes in root-associated Fe(III) reductase activity and Fe concentration during recovery from temporary iron starvation were investigated in hydroponically grown Plantago lanceolata L. Within two days, interruption of the Fe supply resulted in enhanced rates of reduction by intact plant roots. Transfer of iron deficient plants to a solution containing various amounts of chelated Fe caused a transient increase in reduction activity before the rates declined to a level determined by the amount of Fe added. Repression of root-associated redox activity was independent of the Fe concentration in the preculture. When iron deficient plants were submitted to a supply of Fe localized to a part of the root system (split-root plants), the decrease in reduction rates was much more pronounced in the Fe-deprived portion of the roots than in the Fe-supplied one. No correlation was observed between root Fe concentration and Fe(III) reductase activity. Continued growth of split-root plants in the +Fe/-Fe regime increased the reduction rates of the +Fe-grown portion of the root system over the rates in iron sufficient plants with non-divided roots. The results are discussed in relation to putative factors mediating intra- and interorgan regulation of iron nutrition.     

Tungstate, a molybdate analog inactivating nitrate reductase, deregulates the expression of the nitrate reductase structural gene

Nitrate reductase (NR, EC 1.6.6.1) from higher plants is a homodimeric enzyme carrying a molybdenum cofactor at the catalytic site. Tungsten can be substituted for molybdenum in the cofactor structure, resulting in an inactive enzyme. When nitratefed Nicotiana tabacum plants were grown on a nutrient solution in which tungstate was substituted for molybdate, NR activity in the leaves decreased to a very low level within 24 hours while NR protein accumulated progressively to a level severalfold higher than the control after 6 days. NR mRNA level in molybdate-grown plants exhibited a considerable day-night fluctuation. However, when plants were treated with tungstate, NR mRNA level remained very high. NR activity and protein increased over a 24-hour period when nitrate was added back to N-starved molybdate-grown plants. NR mRNA level increased markedly during the first 2 hours and then decreased. In the presence of tungstate, however, the induction of NR activity by nitrate was totally abolished while high levels of NR protein and mRNA were both induced, and the high level of NR mRNA was maintained over a 10-hour period. These results suggest that the substitution of tungsten for molybdenum in NR complex leads to an overexpression of the NR structural gene. Possible mechanisms involved in this deregulation are discussed.     

The effects of nitrate on the enzymes involved in nitrogen assimilation in nodulated pea roots

Pea Plants ( Pisum sativaum L. ev. Little Marvel) were grown in N-free medium and when well nodulated (28 days) were supplied for 8 days with nitrate or ammonium. Over the 8 days of nitrate treatment, total amino and amide N in sap declined, and the proportion of aspartate relative to the other amino acids increased. After 8 days of treatment, nitrogenase (EC 1.18.2.1) activity in nitrate-treated plants declined to about 30% of the activity in controls even though nodules were not directly in contact with nutrient solution. Nitrogenase activity was also decreased by the addition of ammonium chloride (10 m M ). With addition of nitrate or ammonium. clear signs of senescence began to show in the nodules after 4 days. Nitrate reductase (EC 1.6.6.1) activity was induced in roots by nitrate, but decreased sharply in nodules. In response to nitrate addition, newly formed root tissues showed 3- to 5-times higher glutamine synthetase (GS. EC 6.3.1.4) activity than newly formed tissues of control plants, expressed on a protein or weight basis. In complementary experiments, when ammonium salts were used instead of nitrates, the increase in GS activity was significantly lower. GS activity decreased in nodules of treated plants and total extractable protein was 3 times lower in nodules of nitrate-treated plants than in controls at day 8 of treatment.     

硝酸盐对硝酸还原酶活性的诱导及硝酸还原酶基因的克隆

硝酸盐在植物体内的积累过多已成为影响蔬菜品质并影响人类健康的重要因素。硝酸还原酶（NR）是硝酸盐代谢中的关键酶,提高其活性有利于硝酸盐的降解。为了解植物不同组织中NR的活性,用活体测定法检测了经50mmol/L的KNO₃诱导不同时间后的油菜、豌豆和番茄幼苗根茎叶中NR活性,同时为了明确外源诱导剂浓度与植物体内NR活性的关系,检测了经不同浓度KNO₃诱导2h后的矮脚黄、抗热605、小白菜和番茄叶片中的NRA。结果表明,不同植物组织NR活性有很大差异,叶中NR活性较高,根其次,茎最低;不同植物的NR活性随诱导时间呈不同的变化趋势,相同植物不同组织的NR活性变化趋势相似;不同植物叶片NRA为最高时KNO₃浓度不同。用30mmol/L的KNO3诱导番茄苗2h后,从番茄根和叶中提取总RNA,用RT-PCR方法获得NR cDNA,全长2736bp,编码911个氨基酸。为进一步利用该基因提高植物对硝酸盐的降解能力打下基础。     

Partitioning of Sugar between Growth and Nitrate Reduction in Cotton Roots

The level of endogenous sugars was inversely related to nitrate availability in young cotton (Gossypium hirsutum L.) plants, with high nitrate causing a greater decline in sugar content of roots than of shoots. High nitrate (low sugar) plants also displayed relatively more shoot growth and less root growth than low nitrate (high sugar) plants. These data are consistent with the theory that roots are poor competitors for sugar, and that sugar supply is a major factor limiting root growth in vivo.

The effects of endogenous sugar level on root growth and on nitrate reductase activity in the root were different. When root sugar level was experimentally controlled by varying nitrate concentration in the nutrient solution, root growth was less sensitive than nitrate reductase activity to sugar deficiency. Also, in sterile root tips cultured on media containing a wide range of sucrose concentrations, growth rate was considerably less sensitive to endogenous sugar deficiency than was nitrate assimilation rate. Similarly, in plants which were detopped or girdled, nitrate reductase activity in the roots declined more rapidly than did root sugars, especially glucose and fructose. These results suggest that when sugar is deficient, cotton roots preferentially use it for growth at the expense of nitrate reduction.

     

Expression of arabidopsis cytosolic ascorbate peroxidase gene in response to ozone or sulfur dioxide

The effects of ozone or sulfur dioxide on antioxidant enzymes were investigated in Arabidopsis thaliana. Plants were fumigated with 0.1–0.15 ppm ozone or sulfur dioxide up to about 1 week in an environment-controlled chamber. Both pollutants increased the activities of ascorbate peroxidase and guaiacol per-oxidase in leaves, but had little effect on the activities of superoxide dismutase, catalase, monodehydroascorbate reductase, dehydroascorbate reductase or glutathione reductase. Ozone was more effective than sulfur dioxide in increasing the activities of the peroxidases. Ascorbate peroxidase activity increased 1.8-fold without a lag period during fumigation with 0.1 ppm ozone, while guaiacol peroxidase activity increased 4.4-fold with a 1-day lag. Expression of the APX1 gene encoding cytosolic ascorbate peroxidase was further investigated. Its protein levels in leaves exposed to 0.1 ppm ozone for 4 or 8 days were 1.5-fold higher than in controls. Both ozone and sulfur dioxide elevated APX1 mRNA levels in leaves at 4 and 7 days, whereas at 1 day only ozone was effective. The induction of APX1 mRNA levels by ozone (3.4- to 4.1-fold) was more prominent than that by sulfur dioxide (1.6-to 2.6-fold). The APX1 mRNA level increased by day and decreased by night. Exposure of plants to 0.1 ppm ozone enhanced the APX1 mRNA level within 3 h, which showed a diurnal rhythm similar to that of the control. These results demonstrate that near-ambient concentrations of ozone as well as similar concentrations of sulfur dioxide can induce APX1 gene expression in A. thaliana.Environmental Biology Division