ISOLATION AND PARTIAL CHARACTERIZATION OF NITRATE ASSIMILATION MUTANTS OF DUNALIELLA TERTIOLECTA (CHLOROPHYCEAE)1

Fifteen nitrate assimilation-deficient mutants of the euryhaline green alga, Dunaliella tertiolecta Butcher were selected by their chlorate resistance. Ten mutants, unable to grow on NO₃^? but able to grow on NO₂^?, had no detectable nitrate reductase activity. Five mutants, unable to grow on either NO₃^? or NO₂^?, had depressed levels of both nitrate and nitrite reductase. A method for assaying methyl viologen-nitrate reductase in the presence of nitrite reductase is described.     

斜生栅藻在不同磷条件下氮生态幅的研究

为获得斜生栅藻（Scendesmus obliquus）的氮生态幅,研究根据中华人民共和国地表水环境质量标准磷浓度界定,利用谢尔福德（Shelford）耐受定律进行曲线拟合对斜生栅藻在低磷（0.02 mg/L）、中磷（0.2 mg/L）和高磷（0.4 mg/L）三种不同磷浓度下氮的生态幅进行定量表达,获得三种磷起始条件下斜生栅藻生长的最佳氮浓度、氮适宜生长范围和氮耐受范围。研究表明,在三种磷条件下斜生栅藻生长的最佳氮浓度分别为1.02、8.91和18.05 mg/L,对应的最大比生长速率分别为（0.1420.006）、（0.3140.002）和（0.3460.007） /d,氮适宜生长范围分别为（0.521.52）、（4.4813.34）和（11.7224.38） mg/L,氮耐受限度分别为（0.022.02）、（0.0517.77）和（5.3930.71） mg/L。这表明富营养化水体可能引起斜生栅藻的大量生长、繁殖,也暗示了斜生栅藻能作为高氮水环境的一个良好指示生物。       

COMPARISONS OF NITRATE UPTAKE, STORAGE, AND REDUCTION IN MARINE DIATOMS AND FLAGELLATES

Diatoms, but not flagellates, have been shown to increase rates of nitrogen release after a shift from a low growth irradiance to a much higher experimental irradiance. We compared NO₃ ^? uptake kinetics, internal inorganic nitrogen storage, and the temperature dependence of the NO₃ ^? reduction enzymes, nitrate (NR) and nitrite reductase (NiR), in nitrogen‐replete cultures of 3 diatoms (Chaetoceros sp., Skeletonema costatum, Thalassiosira weissflogii) and 3 flagellates (Dunaliella tertiolecta, Pavlova lutheri, Prorocentrum minimum) to provide insight into the differences in nitrogen release patterns observed between these species. At NO₃ ^? concentrations <40 μmol‐N·L ^{? 1}, all the diatom species and the dinoflagellate P. minimum exhibited saturating kinetics, whereas the other flagellates, D. tertiolecta and P. lutheri, did not saturate, leading to very high estimated K _s values. Above ～60 μmol‐N·L ^{? 1}, NO₃ ^? uptake rates of all species tested continued to increase in a linear fashion. Rates of NO₃ ^? uptake at 40 μmol‐N·L ^{? 1}, normalized to cellular nitrogen, carbon, cell number, and surface area, were generally greater for diatoms than flagellates. Diatoms stored significant amounts of NO₃ ^? internally, whereas the flagellate species stored significant amounts of NH₄ ⁺ . Half‐saturation concentrations for NR and NiR were similar between all species, but diatoms had significantly lower temperature optima for NR and NiR than did the flagellates tested in most cases. Relative to calculated biosynthetic demands, diatoms were found to have greater NO₃ ^? uptake and NO₃ ^? reduction rates than flagellates. This enhanced capacity for NO₃ ^? uptake and reduction along with the lower optimum temperature for enzyme activity could explain differences in nitrogen release patterns between diatoms and flagellates after an increase in irradiance.     

NITRATE REDUCTASE ACTIVITY OF AMPHIDINIUM CARTERI AND CACHONINA NIEI (DINOPHYCEAE) IN BATCH CULTURE: DIEL PERIODICITY AND EFFECTS OF LIGHT INTENSITY AND AMMONIA1,2

The activity of extracted NADH-NO₃^? reductase was measured in the marine dinoflagellates Amphidinium carteri Hulburt and Cachonina niei Loeblich. Its activity showed a diel periodicity and was ca. twice as great at midday as at midnight. The enzyme activity was unstable, with an in vitro half-life of 2–3 h. Values of enzyme activity were low or undetectable during lag phase but paralleled the instantaneous growth rate value during log phase. Nitrate reductase activity was not found in the stationary phase of growth, but additions of NO₃^? resulted in enzyme activity after 24h. When A. carteri was exposed to a series of light intensities for several weeks, the division rate and enzyme activity increased with increasing light intensity up to saturating intensities. In 6 h exposures, enzyme activity decreased with decreasing light intensities below light intensities saturating division rate. Additions of NH₄⁺ (0.5–50 μm) to A. carteri cultures decreased the amount of extractable enzyme. The in vitro activity was not inhibited by similar NH⁺₄ concentrations.     

CHARACTERIZATION OF DIATOM (BACILLARIOPHYCEAE) NITRATE REDUCTASE GENES AND THEIR DETECTION IN MARINE PHYTOPLANKTON COMMUNITIES1

The complete assimilatory nitrate reductase (NR) gene from the pennate diatom Phaeodactylum triconutum Bohlin was sequenced from cDNA and compared with NR sequences from fungi, green algae, vascular plants, and the recently sequenced genome of the centric diatom Thalassiosira pseudonana Hasle and Heimdal CCMP1335. In all the major eukaryotic nitrate reductase (Euk‐NR) functional domains, diatom NR gene sequences are generally 50%–60% identical to plant and alga sequences at the amino acid level. In the less conserved N‐terminal, hinge 1, and hinge 2 regions, homology to other NR sequences is weak, generally<30%. Two PCR primer sets capable of amplifying Euk‐NR from plants, algae, and diatoms were designed. One primer set was used to amplify a 750‐base pair (bp) NR fragment from the cDNA of five additional diatom strains. The PCR amplicon spans part of the well‐conserved dimer interface region, the more variable hinge 1 region, and part of the conserved cytochrome b heme binding region. The second primer set, targeted to the dimer region, was used to amplify an approximately 400‐bp fragment of the NR gene from DNA samples collected in Monterey Bay, California and in central New Jersey inner continental shelf (LEO‐15 site) waters. Only diatom‐like NR sequences were recovered from Monterey Bay samples, whereas LEO‐15 samples yielded NR sequences from a range of photosynthetic eukaryotes. The prospect of using DNA‐ and RNA‐based methods to target the NR genes of diatoms specifically is a promising approach for future physiological and ecological experiments.     

低pH对水稻黄化叶片硝酸还原酶活性暗诱导的调节

在低pH条件下,水稻离体黄化叶片的硝酸还原酶(NR)活性能在暗中诱导产生,其诱导过程约有2h的滞后期,亚胺环已酮(CHI,5ppm)和Na_2WO_4(25 mmol/L)能完全抑制这种诱导作用。在最适pH 3.0时,H~3标记氨基酸掺入NR的量比pH 7.0时约高2倍,表明酶活性的产生与酶蛋白的重新合成有关。 当低pH暗诱导时,BA(5ppm)和ABA(15ppm)能使酶活性分别提高约30％和80％,但它们都不能取代低pH在NR活性暗诱导中的作用。当存在1ppm CHI的时候,BA仍促进NR活性,而ABA则加强CHI对酶活性的抑制作用,这提示BA与ABA在低pH暗诱导条件下促进NR活性的机制是不同的。在pH 7.0的光诱导条件下,ABA对NR活性起抑制作用。     

EFFECT OF SODIUM AND NITRATE ON GROWTH OF ANABAENA FLOS-AQUAE (CYANOPHYTA)1

The growth response of a nitrogen fixing cyanobacterium, Anabaena flos-aquae (Lyng) Bréb., to sodium and nitrate was examined in batch culture under controlled laboratory conditions. Sodium (range 0-12 mg Na⁺· L^-1) enhanced growth of the cyanobacterium under nitrate-sufficient (5.7 mg NO³-N · L^-1) but not nitrate-limited (0.49 mg NO³- N · L^-1) conditions. The magnitude of the growth response was related to the nutritional history of the culture. No significant effect of sodium on nitrate utilization was observed. The increase in ambient sodium levels in many lakes may provide a competitive advantage to cyanobacteria.     

重庆市蔬菜硝酸盐、亚硝酸盐含量及其与环境的关系

在重庆市的主要蔬菜中,硝酸盐含量依次为根菜类＞叶菜类＞葱蒜类＞瓜类＞豆类＞茄果类,前３类的硝酸盐含量超标,但各种蔬菜的亚硝酸盐含量一般较低,未超过卫生标准。就同一种蔬菜的不同样品而言,硝酸盐和亚硝酸盐含量的差异很大,说明品种或环境条件可显著影响其含量。重庆市多雾少光,冬春低温,土壤含氮量和钠高子含量较高,有效钾含量较低可能是导致蔬菜大量积累硝酸盐的环境因素。蔬菜不同器官硝酸盐和亚硝酸盐含量各异,根＞茎＞叶柄＞叶片。     

CARBOHYDRATE RELEASE BY A SUBTROPICAL STRAIN OF SPONDYLOSIUM PYGMAEUM (ZYGNEMATOPHYCEAE): INFLUENCE OF NITRATE AVAILABILITY AND CULTURE AGING1

This paper describes the influence of nitrate availability on growth and release of dissolved free and combined carbohydrates (DFCHOs and DCCHOs) produced by Spondylosium pygmaeum (Cooke) W. West (Zygnematophyceae). This strain was isolated from a subtropical shallow pond, located at the extreme south of Brazil (Rio Grande, RS). Experiments were carried out in batch culture, comparing two initial nitrate levels (10/100 μM) in the medium. Growth was monitored by direct microscopic cell counts and chl a content. Nitrate consumption was determined by ion chromatography, while the production of extracellular carbohydrates was monitored by the phenol‐sulfuric method. The monosaccharide compositions of DFCHOs and DCCHOs were determined in each growth phase by HPLC with pulse amperometric detection (HPLC‐PAD). At the end of the experiment, the total composition of extracellular polysaccharide (EPS) molecules >12 kDa was determined by gas chromatography. Nitrate availability had no influence on S. pygmaeum cell density at any phase. On the other hand, chl a content decreased after a few days growth when the availability of nitrate was restricted, but continued to rise when nitrate was plentiful. Also, nitrate depletion was faster at 10 μM nitrate. No influence of the growth phase or nitrate availability on the total carbohydrates (TDCHOs) released per cell was observed. Only DCCHOs were released by S. pygmaeum, and the composition varied between growth phases, especially at lower nitrate availability. EPS molecules >12 kDa were composed mainly of xylose, fucose, and galactose, as for other desmids. However, a high N‐acetyl‐glucosamine content was found, uniquely among desmid EPSs.     

The nitrogen balance of Raphanus sativus X raphanistrum plants. I. Daily nitrogen use under high nitrate supply

Abstract Growth-chamber cultivated Raphanus plants accumulate nitrate during their vegetative growth. After 25 days of growth at a constant supply to the roots of 1 mol m^?3 (NO^?₃) in a balanced nutrient solution, the oldest leaves (eight-leaf stage) accumulated 2.5% NO^?₃-nitrogen (NO₃-N) in their lamina, and almost 5% NO₃-N in their petioles on a dry weight basis. This is equivalent to approximately 190 and 400 mol^?3 m^?3 concentration of NO^?₃ in the lamina and the petiole, respectively, as calculated on a total tissue water content basis. Measurements were made of root NO^?₃ uptake, NO^?₃ fluxes in the xylem, nitrate uptake by the mesophyll cells, and nitrate reduction as measured by an in vivo test. NO^?₃ uptake by roots and mesophyll cells was greater in the light than in the dark. The NO^?₃ concentration in the xylem fluid was constant with leaf age, but showed a distinct daily variation as a result of the independent fluxes of root uptake, transpiration and mesophyll uptake. NO^?₃ was reduced in the leaf at a higher rate in the light than in the dark. The reduction was inhibited at the high concentrations calculated to exist in the mesophyll vacuoles, but reduction continued at a low rate, even when there was no supply from the incubation medium. Sixty-four per cent of the NO^?₃ influx was turned into organic nitrogen, with the remaining NO^?₃ accumulating in both the light and the dark.     

千金藤属植物小叶地不容中的生物碱(Ⅷ)

从小叶地不容(Steghania succitera Lo.et Tsoong)的块根中分得11种生物碱,根据理化性质及波谱测定,鉴定为克班宁(crebanine)(Ⅰ),四氢巴马汀(tetrahydropalmatine)(Ⅱ),去氢克班宁(dehydrocrebanine)(Ⅲ),巴马汀(palmatine)(Ⅳ),去氢紫堇单酚碱(dehydro-corydalmiae)(Ⅴ),克班宁硝酸盐(Ⅵ),氧代克班宁(oxocrebanine)(Ⅶ),紫堇单酚碱(corydalmine)(Ⅷ),phanostenine(Ⅸ),离木明碱 discretamine(Ⅹ),及 corypalmine(Ⅺ),化合物(Ⅳ)、(Ⅴ)、(Ⅵ)、(Ⅶ)、(Ⅸ)、(Ⅹ)和Ⅺ为首次报道从该植物中分得。     

光合作用光能转换过程中与耗能代谢有关的光保护机制(综述)

对近年来光合电子传递过程中各种耗能代谢（包括光呼吸、Ｍｅｈｌｅｒ反应、循环电子传递、硝酸还原代谢等）的运转对光合机构的保护作用作一简要综述。     

EFFECTS OF EXTERNAL INORGANIC NITROGEN CONCENTRATION ON METABOLISM,GROWTH AND ACTIVITIES OF KEY CARBON AND NITROGEN ASSIMILATORY ENZYMES OF LAMINARIA SACCHARINA (PHAEOPHYCEAE) IN CULTURE1

The growth rate of Laminaria saccharina (L.) Lamour. is dependent on inorganic nitrogen in culture. Growth rates were saturated between 5 and 10 μmol · L^?1 nitrate. The activities of ribulose-1,5 bisphosphate carboxylase, phosphoenolpyruvate carboxykinase, mannitol-1-phosphate dehydrogenase, nitrate reductase and glutamine synthetase also varied with the concentration of inorganic nitrogen in the medium. All enzyme activities were lowest at 2.5 μmol · L^?1 nitrate (the lowest concentration used) increasing to a maximum activity between 10 and 30 μmol · L^?1 nitrate. Most enzyme activities followed a hyperbolic curve resembling those described by the Michaelis-Menten equation, with different half-saturation constants.