Ammonium rhythm in cultures of the cyanobacterium Microcystis firma

Over a period of several days, rhythmic changes in extracellular NH⁺₄ concentration take place in cultures of the cyanobacterium Microcystis firma (Bré et Lenorm.) Schmidle, strain Gromov/St. Petersb. 398, under conditions of restricted CO₂ supply and light/dark alternation. The changes are enhanced by nitrate supply. Among the various processes generating intracellular NH⁺₄ (NH⁴₄ uptake, NO⁻₃ reduction, protein and amino acid degradation, photorespiration), NO⁻₃ reduction appears as the one most important. This can be concluded from experiments with and without nitrate and/or ammonium in the medium. In the presence of saturating CO₂, continuous light, or continuous darkness, rhythmic NH⁺⁴₄ oscillations are not induced. Studies of the incorporation of NH⁺₄ nitrogen by in vivo ¹⁵N-NMR show that if CO₂ is supplied, ¹⁵N is accumulated in several components with the following time course: in the first hour in Gln (δ), in the second hour in the α-amino groups of most nonbranched amino acids, in the third hour in γ-aminobutyric acid (GABA), Orn (δ) and Lys (ε), and in the sixth hour in Ala. Carbon limitation, however, results in accumulation of label in the amide nitrogen of glutamine only.     

Characteristics of inorganic nitrogen assimilation of plants in fire-prone Mediterranean-type vegetation

A range of approaches was used to investigate how species within a fire-prone Banksia woodland in South West Australia exploited inorganic soil nitrogen sources and how this changes through the development of the fire chronosequence. Nitrate and ammonium were present in soil solution throughout the chronosequence but nitrate predominated in recently burnt sites. Mean shoot nitrate reductase activities were high for all species in recently burnt sites and showed little increase when nitrate was supplied via the transpiration stream. Nitrate reductase of shoots of most species was low at sites not burnt for several years, but following transpirational induction with nitrate, developed activities similar to those at recently burnt sites. The principal amino compounds transported in the xylem were species specific, including asparagine, glutamine and citrulline-dominated species, and changed little in relative composition across the chronosequence. Species most active in leaf nitrate reduction transported the largest amounts of nitrate in their xylem sap and proportional amounts of nitrate in xylem tended to be greatest in recently burnt sites. Most of the species examined appeared to be shoot rather than root nitrate assimilators, but marked differences were recorded in potential of leafy shoots of different species to reduce nitrate. As a general rule, shallow-rooted herbaceous, non-mycorrhizal or VAM-positive species had the highest capacity to reduce nitrate, whereas woody species with ericoid mycorrhizae or combined vesicular arbuscular/ectomycorrhizal associations exhibited little capacity to reduce nitrate in roots or shoots. It seems likely that this latter group utilize ammonium or even organic forms of nitrogen rather than nitrate. Some putative nitrogen-fixing species were active in reducing and transporting nitrate, others were virtually inactive in these respects.     

Effect of copper sulfate on experimental atherosclerosis

Serum copper concentration increases significantly (p<0.01) in rats with experimental atherosclerosis compared to a control group. The serum zinc, the zinc, and copper concentration in abdominal aorta and in liver decreases significantly (p<0.05) compared to the control group. Administration of copper sulfate for 100 d in these animals induces a significant increase of serum copper (p<0.01), decrease of serum cholesterol (p<0.05) and increase of liver copper concentration as compared with the group fed only a high cholesterol diet. In the aorta of these animals the copper concentration increases and edema and lipid infiltration are considerably less than in the group of animals fed only a high lipid diet.     

Evaluation of the role of State transitions in determining the efficiency of light utilisation for CO2 assimilation in leaves

Wheat leaves were exposed to light treatments that excite preferentially Photosystem I (PS I) or Photosystem II (PS II) and induce State 1 or State 2, respectively. Simultaneous measurements of CO₂ assimilation, chlorophyll fluorescence and absorbance at 820 nm were used to estimate the quantum efficiencies of CO₂ assimilation and PS II and PS I photochemistry during State transitions. State transitions were found to be associated with changes in the efficiency with which an absorbed photon is transferred to an open PS II reaction centre, but did not correlate with changes in the quantum efficiencies of PS II photochemistry or CO₂ assimilation. Studies of the phosphorylation status of the light harvesting chlorophyll protein complex associated with PS II (LHC II) in wheat leaves and using chlorina mutants of barley which are deficient in this complex demonstrate that the changes in the effective antennae size of Photosystem II occurring during State transitions require LHC II and correlate with the phosphorylation status of LHC II. However, such correlations were not found in maize leaves. It is concluded that State transitions in C₃ leaves are associated with phosphorylation-induced modifications of the PS II antennae, but these changes do not serve to optimise the use of light absorbed by the leaf for CO₂ assimilation.Abbreviations Fm, Fo, Fv maximal, minimal and variable fluorescence yields - Fm, Fv maximal and variable fluorescence yields in a light adapted state - LHC II light harvesting chlorophyll a/b protein complex associated with PS II - q_P photochemical quenching - A₈₂₀ light-induced absorbance change at 820 nm - _{PS I}, _{PS II} relative quantum efficiencies of PS I and PS II photochemistry - _{CO 2} quantum yield of CO₂ assimilation     

Fibrolast growth factors in the nervous system

Fibroblast growth factors (FGFs) exhibit widespread mitogenic and neurotrophic activities. Nine members of the family are currently known, and FGF-1 and FGF-2 are present in relatively high levels in CNS. FGF-1 is expressed by a subset of neuronal populations, while FGF-2 is expressed by astrocytes. FGF-1 and FGF-2 lack signal peptides and appear to be present mainly in inracellular compartmens. This suggests that the factors may act as initiators of a repair response after injury. Support for this notion comes from observations that FGF-1 and FGF-2 levels are low during critical phases of development, but high in the adult CNS. A family of transmembrane tyrosine kinase receptors (FGFRs) mediates the effects of FGFs. Four different genes coding for FGF receptors are currently known, three of which are expressed in cell type-specific patterns in the CNS The main receptor variants present in this tissue, however, can by themselves not distinguish between FGF-1 and FGF-2. Additional selectivity may be established by interaction of the FGFs and their receptors with select heparan proteoglycans (HSPGs). Therefore, the precise physiological role of FGFs is determined by the combination of cell type-specific patterns of expression of FGFs, FGFRs and HSPGs together with the mechanisms that regulate the extracellular availability of FGFs. 1994 John Wiley & Sons, Inc.     

The SV2 Protein of Synaptic Vesicles Is a Keratan Sulfate Proteoglycan

Abstract: We have determined that synaptic vesicles contain a vesicle-specific keratan sulfate integral membrane proteoglycan. This is a major proteoglycan in electric organ synaptic vesicles. It exists in two forms on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, i.e., the L form, which migrates like a protein with an M_r of 100, 000, and the H form, with a lower mobility that migrates with an M_r of ∼250, 000. Both forms contain SV2, an epitope located on the cytoplasmic side of the vesicle membrane. In addition to electric organ, we have analyzed the SV2 proteoglycan in vesicle fractions from two other sources, electric fish brain and rat brain. Both the H and L forms of SV2 are present in these vesicles and all are keratan sulfate proteoglycans. Unlike previously studied synaptic vesicle proteins, this proteoglycan contains a marker specific for a single group of neurons. This marker is an antigenically unique keratan sulfate side chain that is specific for the cells innervating the electric organ; it is not found on the synaptic vesicle keratan sulfate proteoglycan in other neurons of the electric fish brain.     

Short-term photosynthesis measurements predict leaf carbon balance in tropical rain-forest canopy plants

Diel (24 h) courses of net CO₂ exchange of leaves were determined in eight species of tropical rainforest plants on Barro Colorado Island, Panama, during 1990 and 1991. The species included three canopy trees, one liana, two epiphytes and one hemiepiphyte. One of the species studied was growing in a rain-forest gap. Daily carbon gain varied considerably across species, leaf age, and season. The analysis of data for all plants from 64 complete day/night cycles revealed a linear relationship between the diurnal carbon gain and the maximum rate of net CO₂ uptake, A_max. Nocturnal net carbon loss was about 10% of diurnal carbon gain and was positively related to A_max. We conclude that short-term measurements of light-saturated photosynthesis, performed at periodic intervals throughout the season, allow the annual leaf carbon balance in these rain-forest plants to be predicted.     

硫酸铝钾对小鼠肝损害的实验研究

本文主要观察硫酸铝钾——饮用水净化剂引致小鼠肝酶组化,超微结构和组织结构的变化。动物30只,分为正常组、硫酸铝钾大、小剂量组。实验结果:硫酸铝钾10mg/kg/日(大剂量组)与5mg/kg/日(小剂量组)动物用药10天、80天均可使肝SDH酶活性降低;肝细胞线粒体肿胀、嵴断裂和溶解。在光学显微镜下用药80天后大部分肝细胞肿胀,胞浆疏松淡染、肝小叶内可见呈小灶状分布的炎性细胞浸润,主要为淋巴细胞及浆细胞,门管区偶见少许炎性细胞,但肝小叶和门管区未见结缔组织增生。为此,硫酸铝钾作为净水剂,不宜用量过大。     

硫酸盐对淡水养殖池塘表层底泥微生物的影响

硫酸盐引起的生态学效应已得到了越来越多的关注,但目前关于硫酸盐对养殖池塘底泥微生物的影响还知之甚少。【目的】探究不同浓度硫酸盐对养殖池塘底泥微生物的影响规律及可能的机制。【方法】本研究利用采集自养殖池塘的底泥和表层水构建了试验系统,研究了加入约0 mg/L （对照组）、30 mg/L （T1处理组）、150 mg/L （T2处理组）、500 mg/L （T3处理组） Na₂SO₄后表层底泥微生物的丰度、多样性、组成和共生网络的变化规律,并分析了环境影响因素。【结果】孵育第30天前,各实验组底泥微生物变化不大;但到第50天时,T2和T3处理组微生物丰度和多样性相比对照组均明显下降。相比其他实验组,T1处理组酸杆菌门（Acidobacteriota）、拟杆菌门（Bacteroidota）相对丰度出现显著升高（P<0.05）,T3处理组变形菌门（Proteobacteria）和放线菌门（Actinobacteriota）相对丰度出现显著升高（P<0.05）。与对照组相比,T1处理组增加了较多差异类群（62种）,而T3处理组差异类群大量减少（45种）。共生网络图分析显示硫酸盐浓度的增加引起了底泥微生物网络复杂性的增加,说明微生物群落可能通过自身的调节来响应硫酸盐引起的环境改变。冗余分析（redundant analysis,RDA）和相关性分析揭示底泥总有机碳、总氮和氧化还原电位是影响底泥微生物的主要环境因素,提示底泥微生物可能受到硫酸盐和有机质作用的影响。【结论】较长时间的高浓度硫酸盐会对池塘底泥微生物群落造成重要影响,微生物群落自身的转变和硫酸盐引起的有机质分解改变可能是造成微生物群落变化的关键因素。