The effect of Walker-256 tumour development upon Kupffer cell metabolism

The liver plays a central role in the establishment and maintenance of the cachectic state in rats bearing extra-hepatic tumours. Kupffer cells, which as macrophages, show a strong relationship between metabolism and function could be involved in the alterations observed in the disruption of many functions of the organ as a whole. To assess whether the metabolic/functional pattern of Kupffer cells was altered by cachexia we have investigated the utilization of glucose, glutamine and palmitate by the cells from tumour-bearing and control rats. We have found an enhanced utilization of the three substrates by the cells from tumour-bearing rats as compared with controls, which was related to greater energy production through the Krebs cycle and enhanced production of precursors for the synthesis of the many substances the cells secrete when activated. The use of palmitate as substrate was also augmented in these cells, in the opposition to the observation in stimulated peritoneal macrophages. The availability of palmitate however, was not associated with a reduction of glucose or glutamine consumption. The cycle of interconversion, free fatty acids/triacyglycerol in Kupffer cells from tumour-bearing rats was also found to be increased, as was hydrogen peroxide production. Taken together the results suggest an increased utilization of substrates for both energy production and for synthetic processes (e.g. NADPH for hydrogen peroxide production). © 1998 John Wiley & Sons, Ltd.     

Severe reduction in growth rate and grain filling of rice mutants lacking OsGS1;1, a cytosolic glutamine synthetase1;1

Rice (Oryza sativa L.) plants possess three homologous but distinct genes for cytosolic glutamine synthetase (GS1): these are OsGS1;1, OsGS1;2, and OsGS1;3. OsGS1;1 was expressed in all organs tested with higher expression in leaf blades, while OsGS1;2, and OsGS1;3 were expressed mainly in roots and spikelets, respectively. We characterized knockout mutants caused by insertion of endogenous retrotransposon Tos17 into the exon-8 (lines ND8037 and ND9801) or the exon-10 (line NC2327) of OsGS1;1. Mendelian segregation occurred in each progeny. Homozygously inserted mutants showed severe retardation in growth rate and grain filling when grown at normal nitrogen concentrations. Abnormal mRNA for GS1;1 was transcribed, and the GS1 protein and its activity in the leaf blades were barely detectable in these mutants. The glutamine pool in the roots and leaf blades of the mutants was lower than that of the wild type. Re-introduction of OsGS1;1 cDNA under the control of its own promoter into the mutants successfully complemented these phenotypes. Progeny where Tos17 was heterozygously inserted or deleted during segregation showed normal phenotypes. The results indicate that GS1;1 is important for normal growth and grain filling in rice; GS1;2 and GS1;3 were not able to compensate for GS1;1 function.     

低温胁迫后抗寒茶树品种‘紫阳圆叶’的基因差异表达分析

采用DDRT—PCR技术,对低温（4℃）胁迫处理不同时间（0、8、12、24和48h）后茶树[Camellia sinensis（Linn．）O．Ktze．]抗寒品种‘紫阳圆叶’（‘Ziyangyuanye’）叶片中差异表达的基因进行分离和测序,并采用半定量RT-PCR对差异表达基因的表达特性进行了比较。结果表明：有12个引物对扩增出有明显差异的cDNA片段,其中3个片段是与抗寒性相关的差异片段,分别被命名为Csgsf．Cscafl和Cscaf2,碱基数分别为217、316和232bp。比对结果显示：Cscaf与茶树品种‘安吉白茶’（‘Anjibaicha’）和‘龙井43’（‘Longjing43’）的谷氨酰胺合成酶基因的同源性分别为96％和91％,与菜豆（Phaseolus vulgaris Linn．）、蒺藜苜蓿（Medicago truncatula Gaertn．）、油棕（ElaeisguineensisJacq．）、西洋参（Panax quinquefolius Linn．）和水稻（Oryza sativa Linn．）等植物的谷氨酰胺合成酶的基因序列同源性均达到90％以上,因此,Cscafl应为茶树谷氨酰胺合成酶基因片段;Cscaf2与干旱胁迫条件下茶树表达的cDNA的同源性为100％,为茶树应答干旱和低温胁迫的基因片段;Cscafl未检索出同源序列,推测其为与冷胁迫相关的未知基因片段。半定量RT—PCR分析结果表明：Cscafl和Cscafl在低温胁迫的初始期即开始表达且表达量随低温胁迫时间延长逐渐下调;而Cscaf2的表达量随低温胁迫时间延长逐渐上调并在胁迫48h后达到最大,3个片段的表达特性均与差异扩增结果相符。     

不同生育期花生叶片蛋白质含量及氮代谢相关酶活性分析

以5个珍珠豆型花生(Arachis hypogaea Linn.)品种(系)‘汕E’(‘Shan E’)、‘汕G’(‘Shan G’)、‘TH’、‘TJ’和‘泉花7号’(‘Quanhua No.7’)为研究对象,分析了花针期、结荚期和饱果期花生叶片中可溶性蛋白质含量及硝酸还原酶(NR)、谷氨酰胺合成酶(GS)和谷氨酸脱氢酶(GDH)活性的变化趋势,并比较了5个品种(系)荚果和秆产量的差异。结果表明:在3个生育期内,5个花生品种(系)叶片可溶性蛋白质含量和GDH活性的变化趋势基本一致,而NR和GS活性的变化趋势则有差异。其中,可溶性蛋白质含量均呈"低—高—低"的变化趋势,在结荚期最高;GDH活性均逐渐升高,至饱果期达最高;‘泉花7号’叶片NR活性呈"高—低—高"的变化趋势,而其他4个品种(系)叶片NR活性均逐渐降低;‘汕E’、‘TJ’和‘泉花7号’叶片GS活性呈逐渐降低趋势,而‘汕G’和‘TH’叶片GS活性呈"低—高—低"的变化趋势。总体上看,5个品种(系)中,‘汕G’和‘泉花7号’叶片的可溶性蛋白质含量及NR和GDH活性、‘汕E’叶片的NR和GS活性以及‘TH’叶片的GDH活性均较高。5个品种(系)的2个产量指标(单株荚果鲜质量和单株秆鲜质量)均有明显差异,总体上看,‘汕G’、‘泉花7号’和‘TH’的2个产量指标均较高,而‘汕E’和‘TJ’的2个产量指标均较低。综合分析结果显示:‘汕G’和‘泉花7号’叶片可溶性蛋白质含量及NR和GDH活性均相对较高,其荚果和秆产量也均较高,表明花生荚果和秆产量与不同生育期叶片氮代谢水平有一定关系。     

施钾对甘薯氮素转移分配及氮代谢酶活性的影响

利用¹⁵N示踪技术,研究了施钾对甘薯发根结薯期、薯块膨大期地上和地下部氮素转移分配、光合特性及氮代谢酶活性的影响.结果表明: 在发根结薯期,施钾显著提高¹⁵N向地上部的转移分配,其中K₃(K₂O, 300 mg·kg^-1)处理与对照相比¹⁵N向叶片转移速率提高了76.2%,¹⁵N积累量提高了92.1%.在薯块膨大期,随施钾量增加地上部叶片¹⁵N总分配率由33.7%降低至24.4%,块根¹⁵N分配率由5.8%升高至17%,其中K₃处理块根¹⁵N积累量是对照的3倍.两个关键生长期硝酸还原酶、谷氨酸脱氢酶、谷氨酰胺合酶、谷氨酸合酶和净光合速率(P_n)均随施钾量的增加而提高.逐步回归分析表明,氮代谢酶活性和P_n是影响甘薯¹⁵N转移和分配的主要因素(R分别为0.965和0.942),通径分析表明,在发根结薯期主要通过促进硝酸还原酶和谷氨酸脱氢酶介导的氮素催化能力促进氮素向地上部分配;在薯块膨大期主要通过提高谷氨酰胺合酶/谷氨酸合酶循环介导的氮素同化能力促进氮素向地下部分配.     

Arabidopsis glt1-T mutant defines a role for NADH-GOGAT in the non-photorespiratory ammonium assimilatory pathway

The physiological role of the NADH-dependent glutamine-2-oxoglutarate aminotransferase (NADH-GOGAT) enzyme was addressed in Arabidopsis using gene expression analysis and by the characterization of a knock-out T-DNA insertion mutant (glt1-T) in the single NADH-GOGAT GLT1 gene. The NADH-GOGAT GLT1 mRNA is expressed at higher levels in roots than in leaves. This expression pattern contrasts with GLU1, the major gene encoding Fd-GOGAT, which is most highly expressed in leaves and is involved in photorespiration. These distinct organ-specific expression patterns suggested a non-redundant physiological role for the NADH-GOGAT and Fd-GOGAT gene products. To test the in vivo function of NADH-GOGAT, we conducted molecular and physiological analysis of the glt1-T mutant, which is null for NADH-GOGAT, as judged by mRNA level and enzyme activity. Metabolic analysis showed that the glt1-T mutant has a specific defect in growth and glutamate biosynthesis when photorespiration was repressed by 1% CO2. Under these conditions, the glt1-T mutant displayed a 20% decrease in growth and a dramatic 70% reduction in glutamate levels. Herein, we discuss the significance of NADH-GOGAT in non-photorespiratory ammonium assimilation and in glutamate synthesis required for plant development.     

MOLECULAR EVOLUTION OF GLUTAMINE SYNTHETASE II AND III IN THE CHROMALVEOLATES1

Glutamine synthetase (GS) is encoded by three distinct gene families (GSI, GSII, and GSIII) that are broadly distributed among the three domains of life. Previous studies established that GSII and GSIII isoenzymes were expressed in diatoms; however, less is known about the distribution and evolution of the gene families in other chromalveolate lineages. Thus, GSII cDNA sequences were isolated from three cryptophytes (Guillardia theta D. R. A. Hill et Wetherbee, Cryptomonas phaseolus Skuja, and Pyrenomonas helgolandii Santore), and GSIII was sequenced from G. theta. Red algal GSII sequences were obtained from Bangia atropurpurea (Mertens ex Roth) C. Agardh; Compsopogon caeruleus (Balbis ex C. Agardh) Mont.; Flintiella sanguinaria F. D. Ott and Porphyridium aerugineum Geitler; Rhodella violacea (Kornmann) Wehrmeyer and Dixoniella grisea (Geitler) J. L. Scott, S. T. Broadwater, B. D. Saunders, J. P. Thomas et P. W. Gabrielson; and Stylonema alsidii (Zanardini) K. M. Drew. In Bayesian inference and maximum‐likelihood (ML) phylogenetic analyses, chromalveolate GSII sequences formed a weakly supported clade that nested among sequences from glaucophytes, red algae, green algae, and plants. Red algal GSII sequences formed two distinct clades. The largest clade contained representatives from the Cyanidiophytina and Rhodophytina and grouped with plants and green algae. The smaller clade (C. caeruleus, Porphyra yezoensis, and S. alsidii) nested within the chromalveolates, although its placement was unresolved. Chromalveolate GSIII sequences formed a well‐supported clade in Bayesian and ML phylogenies, and mitochondrial transit peptides were identified in many of the sequences. There was strong support for a stramenopile‐haptophyte‐cryptophyte GSIII clade in which the cryptophyte sequence diverged from the deepest node. Overall, the evolutionary history of the GS gene families within the algae is complex with evidence for the presence of orthologous and paralogous sequences, ancient and recent gene duplications, gene losses and replacements, and the potential for both endosymbiotic and lateral gene transfers.     

Cyanobacterial bioactive metabolites—A review of their chemistry and biology

Cyanobacterial blooms occur when algal densities exceed baseline population concentrations. Cyanobacteria can produce a large number of secondary metabolites. Odorous metabolites affect the smell and flavor of aquatic animals, whereas bioactive metabolites cause a range of lethal and sub-lethal effects in plants, invertebrates, and vertebrates, including humans. Herein, the bioactivity, chemistry, origin, and biosynthesis of these cyanobacterial secondary metabolites were reviewed. With recent revision of cyanobacterial taxonomy by Anagnostidis and Komárek as part of the Süβwasserflora von Mitteleuropa volumes 19(1–3), names of many cyanobacteria that produce bioactive compounds have changed, thereby confusing readers. The original and new nomenclature are included in this review to clarify the origins of cyanobacterial bioactive compounds.Due to structural similarity, the 157 known bioactive classes produced by cyanobacteria have been condensed to 55 classes. This review will provide a basis for more formal procedures to adopt a logical naming system. This review is needed for efficient management of water resources to understand, identify, and manage cyanobacterial harmful algal bloom impacts.     

Effects of sodium on mineral nutrition in rose plants

The effects of sodium (Na⁺) ion concentration on shoot elongation, uptake of ammonium (NH₄⁺) and nitrate (NO₃^?) and the activities of nitrate reductase (NR) and glutamine synthetase (GS) were studied in rose plants (Rosa hybrida cv. “Lambada”). The results showed that shoot elongation was negatively correlated with sodium concentration, although no external symptoms of toxicity were observed. Nitrate uptake decreased at high sodium levels, specifically at 30 meq litre4 of sodium. As flower development was normal under high saline conditions, this could suggest that nitrogen was being mobilised from shoot and leaf reserves. Ammonium uptake was not affected by any of the salt treatments applied probably because it diffuses through the cell membrane at low concentrations. Nitrate reductase activity was reduced by 50% at 30 meq litre 1 compared with control treatment, probably due to a decrease in the free nitrate related to nitrate uptake pattern. None of the salt treatments used affected total leaf GS activity (both chloroplastic and cytosolic isoforms) or leaf NPK mineral contents. Nitrate reductase activity in leaves increased at 10 meq litre^?1 of sodium and GS activity in roots (cytosolic isoform only) followed the same pattern as NR. It is suggested that the activation of both enzymes at low salt level could be attributed to the beneficial effect of increased sulphur in the nutrient solutions.     

Chick brain glutamine synthetase and Mn2+−Mg2+ interactions

Glutamine synthetase (GS) from the chick brain was purified to apparent homogeneity by ammonium sulfate fractionation followed by affinity chromatography, electrofocusing and Sephadex G-150 chromatography. The purified enzyme showed a single band on sodium dodecyl sulfate analysis in polyacrylamide gel. By sedimentation equilibrium analysis and gel electrophoresis analysis, it was shown that the enzyme has a subunit molecular weight of 45,000 and a native molecular weight of 364,000, which is consistent with an octameric structure. Sedimentation analysis in the presence of Mg²⁺ revealed three different forms of macromolecules corresponding respectively to a monomer, a tetramer and an octamer. Among eight cations tested (Ca²⁺, Co²⁺, Fe²⁺, Li⁺, Mg²⁺, Mn²⁺, Ni²⁺, Zn²⁺) only Co²⁺, Mg²⁺ and Mn²⁺ supported GS activity; the order of activatory ability was Mg²⁺>Co²⁺>Mn²⁺. The maximum activating effect of Mn²⁺ occurs only within a very narrow range of concentration: with an excess of cation causing strong inhibition of GS activity. For each cation, maximal GS activity occurs at a defined cation/ATP ratio. A regulatory system in which Mn²⁺, modulates the Mg²⁺ dependent GS activity, is proposed; such cation interactions may be of significance in the intracellular control of glutamine synthesis.