Some aspects of the regulation of arginine biosynthesis in soybean cell cultures

The levels of the activities of argininosuccinate synthetase and argininosuccinate lyase were measured in soybean (glycine max L. var. Mandarin) cell suspension cultures grown in the presence or absence of exogenous arginine. In some experiments, actinomycin D or cycloheximide were also added to the cultures, at critical stages of their growth. The results obtained led to the conclusion that activity of argininosuccinate synthetase is subject to significant inhibition by levels of arginine similar to those found to occur within the cells. Argininosuccinate lyase activity appeared to be enhanced, when arginine levels were increased above those occurring physiologically. Both enzymes appeared to be subject to inactivation, possibly via proteolysis.     

Some aspects of relation between nitrogen metabolism inPisum sativum and mineral nutrition

Summary Plants ofPisum sativum grown in water culture were subjected to deficiencies in the macronutrients N, P, K, S, Ca, Mg, substitution of ammonium for nitrate and change in pH to pH 3 or 9. Free amino acids, soluble nitrogen, protein and glutamate dehydrogenase activity of shoots were measured for all nutrient types. Changes in amino acid concentrations correlated well with changes in glutamate dehydrogenase. It is considered whether this enzyme is indicative of the nutritional state of plants.     

Pisatin metabolism in pea (Pisum sativum L.) cell suspension cultures

Cell suspension cultures were established from germinating pea (Pisum sativum L.) seeds. This cell culture, which accumulated pisatin, consisted mostly of single cells containing a few cell aggregates. The cells responded to treatment with a yeast glucan preparation with transient accumulation of pisatin in both cells and culture media. Addition of pisatin to cell cultures resulted in increased synthesis of pisatin. Phenylalanine ammonia-lyase, chalcone synthase and isoflavone reductase activities were present in untreated cells. Upon treatment with an elicitor preparation the activities of the first two enzymes showed a rapid, transient increase up to 20 hours after treatment. Isoflavone reductase showed a major and minor peak at 16 and 36 h, respectively, after elicitor treatment. The time course of the enzyme activity and pisatin accumulation is consistent with an elicitor-mediated response.Abbreviations CHS chalcone synthase - 2,4-D 2,4-dichlorophenoxyacetic acid - IBA indole-3-butyric acid - IFR isoflavone reductase - 2iP 6-(dimethylallylamino)-purine - MS Murashige & Skoog basal salt medium - PAL phenylalanine ammonia-lyase - PMSF phenylmethylsulfonyl fluoride - POPOP 1,4-bis-2-(4-methyl-5-phenyloxazolyl)-benzene - PPO 2,5-diphenyloxazole     

溶藻细菌L7对水华鱼腥藻氮代谢的影响

【目的】进一步探明藻菌关系,研究溶藻细菌对藻类氮代谢的影响及其作用机制。【方法】将水华鱼腥藻和溶藻细菌L7按两种比例接种入BG11培养液中,在室内进行共培养(藻细胞初始密度为1.21×108cells/L;溶藻细菌L7初始密度分别为1.75×107、1.75×108CFU/mL)。连续7 d测定藻细胞数、异形胞频率和藻细胞内的硝酸还原酶(NR)活性、谷氨酰胺合成酶(GS)活性、谷氨酸合成酶(GOGAT)活性、蛋白质含量、丙二醛(MDA)含量。【结果】低密度溶藻细菌L7能够促进藻生长(第7天藻细胞密度是对照组的1.58倍),增加异形胞频率(第7天高于对照组66.67%);高密度则会抑制藻生长(第7天藻细胞密度相比对照组下降98.84%),降低异形胞频率(第7天为0)。在藻细胞内氮代谢关键酶活性方面,接种后2 5 d,两处理组中藻细胞内NR和GOGAT活性均极显著高于对照组(P<0.01);接种后0 5 d,高密度处理组的GS活性极显著高于对照组(P<0.01),而低密度处理组的则在大部分时间内极显著低于对照组(P<0.01)。在整个实验期内,低密度处理组中藻细胞内蛋白质含量一直极显著高于对照组(P<0.01);而在高密度处理组中,除第5天外,细胞内蛋白质含量则全部极显著低于对照组(P<0.01)。接种后2 4 d,高密度处理组中藻细胞内MDA含量呈现上升趋势,并极显著高于其余两组(P<0.01)。【结论】低密度溶藻细菌L7能够提高水华鱼腥藻对氮源的需求,加速蛋白质合成,促进氮代谢;而高密度溶藻细菌L7会对藻细胞产生过氧化伤害,阻碍蛋白质合成和氮代谢过程。     

Acetate metabolism in cell suspension cultures

Cell suspension cultures of Paul's Scarlet rose were grown over a 14-day period, during which a 50-fold increase in fresh weight occurred. Three phases could be recognized from weight, DNA determinations, and microscopic examination. From days 0 to 7, cell division was accompanied by cell expansion; from days 7 to 10, only cell expansion occurred; and from days 10 to 14, there was no further growth.     

Regulatory aspects of inorganic nitrogen metabolism in the Rhodospirillaceae

Regulatory aspects of the assimilation of inorganic nitrogen compounds (ammonia, nitrate, nitrogen) were studied in 12 strains belonging to the Rhodospirillaceae. All strains possessed an ammonium transport system, as demonstrated by ¹⁴C-methylammonium uptake. This uptake showed saturation kinetics (K _m between 50–150 M), and was competitively inhibited by ammonium (K _i between 5–18 M). The ammonium transport systems were repressed by ammonium in the growth medium. The nitrogenase activity of all strains was reversibly inhibited by ammonium (switch-off). This effect was not shown under nitrogen starvation conditions with the exception of some strains of Rhodopseudomonas capsulata, the nitrogenase of which was always susceptible to switch-off by ammonium. Assimilation of nitrate was confined to some strains of Rhodopseudomonas capsulata.Abbreviations ATCC American Type culture Collection, Rockville, MD, USA - DSM Deutsche Sammlung von Mikroorganismen, Göttingen, FRG     

Some aspects of glutathione metabolism in ataxia-telangiectasia fibroblasts

Levels of glutathione (GSH) and two enzymes involved in GSH metabolism, glutathione reductase (GR) and glutathione-S-transferase(s) (GST), were measured in four SV40-transformed human fibroblast cell lines. MRC5-V1 and GM0637, derived from normal individuals, had mean GSH levels of 4.2 and 6.5 nmoles/10(6) cells, respectively. TAT2SF and AT5BIVA, both from ataxia-telangiectasia (A-T) patients, respectively had 6.5 and 4.2 nmol/10(6) cells, indicating that basal GSH levels were similar in A-T and normal cells. There was some variation in GST activity among the four cell lines but deficiency in this enzyme cannot be associated with radiosensitivity in A-T. When GR activity was measured, A-T cells had approximately 82 per cent of the mean normal activity. Though statistically significant, (P = 0.05), this small deficiency could be due to chance and is unlikely to be responsible for the radiosensitive phenotype of A-T.     

Regulatory aspects of bakers' yeast metabolism in aerobic fed-batch cultures

A highly instrumented computer-coupled bioreactor is used to investigate metabolic changes of Saccharomyces cerevisiae in aerobic fed-batch systems which are generally applied in bankers' yeast manufacture. The four types of metabolism (oxidation of glucose, aerobic fermentation, oxidation of glucose and ethanol, and oxidation of ethanol) appearing in such systems are characterized by four significant fermentation parameters: Respiratory quotient (RQ), glucose uptake rate (Q_g), ethanol turnover rate (Q_EtOH), and growth yield on glucose (Y_g). Below the critical glucose concentration glucose and ethanol are utilized simultaneously. The shift from aerobic fermentation to nondiauxic growth on glucose and ethanol is not only dependent on glucose concentration. but also on the precultivation on cells. The uptake of ethanol is controlled by the glucose supply except in the case when ethanol is limiting; the oxygen uptake rate (Q_o2), however, is unaffected by the ratio of Q_g and Q_EtOH. Critical glucose concentration is not a constant value for a particular strain, but varies corresponding to the nutritional state of the cells.