Components of woody-tissue respiration in young Abies amabilis (Dougl.) Forbes trees

Summary Woody-tissue respiration was measured on five different dates at three to five locations on each of 12 30-year-old Abies amabilis trees. On any given date, temperature-corrected respiration per unit surface area varied 10 to 40-fold between sampling locations. In stems, the two major components of respiration were growth respiration and sapwood maintenance respiration, which were of roughly equal importance during the growing season. There was no evidence of significant cambial maintenance respiration, suggesting that a stand with high bole surface area would not automatically have high respiration. Respiration in branches was much greater than in boles of comparable volume and growth rates, and was significantly correlated with branch height. Branch respiration may include an another significant component in addition to the two seen in bole respiration, possibly associated with carbohydrate mobilization and transport or with CO₂ efflux from the transpiration stream.     

Dependency of growth yield,maintenance and K s-values on the dissolved oxygen concentration in continuous cultures of Azotobacter vinelandii

Azotobacter vinelandii was grown diazotrophically in sucrose-limited chemostat cultures at either 12, 48, 108, 144 or 192 M dissolved oxygen. Steady state protein levels and growth yield coefficients (Y) on sucrose increased with increasing dilution rate (D). Specific rate of sucrose consumption (q) increased in direct proportion to D. Maintenance coefficients (m) extrapolated from plots of q versus D, as well as from plots of 1/Y versus 1/D exhibited a nonlinear relationship to the dissolved oxygen concentration. Constant maximal theoretical growth yield coefficients (Y ^G) of 77.7 g cells per mol of sucrose consumed were extrapolated irrespective of differences in ambient oxygen concentration. For comparison, glucose-, as well as acetate-limited cultures were grown at 108 M oxygen. Fairly identical m- and Y ^G-values, when based on mol of substrate-carbon with glucose and sucrose grown cells, indicated that both substrates were used with the same efficiency. However, acetate-limited cultures showed significantly lower m- and, at comparable, D, higher Y-values than cultures limited by either sucrose or glucose. Substrate concentrations (K _s) required for half-maximal growth rates on sucrose were not constant, they increased when the ambient oxygen concentration was raised and, at a given oxygen concentration, when D was decreased. Since biomass levels varied in linear proportion to K _s these results are interpreted in terms of variable substrate uptake activity of the culture.Abbreviations D dilution rate - K _s substrate concentration required for half maximal growth rate - m maintenance coefficient - q specific rate of substrate consumption - Y growth yield coefficient - Y ^G maximum theoretical growth yield coefficient     

The complete nucleotide sequence of the colicinogenic plasmid ColA. High extent of homology with ColE1

Summary The complete nucleotide sequence of the colicinogenic plasmid ColA has been determined. The plasmid DNA consists of 6720 bp (molecular weight 4.48×10⁶). Fifteen putative biological functions have been identified using the functional map previously determined. These include 11 genes and 3 DNA sites. Nine genes encode proteins of which 3 have been fully characterized. The replication region of ColA coding for RNAI and RNAII is highly homologous to that of ColE1 andClo DF13. The same holds true for the site-specific recombination region containing palindromic symmetry and involved in stable maintenance of the plasmids. A high percentage of homology has been detected for putative mobility proteins encoded by ColA and ColE1. The exclusion proteins are also highly homologous.     

A method for the determination of confidence limits for the P/2e − ratio for chosen values of Y ATP max from the results of continuous culture experiments

A model is described, which allows the determination of 95% confidence limits for the maintenance coefficient and the efficiency of oxidative phosphorylation for chosen values of the growth yield for ATP corrected for energy maintenance (Y _ATP ^max ). As experimental data the specific rates of substrate consumption, product formation and oxygen uptake in chemostat cultures at various growth rates are used.     

Energy conservation during nitrate respiration in Paracoccus denitrificans

P/2e ratios were calculated from anaerobic chemostat cultures of Paracoccus denitrificans with nitrogenous oxides as electron acceptor. P/2e ratios were calculated, using the Y _ATP ^max values determined for aerobic cultures. When succinate was the carbon and energy source the average P/2e values of the sulphate-and succinate-limited cultures with nitrate as electron acceptor were 0.5 and 0.7, respectively, and of the nitrite-limited culture 0.9. With gluconate as carbon and energy source the average P/2e values of the gluconate-limited with nitrate as electron acceptor and nitrate limited cultures were 0.9 and 1.1, respectively.H⁺/O ratios measured in cells obtained from sulphate-, succinate, nitrite-, gluconate-and nitratelimited cultures yielded respective average values of 3.4, 4.5, 3.5, 4.8 and 6.2 for endogenous substrates. From our data we conclude that sulphate-and nitritelimitation causes the loss of site I phosphorylation. Nitrite has no influence on the maximum growth yield on ATP. We propose that metabolism in heterotrophically grown cells of Paracoccus dentrificans is regulated on the level of phosphorylation in the site I region of the electron transport chain.     

Maintenance energy demand affects biomass synthesis but not cellulase production by a mesophilicClostridium

Summary Secretion of cellulolytic activity by the mesophilClostridium strain C7 was studied while the bacterium underwent progressive carbon/energy starvation and the ensuing continuous decline in growth rate. In the slowest range of growth rates studied the organism was in full response to the global regulation imposed by guanosine 5, 3-bispyrophosphate (ppGpp). The exoenzymes of the cellulase complex were produced at the same volumetric rate whether or not the response was active. However, the volumetric rate of biomass synthesis was reduced 45% or more by the response. Energy necessary to maintain the ppGpp-regulated state (i.e., maintenance energy) was, therefore, diverted from energy going to synthesis of biomass but not from that going to exoenzyme synthesis, making the yield of cellulase activity per mole of carbon-energy substrate independent of growth rate and the exoenzyme complex produced from the substrate with equal efficiency at all growth rates. The primary consideration in improving exoenzyme productivity by bacteria with this type of energy distribution between secretion, growth, and maintenance is simply increasing yield per mole of carbon-energy substrate, with growth rate effects on yield a secondary and minimum concern.     

Survival of Chromatium vinosum at low light intensities

The effect of low irradiation on the viability of Chromatium vinosum was investigated. Cultures were precultivated at 1,000 lux (=0.1/h). Then, before the substrate was depleted, illumination was changed to either complete darkness or about 30 lux. Previously, the latter light intensity had been found not to promote growth.The parameters assayed were viability, protein, bacteriochlorophyll, ATP, RNA, DNA, absorbance (E ₂₆₀) of the supernatant, and total anthron-positive material.The data show that irradiation insufficiently high to promote growth, results in viability percentages as high as 90% after 8 days, whereas cultures incubated in complete darkness are virtually dead by then. Neither in the light nor in the dark a degradation of protein or cell wall hexoses was observed. The RNA content also remained constant. However, particularly in the dark cultures DNA was found to decrease concomitant with increased E ₂₆₀ readings of the supernatant. It is considered unlikely that such essential macromolecules are degraded to serve the maintenance energy requirements. The ecological impact of the observations is discussed.Non-Standard Abbreviations PHB poly--hydroxybutyric acid - Bchl Bacteriochlorophyll     

生态系统健康与人类可持续发展

生态系统健康学是近年来出现的一门探讨资源环境管理对策的综合性新学科．本文介绍了生态系统健康概念的由来、内涵以及生态系统健康学的主要研究内容;阐述了生态系统健康与人类可持续发展的关系;文中还对国际上一些主要的生态系统健康实践作了介绍,并建议我国应尽快开展生态系统健康研究．作者认为生态系统健康学必然为人类社会的健康、持续发展提供新的希望．     

Regulation of phosphorus stoichiometry and growth rate of consumers: theoretical and experimental analyses with Daphnia

Initial theories of ecological stoichiometry were based on the assumption that the mass-specific content of key nutrient elements (such as P), changes little within a consumer species. However, evidence has shown that this content changes substantially according to feeding conditions. To clarify how the specific P content (S _P) of a consumer species depends on food conditions and relates to the growth rate, we constructed a multiple mass-balance model incorporating feeding and metabolic costs and stoichiometrically regulated releases for C and P. The validity of the model was then tested experimentally by examining the growth rates and S _P of Daphnia pulicaria under various food conditions. The experimental observation agreed qualitatively well with the model, showing that the S _P of consumers relates positively to growth rate at high food C:P ratios but negatively at low food C:P ratios. Thus, within a consumer species, individuals with high S _P do not necessarily grow at high rates. The concordance in results between the model and our observation suggests that maintenance costs for both P and C are substantial regardless of food conditions and play crucial roles in determining the relationship between the S _P and growth rate of consumers.     

PS1基因突变敲入小鼠B免疫记忆细胞功能变化

探讨PS1基因突变敲入小鼠B免疫记忆细胞功能变化。OVA免疫PS1基因突变敲入小鼠,通过ELISA抗体检测观察B细胞免疫记忆功能;分离小鼠脾淋巴细胞,检测脾淋巴细胞增殖实验、B细胞表面抗原表达情况。痘苗病毒免疫正常和基因突变敲入小鼠两次,在免疫后的一年进行痘病毒腹腔攻毒实验,观察PS1基因突变敲入小鼠存活情况。通过分离中枢和外周淋巴细胞进行体外功能检测表明,PS1基因突变敲入小鼠细胞增殖功能明显降低(P0.0001);B记忆细胞表面蛋白表达有差异(P=0.045);痘苗攻毒实验结果表明,PS1基因突变敲入小鼠死亡率明显增高(P0.0001)。研究结果表明,PS1基因在调控B记忆细胞功能方面发挥重要作用,但是通过调控T细胞功能而发挥间接还是直接针对B细胞发挥调控作用,还需要进一步研究结果确认。