The influence of the tension of oxygen on the respiration of rhizobia

Summary Cultures of Rhizobium trifolii, Rh. leguminosarum, Rh. meliloti and Rh. japonicum were grown in the Novy-Soule type of respiration apparatus and the oxygen consumed, CO ₂ produced and glucose fermented determined. From these data the respiratory quotient, the percentage of glucose used, and the carbon of the glucose used that appeared as CO₂-carbon were calculated. Since very little acids or neutral products are formed by these organisms, the carbohydrate destroyed and not appearing as CO₂ is a measure of gum production by the organisms.With Rh. trifolii, Rh. leguminosarum and Rh. meliloti, the glucose used, the rate of respiration, and to some extent the glucose that appeared as CO₂, increase with increasing p _O2. About 60 to 80 per cent of the carbon in the glucose utilized appears in the CO₂ produced. All of these cultures had an R. Q. close to unity which was independent of the p _O2. The respiratory quotient of Rh. leguminosarum was inclined to be erratic.With Rh. japonicum, the rate of respiration, total oxygen consumed, and total CO₂ produced were much lower than the values observed for the other cultures, Also the glucose used increased with decreasing p _O2. The apparatus used was not sufficiently sensitive to detect marked differences in the rate of respiration under the various tensions of oxygen with this organism, but there appeared to be a small increase in the rate of respiration with the higher tensions of oxygen.With all organisms, excellent fermentation of glucose with a high conversion into CO₂ was observed under low tensions of oxygen (five per cent or less), provided the absolute quantity of this gas was present in excess of the requirements of the organisms.Herman Frasch Foundation in Agricultural Chemistry Paper No. 66.     

Influence of oxygen tension on the respiratory activity of Mycobacterium phlei

Growth of Mycobacterium phlei under low oxygen tension resulted in specific activities two to twenty times lower for formate dehydrogenase, malate dehydrogenase, beta-hydroxybutyrate dehydrogenase, lactate oxidase and NADH dehydrogenase than when cultures were grown under high aeration. An increase in fumarate reductase and succinate dehydrogenase occurred with M. phlei grown under low oxygen tension. Malate: vitamin K dehydrogenase and glucose-6-phosphate dehydrogenase activity were not significantly affected by the oxygen tension used to grow the bacteria, and neither culture contained a lactate dehydrogenase. With growth of M. phlei in conditions of low oxygen tension, cytochrome a was not detected, but cytochrome b was prominent in membranes and cytochrome c was present in the soluble fraction.     

The DNA-Content of nuclei in the meristem of onion roots

Summary The techniques of making and evaluating measurements of nuclear DNA-contents by the two wave length method, including wave length determination were worked out. The efficiency of the analysis increased by unbiased elimination of off-values. Correction for non-specific absorption was made but remained, with the present material (sections), necessarily imperfect. This seems to be the factor which limited the, otherwise apparently very high, optical accuracy of which instrument and methods are capable. Errors in the determination of the nuclear dye-content were, even so, small compared with the more extreme cases of proportionality errors in the determination of the DNA-content that resulted from disproportionality of Feulgen dye- and DNA-content.Direct evidence of proportionality errors entering the DNA determination was found when different mitotic stages were compared. The ratio of mean dye-contents of two stages varied in slides which were prepared differently in regard to fixation, hydrolysing agent, or duration of hydrolysis. In seven such samples the mean dye-content of metaphases ranged from 80 to 115% (with mean 100.2%) of the prophase mean, the mean dye-content of mid-anaphases from 92 to 112% (with mean 105.5%). Similarly the mean dye-contents of daughter nuclei in late anaphases and telophases bracketed 50% of the prophase value. It appears virtually certain that this variation is not caused by a corresponding natural DNA variation but is due to proportionality errors.The results strongly support the view that the DNA-content does not change at all during mitosis apart from its halving brought about by the anaphase separation of sister chromatids. The results are further fully compatible with the hypothesis that the DNA-content per complete genome is strictly constant except during the period of DNA doubling. The dye-contents of prophase nuclei (also of metaphases) of the same sample have a coefficient of variation (corrected for non-systematic reading errors) of about 5.5%. This appears to be well within the limits of errors due to imperfectly corrected non-specific absorption and of proportionality errors.The proportionality errors found in measurements of different mitotic stages reveal a pattern similar to that prevailing in published DNA measurements: apparent deviations from DNA constancy are usually small and often negligible, but are occasionally large enough to be misleading. None of the claimed disproofs of DNA constancy is in any way conclusive, as such claims necessarily rest upon the unwarranted assumption that proportionality errors are always very small or absent.The development of the DNA-content during interphase was studied by correlating DNA-content and nuclear volume. Earlier findings on roots of other plants are confirmed. An interphase I with the DNA-content 2C is followed by a period of DNA synthesis (during this period the nuclear volume seems to increase only slowly, if at all) and this by an interphase III with the DNA-content 40. Each phase lasts several hours. Mitosis and DNA synthesis are essentially independent processes.Measurements on nuclei which are technically more favourable than those in sectioned onion roots have yielded a smaller or even disappearing inter-nuclear variation of the Feulgen dye-content. A strict DNA constancy per complete genome appears more and more likely.Contribution from the programme in Cytology, Department of Botany, University of Wisconsin, Madison, supported by grants to the late Dr. C. Leonard Huskins, from the American Cancer Society upon recommendation of the Committee on Growth of the National Research Council, from the Rockefeller Foundation and from the Research Committee of the Graduate School with funds supplied by the Wisconsin Alumni Research Foundation.     

The effect of dissolved oxygen tension and the utility of oxygen uptake rate in insect cell culture

Dissolved oxygen tension and oxygen uptake rate are critical parameters in animal cell culture. However, only scarce information of such variables is available for insect cell culture. In this work, the effect of dissolved oxygen tension (DOT) and the utility of on-line oxygen uptake rate (OUR) measurements in monitoring Spodoptera frugiperda (Sf9) cultures were determined. Sf9 cells were grown at constant dissolved oxygen tensions in the range of 0 to 30%. Sf9 metabolism was affected only at DOT below 10%, as no significant differences on specific growth rate, cell concentration, amino acid consumption/production nor carbohydrates consumption rates were found at DOT between 10 and 30%. The specific growth rate and specific oxygen uptake rate followed typical Monod kinetics with respect to DOT. The calculated _max and max were 0.033 h^-1 and 3.82×10^-10 mole cell^-1h^-1, respectively, and the corresponding saturation constants were 1.91 and 1.57%, respectively. In all aerated cultures, lactate was consumed only after glucose and fructose had been exhausted. The yield of lactate increased with decreasing DOT. It is proposed, that an apparent DOT in non-instrumented cultures can be inferred from the lactate yield of bioreactors as a function of DOT. Such a concept, can be a useful and important tool for determining the average dissolved oxygen tension in non-instrumented cultures. It was shown that the dynamic behavior of OUR can be correlated with monosaccharide (fructose and glucose) depletion and viable cell concentration. Accordingly, OUR can have two important applications in insect cell culture: for on-line estimation of viable cells, and as a possible feed-back control variable in automatic strategies of nutrient addition.Abbreviations DOT Dissolved oxygen tension - OUR Oxygen uptake rate - specific oxygen uptake rate - specific growth rate - X_v viable cell concentration - C_L, C^*, and oxygen concentrations in liquid phase, in equilibrium with gas phase, and medium molar concentration, respectively - H Henry's constant - K_La volumetric oxygen transfer coefficient - P_T total pressure - oxygen partial pressure - oxygen molar fraction - i discrete element     

Measuring and interpreting respiratory critical oxygen pressures in roots

BACKGROUND AND AIMS: Respiratory critical oxygen pressures (COPR) determined from O(2)-depletion rates in media bathing intact or excised roots are unreliable indicators of respiratory O(2)-dependency in O(2)-free media and wetlands. A mathematical model was used to help illustrate this, and more relevant polarographic methods for determining COPR in roots of intact plants are discussed. METHODS: Cortical [O(2)] near the root apex was monitored indirectly (pea seedlings) from radial oxygen losses (ROL) using sleeving Pt electrodes, or directly (maize) using microelectrodes; [O(2)] in the root was controlled by manipulating [O(2)] around the shoots. Mathematical modelling of radial diffusive and respiratory properties of roots used Michaelis-Menten enzyme kinetics. KEY RESULTS: Respiration declined only when the O(2) partial pressure (OPP) in the cortex of root tips fell below 0.5-4.5 kPa, values consistent with depressed respiration near the centre of the stele as confirmed by microelectrode measurements and mathematical modelling. Modelling predictions suggested that the OPP of a significant core at the centre of roots could be below the usual detection limits of O(2)-microelectrodes but still support some aerobic respiration. CONCLUSIONS: In O(2)-free media, as in wetlands, the COPR for roots is likely to be quite low, dependent upon the respiratory demands, dimensions and diffusion characteristics of the stele/stelar meristem and the enzyme kinetics of cytochrome oxidase. Roots of non-wetland plants may not differ greatly in their COPRs from those of wetland species. There is a possibility that trace amounts of O(2) may still be present in stelar 'anaerobic' cores where fermentation is induced at low cortical OPPs.     

The influence of dissolved oxygen tension on the synthesis of the antibiotic difficidin by bacillus subtilis

The antibiotic, difficidin, and its hydroxylated derivative oxydifficidin, were synthesized by cultures of Bacillus subtilis grown on a complex medium. Maximum titers of about 200 and 130 mg/L, respectively, were obtained. In fermentations where the dissolved oxygen tension (DOT) was controlled, the maximum specific growth rate was only reduced below 5% air saturation. DOT had little effect on the volumetric rateof synthesis of oxydifficidin but greatly influenced the rate for difficidin, which was reduced at DOT values below 40% air saturation. (c) 1994 John Wiley & Sons, Inc.     

The influence of the rate of rigor state development on its tension in single muscle fibre

The rigor tension and stiffness of glycerinated fibres from rabbit psoas muscle were found to vary markedly in dependence on the rate of substitution of the solutions in the experimental chamber. The maximum value of rigor tension, which is close to that activated by Ca2+ with pCa4, was obtained at the slow development of rigor in the absence of Ca2+ ions. The observed dependence is assumed to be due to the different degrees of removal of the 'slack' in fibres, which may be contributed by compliant ends of the preparation. A new method allowing to obtain rather reproducible values of rigor tension is proposed.     

Postural influence on maternal capillary oxygen and carbon dioxide tension

The effect of posture on maternal capillary blood Po₂ and Pco₂ was studied in pregnant and non-pregnant women. There was a significant decrease of Po₂ (mean 13·0 mm. Hg) and significant decrease of Pco₂ (mean 2·4 mm. Hg) when pregnant women sat up, but these changes did not occur in the non-pregnant. These findings may be relevant to debate on the optimum posture for labour.     

Microtubular fir-trees in mitotic spindles of onion roots

Summary The organization of kinetochore fibers was examined inAllium root cells processed for tubulin immunocytochemistry. Metaphase fibers consist of a core or trunk of Mts to which are attached numerous branches, yielding a bottle-brush of fir-tree pattern similar to that reported inHaemanthus endosperm cells. Many of the branches cross the midzone and extend into the opposite half-spindle. In addition, branch Mts associate with more than one kinetochore fiber. During anaphase, branch Mts elongate while the trunks shorten and fuse into polar caps. Our results are discussed in terms of spindle fiber organization and Mt polarity.Abbreviations K Kinetochore - Mt microtubule