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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 371-379 
    ISSN: 0006-3592
    Keywords: plant tissue culture ; Papaver somniferum ; linear growth ; phosphate limitation ; modeling ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In examining the growth kinetics of cell suspensions of opium poppy (Papaver somniferum), the increase in biomass with time was observed to be linear over the entire batch growth period of up to 20 days. Although batch growth profiles were reproducible utilizing the same inoculum, growth rates varied tremendously when experiments were inoculated with cells from different flasks. Both of these phenomena are difficult to explain with conventional batch growth models. In a series of a experiments, phosphate was determined to be the growth-rate-limiting substrate. By expressing growth rate in terms of the intracellular reserves of phosphorus, a growth model which expresses kinetics in terms of the intracellular phosphorus contents of the cells is shown to predict both linear growth character and inoculum dependent variability in growth. The stationary phase phosphate content of seven plant suspension cultures of different plant species was found to be comparable to phosphorus levels of phosphate-starved poppy cells, which suggests that phosphate limitation may be common for plant tissue culture. The applicability of this model to other biological systems which display similar batch growth patterns when subjected to inorganic nutrient deprivation is discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0006-3592
    Keywords: plant cell suspensions ; carbon utilization ; growth yield ; maintenance coefficient ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Methodology is presented for the determination of growth yield (Yg) and maintenance coefficient (m) for carbon utilization of plant cells grown in suspension culture. Estimation of Yg and m requires measurements of specific growth rate (µ) and specific rate of substrate uptake (q) at different growth limiting substrate concentrations. Batch culture of tobacco cells did not permit evaluation of Yg and m because µ is constant and maximal during most of the growth cycle. In batch culture, the period of declining specific growth rate is extremely brief because of the rapid transition from logarithmic growth to stationary phase. This occurs because the Km for growth is relatively small compared to the initial sucrose concentration. Thus, when the substrate level reaches the Km, the large mass of cells rapidly depletes the remaining substrate. In contrast, semicontinuous culture facilitates the determination of Yg and m because various steady-state growth rates can be achieved. Mathematical expressions were developed to determine the effective values of µ and q over the semicontinuous replacement interval. The validity of this approach was verified by conducting simulations using experimentally determined parameters.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 241-246 
    ISSN: 0006-3592
    Keywords: fed-batch operation ; continuous approximation ; growth kinetics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In Cephalotaxus harringtonia plant cell cultures, periods of batch growth that are limited by hexose uptake are too short to make an accurate estimate of the Monod saturation constant. Continuous cultures are infeasible on a laboratory scale, and semicontinuous cultures require too frequent sampling. Fed-batch operation, consisting of intermittent removal from a culture that is fed continuously, was investigated as a possible solution to these problems. For a constant feed rate, computer simulations showed that a steady state can be achieved which is useful for studying growth at different specific growth rates. In terms of the dilution rate it was confirmed that the operation is essentially equivalent to continuous culture when the samples represent a small fraction of the total culture volume. Experiments with glucose or fructose as the carbon source were carried out in shake flasks fed by a multichannel syringe pump. Results indicate that Monod kinetics based on medium glucose levels cannot adequately describe growth under these conditions. Monod's expression for specific growth rate using internal glucose concentration gives an improved correlation.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1042-7163
    Keywords: Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have shown that the MNDO-PM3 semiempirical molecular orbital method is capable of yielding calculated structures of oxaphosphetanes and ylides that are comparable with the experimentally known structures.The MNDO-PM3 method also reproduces the geometric and thermodynamic parameters of the “mythyical Witting half-reaction”, previously calculated using a more elaborate and costly ab initio molecular orbital approach. In addition, using the SADDLE routine, we were able to find a transition state for this half-reaction. This transition state resembles geometrically the transition state found using the ab initio approach (4-31G* level). The energy of activation was calculated to be 9.2 kcal/mole, which is fairly comparable with the ab initio reslt of 5.2 kcal/mole.According to our calculations, and in general agreement with findings of Volatron and Eisenstein [11], the mythical Witting reaction reaction would be expected to proceed through a planar transition state for the cycloaddition of the ylide and the aldehyde in a process that superficially seems to be a synchronous one. However, an analysis of the evolution of the bond orders and the localized molecular orbitals throughout the reaction indicates that the P—O bond has not been formed in the transition state, whereas the C—C bond is about 40% formed. Therefore, the mythical Wittig half-reaction is best described as a very asynchronous cycloaddition (a bordeline two step mechanism) with a planar geometry in the transition state, composed of a multi-centered mP—C—C—O bond orbital and with the phosphorus and the oxygen atoms sharing a strong attractive charge interaction. A similar description results from computations of the Wittig reactions of H3=CHCH3 and (C6H5)3P=CHCH3 with H3CCHO, which is inconsistent with the Vedejs geometry.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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