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High- and low-temperature limits to growth of tomato cells (1994)

Hansen, L. D. ; Afzal, Mohammed ; Breidenbach, R. W. ; [et al.]

Springer

Planta 195 (1994), S. 1-9

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ISSN: 1432-2048

Keywords: Calorimetry ; Chilling ; Heat-stress injury ; Lycopersicon

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The temperature dependence of the metabolic rates of cultured tomato cells (Lycopersicon esculentum Mill.) has been studied by differential scanning calorimetry as a continuous function over the range from near 0 to above 45°C. Metabolic rates increase exponentially with temperature over the permissive range for growth (approx. 10–30°C). Outside this range irreversible loss of metabolic activity occurs. The rate of activity loss is time and temperature dependent, increasing as the exposure temperature diverges from the permissive range and increasing with time at any nonpermissive temperature. Metabolic heat rates obtained while scanning down from intermediate (25°C) to low temperature (0°C) yielded Arrhenius plots with pronounced downward curvature below about 12°C. The increase in apparent activation energy below 12°C is a function of the scan rate, showing its time dependency. This time dependency caused by inactivation confounds many estimates of apparent activation energy. Scanning up to high temperature shows that activity loss at high temperature is also time and temperature dependent. No first-order phase transitions associated with the changes in metabolism were detected at either low or high temperatures. Studies with lamellar lipid preparations added to cells show that temperature-induced transitions of lipids at levels equivalent to 4% of the lipid content of the cells were detectable. Cells with altered lipid composition showed altered temperature dependence of inactivation. High pressures (in the range from 10 to 14 MPa) shift the high temperature threshold and the rate of metabolic activity loss, supporting a postulate that higher-order transitions may be associated with inactivation of metabolism. Higher-order transitions of lipids or first-order transitions encompassing only a small fraction of total lipid remain among several viable postulates to explain temperature-dependent loss in activity. Alternative postulates are discussed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00206284

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Recombination in yeast mitochondrial DNA (1972)

Shannon, Charles ; Rao, Ayyagari ; Douglass, Stephen ; [et al.]

New York, N.Y. : Wiley-Blackwell

Journal of Supramolecular Structure 1 (1972), S. 145-152

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ISSN: 0091-7419

Keywords: Life Sciences ; Molecular Cell Biology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Biology , Chemistry and Pharmacology , Medicine

Notes: When haploid yeast strains containing mitochondrial DNAs (mtDNAs) of different buoyant densities are mated, the resulting zygotes contain a mixed population of mitochondria and mitochondrial DNAs. During vegetative growth of diploid cells formed from such a cross between a petite strain with mtDNA of density 1.677 g cm-3 and a respiratory competent strain with mtDNA of density 1.684 g cm-3, mtDNAs with intermediate buoyant densities are obtained. Virtually all newly synthesized mtDNA in diploid ρ- progeny has the intermediate buoyant density. Therefore, within 2 generations of growth of the diploid cells, the intermediate buoyant density species predominate. In crosses between a respiratory competent strain and other petite strains with different values of genetic suppressiveness, it was found that the amount of recombination yielding mtDNAs of intermediate buoyant densities roughly parallels the degree of suppressiveness. Individual clones of respiratory deficient cells from such crosses were also isolated to confirm that stable mtDNAs with intermediate buoyant densities were obtained. Thus, it is apparent that some form of recombination takes place within the mtDNAs of yeast cells that results in stable mtDNA species.

Additional Material: 3 Ill.