Journal of Experimental Botany, Vol. 52, No. 362, pp. 1769-1777,
September 1, 2001
© 2001 Oxford University Press
Original Papers |
Comparative study of the O2, CO2 and temperature effect on respiration between Conference pear cell protoplasts in suspension and intact pears
Flanders Centre/Laboratorium of Postharvest Technology, Katholieke Universiteit Leuven, Willem de Croylaan 42, B-3001, Leuven, Belgium
The influence of the O2 and CO2 concentration and the temperature on the O2 uptake rate of cool-stored intact pears and pear cell protoplasts in suspension was compared. Protocols to isolate pear cell protoplasts from pear tissue and two methods to measure protoplast respiration have been developed. Modified MichaelisMenten kinetics were applied to describe the effect of the O2 and the CO2 concentration on the O2 uptake rate and temperature dependence was analysed with an Arrhenius equation. Both systems were described with a non-competitive type of CO2 inhibition. Due to the inclusion of gas diffusion properties, the MichaelisMenten constant for intact pears (2.5 mM) was significantly larger than the one for protoplasts in suspension (3 µM), which was in turn larger than the MichaelisMenten constant obtained in mitochondrial respiration measurements described in the literature. It was calculated that only 3.6% of the total diffusion effect absorbed in the MichaelisMenten constant for intact pears, could be attributed to intracellular gas diffusion. The number of cells per volume of tissue was counted microscopically to establish a relationship between the pear cell protoplast and intact pear O2 uptake rate. A remarkable similarity was observed: values of 61.8 nmol kg-1 s-1 for protoplasts and 87.1 nmol kg-1 s-1 for intact pears were obtained. Also, the inhibitory effect of CO2 on the respiration rate was almost identical for protoplasts and intact pears, suggesting that protoplast suspensions are useful for the study of other aspects of the respiration metabolism.
Key words: Pyrus communis L., protoplast isolation, respiration, metabolism, modelling.
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