Aerobic–anaerobic Respiratory Transition in Pear Fruit and Cultured Pear Fruit Cells

Abstract

Abstract The extinction point (EP), defined as the lowest O2 concentration at which alcohol production ceases, was a useful concept in early interpretations of the Pasteur effect in fruit. However, ethanol is now known to be a normal constituent of many fruits under aerobic conditions. Therefore, we propose an alternative concept, the anaerobic compensation point (ACP), defined as the O2 concentration at which CO2 evolution is minimum. After 2 to 4 hr under various O2 concentrations, the ACPs of mature-green pears (Pyrus communis L.) and pear cell cultures are 1.6% to 1.7% and 1.1% to 1.3% O2, respectively. The ACP shifts to lower O2 concentrations upon extended exposure of the cells to low-O2 atmospheres and to higher O2 concentrations as pear fruit mature physiologically or as the diffusion coefficient of cell suspensions is decreased. With O2 diffusion coefficients of 4.4, 3.7, and 2.5 × 10−6 cm2·s−1, the ACP effect is observed just below 1.3%, 3.0%, and 5.0% O2, respectively. Analogies between the responses of intact fruit and suspension-cultured cells to limiting O2 are illustrated and use of the latter in assessing the response of pear cells to changing coefficients of diffusion is discussed.