Regulation of respiratory metabolism in fruits and vegetables by carbon dioxide

The respiratory rate of fruits and vegetables can be used as an indicator for designing storage conditions to maximize the longevity of these commodities. One postharvest technique that has been used to prolong the storage life of some of these commodities is the use of a controlled atmosphere. The modulation of respiratory metabolism of such commodities held in controlled atmospheres containing reduced oxygen and/or elevated carbon dioxide levels has been thought of as the primary reason for the beneficial effects on the commodities. However, the mechanism by which elevated carbon dioxide influences the regulation of respiratory metabolism is still obscure and several hypotheses have been proposed for its mode(s) of action. The regulation may be directed towards the glycolytic pathway, the fermentative metabolism, the tricarboxylic acid cycle or the electron transport system, presumably through its influence on the synthesis, degradation, inactivation and/or activation of the respective enzymes. It may also be through the antagonistic effects of carbon dioxide on ethylene action as well as its influence on secondary metabolism through an alteration in cell pH. This article discusses the recent developments on the biochemical and physiological fronts as well as the possible mode(s) of action of elevated carbon dioxide in the regulation of respiratory metabolism in fruits and vegetables.