ABSTRACT
CONTENTS 22.1 Introduction ...................................................................................................................... 553 22.2 Low O2 Effects in CA=MA Applications ..................................................................... 554
22.2.1 Physiological Aspects ......................................................................................... 554 22.2.2 Gene Expression under Low O2 Availability ................................................. 556 22.2.3 Acclimation to Low O2 ...................................................................................... 558 22.2.4 Postanoxic and Posthypoxic Injury.................................................................. 559 22.2.5 Model of Low O2 Sensing and Action in Plant Tissues................................ 559
22.3 Responses to High CO2 .................................................................................................. 560 Acknowledgments ..................................................................................................................... 563 References.................................................................................................................................... 563
The quality of fresh fruit and vegetables during storage is greatly influenced by temperature, relative humidity, and atmospheric composition (oxygen, carbon dioxide, and ethylene) of their environment. Application of controlled and=or modified atmosphere (CA-MA) storage (low oxygen alone or coupled with carbon dioxide) prevents and=or delays the rate of ripening of fruit, resulting in the maintenance of their commercial life (Kader, 1986). In addition, ultra low oxygen or anaerobic conditions have been recently applied as new postharvest quarantine treatments to confine insect infestations (Shellie, 2002; Shellie et al., 1997). Furthermore, there are a number of standard commercial practices such as wax coatings, packing in plastic liners, etc. in which the supply of oxygen to fruit in general may be limited. In spite of these commercial practices of CA-MA, the precisemode of action of low O2 and=or highCO2 in fresh produce and in ripening is notwell understood. In general, plants have developed strategies to manage with low oxygen levels. For example, a rapid decline in respiration, a fall in the adenylate energy charge, and a synchronized downregulation of the Krebs cycle and glycolysis are the first metabolic responses of tissues to low O2 regimes (Geigenberger, 2003; Solomos, 1982). However, the entire course, beginning with the sensing of oxygen levels and including the acclimation to oxygen deficiency, irrespective of plant tissue (root or plant organs) subjected to stress, includes a series of physiological, biochemical, and molecular mechanisms, which have not been unequivocally defined (Drew, 1997; Fukao and Bailey-Serres, 2004; Geigenberger, 2003; Kanellis, 1994; Solomos and Kanellis, 1997).
