ABSTRACT
In plants, the main substrate for respiration is carbohydrates assimilated during photosynthesis. Each day, a large fraction of all assimilated carbohydrates (from 30% to 70%) are expended in respiration (Golovko 1999, Lambers et al. 2005, Van der Werf et al. 1992). Production of energy as
5.1 Introduction .......................................................................................................................... 139 5.2 Respiratory System in Plants ................................................................................................ 140
5.2.1 Course of Respiratory Process ................................................................................. 140 5.2.2 Mitochondrial Electron-Transport Chain ................................................................. 140 5.2.3 Respiratory Control .................................................................................................. 141
5.3 Characteristics of Alternative Oxidase ................................................................................. 141 5.3.1 AOX Structure .......................................................................................................... 141 5.3.2 AOX Genes ............................................................................................................... 142 5.3.3 AOX Activation: Transcriptional and Posttranslational Mechanisms of Regulation ......142 5.3.4 AOX Capacity and Activity ...................................................................................... 143
5.4 Physiological Role of Alternative Respiration in Plants ....................................................... 143 5.4.1 Cyanide Resistance ................................................................................................... 143 5.4.2 Thermogenesis .......................................................................................................... 143 5.4.3 Energy Overow: Balancing the Respiratory Metabolism....................................... 144 5.4.4 Prevention of Oxidative Stress .................................................................................. 145 5.4.5 Maintenance of Interaction between Respiration and Other Metabolic Processes..........148 5.4.6 “Antiapoptotic Protein” ............................................................................................ 150
5.5 Concluding Remarks ............................................................................................................ 150 Acknowledgments .......................................................................................................................... 151 References ...................................................................................................................................... 151
ATP proceeds in specialized respiratory organelles-mitochondria in the electron-transport chain (ETC). The terminal part of the respiratory path consists of, among other components, two respiratory pathways for electron transport-the main cytochrome pathway (CP) and the alternative pathway (AP) through alternative oxidase (AOX). The major characteristic of AP is that it is not coupled with the synthesis of ATP and therefore considered a wasteful pathway (Moore and Siedow 1991). The unproductive characteristic of AP has, for a long time, raised questions regarding its regulation in vivo and the role in plant metabolism. Many important reviews have discussed the hypotheses concerning its role (Juszczuk and Rychter 2003, Millenaar and Lambers 2003, Moore and Siedow 1991, Shugaev 1999, Vanlerberghe and McIntosh 1997, Vanlerberghe et al 2009, Wagner and Krab 1995). Plants as sessile organisms developed biochemical strategies, and alternative respiratory pathway is considered to play an important role for plant acclimation.
