Regulation of Electron Transport in the Respiratory Chain of Plant Mitochondria

Abstract

The aim of this chapter is to gather updated understanding of electron flow and H+ flux-linked processes in plant mitochondria. New understanding of molecular mechanisms of redox pumps and ATP synthase are described. Special attention is paid to the non-phosphorylating electron flow pathways and to H+ electrochemical gradient consumers. Partitioning of electrons between ubiquinol oxidizing pathways (alternative oxidase, AOX, and cytochrome pathway) is analyzed at the level of methodological aspects and interpreted in terms of energy conservation efficiency and of cell metabolism regulation. Partitioning of H+ electrochemical gradient between ATP synthase and uncoupling protein (UCP) is tackled through the ADP/O method. It is shown how efficiently UCP activity can divert energy from oxidative phosphorylation. It is also stressed that AOX and UCP are not redundant as cnergy-dissipating proteins because AOX is inhibited by free fatty acids that stimulate UCP and because AOX and UCP have completely different kinetic behavior regarding the redox State of ubiquinone. It is concluded that we are still very far from having a clear idea about the physiological role and interplay of energy-wasting and energy-conserving Systems.