Succinate dehydrogenase: the complex roles of a simple enzyme.

Succinate dehydrogenase (SDH) oxidises succinate to fumarate as a component of the tricarboxylic acid cycle and ubiquinone to ubiquinol in the mitochondrial electron transport chain. Studies of SDH mutants have revealed far-reaching effects of altering succinate oxidation in plant cells. The plant SDH complex composition, structure and assembly are all beginning to be understood but the implications of the divergence across eukaryotes is still unclear. We propose an integration of the reported physiological roles of SDH in plants which influence photosynthesis, the function of stomata, root elongation and fungal defence. Future SDH research needed in plants should involve tissue-specific studies of mutants, analysis of the pathways induced by succinate-dependent reactive oxygen species generation and assessment of the impact of succinate accumulation on metabolism.