Biochemical and genetic controls exerted by plant mitochondria

Higher plant mitochondria contain two terminal oxidases, cytochrome c oxidase and a cyanide-resistant 'alternative' oxidase. Electron flux through these two respiratory pathways is controlled by environmental conditions, stimuli received by mitochondria. In general, stresses such as cold, wounding, pathogen attack and others favor electron flow through the alternative oxidase. One of the proposed functions of the alternative pathway is to relieve the tricarboxylic acid (TCA) cycle of inhibition from cytochrome pathway products and allow the cycle to furnish carbon skeletons for anabolic requirements. We are currently investigating, with an NADP-linked isocitrate dehydrogenase in plant mitochondria, a possible link between respiratory control and carbon flux from the TCA cycle. Regulation of the nuclear gene encoding the alternative oxidase, Aox1, is also being employed as a model for perception of the many stresses by the mitochondria and transfer of these signals to the nucleus. Our initial results indicate that hydrogen peroxide is an intermediate in this signalling process. (C) 1998 Elsevier Science B.V.