Chlororespiration

Abstract

Chlororespiration is the term used to describe the activity of a potential respiratory electron transfer chain in the chloroplast. Such a concept was initially proposed, following studies on green algae, to explain effects on the redox state of the plastoquinone pool in the absence of photosynthetic electron transfer [1]. In the original model of Bennoun [1], the plastoquinone pool was suggested to be reduced through the activity of a NAD(P)H dehydrogenase and to be oxidised by oxygen via an oxidase. The subsequent realisation that mitochondrial respiration affects redox events within the thylakoid membrane has complicated the analysis of chlororespiration in vivo and indeed has led to doubts about its existence. However, more recent biochemical and genetic evidence indicates that higher plant chloroplasts do indeed contain possible chlororespiratory complexes including homologues of the mitochondrial alternative oxidase and complex I. This lecture will review our knowledge of these respiratory complexes, and assess their importance for chlororespiration and chloroplast metabolism in general.