Regulation of uncoupled respiratory electron transport in plants

[Truncated] Plant mitochondria contain a branched respiratory electron transport chain that terminates in two terminal oxidases, the cytochrome oxidase and the alternative oxidase (AOX). Electron transport through the cytochrome oxidase pathway results in the formation of a proton motive force that can be used to drive ATP synthesis. AOX, however, directly oxidises ubiquinol and thus bypasses two proton translocation sites. This pathway mediates non-coupled respiratory electron transport. Plant mitochondria also contain an uncoupling protein (UCP), which dissipates the proton motive force as it is generated, resulting in uncoupled respiratory electron transport. This project aimed to investigate the coordination of expression of the UCP and AOX proteins as well as the role of a highly conserved cysteine residue in the regulation of AOX activity.
The coordination of UCP and AOX protein expression was investigated in ripening and chilled tomato (Lycopersicon esculentum L.) fruit, two situations that have previously been shown to induce AOX expression in other species. The peak in expression of both proteins was found to occur after the respiratory climacteric in tomato. The abundance of bothproteins was also found to increase in response to chilling of mature green tomatoes. A multigene family for AOX was cloned from a tomato fruit cDNA library.