Abstract
Chloroplasts have many defense systems against excess light. Some of these systems, including the photorespiration and the reductant export by the shuttle machineries, involve the reactions with mitochondria. For the latter, however, detailed mechanisms and the actual contribution to dissipation of the excess energy have not been clarified. The cyanide-insensitive respiratory pathway (AOX) can efficiently dissipate excess reducing equivalents independent of the ATP demand, because AOX is uncoupled from ATP synthesis. In our experiments using Vicia faba leaves, inhibition of AOX caused the decrease in the photosynthetic rate and the increase in non-photochemical quenching even at low PPFD. These results indicate that AOX would have important roles in photosynthesis of the leaves. We will discuss the functions of two respiratory pathways, the cytochrome pathway and AOX, as the excess energy sink and other functional roles in the light.
