Abstract
RNA silencing shares common features among different eukaryotes. However little is known about the metabolic consequences of this mechanism relate to the (plant) cell homeostasis. Here, we probe the chlroroplast bioenergetics in transgenic plants undergoing silencing. An increased capacity for non-photochemical energy quenching followed by a limiting photosystem II functionality characterize the photosynthesis of silenced cells compared to non-silenced ones. These alterations are accompanied by a significant up-regulation of photosystem I, providing evidence for active cyclic electron flow in silencing conditions. The biological significance of our results is discussed related to possible energetic inter-communication between photosynthesis and RNA silencing.