Recycling of energy dissipated as heat accounts for high activity of Photosystem II

Photosystem II (PSII) converts light into chemical energy powering almost entire life on Earth. The primary photovoltaic reaction in the PSII reaction centre requires energy corresponding to 680 nm that is higher than in the case of low-energy states in complexes involved in the harvesting of excitations driving PSII. This promotes the process of out of the center energy migration and thermal dissipation, reducing photosynthesis efficiency. Here we show that part of energy dissipated as heat is used to drive PSII thanks to the thermally-driven up-conversion. We demonstrate the operation of this mechanism both in isolated antenna complex LHCII and in leaves. A mechanism is proposed, according to which the utilization of thermal energy in the photosynthetic apparatus is possible owing to the formation of LHCII supramolecular structures, leading to the coupled energy levels, corresponding to approx. 680 nm and 700 nm, capable of exchanging excitation energy through the spontaneous relaxation and the thermal up-conversion.