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

Abstract

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 significantly higher than in the case of the low-energy states in the antenna complexes involved in the harvesting of excitations driving PSII. Here we show that despite seemingly insufficient energy, the low-energy excited states can power PSII thanks to the activity of the thermally-driven up-conversion. We demonstrate the operation of this mechanism both in intact leaves and in isolated pigment-protein complex LHCII. A mechanism is proposed, according to which the effective 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. TOC GRAPHICS O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=134 SRC="FIGDIR/small/842591v3_ufig1.gif" ALT="Figure 1"> View larger version (53K): org.highwire.dtl.DTLVardef@12af7d4org.highwire.dtl.DTLVardef@1f4ad08org.highwire.dtl.DTLVardef@8bf274org.highwire.dtl.DTLVardef@1dab06a_HPS_FORMAT_FIGEXP M_FIG C_FIG