| We aim to characterise the mechanism underlying adaptation of photosynthetic membranes of oxygenic photosynthetic organisms to light conditions and want to realize two major breakthroughs: i) obtain a full functional and structural description of these complex membranes and of their dynamics upon adaptations at high spectral, spatial and time resolution and ii) accomplish an integrated physico-chemical model of their function: from isolated photosynthetic complexes to the entire thylakoid membrane. Higher plants and algae need a permanent adaptation of their photosynthetic apparatus to the changing light conditions of their environment. When they are exposed to bright sunlight, a process called ?non photochemical quenching? or NPQ induces the appearance, in the photosynthetic membrane, of energy traps to protect the plants against damaging photooxidising effects, specifically Photosystem II (PSII). Plants are also able to balance the excitation energy between their photosystems, to maintain the proper functioning of the electron carrier chains involved in photosynthesis. To be efficient, these regulations must occur in the first seconds/minutes upon the change in light, and therefore they depend on fast and efficient dynamical reorganisations of the thylakoid membrane which are just beginning to be understood. Thus, the photosynthetic membrane is an ideal object for understanding the relationship between membrane architecture and regulation, in vivo. The elucidation of these molecular mechanism(s) is essential for the understanding of the efficiency of photosynthesis in oxygenic organisms in general as well as for abiotic stress tolerance (drought and cold stress occur in particular through imbalance in the photosynthetic activity), which is in turn relevant for strategies to optimize agriculture and biofuels production. In light-limiting conditions, PSII collects light very efficiently, and the peripheral antenna complex LHCII (containing several hundreds of chlorophyll and carotenoid molecules) plays an essential role. In excess light, or in other conditions that induce imbalance in photosynthetic activity, reorganizations of the photosynthetic membranes are induced, which switches the membranes to a state where energy is redirected to PSI or where excess excitation energy transfer is switched off by harmless conversion into heat. Here we propose to quantitatively establish the mechanisms which operate in whole leaves, and find their loci. To do so we have identified 3 interrelated projects which allow a full modeling of the excitation energy transfer and quenching, from single molecule to the whole thylakoid membrane. In project 1 we wish to further investigate the switching of LHCII (and other LHCs) by single molecule fluorescence microscopy and aim to find the precise requirements that drive LHCII from a quenching to a non-quenching state and vice versa. In project 2 we wish to functionally image the plant photosynthetic membrane using new microscopic techniques, such as Multi-Pulse Microscopy (MPM) and Stimulated Emission Depletion (STED), to find energy transfer and quenching pathways in relation to the organization and quenching states of the thylakoid membranes. In project 3 we wish to build up a model for energy transfer, charge separation and switching to quenched states in thylakoid membranes, on the one hand based on our functional characterization of the photosynthetic membranes, on the other hand based on our studies of the individual photosynthetic complexes. |
