Light harvesting complexes are crucial for supplying the reaction centers of photosystems I and II (PS and PSII) with sufficient excitation energy to sustain photosynthesis. Available excitation energy depends, of course, on the intensity and spectral composition of the light but also on the composition and organization of the light-harvesting antenna systems. The light-harvesting capacity of a photosystem can be approximated by the product of two parameters: its absorption cross section, which becomes larger as the antenna system size increases, and the quantum efficiency of charge separation, which usually decreases as the antenna size increases.
For optimal performance in specific light conditions, photosynthetic organisms often adapt the antenna systems of PSI and/or PSII on a short (regulatory) and long (acclimatory) time scale by changing either or both of these parameters. Examples of such dynamic processes include state transitions (ST), which balance the excitation energy between PSI and PSII, and nonphotochemical quenching (NPQ), a protective mechanism that dissipates excess energy to prevent photodamage. Remarkably, the underlying mechanisms of these processes can vary significantly among species, reflecting the rich biodiversity of photosynthetic organisms. With the help of advanced spectroscopy and microscopy techniques, these processes can now be studied in vivo over a broad time scale, i.e. from (sub)picoseconds to days.
In this presentation I will show several recent results from our laboratory, some of which challenge long-standing views on different regulation mechanisms. These insights, drawn from a variety of organisms, underscore the complexity and diversity of strategies employed in light energy management in oxygenic photosynthesis.