title: State transitions in Chlamydomonas reinhardtii strongly modulate the functional size of photosystem II but not of photosystem I.
abstract: Plants and green algae optimize photosynthesis in changing light conditions by balancing the amount of light absorbed by photosystems I and II. These photosystems work in series to extract electrons from water and reduce NADP(+) to NADPH. Light-harvesting complexes (LHCs) are held responsible for maintaining the balance by moving from one photosystem to the other in a process called state transitions. In the green alga Chlamydomonas reinhardtii, a photosynthetic model organism, state transitions are thought to involve 80% of the LHCs. Here, we demonstrate with picosecond-fluorescence spectroscopy on C. reinhardtii cells that, although LHCs indeed detach from photosystem II in state 2 conditions, only a fraction attaches to photosystem I. The detached antenna complexes become protected against photodamage via shortening of the excited-state lifetime. It is discussed how the transition from state 1 to state 2 can protect C. reinhardtii in high-light conditions and how this differs from the situation in plants.
authors.affiliation: Laboratory of Biophysics and MicroSpectroscopy Centre, Wageningen University, 6703 HA, Wageningen, The Netherlands.
authors.forename: Caner
authors.initials: C
authors.lastname: Ünlü
authors.forename: Bartlomiej
authors.initials: B
authors.lastname: Drop
authors.forename: Roberta
authors.initials: R
authors.lastname: Croce
authors.forename: Herbert
authors.initials: H
authors.lastname: van Amerongen
mesh_terms: D016825:Chlamydomonas reinhardtii / Q000502:physiology*; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology*; D045331:Photosystem I Protein Complex / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
chemical_list: D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex
keywords: photoprotection; time-resolved fluorescence spectroscopy