State transitions in Chlamydomonas reinhardtii strongly modulate the functional size of photosystem II but not of photosystem I


Ünlü C. , Drop B., Croce R., van Amerongen H.

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, vol.111, no.9, pp.3460-3465, 2014 (Journal Indexed in SCI) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 111 Issue: 9
  • Publication Date: 2014
  • Doi Number: 10.1073/pnas.1319164111
  • Title of Journal : PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
  • Page Numbers: pp.3460-3465
  • Keywords: time-resolved fluorescence spectroscopy, photoprotection, LIGHT-HARVESTING-COMPLEX, EXCITATION-ENERGY TRANSFER, RESOLVED CHLOROPHYLL FLUORESCENCE, ALGA SCENEDESMUS-OBLIQUUS, PROTEIN-PHOSPHORYLATION, THYLAKOID MEMBRANE, CHARGE SEPARATION, SUPRAMOLECULAR ORGANIZATION, ARABIDOPSIS-THALIANA, ANGSTROM RESOLUTION

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.