PH dependence, kinetics and light-harvesting regulation of nonphotochemical quenching in Chlamydomonas

Lijin Tian*, Wojciech J. Nawrocki, Xin Liu, Iryna Polukhina, Ivo H.M. Van Stokkum, Roberta Croce

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review


Sunlight drives photosynthesis but can also cause photodamage. To protect themselves, photosynthetic organisms dissipate the excess absorbed energy as heat, in a process known as nonphotochemical quenching (NPQ). In green algae, diatoms, and mosses, NPQ depends on the light-harvesting complex stress-related (LHCSR) proteins. Here we investigated NPQ in Chlamydomonas reinhardtii using an approach that maintains the cells in a stable quenched state. We show that in the presence of LHCSR3, all of the photosystem (PS) II complexes are quenched and the LHCs are the site of quenching, which occurs at a rate of ∼150 ps −1 and is not induced by LHCII aggregation. The effective light-harvesting capacity of PSII decreases upon NPQ, and the NPQ rate is independent of the redox state of the reaction center. Finally, we could measure the pH dependence of NPQ, showing that the luminal pH is always above 5.5 in vivo and highlighting the role of LHCSR3 as an ultrasensitive pH sensor.

Original languageEnglish
Pages (from-to)8320-8325
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number17
Early online date8 Apr 2019
Publication statusPublished - 23 Apr 2019


  • Fluorescence
  • Low pH
  • Photosynthesis
  • Photosystem II
  • Ultrafast spectroscopy


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