Photosystem II-cyclic electron flow powers exceptional photoprotection and record growth in the microalga Chlorella ohadii

Gennady Ananyev, Colin Gates, Aaron Kaplan, G Charles Dismukes

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

The desert microalga Chlorella ohadii was reported to grow at extreme light intensities with minimal photoinhibition, tolerate frequent de/re-hydrations, yet minimally employs antenna-based non-photochemical quenching for photoprotection. Here we investigate the molecular mechanisms by measuring Photosystem II charge separation yield (chlorophyll variable fluorescence, Fv/Fm) and flash-induced O2 yield to measure the contributions from both linear (PSII-LEF) and cyclic (PSII-CEF) electron flow within PSII. Cells grow increasingly faster at higher light intensities (μE/m2/s) from low (20) to high (200) to extreme (2000) by escalating photoprotection via shifting from PSII-LEF to PSII-CEF. This shifts PSII charge separation from plastoquinone reduction (PSII-LEF) to plastoquinol oxidation (PSII-CEF), here postulated to enable proton gradient and ATP generation that powers photoprotection. Low light-grown cells have unusually small antennae (332 Chl/PSII), use mainly PSII-LEF (95%) and convert 40% of PSII charge separations into O2 (a high O2 quantum yield of 0.06 mol/mol PSII/flash). High light-grown cells have smaller antenna and lower PSII-LEF (63%). Extreme light-grown cells have only 42 Chl/PSII (no LHCII antenna), minimal PSII-LEF (10%), and grow faster than any known phototroph (doubling time 1.3 h). Adding a synthetic quinone in excess to supplement the PQ pool fully uncouples PSII-CEF from its natural regulation and produces maximum PSII-LEF. Upon dark adaptation PSII-LEF rapidly reverts to PSII-CEF, a transient protection mechanism to conserve water and minimize the cost of antenna biosynthesis. The capacity of the electron acceptor pool (plastoquinone pool), and the characteristic times for exchange of (PQH2)B with PQpool and reoxidation of (PQH2)pool were determined.

Original languageEnglish
Pages (from-to)873-883
Number of pages11
JournalBiochimica et Biophysica Acta - Bioenergetics
Volume1858
Issue number11
DOIs
Publication statusPublished - Nov 1 2017

Fingerprint

Chlorella
Photosystem II Protein Complex
Electrons
Antennas
Light
Plastoquinone
Growth
High intensity light
Dark Adaptation
Biosynthesis
Quantum yield
Chlorophyll
Hydration
Power generation
Protons
Quenching
Adenosine Triphosphate
Fluorescence
Costs and Cost Analysis
Oxidation

Keywords

  • Chlorella ohadii
  • Cyclic electron transfer
  • Oxygen evolution
  • Photosynthetic efficiency
  • VZAD model
  • Water oxidation

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

Cite this

Photosystem II-cyclic electron flow powers exceptional photoprotection and record growth in the microalga Chlorella ohadii. / Ananyev, Gennady; Gates, Colin; Kaplan, Aaron; Dismukes, G Charles.

In: Biochimica et Biophysica Acta - Bioenergetics, Vol. 1858, No. 11, 01.11.2017, p. 873-883.

Research output: Contribution to journalArticle

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