Glycolate Induces Redox Tuning Of Photosystem II in Vivo: Study of a Photorespiration Mutant

Plant Physiol. 2018 Jul;177(3):1277-1285. doi: 10.1104/pp.18.00341. Epub 2018 May 23.


Bicarbonate removal from the nonheme iron at the acceptor side of photosystem II (PSII) was shown recently to shift the midpoint potential of the primary quinone acceptor QA to a more positive potential and lowers the yield of singlet oxygen (1O2) production. The presence of QA- results in weaker binding of bicarbonate, suggesting a redox-based regulatory and protective mechanism where loss of bicarbonate or exchange of bicarbonate by other small carboxylic acids may protect PSII against 1O2 in vivo under photorespiratory conditions. Here, we compared the properties of QA in the Arabidopsis (Arabidopsis thaliana) photorespiration mutant deficient in peroxisomal HYDROXYPYRUVATE REDUCTASE1 (hpr1-1), which accumulates glycolate in leaves, with the wild type. Photosynthetic electron transport was affected in the mutant, and chlorophyll fluorescence showed slower electron transport between QA and QB in the mutant. Glycolate induced an increase in the temperature maximum of thermoluminescence emission, indicating a shift of the midpoint potential of QA to a more positive value. The yield of 1O2 production was lowered in thylakoid membranes isolated from hpr1-1 compared with the wild type, consistent with a higher potential of QA/QA- In addition, electron donation to photosystem I was affected in hpr1-1 at higher light intensities, consistent with diminished electron transfer out of PSII. This study indicates that replacement of bicarbonate at the nonheme iron by a small carboxylate anion occurs in plants in vivo. These findings suggested that replacement of the bicarbonate on the nonheme iron by glycolate may represent a regulatory mechanism that protects PSII against photooxidative stress under low-CO2 conditions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / genetics*
  • Arabidopsis Proteins / metabolism
  • Bicarbonates / metabolism
  • Electron Transport
  • Fluorescence
  • Glycolates / metabolism*
  • Glycolates / pharmacology
  • Luminescent Measurements
  • Mutation
  • Photosystem II Protein Complex / genetics
  • Photosystem II Protein Complex / metabolism*
  • Plant Leaves / genetics
  • Plant Leaves / metabolism
  • Singlet Oxygen / metabolism
  • Spinacia oleracea / drug effects
  • Spinacia oleracea / metabolism
  • Thylakoids / drug effects
  • Thylakoids / metabolism


  • Arabidopsis Proteins
  • Bicarbonates
  • Glycolates
  • NPR1 protein, Arabidopsis
  • Photosystem II Protein Complex
  • Singlet Oxygen