The role of plastoquinone and beta-carotene in the primary reaction of plant photosystem II

Biochim Biophys Acta. 1977 Mar 11;459(3):402-11. doi: 10.1016/0005-2728(77)90041-x.


Extraction of Triton Photosystem II chloroplast fragments with 0.2% methanol in hexane for 3 h results in the removal of 90 to 95% of the plastoquinone in the original preparation. The extracted fragments (chlorophyll:plastoquinone ratio, 900: 1) showed no P-680 photooxidation at 15 K after a single laser flash. The extracted fragments also showed no light-induced C-550 absorbance change at 77 K. Reconstitution of the primary reaction of Photosystem II, as evidenced by restoration of low-temperature photooxidation of P-680, could be obtained by the addition of plastoquinone A but not by the addition of beta-carotene. The addition of beta-carotene plus plastoquinone A restored the C-550 absorbance change. These results indicate that plastoquinone functions as the primary electron acceptor of Photosystem II and that beta-carotene does not play a direct role in the primary photochemistry but is required for the C-550 absorbance change.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Carotenoids / metabolism*
  • Chloroplasts / metabolism*
  • Cytochromes / metabolism
  • Lasers
  • Light
  • Oxidation-Reduction
  • Photochemistry
  • Photophosphorylation*
  • Plants
  • Plastoquinone / metabolism*
  • Polyethylene Glycols
  • Quinones / metabolism*


  • Cytochromes
  • Quinones
  • Carotenoids
  • Polyethylene Glycols
  • Plastoquinone