Operation of dual mechanisms that both lead to photoinactivation of Photosystem II in leaves by visible light

Riichi Oguchi, Ichiro Terashima, Jiancun Kou, Wah Soon Chow

Research output: Contribution to journalReview articlepeer-review

58 Citations (Scopus)


Photosystem II (PS II) is photoinactivated during photosynthesis, requiring repair to maintain full function during the day. What is the mechanism(s) of the initial events that lead to photoinactivation of PS II? Two hypotheses have been put forward. The 'excess-energy hypothesis' states that excess energy absorbed by chlorophyll (Chl), neither utilized in photosynthesis nor dissipated harmlessly in non-photochemical quenching, leads to PS II photoinactivation; the 'Mn hypothesis' (also termed the two-step hypothesis) states that light absorption by the Mn cluster in PS II is the primary effect that leads to dissociation of Mn, followed by damage to the reaction centre by light absorption by Chl. Observations from various studies support one or the other hypothesis, but each hypothesis alone cannot explain all the observations. We propose that both mechanisms operate in the leaf, with the relative contribution from each mechanism depending on growth conditions or plant species. Indeed, in a single system, namely, the interior of a leaf, we could observe one or the other mechanism at work, depending on the location within the tissue. There is no reason to expect the two mechanisms to be mutually exclusive.

Original languageEnglish
Pages (from-to)47-55
Number of pages9
JournalPhysiologia Plantarum
Issue number1
Publication statusPublished - 2011 May 1
Externally publishedYes

ASJC Scopus subject areas

  • Physiology
  • Genetics
  • Plant Science
  • Cell Biology


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