Inactivation of photosynthetic oxygen evolution by UV-B irradiation: A thermoluminescence study

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Abstract

The influence of UV-B irradiation on photosynthetic oxygen evolution by isolated spinach thylakoids has been investigated using thermoluminescence measurements. The thermoluminescence bands arising from the S2QB- (B band) and S2QA- (Q band) charge recombination disappeared with increasing UV-B irradiation time. In contrast, the C band at 50°C, arising from the recombination of QA- with an accessory donor of Photosystem II, was transiently enhanced by the UV-B irradiation. The efficiency of DCMU to block QA to QB electron transfer decreased after irradiation as detected by the incomplete suppression of the B band by DCMU. The flash-induced oscillatory pattern of the B band was modified in the UV-B irradiated samples, indicating a decrease in the number of centers with reduced QB. Based on the results of this study, UV-B irradiation is suggested to damage both the donor and acceptor sides of Photosystem II. The damage of the water-oxidizing complex does not affect a specific S-state transition. Instead, charge stabilization is enhanced on an accessory donor. The acceptor-side modifications decrease the affinity of DCMU binding. This effect is assumed to reflect a structural change in the QB/DCMU binding site. The preferential loss of dark stable QB- may be related to the same structural change or could be caused by the specific destruction of reduced quinones by the UV-B light.

Original languageEnglish
Pages (from-to)455-462
Number of pages8
JournalPhotosynthesis research
Volume38
Issue number3
DOIs
Publication statusPublished - Jan 1 1993

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Keywords

  • Photosystem II
  • UV-B radiation
  • oxygen evolution
  • photodamage
  • thermoluminescence

ASJC Scopus subject areas

  • Biochemistry
  • Plant Science
  • Cell Biology

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