Journal Article

The Involvement of Dual Mechanisms of Photoinactivation of Photosystem II in <i>Capsicum annuum</i> L. Plants

Riichi Oguchi, Ichiro Terashima and Wah Soon Chow

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 50, issue 10, pages 1815-1825
Published in print October 2009 | ISSN: 0032-0781
Published online October 2009 | e-ISSN: 1471-9053 | DOI:
The Involvement of Dual Mechanisms of Photoinactivation of Photosystem II in Capsicum annuum L. Plants

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry


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For plants, light is an indispensable resource. However, it also causes a loss of photosynthetic activity associated with photoinactivation of photosystem II (PSII). In studies of the mechanism of this photoinactivation, there are two conflicting hypotheses at present. One is that excess energy received by leaves, being neither utilized by photosynthesis nor dissipated safely in non-photochemical quenching, causes the photoinactivation. The other involves a two-step mechanism in which excitation of Mn by photons is the primary cause. In the former hypothesis, photoinactivation of PSII should not occur in low light that provides little excess energy, but in the latter hypothesis it should. Therefore, we tested these two hypotheses in different irradiances. We used a system that can measure the fraction of functional PSII complexes under natural conditions and over a long period in intact leaves, which were attached to a plant treated with lincomycin taken up via the roots. The leaves were photoinactivated in low, medium or high light (30, 60 or 950 μmol m−2 s−1) with white, blue, green or red light-emitting diode arrays. Our results showed that the extent of photoinactivation per photon exposure was higher in high light than in low light, consistent with the abundance of excess energy. However, photoinactivation did occur in low light with little excess energy, and blue light caused the greatest extent of photoinactivation followed by white, green and red light in this order, an order that can be predicted from the Mn absorbance spectrum. These results suggest that both mechanisms occur in the photoinactivation process.

Keywords: adaxial and abaxial side of leaves; chlorophyll fluorescence; excess energy hypothesis; intact leaves; photoinhibition; two-step hypothesis

Journal Article.  6197 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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