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Mechanism of copper‐enhanced photoinhibition in thylakoid membranes

2001; Wiley; Volume: 113; Issue: 1 Linguagem: Inglês

10.1034/j.1399-3054.2001.1130119.x

1399-3054

Eija Pätsikkä, Eva‐Mari Aro, Esa Tyystjärvi,

Antioxidant Activity and Oxidative Stress

The effect of copper on photoinhibition of photosystem II (PSII) in vitro was studied in bean ( Phaseolus vulgaris L. cv. Dufrix) and pumpkin ( Cucurbita pepo L.) thylakoids. The thylakoids were illuminated at 200–2 000 μmol photons m −2 s −1 in the presence of 70–1 830 added Cu 2+ ions per PSII. Three lines of evidence show that the irreversible damage of PSII caused by illumination of thylakoids in the presence of Cu 2+ was mainly due to donor‐side photoinhibition resulting from inhibition of the PSII donor side by Cu 2+ . First, addition of an artificial electron donor partially restored PSII activity of thylakoids that had been illuminated in the presence of Cu 2+ . Second, already moderate light was enough to cause rapid inhibition of PSII, and the inhibition could be saturated by light. Third, the extrinsic polypeptides of the oxygen‐evolving complex were found to become oxidized by the combined effect of Cu 2+ and light. The presence of oxygen was not necessary for the copper‐induced enhancement of photoinhibition of PSII. When the illumination was prolonged, copper caused a gradual collapse of the thylakoid structure by increasing degradation of thylakoid proteins.