On the other hand the dark reductio

On the other hand the dark reduction of its intermediates,
specifically of tyrosine YD, the only Photosystem II component known to compete with water oxidation, is ruled out. It appears that the cyclic
electron transfer pathway can be fully opened by reduction of the plastoquinone pool in the dark. Oxygen evolution reappears after partial
oxidation of the pool by Photosystem I, but the pool itself is not involved in cyclic electron transfer.
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