Can charge recombination as caused by pH-dependent donor-side limitation in PS 2 account for high-energy-state quenching?

Schreiber and Neubauer (Photosynthesis Research 25: 279-293, 1990) have proposed a model which explains energy quenching by enhanced triplet formation as caused by charge recombination due to pH-dependent donor-side limitation. Quenching under these conditions is assumed to result from two mechanisms. Firstly, there is the withdrawal of excited states by charge recombination and formation of triplet states. Secondly, these triplet states can result in carotenoid triplets in the antenna which are supposed to quench excitons. Here, it is shown that quenching caused by both mechanisms can account for only about 25% of the experimentally observed energy quenching even under extremely favorable conditions. More likely, this number is less than 15%, as the contribution of the second step in the proposed triplet cycle is expected to be low as the life times of the carotenoid triplets are not long enough to cause the assumed quenching of excitons in the antenna.