Zeaxanthin-dependent nonphotochemical quenching does not occur in photosystem I in the higher plant Arabidopsis thaliana

Significance Carotenoids play essential roles in protecting plants from photodamage. In particular, zeaxanthin is synthesized in high light, and it is important for the fast response of plants to high-light stress. The role of zeaxanthin in photosystem II fluorescence quenching has been extensively studied, but a recent report has shown that it can also be involved in photosystem I (PSI) quenching. However, these results have been obtained using a mutant of the higher plant Arabidopsis thaliana , which contains zeaxanthin constitutively. Here, we have tested this suggestion in biologically relevant conditions. We show that zeaxanthin does not lead to PSI quenching, but it is probably involved in PSI protection indirectly. Our findings highlight the fact that two photosystems possess fundamentally different photoprotective mechanisms.