The Arabidopsis vte1 mutant is devoid of tocopherol and plastochromanol (PC-8). When exposed to excess light energy, vte1 produced more singlet oxygen (1 O2 ) and suffered from extensive oxidative damage compared with the wild type. Here, we show that overexpressing the solanesyl diphosphate synthase 1 (SPS1) gene in vte1 induced a marked accumulation of total plastoquinone (PQ-9) and rendered the vte1 SPS1oex plants tolerant to photooxidative stress, indicating that PQ-9 can replace tocopherol and PC-8 in photoprotection. High total PQ-9 levels were associated with a noticeable decrease in 1 O2 production and higher levels of Hydroxyplastoquinone (PQ-C), a 1 O2 -specific PQ-9 oxidation product. The extra PQ-9 molecules in the vte1 SPS1oex plants were stored in the plastoglobules and the chloroplast envelopes, rather than in the thylakoid membranes, whereas PQ-C was found almost exclusively in the thylakoid membranes. Upon exposure of wild-type plants to high light, the thylakoid PQ-9 pool decreased, whereas the extrathylakoid pool remained unchanged. In vte1 and vte1 SPS1oex plants, the PQ-9 losses in high light were strongly amplified, affecting also the extrathylakoid pool, and PQ-C was found in high amounts in the thylakoids. We conclude that the thylakoid PQ-9 pool acts as a 1 O2 scavenger and is replenished from the extrathylakoid stock.

CEA Cadarache CNRS UMR 7265 Biologie Végétale et Microbiologie Environnementales Aix Marseille Université Laboratoire d'Ecophysiologie Moléculaire des Plantes 13108 Saint Paul lez Durance France

CEA Cadarache CNRS UMR 7265 Biologie Végétale et Microbiologie Environnementales Aix Marseille Université Laboratoire de Bioénergétique et Biotechnologie des Bactéries et Microalgues 13108 Saint Paul lez Durance France

Department of Biophysics Centre of the Region Haná for Biotechnological and Agricultural Research Faculty of Science Palacký University Šlechtitelů 27 783 71 Olomouc Czech Republic

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