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International audience; 30 The Arabidopsis vte1 mutant is devoid of tocopherol and plastochromanol (PC-8). When exposed to 31 excess light energy, vte1 produced more singlet oxygen (1 O2) and suffered from extensive oxidative 32 damage compared to the wild type. Here we show that overexpressing the SOLANESYL DIPHOSPHATE 33 SYNTHASE 1 (SPS1) gene in vte1 induced a marked accumulation of plastoquinone (PQ-9) and rendered 34 the vte1 SPS1oex plants tolerant to photooxidative stress, indicating that PQ-9 can replace tocopherol 35 and PC-8 in photoprotection. High PQ-9 levels were associated with a noticeable decrease in 1 O2 36 production and with higher levels of PQ-C, a 1 O2-specific PQ-9 oxidation product. The extra PQ-9 37 molecules in the vte1 SPS1oex plants were stored in the plastoglobules and the chloroplast envelopes, 38 rather than in the thylakoid membranes, whereas PQ-C was found almost exclusively in the thylakoid 39 membranes. Upon exposure of wild-type plants to high light, the thylakoid PQ-9 pool decreased, while 40 the extra-thylakoid pool remained unchanged. In vte1 and vte1 SPS1oex plants, the PQ-9 losses in high 41 light were strongly amplified, affecting also the extra-thylakoid pool, and PQ-C was found in high 42 amounts in the thylakoids. We conclude that the thylakoid PQ-9 pool acts as a 1 O2 scavenger and is 43 replenished from the extra-thylakoid stock. 44 45 KEYWORDS 46 plastoquinone, antioxidant, reactive oxygen species, photoprotection, tocopherol 47 48 49