Triplet Photoprotection by Carotenoid in Intact Photosystem II Cores

Two ²-carotenes are located in the D1–D2 reaction center (RC) of photosystem II (PSII) in the X-ray structure (Loll et al. 2005). Despite the presence of these ²-carotenes and a high yield of reaction center (RC) triplet chlorophyll (Chl) production, no Chl triplet quenching by ²- carotene has been observed so far in the RC of PS II (see Telfer 2005 for a review). We have used nanosecond transient absorption spectroscopy to study the triplet kinetics and photoprotection in intact PS II cores with closed RC from T. elongatus. We report efficient photoprotection by 3Chl-to-Car quenching. We assign the 3Car to the D2 carotene, proposing a photoprotective role to the otherwise inactive branch of the RC