Too much light? How β-carotene protects the photosystem II reaction centre

Abstract

The photosystem II reaction centre of all oxygenic organisms is subject to photodamage by high light i.e. photoinhibition. In this review I discuss the reasons for the inevitable and unpreventable oxidative damage that occurs in photosystem II and the way in which beta-carotene bound to the reaction centre significantly mitigates this damage. Recent X-ray structures of the photosystem II core complex (reaction centre plus the inner antenna complexes) have revealed the binding sites of some of the carotenoids known to be bound to the complex. In the light of these X-ray structures and their known biophysical properties it is thus possible to identify the two beta-carotenes present in the photosystem II reaction centre. The two carotenes are both bound to the D2 protein and this positioning is discussed in relation to their ability to act as quenchers of singlet oxygen, generated via the triplet state of the primary electron donor. It is proposed that their location on the D2 polypeptide means there is more oxidative damage to the D1 protein and that this underlies the fact that this latter protein is continuously re-synthesised, at a far greater rate than any other protein involved in photosynthesis. The relevance of a cycle of electrons around photosystem II, via cytochrome b(559), in order to re-reduce the beta-carotenes when they are oxidised and hence restore their ability to quench singlet oxygen, is also discussed.

Increased Air Temperature during Simulated Autumn Conditions Does Not Increase Photosynthetic Carbon Gain But Affects the Dissipation of Excess Energy in Seedlings of the Evergreen Conifer Jack Pine

“…Our observation of a significant increase in b-carotene in SD/HT (Fig. 5) points toward an increased formation of singletexcited oxygen ( 1 O 2 *), which can efficiently be quenched by b-carotene (Cantrell et al, 2003;Krieger-Liszkay, 2005;Telfer, 2005). 1 O 2 * is generated from singletexcited Chl via the Chl triplet state, if the energy of excited Chl cannot be used for photochemistry or dissipated as heat (Adams et al, 2004).…”

Connecting thermal physiology and latitudinal niche partitioning in marine Synechococcus

“…A number of b-carotene molecules bound to the reaction centre II act as quenchers of singlet oxygen and under light, are regenerated through a repair cycle (Telfer 2005;Ishikita et al, 2007;Mella-Flores et al, 2012). This carotenoid is essential for the protection of reaction centres (Cazzaniga et al, 2012) and thus may be used as an indicator of oxidative stress intensity.…”

Does a terminal drought tolerance QTL contribute to differences in ROS scavenging enzymes and photosynthetic pigments in pearl millet exposed to drought?

“…Many reports emphasize the role of carotenoids (especially xanthophylls) in direct deactivation of ROS in homoiochlorophyllous plants (e.g. Demmig-Adams and Adams, 1992;MunneÂ-Bosch and Alegre, 2000;Takano et al, 2005;Telfer, 2005;Farooq et al, 2009). Xanthophylls were shown to be spatially associated with chlorophylls (Schmid, 2008) where they can account up to 50% of total carotenoids content and contribute sustaining the photochemical functions (Demmig-Adams and Adams, 1992;Farooq et al, 2009).…”