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

Division of Molecular Biosciences, Imperial College London, South Kensington Campus, London, UK SW7 2AZ.
Photochemical and Photobiological Sciences (Impact Factor: 2.94). 01/2006; 4(12):950-6. DOI: 10.1039/b507888c
Source: PubMed

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.

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    • "The observation may be explained as the conformation changes of β-carotene (II) pool, which tends to more perpendicular orientation respective to the membrane plane. Multiple photoprotective hypotheses have been established including Mn-mediated UV photoinactivation (Hakala et al., 2005; Ohnishi et al., 2005; Wei et al., 2011; Hou et al., 2013), cytochrome b-559 cyclic electron flow or cytochrome b-559 reversible interconvertion between the two redox forms (Thompson and Brudvig, 1988; Barber and De Las Rivas, 1993; Shinopoulos and Brudvig, 2012), and a β-carotene photooxidation (Telfer et al., 2003; Alric, 2005; Shinopoulos et al., 2014). The unidirectional photodamage of pheophytin in photosynthesis is discovered. "
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    • "The levels of chlorophyll and carotenoids are directly involved in the photosynthetic apparatus activity and can induce modifications in values of chlorophyll fluorescence parameters (Havaux et al. 2000). Carotenoids participate in the photoprotection of the photosynthetic apparatus by neutralizing triplet chlorophyll and reactive oxygen species (Telfer 2005). Another example of biochemically active substances is plant phenolics, which are effective photoprotectors and scavengers of reactive oxygen species that may not directly increase the activity of the photosynthetic apparatus and photosynthetic carbon metabolism (Blokhina et al. 2003). "
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    • "PS II plays an important role in response to the environmental conditions such as excess light, which is known as photoinhibition and is observed either under high intensity light conditions when the repair mechanisms have reached maximum capacity or at lower light intensities when an additional external factor inhibits the repair of PS II (Kok et al., 1966; Powles, 1984). The molecular mechanisms of photoinhibition were extensively investigated with great progress made during last decades (Ohad et al., 1990; Aro et al., 1993; Chow, 1994; Stewart and Brudvig, 1998; Niyogi, 1999; Tracewell et al., 2001; Adir et al., 2003; Allakhverdiev and Murata, 2004; Frank and Brudvig, 2004; Carpentier, 2005; Nishiyama et al., 2005; Szabó et al., 2005; Telfer, 2005; Nishiyama et al., 2006; Zsiros et al., 2006; Murata et al., 2007; Tyystjarvi, 2008; Kramer, 2010; Sarvikas et al., 2010a; Sarvikas et al., 2010b). Light-induced damage is targeted mainly to PS II (Powles, 1984; Barber and Andersson, 1992). "
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