Photoprotective carotenoids

Thus, chlorophyll-based triad species can also successfully mimic the multistep strategy of natural photosynthesis to yield long-lived, energetic charge-separated states. Triad 13 and related molecules also mimic carotenoid photoprotection from singlet oxygen and carotenoid antenna function. These aspects of the molecules will be discussed in later sections. 

While the role of carotenoid photoprotection seems well justified in copepods, it is more obscure in the cladocera [16,41]. Sub-Arctic alpine copepods (Hetero-cope) were found to have ten times more carotenoids than sympatric populations of cladocerans, and even low-land transparent copepods have higher carotenoid levels than highly light-exposed Daphnia [41]. Carotenoids are also widespread in fish, notably anadromous salmonids, yet the role of carotenoids in photoprotection in these species is not settled. 

N.G. Hairston Jr. (1979). The effect of temperature on carotenoid photoprotection in the copepod Diaptomus nevadensis. Comp. Biochem. Physiol. A, 62,445-448. 

The first demonstration that /3-carotene could inhibit photosensitized oxidation and was, therefore, an efficient quencher of O was reported by Foote and Denny (1968). Wilkinson and Ho (1978) showed that quenching by electron exchange energy transfer to produce the carotenoid triplet state ( CAR) is the principal mechanism of carotenoid photoprotection against O ... 

Gust D, Moore TA, Moore AL, Kuciauskas D, Liddell PA and Halbert BD (1997b) Mimicry of carotenoid photoprotection in artificial photosynthetic reaction centers Triplet-triplet energy transfer by a relay mechanism. J. Photochem Photobiol 43 209-216... 

BARTLEY G E and SCOLNIK P A (1995) Plant carotenoids pigments for photoprotection, visual attraction, and hmnan health . Plant Cell, 7, 1027-38. 

The photoprotective role of carotenoids is demonstrated in plant mutants that cannot synthesize essential leaf carotenoids. These mutants are lethal in nature since without carotenoids, chlorophylls degrade, their leaves are white in color, and photosynthesis cannot occur. Generally, the carotenoids are effective for visible light but have no effects in ultraviolet, gamma, or x-radiation. The reactions are listed as follows ... 

The comparison of the light effect on carotenoids in foods is very difficult to carry out because different foods with different isomer compositions are employed at the beginnings of experiments. The presence of large molecules offers some photoprotection to carotenoids in food systems, either by complexation with proteins as found in carrots or acting as a filter to reduce the light incidence. Different storage conditions are often found because different light intensities are used or sometimes they are not even reported and experiments are carried out under air, N2, or in a vacuum. 

Natural pigment production for food coloration includes the entire spectrum of biotechnologies. For example, biological production of carotenoid pigments has medical implications because carotenoids are nutritive (pro-vitamin A), antioxidant, and photoprotective. Carotenoids are produced alternately in agricultural systems (plants), industrial bioreactors (bacterial and fungi), and marine systems (cyanobacteria and algae). 

Niyogi, K.K., Safety valves for photosynthesis, Curr. Opin. Plant Biol. 3, 455, 2000. Pogson, B.J. and Rissler, H.M., Genetic manipulation of carotenoid biosynthesis and photoprotection, Philos. Trans. R. Soc. Lond B 355, 1395, 2000. 

Despite their absence in phycobilisomes, carotenoids, especially the so-called secondary carotenoids such as echinenone, were presumed to play a role in cyanobacterial photoprotection. Indeed, classic biochemical approaches have led to several reports of cyanobacterial carotenoid-proteins and evidence for their photoprotective function (Kerfeld et al. 2003, Kerfeld 2004b). One of these, the water soluble orange carotenoid protein (OCP), has been structurally characterized and has recently emerged as a key player in cyanobacterial photoprotection. 

Bailey, S., N. Mann, C. Robinson, and D. J. Scanlan (2005). The occurrence of rapidly reversible non-photochemical quenching of chlorophyll a fluorescence in cyanobacteria. FEBS Lett 579(1) 275-280. Boulay, C., L. Abasova, C. Six, I. Vass, and D. Kirilovsky (2008a). Occurrence and function of the orange carotenoid protein in photoprotective mechanisms in various cyanobacteria. Biochim Biophys Acta 1777(10) 1344-1354. 

Demmig-Adams, B. (1990). Carotenoids and photoprotection in plants A role for the xanthophyll zeaxanthin. Biochim Biophys Acta 1020 1-24. 

Kirilovsky, D. (2007). Photoprotection in cyanobacteria The orange carotenoid protein (OCP)-related non-photochemical-quenching mechanism. Photosynth Res 93 7-16. 

Kodis, G., C. Herrero, R. Palacios, E. Marino-Ochoa, S. Gould, L. de la Garza, R. van Grondelle, D. Gust, T. A. Moore, A. L. Moore, and J. T. M. Kennis. 2004. Light harvesting and photoprotective functions of carotenoids in compact artificial photosynthetic antenna designs. J. Phys. Chem. B 108 414-425. 

Afzal, A. and M. Afzal (2008). Photoprotective carotenoids lutein and zeaxanthin Their role in AMD. Curr. Nutr. Food Sci. 4(2) 127-134. 

In summary, the amazing breadth and depth of research in carotenoids are reasons why it draws investigators are drawn to this fascinating field of research. The research spans the continuum, from detailed studies of the roles of photoprotective carotenoids in plants to the potential application in the prevention of disease in humans. This is translational research at its best and I commend the editor, Dr. John Landrum, for assembling such an interesting and informative collection of current research. 

In the case of the carotenoid-containing LH2 complex, the triplet states of BChl a and carotenoid (spheroidene) were generated immediately after excitation, but the triplet-state BChl a was quenched efficiently by the carotenoid so that no BChl a cation-radical was generated. Thus, the photoprotective function of the carotenoid in this antenna complex has been proven. 

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