Carotenoids photoprotective role

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 ... 

In order to test this proposition and to mimic the photoprotective role of carotenoid pigments, we undertook a study of triplet energy transfer in... 

The Photoprotective Role of Carotenoids Triplet-Triplet Energy Transfer.245... 

Fig. 1 (B) illustrates the second major function of carotenoids, namely, photoprotection of chlorophyll, either by direct triplet-triplet energy transfer [labeled T-T j from Chl to the carotenoid or by indirect transfer via the formation of singlet oxygen. The reaction steps for each of the two mechanisms are shown in Fig. 1, bottom, right. Further details on both the light harvesting by carotenoids and photoprotective role of carotenoids will be described in the following 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. 

Wu Y, Piekara-Sady L and Kispert LD(1991) Photochemically generated carotenoid radicals on Nafion film and silica gel An EPR and ENDOR study. Chem Phys Lett 180 573-577 Yeates TO, Komiya H, Chirino A, Rees DC, Allen JP and Feher G (1988) Structure of the reaction center from Rhodobacter sphaeroides R-26 and 2.4.1 Protein-cofactor (bacterio-chlorophyll, bacteriopheophytin, and carotenoid) interactions. Proc Natl Acad Sci USA 85 7993-7997 Young AJ (1991) The photoprotective role of carotenoids in higher plants. Physiol Plant 83 702-708 Young AJ and Frank HA (1996) Energy transfer reactions involving carotenoids Quenchingofchlorophyll fluorescence. J Photochem Photobiol B Biol 36 3-15... 

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. 

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

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 addition to the two well-established roles, recent reports have suggested a structural role for some carotenoids in green plants. Havaux" reported that carotenoids of the xanthophyll family and some other terpenoids may stabilize and photoprotect the lipid phase of thylakoid membranes. Available evidence... 

This chapter presents a personal historical perspective of the role of carotenoids in photosynthesis. It leads the reader into the early literature on the carotenoids and photosynthesis that are related to the discoveries on the excitation energy transfer and, to a lesser extent, on photoprotection. Excitation energy transfer from the carotenoid fucoxanthin to chlorophyll (Chi) a was shown first in the diatoms by H. Dutton, W. M. Manning and... 

The hypotheses to explain how carotenoids play a role in protecting plants against damage by excess light have been discussed very extensively. Crucial work on the topic of photoprotection was done in the summer of 1954 in C. B. van Niel s Lab at the Hopkins Marine Station by Roger Stanier and his... 

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