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Distributions, biosyntheses and functions of carotenoids in algae


Nippon Medical School, Department of Biology, Kosugi-cho 2, Nakahara, Kawasaki 211-0063, Japan


Phototrophic organisms including algae necessarily synthesize both chlorophylls and carotenoids for photosynthesis. Many kinds of carotenoids are found in algae, and the new taxonomic technologies have been developed for the phylogenetics of the algae. In this review, relationship of the distribution of carotenoids and the phylogeny of oxygenic phototrophs in sea and fresh water, including cyanobacteria, red algae, brown algae and green algae, is summarized. These phototrophs contain division- or class-specific carotenoids, such as fucoxanthin, peridinin and siphonaxanthin. In addition, carotenogenesis pathways are discussed based on the chemical structures of carotenoids and known characteristics of carotenogenesis enzymes in other organisms; genes and enzymes for carotenogenesis in algae are not yet known. Most carotenoids bind to membrane-bound pigment-protein complexes, such as reaction center, light-harvesting and cytochrome b6f complexes. Some functions of carotenoids in photosynthesis are briefly summarized.


Algae are classified throughout many divisions of the Kingdom Plantae. With the development of culture techniques, some single-cell species can be cultured, and their characteristics, including pigments, can be studied. With the development of taxonomic technologies, including DNA base sequences of 16S for prokaryote or 18S rRNA for eukaryote and some genes, algal phylogenetics has been developed.
In this review, algae mean oxygenic phototrophs found in both seawater and fresh water, including prokaryotic cyanobacteria. Distributions, biosyntheses and functions of carotenoids in algae are summarized. A detailed review has been recently published (1), and others are (2-4).

Nearly 800 structurally defined carotenoids are reported from nature (5). Many kinds of carotenoids are found from many algal species. Approximately 30 carotenoids may have functions in algal photosynthesis, and others may be intermediates of carotenogenesis and accumulated carotenoids. Their distribution in algae is summarized in Table 1. Some specific carotenoids are found only in some algal divisions o ...