|
Phlorotannins are a type of tannins found in brown algae such as kelps and rockweeds or sargassacean species, and in a lower amount also in some red algae.〔http://eurekamag.com/research/011/190/presence-lectins-tannins-protease-inhibitors-venezuelan-marine-algae.php〕 Contrary to hydrolysable or condensed tannins, these compounds are oligomers of phloroglucinol (polyphloroglucinols). As they are called tannins, they have the ability to precipitate proteins. It has been noticed that some phlorotannins have the ability to oxidize and form covalent bonds with some proteins. In contrast, under similar experimental conditions three types of terrestrial tannins (procyanidins, profisetinidins, and gallotannins) apparently did not form covalent complexes with proteins. These phenolic compounds are integral structural components of cell walls in brown algae, but they also seem to play many other secondary ecological roles such as protection from UV radiation and defense against grazing. == Biosynthesis and localization of phlorotannins == Most of the phlorotannins' biosynthesis is still unknown, but it appears they are formed from phloroglucinols via the acetate-malonate pathway.〔Riitta Koivikko, 2008, (Brown algal phlorotannins: Improving and applying chemical methods ), Ph. D. Thesis, University of Turku, Turku, Finland.〕 They are found within the cell in small vesicles called physodes, where the soluble, polar fraction is sequestrated,〔Mark A. Ragan and K.-W. Glombitza, 1986. Phlorotannins, brown algal polyphenols. ''Prog. Phycol. Res.'' 4: 129–241.〕 and as part of the cell wall, where they are insoluble and act as a structural component.〔Schoenwaelder, M. E. A. 2002. The occurrence and cellular significance of physodes in brown algae. ''Phycologia'' 41:125–139.〕〔Schoenwaelder, M. E. A. and Clayton, M. N. 1998. Secretion of phenolic substances into the zygote wall and cell plate in embryos of ''Hormosira'' and ''Acrocarpis'' (Fucales, Phaeophyceae). ''Journal of Phycology'' 34: 969–980.〕 Their concentration is known to be highly variable among different taxa as well as among geographical area, since they respond plastically to a variety of environmental factors.〔V. Jormalainen, T. Honkanen, R. Koivikko and J. Eränen. 2003. (Induction of phlorotannin production in a brown alga: defense or resource dynamics? ). ''Oikos'' 103: 640–650.〕 Brown algaes also exsude phlorotannins in surrounding seawater.〔〔J.S. Jennings & P.D. Steinberg. 1994. ''In situ'' exudation of phlorotannins by the sublittoral kelp ''Ecklonia radiata''. ''Mar. Biol.'' 121: 349–354.〕 It has been proposed that phlorotannins are first sequestered in physodes under their polar, reactive form before being oxidized and complexed to the alginic acid of brown algla cell wall by a peroxidase.〔T. M. Arnold & N. M. Targett. 2003. To grow and defend: lack of tradeoffs for brown algal phlorotannins. ''Oikos'' 100(2): 406-408.〕 To this date (2012), not much is known about phlorotannins synthesis.〔 The formation of physodes, vesicles containing phenolic compounds, have been insvestigated for many years. These cytoplasmic constituents were thought to be synthesized in the chloroplast or its membrane, but more recent studies suggest that the formation may be related to the endoplasmic reticulum and Golgi bodies.〔M.E.A. Schoenwaelder & M.N. Clayton. 2000. Physode formation in embryos of ''Phyllospora comosa'' and ''Hormosira banksii'' (Phaeophyceae). ''Phycologia'' 39: 1-9.〕 The allocation of phlorotannins among tissues varies along with the species.〔Phlorotannin allocation among tissues of northeastern Pacific kelps and rockweeds. Kathryn L. Van Alstyne, James J. McCarthy III, Cynthia L. Hustead and Laura J. Kearns, Journal of Phycology, June 1999, Volume 35, Issue 3, pages 483–492, 〕 The localization of phlorotannins can be investigated by light microscopy after vanillin–HCl staining giving an orange color.〔Cytological studies on physodes in the vegetative cells of Cystoseira stricter Sauvagea (Phaeophyta, Fucales). Pellegrini L, J. Cell Sci., 1980, volume 41, pages 209–231〕 The ultrastructural localization of physodes can be examined through transmission electron microscopy in samples primarily fixed in 2.5% glutaraldehyde and with postfixation with 1% osmium tetroxide. For staining, uranyl acetate and lead citrate can be used. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Phlorotannin」の詳細全文を読む スポンサード リンク
|