Original Article

Journal of Plant Research

, Volume 117, Issue 2, pp 101-107

Flavonoids in translucent bracts of the Himalayan Rheum nobile (Polygonaceae) as ultraviolet shields

  • Tsukasa IwashinaAffiliated withTsukuba Botanical Garden, National Science Museum Email author 
  • , Yuji OmoriAffiliated withYokosuka City Museum
  • , Junichi KitajimaAffiliated withLaboratory of Pharmacognosy, Showa Pharmaceutical University
  • , Shinobu AkiyamaAffiliated withDepartment of Botany, National Science Museum
  • , Toshisada SuzukiAffiliated withBioorganic Chemistry, Department of Biochemistry and Food Science, Faculty of Agriculture, Kagawa University
  • , Hideaki OhbaAffiliated withDepartment of Botany, University Museum, University of Tokyo

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Abstract

UV-absorbing substances were isolated from the translucent bracts of Rheum nobile, which grows in the alpine zone of the eastern Himalayas. Nine kinds of the UV-absorbing substances were found by high performance liquid chromatography (HPLC) and paper chromatography (PC) surveys. All of the five major compounds are flavonoids, and were identified as quercetin 3-O-glucoside, quercetin 3-O-galactoside, quercetin 3-O-rutinoside, quercetin 3-O-arabinoside and quercetin 3-O-[6″-(3-hydroxy-3-methylglutaroyl)-glucoside] by UV, 1H and 13C NMR, mass spectra, and acid hydrolysis of the original glycosides, and direct PC and HPLC comparisons with authentic specimens. The four minor compounds were characterised as quercetin itself, quercetin 7-O-glycoside, kaempferol glycoside and feruloyl ester. Of those compounds, quercetin 3-O-[6″-(3-hydroxy-3-methylglutaroyl)-glucoside] was found in nature for the first time. The translucent bracts of R. nobile accumulate a substantial quantity of flavonoids (3.3–5 mg per g dry material for the major compounds). Moreover, it was clarified by quantitative HPLC survey that much more of the UV-absorbing substances is present in the bracts than in rosulate leaves. Although the flavonoid compounds have been presumed to be the important UV shields in higher plants, there has been little characterisation of these compounds. In this paper, the UV-absorbing substances of the Himalayan R. nobile were characterised as flavonol glycosides based on quercetin.

Keywords

Flavonoids Himalayan alpine plants Quercetin 3-O-[6″-(3-hydroxy-3-methylglutaroyl)-glucoside] Rheum nobile Translucent bracts UV-absorbing substances