title: Identification of a hydrolyzable tannin, oenothein B, as an aluminum-detoxifying ligand in a highly aluminum-resistant tree, Eucalyptus camaldulensis.
abstract: Eucalyptus camaldulensis is a tree species in the Myrtaceae that exhibits extremely high resistance to aluminum (Al). To explore a novel mechanism of Al resistance in plants, we examined the Al-binding ligands in roots and their role in Al resistance of E. camaldulensis. We identified a novel type of Al-binding ligand, oenothein B, which is a dimeric hydrolyzable tannin with many adjacent phenolic hydroxyl groups. Oenothein B was isolated from root extracts of E. camaldulensis by reverse-phase high-performance liquid chromatography and identified by nuclear magnetic resonance and mass spectrometry analyses. Oenothein B formed water-soluble or -insoluble complexes with Al depending on the ratio of oenothein B to Al and could bind at least four Al ions per molecule. In a bioassay using Arabidopsis (Arabidopsis thaliana), Al-induced inhibition of root elongation was completely alleviated by treatment with exogenous oenothein B, which indicated the capability of oenothein B to detoxify Al. In roots of E. camaldulensis, Al exposure enhanced the accumulation of oenothein B, especially in EDTA-extractable forms, which likely formed complexes with Al. Oenothein B was localized mostly in the root symplast, in which a considerable amount of Al accumulated. In contrast, oenothein B was not detected in three Al-sensitive species, comprising the Myrtaceae tree Melaleuca bracteata, Populus nigra, and Arabidopsis. Oenothein B content in roots of five tree species was correlated with their Al resistance. Taken together, these results suggest that internal detoxification of Al by the formation of complexes with oenothein B in roots likely contributes to the high Al resistance of E. camaldulensis.
authors.affiliation: Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305-8687, Japan.
authors.forename: Ko
authors.initials: K
authors.lastname: Tahara
authors.forename: Koh
authors.initials: K
authors.lastname: Hashida
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Otsuka
authors.forename: Seiji
authors.initials: S
authors.lastname: Ohara
authors.forename: Katsumi
authors.initials: K
authors.lastname: Kojima
authors.forename: Kenji
authors.initials: K
authors.lastname: Shinohara
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects*; D000535:Aluminum / Q000633:toxicity*; D001692:Biological Transport / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D005052:Eucalyptus / Q000187:drug effects / Q000502:physiology*; D047348:Hydrolyzable Tannins / Q000737:chemistry / Q000378:metabolism*; D008658:Inactivation, Metabolic; D008024:Ligands; D018519:Meristem / Q000187:drug effects / Q000378:metabolism; D010936:Plant Extracts / Q000378:metabolism; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D015203:Reproducibility of Results; D014197:Trees / Q000187:drug effects / Q000502:physiology*
chemical_list: D047348:Hydrolyzable Tannins; D008024:Ligands; D010936:Plant Extracts; C080077:oenothein B; D000535:Aluminum