Role of aluminum-binding ligands in aluminum resistance of Eucalyptus camaldulensis and Melaleuca cajuputi |
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Authors: | Ko Tahara Mariko Norisada Takashi Yamanoshita Katsumi Kojima |
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Institution: | (1) Asian Natural Environmental Science Center, the University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan;(2) Present address: Department of Molecular and Cell Biology, Forestry and Forest Products Research Institute, 1 Matsunosato, Tsukuba Ibaraki, 305-8687, Japan |
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Abstract: | We investigated the roles of Al-binding ligands in Al exclusion from roots and in internal Al detoxification in roots as Al
resistance mechanisms in two Al-resistant Myrtaceae trees, Eucalyptus camaldulensis Dehnh. and Melaleuca cajuputi Powell. The amounts of ligands secreted from roots and contained in root tips of these species were compared with those of
an Al-sensitive species, Melaleuca bracteata F. Muell., after the roots were exposed to 0 or 1 mM AlCl3 solution. Secretion of well-known ligands (citrate, oxalate, and malate) from roots under Al treatment was low in all species.
However, in E. camaldulensis, the Al-binding capacity of root exudates under Al treatment was considerable and was higher than that in M. bracteata. Gel filtration chromatography revealed that a low-molecular-weight Al-binding ligand was secreted from roots in response
to Al only in E. camaldulensis. On the other hand, the Al-binding capacity of cell sap in root tips under Al treatment was similar for the resistant and
sensitive species. These results suggest that Al exclusion by secretion of the unknown low-molecular-weight Al-binding ligand
from roots contributes to the Al resistance of E. camaldulensis, whereas M. cajuputi has developed Al-resistance mechanisms other than secretion of ligands from roots or concentration of internal ligands in
root tips. |
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Keywords: | Aluminum-binding capacity Myrtaceae Organic acids Root exudates Root tips |
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