Aluminum-detoxifying compounds in roots of Eucalyptus camaldulensis
We analyzed the aluminum (Al)-binding compounds in root tips of Eucalyptus camaldulensis Dehnh. to examine the high Al resistance of this species. Soluble compounds were extracted from root cells after roots of seedlings were treated with a calcium solution (pH 4.0) containing 0 or 1 mM AlCl3 for 24 h. Al-binding compounds were separated from the root extract by gel filtration or high-performance liquid chromatography (HPLC). The Al-binding compound separated by gel filtration remained soluble when it formed a complex with Al. Its content in the roots increased significantly after the Al treatment, which can be explained, at least partly, by an increase of citrate. The Al-binding compound separated by HPLC became insoluble when it formed a complex with Al, suggesting that this compound is not citrate, oxalate, or malate. These Al-binding compounds might play an important role in the high Al resistance of E. camaldulensis through internal Al detoxification.