JXB Advance Access originally published online on November 28, 2003
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Journal of Experimental Botany, Vol. 55, No. 394, pp. 131-136, January 1, 2004
© 2004 Oxford University Press
Plants and the Environment |
Form of Al changes with Al concentration in leaves of buckwheat
Received 30 August 2003; Accepted 3 October 2003
1 Faculty of Agriculture, Kagawa University, Ikenobe 2393, Miki-cho, Kita-gun, Kagawa 761-0795, Japan
2 State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China
3 Suntory Institute for Bioorganic Research, Wakayamadai 1-1-1, Shimamoto-cho, Mishima-gun, Osaka 618-8503, Japan
* To whom correspondence should be addressed. Fax: +81 87 891 3137. E-mail: maj{at}ag.kagawa-u.ac.jp
Abbreviation: NMR, nuclear magnetic resonance.
Buckwheat (Fagopyrum esculentum Moench. cv. Jianxi) is known as an Al-accumulating plant. The process leading to the accumulation of Al in the leaves was investigated, focusing on the chemical form of Al using 27Al-nuclear magnetic resonance. Leaves with different Al concentrations were prepared by growing buckwheat on a very acidic soil (Andosol) amended with or without CaCO3 (1 or 3 g kg–1 soil). When the Al concentration of the leaves was lower, only one major signal was observed at a chemical shift of 16.1 ppm, which was assigned to an Al-oxalate complex at a 1:3 ratio. However, when the Al concentration of the leaves increased to a high level (e.g. 12 g Al kg–1), an additional signal at a chemical shift of 11.2 ppm was observed. This signal was assigned to an Al-citrate complex at a 1:1 ratio. In the leaf with a high Al concentration, both Al-oxalate (1:3) and Al-citrate (1:1) were detected in marginal and middle parts, while only Al-oxalate was detected in the basal part. The oxalate concentration did not differ very much between leaves with low and high Al concentrations at the same position, while citrate concentration significantly increased with increasing Al concentration when the oxalate/Al ratio became lower than 3.0. As the Al-citrate complex has been demonstrated to be the form of transport in the xylem, the results suggest that when internal oxalate is enough to form a complex with Al at a 3:1 ratio in the leaves with a low Al concentration, Al-citrate converts to Al-oxalate. However, this conversion does not occur in the leaves with a very high Al concentration, resulting in the coexistence of both Al-oxalate and Al-citrate complexes.
Key words: Aluminium form, 27Al-NMR, chelation, Fagopyrum esculentum, organic acid, tolerance mechanism (Al).
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