Growth

Role of organic acids in aluminum accumulation and plant growth in Melastoma malabathricum
Toshihiro Watanabe (1, 2) and Mitsuru Osaki (3, 4)

1. Japan International Research Center for Agricultural Sciences, 1-1 Ohwashi, Tsukuba 305-8686, Japan / 2. Japan Science and Technology corporation, 4-1-8 Honcho, Kawaguchi 332-0012, Japan / 3. Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan / 4. Author to whom correspondence should be addressed (mosaki@chem.agr.hokudai.ac.jp) / Received August 1, 2001; accepted January 5, 2002; published online July 2, 2002

Summary
Melastoma malabathricum L. (melastoma) is an Al-accumulating woody plant that grows in tropical Southeast Asia in acid soils with high aluminum (Al) concentrations and low nutrient concentrations. Because oxalate serves as a ligand for Al accumulation in melastoma leaves and citrate is the ligand associated with Al translocation from roots to shoots, we investigated the role of organic acids in the adaptation of melastoma to growth on these soils. Phosphorus starvation increased oxalate concentration in the rhizosphere, enabling melastoma to solubilize insoluble aluminum phosphate in the rhizosphere. Increased availability of P and Al in the rhizosphere enhanced growth. In the xylem sap, the concentration of citrate increased with increasing Al concentration.

In contrast, the concentrations of malate, succinate and α-ketoglutarate in the xylem sap decreased with increasing Al concentration, suggesting that tricarboxylic acid cycle enzymes were affected by Al treatment.

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