A physiological study of Melastoma malabathricum, an aluminium accumulating woody plant

Toshihiro Watanabe, Steven Jansen and Mitsuru Osaki

Aluminium (Al) accumulating species are widely distributed in tropical acid soils with severe Al stress. These species are considered to develop physiological mechanisms to tolerate high concentrations of Al in their aboveground tissues. We investigated the accumulation and transport of Al and the effects of Al on the growth in Melastoma malabathricum L. (Melastomataceae), an Al accumulator that grows in acid soils in tropical Southeast Asia. Specimens of M. malabathricum that were cultivated in a nutrient solution with 0.5 mM Al for 6 weeks accumulated Al in excess of 10 mg kg^-1 in mature leaves. Monomeric Al and Al-oxalate complexes were the primary forms of Al in leaves, while citrate was the ligand for Al translocation from the roots to the shoot. Al occurred especially in the upper epidermis, but was also distributed in the mesophyll. The Al application into the medium improved the growth of M. malabathricum, suggesting that Al has some physiological role in this species.