The characteristics of aluminum uptake in roots of Melastoma malabathricum, an aluminum accumulating plant

摘要

In general, plants that have Al levels of at least 1000 mg kg~(-1) in their leaves can be defined as Al accumulators. These plants are often found in tropical, strongly acid soils. Mechanisms of Al uptake in strong Al accumulators are still unclear. In this study, the characteristics of Al uptake in Melastoma malabathricum, an Al accumulating plant which grows in tropical acid soils, were investigated. M. malabathricum roots hardly absorb lanthanum (La), indicating that the roots have a specific Al uptake/transport system. Whereas application of La did not affect the concentration of citrate in roots, Al application increased the citrate level considerably, corresponding to the Al accumulation in the symplast. Although mucilage is generally considered to be effective in excluding Al from roots, large quantities of mucilage are exuded by roots of M. malabathricum. The mucilage exuded from M. malabathricum roots showed a high affinity to adsorb Al compared with Ba and La. The removal of the mucilage from roots decreased Al uptake in the seedlings of M. malabathricum, indicating that M. malabathricum roots solubilize the Al concentrated in the mucilage possibly by exuding H~+ or organic acids, and absorb it.