The beneficial effect of aluminium and the role of citrate in Al accumulation in Melastoma malabathricum

Here we investigated the beneficial effect of aluminium (Al) on the development of the Al accumulating plant Melastoma malabathricum. Seedlings of M. malabathricum were cultivated in a nutrient solution containing 0.5 mm Al and compared with barley (Hordeum vulgare). In addition, roots of M. malabathricum were divided into one part growing in a nutrient solution, and the other part growing in a calcium solution. Al (0.5 mm) was applied to either solution. Al-induced improvements of the root activity contributed to a growth enhancement in M. malabathricum. Al exposure without nutrients did not increase root growth and A[ accumulation in the leaves. The beneficial effect, however, was induced by the combination of Al and nutrients. We suggest that without nutrients roots are not able to synthesize an adequate amount of citrate that is required for transporting Al to the leaves. High Al levels in the plant tissues and/or an interaction of Al with particular nutrient elements in the apoplast of root cells appear to be essential to exert the beneficial effect of Al.