Conostegia xalapensis (Melastomataceae): an aluminum accumulator plant

In acidic soils, an excess of Al3+ is toxic to most plants. The Melastomataceae family includes Al-accumulator genera that tolerate high Al3+ by accumulating it in their tissues. Conostegia xalapensis is a common shrub in Mexico and Central America colonizing mainly disturbed areas. Here, we determined whether C. xalapensis is an Al accumulator, and whether it has internal tolerance mechanisms to Al. Soil samples collected from two pastures in the state of Veracruz, Mexico, had low pH and high Al3+ concentrations along with low Ca2+ levels. Leaves of C. xalapensis from pastures showed up to 19 000 mg Al kg-1 DW (dry weight). In laboratory experiments, 8-month-old seedlings treated with 0.5 and 1.0 mM AlCl3 for 24 days showed higher number of lateral roots and biomass. Pyrocatechol violet and hematoxylin staining evidenced that Al localized in epidermis and mesophyll cells in leaves and in epidermis and vascular pith in roots. Scanning electron microscope-energy dispersive X-ray microanalysis of Al-treated leaves corroborated that Al is in abaxial and adaxial epidermis and in mesophyll cells (31.2%) in 1.0 mM Al-treatment. Roots of Al-treated plants had glutathione reductase (EC 1.6.4.2) and superoxide dismutase (EC 1.15.1.1) activity higher, and low levels of O and H 2O2. C. xalapensis is an Al-accumulator plant that can grow in acidic soils with higher Al3+ concentrations, and can be considered as an indicator species for soils with potential Al toxicity.