Anatomical and physiological responses of Billbergia zebrina (Bromeliaceae) to copper excess in a controlled microenvironment

Copper (Cu) plays crucial biochemical and physiological functions in plants. However, at high concentrations, Cu can become extremely toxic, inducing several physiological changes and symptoms of toxicity. The aim was to analyze the anatomical and physiological changes of the bromeliad, Billbergia zebrina, in response to Cu excess under in vitro conditions. B. zebrina plants, previously established in vitro, were transferred to culture media containing 0, 2, 20, or 200 µM Cu. Growth traits and enzyme activity of superoxide dismutase and ascorbate peroxidase were measured over a period of 80 days. To verify the biological activity of roots grown under different Cu concentrations, a biospeckle laser was used at 20 and 80 days. Biomass accumulation, Cu content and anatomical analyses were performed at 80 days. Plants did not show any visible signs of disturbance and all plants survived the experimental treatments. Plants grown with 200 µM Cu showed anatomical changes, such as increased stomatal index and thicker exodermal cell walls of the roots, which may aid in heavy metal tolerance. High biological activity was observed only at 20 days. This biological activity was linked to increased thickness of the cell wall at the exodermis. The Cu content evidenced that the anatomical changes were effective against the transport of excess Cu into the plants. Although Cu exposure affected leaf and root anatomy as well as growth, exposure only induced minimal changes in the antioxidant system. B. zebrina tolerates high amounts of Cu and could potentially be used as a bioindicator species.