Silicon Effects on Metal Tolerance and Structural Changes in Maize (Zea mays L.) Grown on a Cadmium and Zinc Enriched Soil

Silicon presents a close relationship with the amelioration of heavy metals phytotoxicity. However, mechanisms of Si-mediated alleviation of metal stress remains poorly understood. This work aimed at studying the relationship between the accumulation of Si, Cd, and Zn and the tolerance and structural alterations displayed by maize plants grown on a Cd and Zn enriched soil treated with doses of Si (0, 50, 100, 150, and 200mg kg(-1)) as calcium silicate (CaSiO3). The results showed that the maize plants treated with Si presented not only biomass increasing but also higher metal accumulation. Significant structural alterations on xylem diameter, mesophyll and epidermis thickness, and transversal area occupied by collenchyma and midvein were also observed as a result of Si application. The deposition of silica in the endodermis and pericycle of roots seems to play an important role on the maize tolerance to Cd and Zn stress.