The cadmium tolerance development of poplar callus is influenced by silicon

Cadmium-tolerant plants were studied for their possible usage in phytoremediation techniques. However, their response to cadmium cations at a cellular level has not been properly studied. Silicon is a beneficial element that seems to change the plant's response to the Cd²⁺ presence. The aim of the present study was to investigate the Cd²⁺ tolerance patterns of poplar callus cells exposed to Cd⁺² and/or Si over short and long cultivation periods. We determined the growth parameters of the callus, the growth dynamics, cell vitality, photosynthetic pigment concentrations and the activity of antioxidant enzymes. The effects were studied over short (21 days) and long (63 days) cultivation periods. The most important result proved that the poplar callus tissue is able to build up a tolerance to Cd²⁺ after a longer cultivation period. On the 63^rd day of the cultivation, Cd²⁺ stressed calli showed improvement in studied parameters and the callus cells accumulated Cd²⁺ more efficiently than on the 21^st day. Supplementation with Si in higher concentrations (2.5 mM and 5 mM) heightened the Cd-tolerance potential of the tissue. The treatment of Cd²⁺, and Si in a 2.5 mM concentration was the most efficient variant for Cd²⁺ removal from medium. The activity of antioxidant enzymes showed that poplar callus cells effectively develop tolerance against Cd²⁺ after a longer cultivation period.