Ca2+-dependent plant response to Pb2+ is regulated by LCT1

Tobacco plants transformed with TaLCT1 were cultured on Knop's medium with modified calcium concentrations (0.01–3 mM) in the presence of Pb2+, and in soil contaminated by lead. A 4–5 μM Pb2+ administered in the presence of 1 mM Ca2+ inhibited the root growth of transgenic plants to much lesser degree than of control plants, whereas in the presence of 3 mM Ca2+ no differences were found between the studied lines. The reduction of Pb2+ toxicity in the presence of 1 mM Ca2+ was not accompanied by a change in the lead tissue concentration. However, when Ca2+ level in the medium was lowered to 0.01 mM, several fold higher root/shoot Pb ratio in transgenic plants was observed, twofold increase in the total amount of metal accumulated, and lower concentration of Pb in the xylem sap. Results suggest the involvement of TaLCT1 in the regulation of Ca-dependent Pb-detoxification, and under conditions of low calcium in lead uptake and distribution.