Effects of Lanthanum on the Change of Calcium Level in the Root Cells of Rice

Rare-earth elements (REEs) have been widely used in agriculture for the growth of crops in China since the 1980s. As a secondary messenger, calcium ion (Ca²⁺) participates in physiological and biochemical reactions in plants via cellular or intercellular signal transduction networks. The aim of this study was to investigate the effects of trivalent lanthanum (La³⁺) on the change of Ca²⁺ in the root cells of rice (Oryza sativa L. cv. Shengdao 16) with laser-scanning confocal microscopy. The results indicated that Ca²⁺ level in the root cells was affected by the concentrations of La³⁺. The level of Ca²⁺ slightly decreased in the root of rice treated with 0.2 mmol L^–1 La³⁺, and Ca²⁺ oscillation was induced in the root of rice treated with 1.0 mmol L^–1 La³⁺. However, Ca²⁺ level increased in the root of rice treated with 2.0 mmol L^–1 La³⁺. In addition, the results indicated that Ca²⁺ level in the rice roots slightly decreased after Ca²⁺ inhibitors verapamil (VP), ruthenium red (RR), trifluperazine (TFP), and ethylene glycol tetraacetic acid (EGTA) were added. Moreover, the effects of 2.0 mmol L^–1 La³⁺ on Ca²⁺ level in the root cells of rice were investigated after Ca²⁺ was inhibited with VP, TFP, RR, and EGTA. Inhibited with VP, TFP, RR, and EGTA, Ca²⁺ level slightly decreased or was not affected in the rice roots treated with 2.0 mmol L^–1 La³⁺. The results showed that La³⁺ participated in the signal transduction networks via calmodulin (CaM) and that La³⁺ might enter into the root cells via the membrane and intracellular Ca²⁺ channels.