Effect of Mercuric Ion on the Oxidant Response and Calcium Ion in the Protoplasts of Arabidopsis Thaliana

As a non-essential element for plant growth and development, the heavy metal mercury (Hg) has significant toxicity to plants. The aim of this study was to investigate the effect of mercuric ion (Hg²⁺) on the oxidant response and calcium ion (Ca²⁺) in the protoplasts of Arabidopsis thaliana. The protoplast cells were exposed to 5.0, 10.0, and 20.0 mmol/L Hg²⁺ for 0.5 and 1.0 h, respectively. To detect the effect of Hg²⁺ on the Reactive Oxygen Species (ROS) with the laser scanning confocal microscopy, 2’ 7’-Dichlorofluorescent yellow Diacetate (DCFH-DA) was used to label ROS in protoplast cells of Arabidopsis thaliana. The result of confocal microscopy analysis showed that the level of ROS was increased in protoplast cells after the treatments of 5.0, 10.0, and 20.0 mmol/L Hg²⁺. However, the activity of antioxidant enzymes Catalase (CAT), Superoxide Dismutase (SOD), and Glutathione Peroxidase (GSH-PX) in protoplasts was decreased by 5.0, 10.0, and 20.0 mmol/L Hg²⁺ treatments. In addition, ion chromatography was used to study the effect of Hg²⁺ on the content of Ca²⁺ in the protoplasts of Arabidopsis thaliana. It showed that the content of Ca²⁺ in the outer cell of protoplasts was increased after the treatments of 5.0, 10.0, and 20.0 mmol/L Hg²⁺. In conclusion, Hg²⁺ decreases the activity of antioxidant enzymes and induces the elevation of ROS in the protoplast cells. Mercuric ion inhibits the absorption of Ca²⁺ by protoplast cells and the change of Ca²⁺ content may affect ROS level in the protoplasts of Arabidopsis thaliana.