Gypsum (calcium sulfate dihydrate, CaSO4 ·2H₂O) is commonly applied to improve soil quality and nutrient supply. Previous studies also suggested it is a cost-effective soil amendment in alleviating cadmium (Cd) toxicity and accumulation in plants. The aim of this study was to investigate how this is achieved. We used pak choi as our research material because it is a popular vegetable in Asia, and as a leafy vegetable, it accumulates higher Cd level than other types of vegetable. Under Cd stress, application of CaSO4 promoted pak choi seedling growth, decreased the oxidative stress in roots, reduced Cd accumulation, and enhanced the photosynthesis in shoots. We revealed the inhibition of Cd2+ absorption by CaSO4 is largely due to the competition between Ca2+ and Cd2+ for ion channels or transporter. Moreover, under Cd stress, CaSO4 facilitated the sulphate assimilation, increased the biosynthesis of phytochelatins, and activated the expression of transporters for vacuolar sequestration. Together, CaSO4 could benefit plant growth and enhance Cd tolerance by suppressing Cd root uptake and lowering the Cd content in cytoplasm.
Keywords: Cadmium absorption; Cadmium accumulation; Calcium sulfate; Competitive inhibition; Pak choi; Vacuolar sequestration.
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