Cadmium absorption and translocation in rice plants are influenced by lower air temperatures during grain filling stage.

The increasing frequency and severity of low temperatures, and soil cadmium (Cd) pollution threaten food security. However, the interactive effects of Cd exposure and low temperatures on rice yield and quality, as well as the mechanisms of Cd absorption and translocation, remain unclear. In this study, two rice varieties were cultivated in soils with two Cd contamination levels (Cdhigh and Cdlow) and exposed to control (CT25) or lower temperatures of 20 °C (LT20) and 17 °C (LT17) during grain-filling stage. Results showed significant decreases in seed setting rate and grain weight, reduced head rice yield, and increased chalkiness due to low temperatures, particularly in Cdhigh soils. Compared to CT25, LT17 and LT20 increased Cd concentration by 37.6 % and accumulation by 14.8 % in grains grown in Cdhigh soils. Enhanced root activity and upregulation of OsNramp1 and OsNramp5 under both low-temperatures increased Cd levels in roots. Lower temperatures also decreased phytochelatins (PCs) and increased expression of OsHMA2 and OsCAL1, facilitating Cd transport and raising Cd levels in stems. Furthermore, upregulated OsHMA2, OsLCT1, and OsZIP7 in stems under low-temperatures promoted Cd transport to panicles. Overall, low temperatures during grain filling increased Cd uptake and translocation into rice grains, especially in high Cd contaminated soils, raising health risks. The study highlights the need to address climate change's impact on cadmium hazards in rice.