Responses of Different Japonica Rice Varieties to Cadmium Stress

Cadmium (Cd) contamination in paddy soils threatens food security by accumulating in rice grains. This study aimed to elucidate Cd-accumulation mechanisms using major japonica cultivars from Liaoning Province, a key northern Chinese rice-producing region where systematic comparisons remain limited. Four Liaoning japonica varieties (low-Cd: YF47, SN9903; high-Cd: QTXT, TJ) were analyzed for Cd accumulation, physiological responses, including malondialdehyde (MDA), superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and expression of Cd-related transporter genes under Cd stress. Cd distribution in rice plants followed the following order: root > stems and leaves > grain. Varietal differences were attributed to root-to-shoot transport rather than root uptake, as low-Cd varieties exhibited lower transport coefficients and higher root Cd retention. Low-Cd varieties showed smaller MDA increases and significantly higher SOD and CAT activities under Cd stress. Notably, OsLCD was significantly down-regulated in low-Cd varieties but up-regulated in high-Cd varieties, an opposite regulation pattern that clearly distinguishes the two groups. The root-to-shoot translocation process and the OsLCD expression pattern are key determinants differentiating low- from high-Cd japonica varieties. These findings provide region-specific mechanistic insights and screening indicators for breeding low-Cd rice in northern China.