Physiological and Transcriptomic Responses of Rice Cultivars to Combined Cadmium and Elevated Temperature Stress

Cadmium (Cd) contamination and rising temperatures pose significant challenges to rice growth and food safety. Here, we investigated growth responses, Cd accumulation, physiological adaptations, and transcriptomic profiles of two rice cultivars, Yuzhenxiang (YZX) and Xiangwanxian 12 (XWX12), under combined Cd (0, 5, 20 μmol L−1) and temperature (25 °C, 30 °C) stress. Moderate warming (30 °C) generally promoted seedling growth and enhanced Cd uptake, with YZX showing greater increases in plant height and biomass, whereas XWX12 developed longer roots. At maturity, the temperature-induced growth advantage persisted in YZX, accompanied by a 60% increase in root Cd concentration, compared with 36% in XWX12. Antioxidant enzyme activities (POD, SOD, CAT) were significantly induced under combined stress, with XWX12 exhibiting stronger enzymatic responses and broader activation of ABC transporter genes, supporting reduced Cd accumulation in shoots. Malondialdehyde content indicated milder oxidative damage in YZX despite higher Cd accumulation. Transcriptomic analyses revealed extensive early transcriptional reprogramming, with enrichment of antioxidant metabolism, ABC transporters, MAPK signaling, and Cd transport-related genes, demonstrating coordinated physiological and molecular responses. XWX12 favored intracellular Cd sequestration and sustained antioxidant activation, whereas YZX relied more on uptake and translocation processes. Overall, these results highlight genotype-specific strategies in coping with combined Cd and temperature stress, providing mechanistic insights for improving rice tolerance and safety under warming and contaminated environments.