This study aimed to investigate the effects of varying selenium (Se) concentrations on the antioxidant and detoxification responses in rice, and to provide a basis for subsequent research on Se-enriched rice. Using the rice cultivar ‘Meixiangzhan 2’ as the experimental material, a hydroponic experiment was conducted. Four Se concentration treatments (0, 0.01, 0.025, and 0.05 mg/L) were established by adding sodium selenite. Plant height, photosynthetic pigment content, selenium and nutrient (N, P, K) contents were determined, and changes in antioxidant enzyme (SOD, POD, CAT) activities, detoxification enzyme (GST, CarE) activities, and the expression level of rice selenium-binding protein 1 (OsSBP1) were analyzed. The results showed that appropriate Se application promoted rice growth, while excessive Se inhibited growth and caused dwarfing. The plant height was reduced by 21.8%-32.9% when increased Se concentration from 0.01 to 0.05 mg/L. Low Se concentrations had no effect on leaf photosynthetic pigment content, but the content decreased significantly at 0.05 mg/L. With increasing Se concentration, the Se content in rice roots, stems, and leaves continuously increased, reaching 236-, 163-, and 64-fold that of the control at 0.05 mg/L, respectively. However, the absorption and accumulation of nitrogen (N), phosphorus (P), and potassium (K) in rice were not inhibited. Malondialdehyde (MDA) content in roots stems and leaves decreased significantly with increasing Se levels. The lowest MDA values were observed at 0.05 mg/L (roots), 0.025 mg/L (stems), and 0.01 mg/L (leaves), with reductions of 79.5%, 65.7%, and 53.7%, respectively. Within the Se concentration range of 0.01-0.05 mg/L, the activities of superoxide dismutase (SOD), glutathione S-transferase (GST), and carboxylesterase (CarE) in roots, stems and leaves increased significantly. In contrast, the activities of peroxidase (POD) and catalase (CAT) in roots and stems initially increased and then decreased. The relative expression of OsSBP1 also showed a similar trend, decreasing to 0.5- and 0.3-fold the control level in stems and leaves at 0.05 mg/L, respectively. In summary, appropriate Se application increased the Se content, reduced MDA content, enhanced the activities of antioxidant and detoxification enzymes, and upregulated OsSBP1 expression in rice, thereby promoting antioxidant capacity and alleviating Se toxicity symptoms. However, excessive Se application inhibited antioxidant activity, exerted toxic effects, reduced photosynthetic pigment content, and suppressed the growth and development of rice. This study provides a theoretical reference for the rational application of Se fertilizer in rice cultivation.
