Abstract: OBJECTIVE：To investigate effects of low dose (≤30 Gy) ionizing radiation on antioxidant enzyme and photosynthesis activities in Brassica napus L. (B. napus) seedlings. METHODS：B. napus seedlings were obtained through soil culture，with each dose group consisted of 5 rapeseed plants. Intermittent ¹³⁷Cs irradiation instead of chronic irradiation was used. The irradiation was conducted 5 days per week for 7 hours per day at doses of 0 (control group)，5，10，15，20，25，and 30 Gy，with an irradiation dose rate of 8.28 mGy/min. The activities of superoxide dismutase (SOD)，catalase (CAT)，peroxidase (POD)，content of chlorophyll a，b，a+b，carotenoid in leaves，and expression of genes related to photosynthesis (psb A，psb D，psb C，and LOD106434505) in the leaves of the seedlings after irradiation were detected and analyzed. RESULTS：Compared with the control group，the activities of SOD and CAT increased with the increase of irradiation dose (P<0.05)，but there is no significant trend in POD activity (P>0.05). As the irradiation dose increased，the chlorophyll a and b contents of the seedlings first increased，reaching the highest in the 10 Gy dose group (P<0.05)，and then decreased. There was no significant trend in changes in chlorophyll a+b content and carotenoid content，with the highest in the 5 Gy dose group (P<0.05). After irradiation，the expression level of gene psb C was downregulated (except for the 15 Gy dose group，P<0.05). The expression of LOC106434505 was significantly upregulated with increasing irradiation (P<0.05)，while the expression changes of psb A and psb D were not significant. CONCLUSION：Low dose (≤30 Gy) ¹³⁷Cs irradiation enhanced the antioxidant enzyme activities of rapeseed seedlings，and affected photosynthesis by perturbing chlorophyll content，photoelectron transport，and energy capture and transfer.

Key words: low dose radiation, ¹³⁷Cs, Brassica napus L., chlorophyll content, antioxidant enzyme