Abstract: Chlorophyll a, chlorophyll b, carotenoid, superoxide dismutase (SOD) and malondialdehyde (MDA) of Scenedesmus quadricauda were measured to study the injury mechanism of different doses (10-80 Gy) after irradiation by 80 MeV/u ¹²C⁶⁺ of Heavy Ion Research Facility (HIRFL, Lanzhou, China). The obtained results were as follows: 1) Chlorophyll a (Chl a), chlorophyll b (Chl b) and carotenoid were measured in different culture times after irradiation. For low-dose groups (10-20 Gy), contents of Chla, Chlb and carotenoid decreased slightly or did not vary significantly; for middle-dose groups (40-60 Gy), contents of Chl a, Chl b and carotenoid increased apparently, and then went down to the level of control group; for highdose group (80 Gy), contents of Chl a, Chl b and carotenoid were impacted severely and did not show sign of recovery. 2) Malonaldehyde (MDA) was measured in different culture times after irradiation. For low-dose group (10 Gy), the injury of membrane lipid appeared immediately after irradiation, it became lighten after 8 h, and then recovered to the level of control group within 24-48 h; for the 20 Gy group, the content of MDA decreased immediately, and then came back to the normal level; for middle and high-dose groups (40-80 Gy), the injury of membrane lipid did not happen instantly, while it became obviously in 24-48 h, and did not has the ability of recovery to the normal level. 3) Superoxide dismutase (SOD) was measured in different culture times after irradiation. For low-dose group (10 Gy), the activity of SOD rose significantly, and then declined to the normal level in 8 h; for middle-dose groups (20-60 Gy), the activity of SOD ascended markedly and went back to the normal within 48 h; for high-dose group (80 Gy), the activity of SOD did not has a sign of increment, while it descended obviously and did not recover to the normal within 48 h.

Key words: carbon ions beam irradiation, Scenedesmus quadricauda, photosynthetic pigment, MDA, SOD