Abstract:

The 3-year-old pot-cultured Pinus koraiensis seedlings were used in this experiment. The seedings were treated with the following treatments; CK (Control), T1 treatment (3.25 μW ·cm^-2 UV-B radiation), T2 treatment (6.51 μW ·cm^-2 UV-B radiation) and T3 treatment (9.76 μW ·cm^-2 UV-B radiation). Effects of UV-B radiation on the concentration of free radical, the degree of lipid peroxidation and antioxidant system in needles of P. koraiensis were determined after 40 days of UV-B treatment. The results showed that the elevated UV-B radiation significantly increased concentrations of hydroxyl radical (·OH), hydrogen peroxide radicals (H₂O₂) and malondialdehyde (MDA) (P<0.05). The concentrations of H₂O₂ (149.05 mmol ·g^-1) and MDA (12.56 μmol ·g^-1) were maximal under T3 treatment. The elevated UV-B radiation induced the activities of catalase (CAT), ascorbate peroxide (APX), and superoxide dismutase (SOD), but significantly decreased the activity of peroxidase (POD) (P<0.05). Concentration of soluble protein was increased with exposure to UV-B radiation (CK treatment was 0.17 mg ·g^-1, while T3 treatment was 0.26 mg ·g^-1). Carotenoid and flavonoid were decreased significantly by all UV-B radiations treatments. Simultaneously, the results of correlation analysis showed that the concentration of soluble protein had significant positive correlations with the concentrations of free radical and MDA (P<0.01), and the concentration of hydroxyl radical had significant negative correlations with the concentrations of carotenoid and flavonoid (P<0.01). This study demonstrated that the supplemental UV-B radiation increased the concentration of free radical and affected the physiological metabolism in needles of P. koraiensis seedlings. Simultaneously, P. koraiensis was able to increase the activities of CAT, APX, SOD and the concentration of soluble protein against oxidative stress injury caused by supplemental UV-B radiation, but the defense mechanism was not efficient enough to prevent the UV-B induced damage.

Key words: Pinus koraiensis, UV-B radiation, free radical, lipid peroxidation, antioxidant enzyme