Effect of Dietary Vitamin C on the Antioxidant Defense System of Hibernating Juvenile Three-keeled Pond Turtles (Chinemys reevesii)

Juvenile three-keeled pond turtles(Chinemys reevesii) were fed diets supplemented with vitamin C(Vc) at doses of 0(basal diet, Vc0), 100(Vc100), 200(Vc200), 500(Vc500) and 2500(Vc2500) mg/kg diets at 28°C for 4 weeks, respectively. Then, the water temperature was gradually reduced to 10°C, and the turtles were induced into hibernation. Liver tissue samples were collected at three time points: start of hibernation(T1), 4 and 6 weeks’ hibernation(T2 and T3). A control group fed with the basal diet was set to parallel the whole treatment process, but reared at 28°C constantly. The results showed that hibernation mildly affected the antioxidant system and the influence varied with hibernating time. Hepatic malondialdehyde content of the Vc100 group was significantly lower than that of the other groups at T1. At T2, hepatic MDA in the groups of Vc500 and Vc2500 decreased significantly, while no clear differences were found among all groups at T3. The activities of antioxidant enzymes showed a positive correlation with dietary Vc dose before hibernation. After hibernation, total antioxidant capability was not affected by Vc. Superoxide dismutase activity became similar in different groups at T2, but decreased in higher Vc groups(≥ 200 mg/kg) at T3. Glutathione peroxidase and glutathione-S-transferase activities decreased significantly with dietary Vc supplementation(≥ 100 mg/kg) at T2, but recovered at T3. The result indicates that under normal rearing condition, low dietary Vc supplementation(< 100 mg/kg) might be beneficial to the antioxidant defense system. The effect of dietary Vc on the antioxidant defense system differed during hibernation.

Antioxidation of Anthocyanins in Photosynthesis Under High Temperature Stress

Chlorophyll fluorescence and antioxidative capability in detached leaves of the wild type Arabidopsis thaliana L. ecotype Landsberg erecta （Ler） and three mutants deficient in anthocyanins biosynthesis （tt3, tt4, and tt3tt4） were investigated during treatment with temperatures ranging 25-45 ℃. In comparison with the wild type, chlorophyll fluorescence parameters Fv/Fm, φps,, electron transport rate （ETR）, Fv/Fo and qP in three anthocyanin-deficient mutants showed a more rapidly decreasing rate when the temperature was over 35 ℃. Non-photochemical quenching （NPQ） in these mutants was almost completely lost at 44 ℃, whereas the content of heat stable protein dropped and the rate of the membrane leakage increased. Fo-temperature curves were obtained by monitoring Fo levels with gradually elevated temperatures from 22 ℃ to 72 ℃ at 0.5 ℃/min. The inflexion temperatures of Fo were 45.8 ℃ in Ler, 45.1℃ in tt3, 44.1℃ in tt4 and 42.3 ℃ in tt3tt4, respectively. The temperatures of maximal Fo in three mutants were 1.9-3.8℃ lower than the wild type plants. Meanwhile, three mutants had lower activities of superoxide dismutase （SOD） and ascorbate peroxidase （APX） and an inferior scavenging capability to DPPH （1.1-diphenyl-2-picrylhy.drazyl） radical under heat stress, and in particular tt3tt4 had the lowest antioxidative potential. The results of the diaminobenzidine-H2O2 histochemical staining showed that H2O2 was accumulated in the leaf vein and mesophyll cells of mutants under treatment at 40 ℃, and it was significantly presented in leaf cells of tt3tt4. The sensitivity of Arabidopsis anthocyanins-deficient mutants to high temperatures has revealed that anthocyanins in normal plants might provide protection from high temperature injury, by enhancing its antioxidative capability under high temperature stress.