Antioxidlation 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 lLer) and three mutants deficient in anthocyanins biosynthesis (0, tt4, and tt3tt4) were investigated during treatment with temperatures ranging 25-45 degrees C. In comparison with the wild type, chlorophyll fluorescence parameters Fv/Fm, (phi(PSII), 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 degrees C. Non-photochemical quenching (NPQ) in these mutants was almost completely lost at 44 degrees C, 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 degrees C to 72 degrees C at 0.5 degrees C/min. The inflexion temperatures of Fo were 45.8 degrees C in Ler, 45.1 degrees C in H3, 44.1 degrees C in U4 and 42.3 degrees C in tt3tt4, respectively. The temperatures of maximal Fo in three mutants were 1.9-3.8 degrees C 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-diphe nyl-2-picrylhy.drazyl) radical under heat stress, and in particular tt3tt4 had the lowest antioxidative potential. The results of the diaminobenzidine-H2O2 histochernical staining showed that H2O2 was accumulated in the leaf vein and mesophyll cells of mutants under treatment at 40 degrees C, and it was significantly presented in leaf cells of tt3tM. 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.