||When light absorption is higher than photosynthetic utilization under high light stress, excess energy will be accepted by O2 and in turn a large reactive oxygen species (ROS) produce, then leads to alteration of macromolecule structure and subsequently physiological and metabolic changes. This studydiscovered Chlamydomonas reinhardtii (CC400) can survive under 1,400 E m-2 s-1 , and ROS, ascorbic acid (AsA) contents, AsA/DHA ratio increase, and ascorbate peroxidase ( APX ) activity increased in short time. C. reinhardtii has CrAPX1 (CrAPX1;Cre02.g087700.t1.1), CrAPX2 (CrAPX2; Cre06.g285150.t1.1) and CrAPX4 (CrAPX4; Cre05.g233900.t1.1). Under the high light stress, the amount of RNA expression showed that CrAPX4 was higher than CrAPX1 and CrAPX2. The main experiment used the study of mutant strains inhibiting CrAPX4 to study the tolerance of high light stress.|
The downregulation CrAPX4 transformants were made through the transformation of pClamyiRNA_3 vector by PSAD::CrAPX4-amiRNA. Uner high light condition (1,400 E m-2 s-1), the APX activity of downregulation transformants was significantly inhibited, and the ASA increased significantly. DHA also showed an increase in high light stress (AsA may be directly oxidized in response to H2O2 role).The survival rate is lower than that of the wild type, and the level of lipid peroxidation is higher than that of the wild. As a result, the downregulation of CrAPX4 can decrease the APX activity of C. reinhardtii. Under high light stress, ROS can not be effectively removed by decreased APX, which reduces the resistance of unicellular algae to high light stress.