Abstract
Ascorbate (AsA) in chloroplasts plays a crucial role in scavenging of reactive oxygen species (ROS) produced in photosynthetic electron transport. Here, we studied the contribution of dehydroascorbate reductase (DHAR) in chloroplasts. Chimera gene composed of transit peptide region of spinach chloroplastic CuZn-SOD and rice cytosolic DHAR was transformed to tobacco leaf discs. All transformed calli could form shoots but not roots to die under constant illumination. Light/dark cycle enabled transformants to form roots, supposingly because of restricted supply of reducing power to DHAR, while knockout mutant of putative chloroplastic DHAR in Arabidopsis (Salk066273) showed longer roots than col-0. Expressions of chloroplastic DHAR did not affect paraquat resistance and amounts and redox ratio of AsA, but Salk066273 showed resistance against salinity. These results suggest that DHAR does not contribute AsA recycling, but regulation of stress response and growth through redox balance of AsA.
