Antioxidant Metabolism and Function

Chlorophyll Plate

PC: Cory Maryott

Several antioxidant systems in algae and plants cope with ROS that are generated inevitably as byproducts of photosynthetic metabolism. Antioxidants in chloroplasts include small molecules such as carotenoids (xanthophylls and carotenes), tocopherols (vitamin E), ascorbate (vitamin C), and glutathione and enzymes such as ascorbate peroxidase (APX), superoxide dismutase (SOD), and alkyl hydroperoxide reductases. Many of the antioxidant small molecules that are made by algae and plants are also important nutrients in the human diet.

To address the roles of these molecules in photoprotection, we are isolating and characterizing Chlamydomonas and Arabidopsis mutants that affect the synthesis of specific antioxidants. For example, the Chlamydomonas npq1lor1 double mutant, which lacks the carotenoids zeaxanthin and lutein, undergoes photo-oxidative bleaching in high light, likely due to decreased quenching of singlet excited chlorophyll (NPQ) and singlet oxygen. The loss of chlorophyll is accompanied by extensive lipid peroxidation. Extragenic suppressors of npq1lor1 have been isolated that include new mutations affecting antioxidant synthesis. These suppressors are providing insights into the overlapping functions of various antioxidants.