Abstract
Photosystem II (PSII) is particularly sensitive to oxidative stress. We investigated the effects in vivo of reactive oxygen species (ROS) in the photodamage to PSII in Chlamydomonas reinhardtii. Increases in intracellular concentrations of ROS, caused by the presence of ROS-generating reagents, such as methyl viologen, hydrogen peroxide, and rose bengal, stimulated the apparent photodamage to PSII. However, actual photodamage to PSII, as assessed in the presence of chloramphenicol, was unaffected by the presence of these reagents. These observations suggest that ROS act primarily by inhibiting the repair of photodamaged PSII and not by accelerating damage to PSII in Chlamydomonas.
