Abstract
We study the molecular mechanism leading to leaf variegation using the leaf-variegated mutant var2 in Arabidopsis. VAR2 encodes the ATP-dependent metalloprotease FtsH2 in thylakoid membranes. FtsH2 is involved in the PhotosystemII repair cycle (particularly D1 protein of the reaction center). Photodamaged proteins need to be degraded promptly, otherwise leading to improper electron transport and generation of highly toxic reactive oxygen species (ROS). To test if ROS accumulate indeed in var2, we attempted to detect ROS in mature leaves of var2 grown under normal light condition using NBT or DAB histochemical staining for detecting superoxide and hydrogen peroxide, respectively. The result indicated that both ROS accumulated predominantly in the green sectors but not white sectors of the var2 variegated leaves. Signals detected by NBT were exclusively located in chloroplasts, suggesting that the high level ROS is due to the impairment of the PSII repair cycle.
