Type and cellular location of reactive oxygen species determine activation or suppression of programmed cell death in Arabidopsis suspension cultures

Plant programmed cell death (PCD) is a cell-controlled process that plays an essential role in development and stress responses. Apoptotic-like PCD (AL-PCD) results in a characteristic cell corpse containing a condensed cytoplasm. We recently showed that chloroplast-produced reactive oxygen species (ROS) can play a role in regulating AL-PCD. Here we show that ROS may play a variety of roles in AL-PCD regulation, depending on type and localisation of the ROS activity. Treatment of Arabidopsis thaliana cells with the antioxidants ascorbate and glutathione, which are not specific in the forms of ROS that they scavenge, resulted in increased heat stress-induced AL-PCD. However, treatment with catalase, which specifically scavenges hydrogen peroxide (H2O2) only, temporally promoted cell survival and suppressed AL-PCD after the heat treatment. These results suggest that H2O2 functions as an important mobile signal that positively regulates AL-PCD in plants and that other ROS forms may play different roles in AL-PCD regulation, perhaps by acting as positive or negative regulators of components of AL-PCD signaling pathways.