Defective root growth triggered by oxidative stress is controlled through the expression of cell cycle-related genes.

Reactive oxygen species (ROS) have many functions in aerobic organisms. High levels of ROS can have a negative impact on plant cells leading to senescence and cell death. ROS accumulates in cells subjected to environmental stress and induces a cellular response to this external stimulus. To protect cells from the negative impacts of excess ROS, plants also possess a ROS detoxifying system to maintain normal ROS levels. The regulation of ROS levels is particularly important as ROS also functions as an important signal molecule and can regulate plant growth by modulating gene expression. Despite the functional importance of ROS signaling, little is known about the molecular mechanisms involved in the regulation of gene expression through ROS. Therefore, the present study investigated the effect of hydrogen peroxide (H(2)O(2)), a ROS compound, on cell cycle-related gene expression. Gene expression analyses coupled with microdissected sections of the developmental zone of Arabidopsis root tips revealed that H(2)O(2) affects the expression of cell cycle-related genes. Additionally, ROS scavenging enzymes were found to play an important role in the root growth phenotype induced by H(2)O(2). Specifically, root growth inhibition by H(2)O(2) was diminished in transgenic Arabidopis overexpressing peroxidase but increased in a catalase2 (cat2) mutant. The strong root growth inhibition observed in the cat2 mutant upon H(2)O(2) treatment indicated that CAT2 has an essential role in maintaining root meristem activity in the presence of oxidative stress. Overall, these results confirm that ROS function not only as stress-related compounds but that they also function as signaling molecules to regulate the progression of the cell cycle in root tips.