Reactive oxygen species stimulate homologous recombination in plants

Coping with the continuous production of free radicals is a daily routine of the cell. Despite their toxicity, the reactive oxygen species (ROS) are involved in dual physiological action - signal transduction and immune response. We analysed the influence of oxidative stress-generating compounds, rose Bengal (RB), paraquat (PQ) and aminotriazole (ATZ) on the genome stability of Arabidopsis using transgenic recombination-monitoring plants. Homologous recombination frequencies in plants were increased upon the treatment with RB and PQ but not ATZ. Application of the N-acetyl-L-cysteine (NAC), radicals scavenging compound, decreased the DNA damage caused by RB. Interestingly, the incubation of plants with very low concentration of RB (less than 0.2 muM) led to the subsequent increase in plant tolerance to methyl methane sulfonate (MMS): stronger plants with a lower increase of homologous recombination frequency. In contrast, the incubation of plants with 0.5 muM of RB resulted in the potentiation of the MMS effect: the weaker plants with higher frequency of recombination. The data of the present study suggest the existence of a dual concentration-dependent role of ROS in plants.