Differential patterns of reactive oxygen species and antioxidative mechanisms during atrazine injury and sucrose-induced tolerance in Arabidopsis thaliana plantlets.

Besides being essential for plant structure and metabolism, soluble carbohydrates play important roles in stress responses. Sucrose has been shown to confer to Arabidopsis seedlings a high level of tolerance to the herbicide atrazine, which causes reactive oxygen species (ROS) production and oxidative stress. The effects of atrazine and of exogenous sucrose on ROS patterns and ROS-scavenging systems were studied. Simultaneous analysis of ROS contents, expression of ROS-related genes and activities of ROS-scavenging enzymes gave an integrative view of physiological state and detoxifying potential under conditions of sensitivity or tolerance. Toxicity of atrazine could be related to inefficient activation of singlet oxygen (1O2) quenching pathways leading to 1O2 accumulation. Atrazine treatment also increased hydrogen peroxide (H2O2) content, while reducing gene expressions and enzymatic activities related to two major H2O2-detoxification pathways. Conversely, sucrose-protected plantlets in the presence of atrazine exhibited efficient 1O2 quenching, low 1O2 accumulation and active H2O2-detoxifying systems. In conclusion, sucrose protection was in part due to activation of specific ROS scavenging systems with consequent reduction of oxidative damages. Importance of ROS combination and potential interferences of sucrose, xenobiotic and ROS signalling pathways are discussed.