Fast, transient and specific intracellular ROS changes in living root hair cells responding to Nod factors (NFs)

The role of reactive oxygen species (ROS) in root-nodule development and metabolism has been extensively studied. However, there is limited evidence showing ROS changes during the earliest stages of the interaction between legumes and rhizobia. Herein, using ratio-imaging analysis, increasing and transient ROS levels were detected at the tips of actively growing root hair cells within seconds after addition of Nod factors (NFs). This transient response (which lasted up to 3 min) was Nod-factor-specific, as chitin oligomers (pentamers) failed to induce a similar response. When chitosan, a fungal elicitor, or ATP was used instead, a sustained increasing signal was observed. As ROS levels are transiently elevated after the perception of NFs, we propose that this ROS response is characteristic of the symbiotic interaction. Furthermore, we discuss the remarkable spatial and temporal coincidences between ROS and transiently increased calcium levels observed in root hair cells immediately after the detection of NFs.