Aboveground whole-plant live imaging method for nitric oxide (NO) reveals an intricate relationship between NO and H2O2.

Nitric oxide (NO) is a key regulator of plant development, growth, and responses to the environment. Together with hydrogen peroxide (H2O2), NO modifies the structure and function of proteins, controlling redox signaling. Although NO has been studied extensively at the cellular and subcellular levels, very little is known about changes in NO content at the whole-plant level. Here, we report on the development of an aboveground whole-plant live imaging method for NO. Using mutants with altered NO levels, as well as an NO donor/scavenger, we demonstrate the specificity of the detection method for NO. Arabidopsis thaliana plants were found to produce a basal level of NO under control conditions. NO levels accumulated enzymatically in plants following heat stress applied to the entire plant, as well as in a systemic manner following different locally applied stimuli. Similar or opposing accumulation patterns were also found for NO and H2O2 during the response of plants to different stimuli. Our findings reveal that NO accumulates during the systemic response of plants to a local stimulus. In addition, they shed new light on the intricate relationships between NO and H2O2. The new method reported opens the way for multiple future studies of NO's role in plant biology.