Searching for nitroxyl modulators in Arabidopsis thaliana: a new paradigm of redox signaling in plants

Through extensive research, nitroxyl (HNO) has emerged as a newly recognized redox signal in plant developmental and stress responses. The interplay between nitric oxide (●NO) and HNO entails a complex network of signaling molecules and regulatory elements sensitive to the environment-specific redox conditions. However, functional implications for HNO in cell signaling require more detailed studies, starting with identifying HNO-level switches. To obtain insight into possible physiologically relevant HNO modulators, we used real-time detection to examine HNO/●NO production triggered by selected plant-related compounds (PRCs), including non-protein amino acids, antioxidants, and phytohormones, both in vitro and in vivo in the model plant Arabidopsis thaliana. Hydrogen sulfide, ascorbic acid, and salicylic acid were identified as superior PRCs in driving HNO/●NO interconversion in the cellular medium, so that these PRCs could provide ubiquitous bioavailability of HNO in plants. Meanwhile, resistance-inducing compounds tended to down-regulate HNO in Arabidopsis leaves. The present study indicates that non-enzymatic HNO/●NO interconversion mediated by functionally important PRCs constitutes a significant route for controlling endogenous HNO concentrations, providing ubiquitous HNO bioavailability in plant cells. Moreover, concurrent HNO/●NO monitoring shows that the redox signals are highly integrated and create a redox code that can be translated into a specific cellular response.