A Water-Soluble Probe for Visualizing Immune Activation for Microbial Resistance in Rice Crops via NIR-II Fluorescent Imaging

Rice, a vital staple crop, provides sustenance for more than half of the global population, and its production needs to be increased to keep up with the growing global population, while plant diseases threaten the sustainability of rice production, causing significant crop losses and reducing harvest quality. The widespread use of chemical pesticides has raised concerns about environmental pollution, pesticide resistance, and economic burdens. Therefore, alternative, sustainable disease management strategies are urgently needed. One promising solution involves plant immunity inducers, which activate the plant's natural defense mechanisms to combat pathogens. However, the mechanisms underlying immune activation remain poorly understood, and effective tools for the real-time visualization of immune responses are lacking. In this study, we developed a water-soluble and biosafe D-A-D (donor-acceptor-donor)-type fluorescent probe for real-time visualization of immune activation in rice via near-infrared second-window (NIR-II) fluorescence imaging. The probe, featuring a unique electronic structure, with a diphenylaminoxanthene and a benzyl group being the electron donors, the benzo[<i>cd</i>]indolium being the electron acceptor, and a butylamino group for nitric oxide (NO) detection, allows the monitoring of NO production, a key signaling molecule in plant immunity. Our results show that the probe effectively detects NO generation in response to salicylic acid (SA), an immune inducer, and visualizes immune activation and consequent microbial resistance in rice via NIR-II fluorescent imaging. This approach could provide an effective means for obtaining valuable insights into plant immune dynamics and contribute to promoting sustainable agriculture and food security.