Red-emitting fluorescent probe with excellent water solubility for the in situ monitoring of endogenous H2S in wheat under salt and Al3+ stress.

Hydrogen sulfide (H2S) is a pivotal signaling molecule in plants and appropriate levels are essential for normal growth. As such the real-time detection of H2S in plants is required since it enables timely targeted interventions. However, most fluorescent probes for detecting H2S reported to date exhibit fluorescence quenching in aqueous solution thereby significantly constraining their potential for in vivo applications. In response to this challenge, we present a natural flavylium-inspired fluorescent probe with robust water solubility for turn-on detection of H2S in organisms. The probe exhibits a remarkable 28-fold turn-on signal at 619 nm with rapid reaction kinetics (-20 min), coupled with high sensitivity (LOD = 0.37 μM) and exceptional selectivity for H2S. By employing the probe as an imaging agent, we managed to successfully visualize the fluctuations of exogenous and endogenous H2S levels in HeLa cells. More importantly, the probe enabled the facile and precise visualization of H2S in stressed wheat roots, achieving remarkable micron-level resolution through in-situ imaging, thereby confirming the upregulation of H2S in response to aluminum ion and salt stress. Our research provides a novel tool to investigate the response and mitigation mechanisms of H2S in plants under diverse stress conditions, as well as strategies for enhancing crop resilience.