BODIPY–Rhodacycle Fluorescent Probe for In Situ Imaging of Ethylene Dynamics in Live Systems

Endogenous ethylene production occurs across biological kingdoms, yet its pathophysiological roles remain incompletely defined. In situ detection of ethylene is impeded by its inherent volatility and chemical inertness. Here, we report BORh, a new turn-on fluorescent probe that operates via ethylene-triggered displacement of a rhodium quencher from a BODIPY-rhodacycle scaffold, liberating the intensely fluorescent BOET. BORh exhibits high sensitivity and selectivity, broad pH tolerance, and negligible cytotoxicity. In mammalian PC12 cells, it permits real-time visualization of both exogenously supplied and in situ generated ethylene. Within photosynthetic systems, BORh overcomes cell wall barriers and chlorophyll autofluorescence, enabling in situ monitoring of ethylene dynamics in algae (<i>Chlamydomonas reinhardtii</i>) and higher plant (<i>Arabidopsis thaliana</i> and <i>Allium cepa</i>) tissues. Remarkably, BORh-enabled fluorescence imaging revealed synchronous upregulation of ethylene and reactive oxygen species (ROS) under plant abiotic stress. H₂O₂ exhibited concentration-dependent biphasic regulation of ethylene biosynthesis, whereas ethylene exerted no reciprocal effect on ROS generation. These findings establish ROS as upstream regulators of ethylene biosynthesis within plant stress signaling cascades. BORh emerges as a robust chemical tool for spatiotemporal dissection of ethylene biochemistry, offering new insights into ROS-ethylene crosstalk during plant stress responses and paving the way for future investigations of ethylene function in mammalian pathophysiology.