The rational design of a Rhodamine fluorescent probe enables the selective detection and bioimaging of salicylic acid in plants under abiotic stress

Summary Abiotic stress severely hinders plant growth and development, resulting in a considerable reduction in crop yields. Salicylic acid (SA) serves as a central signal mediating abiotic stress responses in plants. Real‐time fluorescence tracking using specific probes can enhance our understanding of the SA‐triggered modulation underlying these events. However, in complicated living plant microenvironments, selective recognition and bioimaging of SA is a great challenge for scientists due to the severe background interference and SA analogues. Herein, an efficient fluorescence probing technology employing a highly selective rhodamine probe—phoxrodam was developed, which realizes the precise bioimaging of SA in salt‐stressed plant seedlings. Experimental findings reveal that phoxrodam demonstrates exceptional selectivity (fluorescence intensity: I Phoxrodam+SA / I Phoxrodam+SA analogues > 4.29‐fold), high sensitivity (limit of detection = 6.42 nM, fluorescence quantum yield: Φ Phoxrodam+SA = 0.36) and good anti‐interference properties. Furthermore, we confirmed that phoxrodam accurately detects SA in the roots of salt‐stressed wheat seedlings, the low‐temperature resistance of Nicotiana benthamiana and the heavy metal resistance of pea seeds, using in vivo confocal imaging. This study provides a feasible strategy for efficiently tracking plant signalling molecules and promotes the in‐depth research of SA‐mediated physiological mechanisms, laying a key foundation for the future development of new immune activation inducers.