A fluorescent probe for visualizing peroxynitrite levels during plant growth under abiotic stresses

The imbalance of reactive nitrogen species (RNS) levels is one of the main pathological changes in plants under abiotic stress. Among them, the imbalance of peroxynitrite (ONOO-) leads to nitrosation reactions that cause plant damage. In this study, a naphthylimide fluorescent probe (NFP) was constructed by using the twisted intramolecular charge transfer (TICT) property with naphthylimide as the fluorophore and methyl (4-hydroxyphenyl) amino group as the recognition group. The interaction mechanism between the probe NFP and ONOO- was verified by density-functional theory (DFT). The organic fluorescent probe NFP has a small size that can easily enter the cell wall. The probe NFP specifically recognizes ONOO- through N-dearomatisation, triggering a 'turn-on' fluorescence response with an approximately 22-fold increase in fluorescence intensity. NFP showed high sensitivity, prominent selectivity, and rapid response to ONOO-. The reaction of NFP with ONOO- proceeded immediately, and the limit of detection was as low as 7.9 nM, almost unaffected by other interferences. In addition, the fluorescence imaging experiment of onion epidermal cells proved that NFP had good cell permeability and could be applied for plant imaging. NFP was applied to the efficient detection of ONOO- in plant shoots and seedlings, and the in-situ dynamic tracking of ONOO- in plants under abiotic stress was realized. The designed method can reveal changes in ONOO- concentration in seed germination and seedling growth in response to external abiotic stress, and explore the visual response of plants under stress.