Exposure to excessive SO 2 will induce severe phytotoxicity to plants. Dissecting mechanisms of SO 2 phytotoxicity is vital for preventing adverse effect of SO 2. But unfortunately, the mechanisms of SO 2 phytotoxicity remain elusive. We speculated that interaction of SO 2 derivatives with mitochondria might be an important mechanism for SO 2 phytotoxicity. To authenticate this speculation, it is urgently need to detect SO 2 derivatives in plant mitochondria when it is suffering from SO 2 phytotoxicity. Herein, we presented a novel ratiometric NIR fluorescent probe for highly sensitive and selective detection of SO 2 derivatives in plant mitochondria. Notably, the probe not only could target into the mitochondria, but also can immobilize in the mitochondria to continue detecting SO 2 derivatives even when the mitochondrial membrane potential was collapsed by high concentration of SO 2 derivatives. Importantly, the probe has been successfully employed for monitoring high concentration of SO 2 derivatives in the plant mitochondria when the plant is suffering from SO 2 phytotoxicity. The results demonstrated that the SO 2 derivatives level in plant mitochondria is strictly associated with SO 2 phytotoxicity. Thus, the interaction of SO 2 derivatives with plant mitochondria could be considered as an important mechanism for SO 2 phytotoxicity. [Display omitted] • The first fluorescent probe that can detect SO 2 derivatives in plant mitochondria has been rationally developed. • The probe not only targets into mitochondria, but also retains in mitochondria when membrane potential is collapsed. • The interaction of SO 2 derivatives with mitochondria was firstly proved as a key mechanism for SO 2 phytotoxicity. [ABSTRACT FROM AUTHOR]