Visualizing plant salt stress with a NaCl-responsive fluorescent probe.

Salt stress is an adverse environmental condition that harms plant growth and development. The development of salt stress probes is critical for tracking the growth dynamics of plants, molecular breeding or screening of growth regulators. The sodium chloride (NaCl)-responsive fluorescent probe Aza-CyBz is designed based on the tenet that NaCl induces formation of ordered aggregates, and the sensitive fluorescence response can enable the visualization of plant salt stress in root tip tissues and live plants. Herein, we describe a detailed three-step route for synthesis of Aza-CyBz and applications to monitoring salt stress in Arabidopsis thaliana. The procedures for operating fluorescence imaging under various stresses are also listed to eliminate interference from the oxidative mechanism of salt stress. Compared with conventional invasive approaches such as inductively coupled plasma emission spectrometry and flame photometer, our protocol can real-time monitor salt stress experienced by plants, which demands simple pretreatment procedure and staining technique. Due to near infrared fluorescence, this method provides direct visual observation of salt stress at both tissue and live plant levels, which is superior to conventional noninvasive approaches. The preparation of probe Aza-CyBz takes ~2 d, and the imaging experiments for assessing salt stress experienced by plants, including the preparation of stressed plant samples takes ~9-11 d for root tip tissues and ~23 d for live plants. Notably, acquisition and analysis visual images of salt stress in plants can be completed within 2 h and they require only a basic knowledge of spectroscopy and chemistry.