A fluorescent molecular probe for live-cell imaging of starch granules

Plants accumulate photosynthetic product as starch, which is also a major carbohydrate source for human. Herein, we report the development of a fluorescent molecular probe for starch. Through a in vivo screening-based approach, we identified fluorescein-5-methy thiocarbamate as a candidate of starch probe that works in living plants. We synthesized 19 derivatives for the structural optimization of the starch probe and discovered that fluorescein-5-tert-butyl carbamate is the most specific probe with the brightest fluorescence among them. Analysis using Arabidopsis thaliana mutants of starch metabolism and in vitro NMR experiments revealed that the probe forms a complex with starch and illuminates starch granules in leaf chloroplasts and root amyloplasts within 10 minutes after the probe infiltration into living plant tissues. The starch probe is applicable to track the changes in intracellular starch contents in response to circadian cycle or light conditions. We concluded that fluorescein-5-tert-butyl carbamate can be used as a probe for live-cell and quantitative imaging of starch granules. The probe could be a useful imaging tool to facilitate finding novel phenomena linked with starch metabolism in crop plants.