Fluorescence study on the nyctinasty of Cassia mimosoides L. using novel fluorescence-labeled probe compounds

We synthesized fluorescence-labeled probe compounds bearing 6-((7-amino-4-methylcoumarin-3-acetyl)amino)-hexanoyl (AMCA, 1), 6-N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl)-aminohexanoyl (NBD, 2), and 6-(4-((5-dimethylaminonaphthalene-1-sulfonyl)-amino))-hexanoyl (dansyl, 3) groups as the fluorescent functionality. In these probe compounds, NBD-type probe, 2, showed leaf-opening activity at 5×10−6 M. The bioactivity of 2 is one-fifth as strong as that of the natural product, potassium isolespedezate (6). We carried out the binding experiment using 1 in a plant body. Then, it was suggested that fluorescence-labeled probe compound directly bound to a motor cell in pulvina of Cassia mimosoides. And this binding was specific to C. mimosoides. Probe compounds cannot bind plant sections of other nyctinastic plants.