Direct observation of a target cell of the leaf-closing factor by using novel fluorescence-labeled phyllanthurinolactone

We report the synthesis of the fluorescence-labeled probe 2 based on phyllanthurinolactone 1, which is a leaf-closing substance of Phyllanthus urinaria L. Bioorganic studies using probe 2 showed leaf-closing activity at 1 × 10−5 M, which was one-hundredth of that of the natural product 1. The fluorescence study using 2 revealed that the target cell for 1 is a motor cell and suggested that some receptors for 1 exist on the plasma membrane of the motor cell as with leaf-opening substances.