[en] The natural occurring radioactivity in various plant samples was observed by using imaging plate (IP) with high sensitivity. The high intensity of ⁴⁰K radioactivity was observed clearly in living organisms in the plants. The autoradiograms were obtained for Azuki bean cutting samples treated with water and KCl solution. The autoradiographic intensity of KCl-treated samples was higher than that of water-treated samples, especially in the part of apices. Potassium content was calculated from PSL (the relative intensity of photo-stimulated luminescence) data of three parts of the samples, epicotyls, leaves and apices. The K content in Azuki cuttings estimated from PSL data was approximately consistent with that determined by neutron activation analysis method. However, there are some problems to be made clear in the use of IP method, for example, validation of each IP, conditions of exposure, measurement of PSL data, fadings of images. (author)