RESPONSE OF LEAF ELECTRICITY TO PHOTO-STIMULI K. Matsumoto, S. Shibusawa, A. Sasao, K. Sakai United graduate School of Agricultural Science Tokyo University of Agriculture and Technology 3-5-8 Saiwai-Cho, Fuchu-shi, Tokyo /83-8509, Japan Correspondent Email sshibu@cc.tuat.ac.)p Abstract: Frequency response of cactus leaf electricity to oscillated illumination stimuli was measured. For this purpose, a sensing system enabling to long term and stable measurement was developed. The illuminations were I minute light - on and 1minute light - off , 8minutes light - on and 8minutes light off, 20minutes light - on and 20minutes light - off, and 60 minutes light - on and 60 minutes light - off The result showed that the response was similar to that of a low pass filter, especially it has relatively higher gain between 0.0006Hz and 0.001 Hz. Copyright <C' 200f/FAC Keyword Plant, Light, Response, Electrical behavior, Sensor systems. I. INTRODUCTION Speaking Plant Approach (SPA) is an attractive method for investigating what the plant needs under variations in its environment changes. The SPA requires in -situ real-time measurement of a living plant. Therefore understanding more about living plants with modeling or system identification IS encouraged. (Morimoto, et ai , 1988) Leaf surface electricity, a kind of bioelectricity, generally rooted in physiological activity (Kano, et aI., 1988). Kano and Yamaguchi, (1996) reported that correlation appeared between freshness and electric potential voltage of plant surface. Leaf electricity is composed of AC and DC ingredients. DC ingredient especially fluctuated when the illumination was changed. DC was suggested to have a relation to photosynthesis activity (Utamaru et al, 1999). There were many reports about the measurement of bioelectricity of plants by using fine needle electrodes, which tended to injure or destroy the plant tissues and cells. This kind of measurement is not available for investigation of long term behavior regarding to living plant activities The objectives of this paper are 91 (I) Measuring of leaf electricity on intact plant by developing a sensing system to enable a long term stable measurement. (2) Detecting electric variations or fluctuations by oscillating illumination stimuli. 2. EXPERIMENTAL MATERIALS AND METHOD The experiment aimed at getting the response data of leaf electricity as output signal to illumination interval changes. Experimental system is shown in Fig. I . 2.1 Test Plant The test plant was Crassula, a kind of cactus whose photosynthesis type is generally CAM (crassulacean acid metabolism). Crassula leaves were tough, flat and smooth. This made it easy to be fairly pasting of sensing devises on the leaf surface. The test plant in a flowerpot was kept in a biophotochamber. 2.2 Biophotochamber.