Long Term Measurement of the Trans-Root Electric Potential in a Persimmon Tree in the Field

kaki tree (Diospyros kaki, Japanese persimmon), which showed clear diurnal oscillation throughout two successive years. The level of the TRP on the average for every ten days had two minima (ca. –70 mV) in mid winter and mid summer, and two maxima (ca. –30 mV) in October and May. A regular seasonal change in the amplitude of the oscillation was observed; it was at its maximum (ca. 70 mV) in early spring just before the sprouting of new leaves, and at its minimum (ca. 10 mV) during summer and early autumn when leaves were fully expanded. The relationship between the TRP, water transport and rainfall is discussed. Received 18 February 1998/ Accepted in revised form 8 November 1998