Investigation of the ion concentration effect on Eucalyptus root growth in a.c. electric field

Electric stimulation of animal tissues, such as nerve fiber or muscle, has prominent effects of strong sensation or contraction of limbs. On the other hand, electric stimulation of plants has been reported to have rather depressing effects on plant growth. It seems to be caused by damages of cells by the electric stimulation. However some plant species showed increased growth rate by application of a.c. electric field in specific field intensity range. In this study, root growth enhancement of Eucalyptus seedling by electric field stimulation was precisely investigated. Especially the effects of soluble factors in culture medium, to the growth rate of Eucalyptus seedling in water, was measured. Eucalyptus seedlings were cultured in diluted M.S. medium. The seedlings in a vessel was exposed to 50 [Hz] a.c. electric field of 0 to 100 [V/m]. In some cases, the seedlings showed enhanced growth rate in 40-60 [V/m], but in some cases, however, growth rate was enhanced in higher intensities. These discrepancy may come from the large growth rate diversity of seedlings in a culture. Ion concentration of medium was investigated by measuring the electric conductivity. Within some 10 [mS/cm] fluctuation, ion concentration showed no specific effects on growth rate. To eliminate the effect of other unknown bioactive factors, culture system with medium circulation is utilized and field effects was measured. From the results, involvement of H+ ion in root growth control was expected, which suggests homologous system with nerve stimulation of animal in plant growth control.