Selection of recording pattern of plant surface electrical signal based on analysis of electrical characteristics

Abstract: Research in plant electrophysiology has been developed for more than 100 years. However, even today, there are still many researchers may be puzzled by the results of different amplitude waveforms when recording plant potential signals. It is necessary to make a discussion of plant electrical potential recording method. In this paper, the history of plant electrical activity recording method and system is introduced. Surface electrical potentials of the wheat (Dekang 961) and Mimosa pudica were respectively recorded by AC (alternating current) and DC (direct current) coupling simultaneously. There is a huge difference in wave shape and amplitude between DC coupling and AC coupling with 0.16 Hz lower cut-off frequency signal in wheat induced by light, and the peak-to-peak value in DC coupling recording wave was 25 times higher than that in AC coupling recording wave. The energy frequency spectrum distribution of local potential was less than 0.2 Hz through the time-frequency mapping of DC coupling recording data. The difference of variation potential induced by burn in Mimosa pudica in DC and AC coupling measurement was relatively smaller than local potential in wheat, and the time-frequency mapping reflected that the main energy frequency spectrum was distributed within 0.6 Hz. Deeply, AC coupling measurement on the experiments of 3 different lower cut-off frequencies (0.03, 0.16, 1.6 Hz) had been made to analyzed the diversity of amplitude and waveform in wheat electrical signal. The signals recorded in this paper, either in DC coupling or in AC coupling, did not appear with randomness. In order to confirm those waves reflecting the electrical activity of plant, transmission experiment and Ca2+ channel block experiment were made. Two electrodes with a distance of 4 cm were fixed on the caudex of Mimosa. The result showed that variation potential was transmitted from Electrode 1 to Electrode 2. The Ca2+ channel blocker LaCl3 was used to decrease the amplitude of local potential wave in wheat, and after 4 h block treatment, the amplitudes of AC coupling and DC coupling wave were reduced obviously. Characteristics of DC coupling and AC coupling measurement were analyzed and discussed. The amplitude of plant electrical potential recorded in DC coupling method was always in dozens of microvolts, and DC coupling recording method may have a better performance in resisting high frequency and low amplitude noise from the view of noise source and analog-to-digital conversion accuracy. However, DC coupling recording method is always impacted by low frequency noise, such as electrode potential drift. AC coupling recording has a significant advantage in resisting low-frequency potential drift and high acquisition accuracy, but it is easy to receive high-frequency noise during the recording and it is difficult to extract the plant electrical activity from noise. In conclusion, DC coupling recording method can fully present the plant slow electrical activity. The data will be more suitable for studying the transmembrane ion movement process of plant cells and the formation mechanism of plant electrical signals. The AC coupling recording method is appropriate for studying rapidly changing plant electrical signals, and the lower cut-off frequency has to be regulated accurately.