Oscillatory Electrical Response to Osmotic Stress in Soybean Plants

Abstract

Oscillations in plants can occur at various levels. Their physiological processes evolve during time, presenting a variable dynamics1. Different oscillatory dynamics in different physiological processes in plants have been observed under different environmental conditions. Oscillatory dynamics allow to organisms flexibility in responses to environmental changes2. Recent studies have evidenced the role of electrical signaling in the physiological processes. At the whole-plant level, oscillations of electrical frequency-coded signals are believed to play an important role in communication between the roots and shoots3. The aim of this work was to test the hypothesis that a severe osmotic stress causes changes in the pattern of electrical signaling in soybean plants, allowing discrimination among signs under different water conditions. Two-week-old soybean seedlings were used for the experiments, carried out under constant environmental conditions and inside a Faraday cage. Electrical time series (n=30) were obtained with an electronic acquisition data system. On previous day of experiments, the plants were transferred to hydroponic cultivation and Needle electrodes were inserted into the stem, for acclimatization. Osmotic stress was applied by replacing the nutrient solution by mannitol solution at -2MPa. Power frequency analysis has confirmed differences in oscillatory characteristic of plant bioelectrical data. Both conditions showed a power spectrum following a power-law distribution, indicating a scale-free pattern of the dynamics. On the other hand, while in the time series scored before osmotic stimuli the range of frequencies from 0.15 to 16Hz followed the power-law trend, after osmotic stimuli this range was from 0.10 to 5Hz. Moreover, before stimuli it was observed a second set of frequencies ranging from 11 to 13Hz, which it was not present in the time series after stimuli. These results have indicates a decrease trend of complexity of the electrical signal to root-shoot communication of soybean seedlings under osmotic stress.