Electrophysiologic Research of Plant Cells by SQUID Systems
Plant cells are electrically excitable and electrical measurements of phenomena like action potential (AP) and action current (AC) are known. We performed SQUID measurements with the aim to obtain a noninvasive information on (i) ionic currents in green algae Chara corallina under either electric field excitation and/or illumination with visible light, and (ii) injury-induced ionic currents in the higher-developed plant Vicia faba .
For the green algae Chara corallina, we found that the action potential spread with the velocity of 3-4 cm/s, that the intracellular current was up to 1 µA and the magnetic field distribution was altered by the influence of light. White light with intensity of 5 - 10 Wm-2 was delivered to the cell under the SQUID microscope by fiber optic bundle. We observed that part of the depolarization slope in the AC and AP signal is prolonged when the cell was exposed to illumination. We call this part of AC or AP signal the preparation part of depolarization signal. A possible hypothesis for this alteration may be connected with the role of Ca2+ and H+ ions. The modified time evolution of AC and AP was observed in about 2/3 of measured internodal cells of Chara corallina. An analysis of complete time course of AC signal is possible because the contributions of all ionic currents are well separated in time.
For the wounded bean plant Vicia faba, the measured magnetic field distribution adjacent to the injury demonstrated that the injury-related ionic current decays with t of 10 min. These results demonstrate the value of SQUID-based measuring systems for noninvasive research of ionic curents in the slowest cells and living tissues in the nature.