Electrical signalling in Nitellopsis obtusa: potential biomarkers of biologically active compounds.

The Nitellopsis obtusa (N.A.Desvaux) J.Groves cell provides a model system for complex investigation of instantaneous effects of various biologically active compounds (BC) on the generation of plant bioelectrical signals in vivo. Experimental evidence using multiple electrical signals as biomarkers of the effects of BC (acetylcholine, asparagine, glutamate, nicotine, aluminium, nickel and cadmium ions) is provided. The effect of BC on membrane transport systems involved in the cell excitability were tested by current clamp, voltage clamp and patch clamp methods. Membrane potential (MP) alterations and action potential (AP) patterns in response to BC were shown to represent the cell state. High discretisation frequency allows precise, high time resolution analysis of real-time processes measuring changes in excitation threshold, AP amplitude and velocity of repolarisation values after application of BC indicating the effect on ion channels involved in AP generation. Application of voltage clamp revealed that changes in AP peak value were caused not only by increment in averaged maximum amplitude of the Cl- current, but in prolonged Cl- channels' opening time also. The cytoplasmic droplet can serve as a model system in which the effects of BC on single tonoplast ion channel can be studied by patch clamping. Investigation of electrical cell-to-cell communication revealed evidence on the electrical signal transduction through plasmodesmata.