Search for biologically active substances of plants by using the electrophysiological method with excitatory plant cells of Mimosa pudica

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Although much attention has been paid on the leaf movement of Mimosa pudica with irritation and the mechanism for the rapid conduction of stimulus is still controversial in the plant, we found that M.pudica L.was very sensitve to the administration of extraneous substnces and such stimulation afforded electrophysiological responses. Actually, during observation of resting potential strong pulses wre recorded by an admistration of methanol extract of other plants. We then searched for the substance responsible for the activity in Melia azedarach L.as an example. ^<13>C- and ^1H-NMR,FT-IR and mass spectrometric analyzes, as well as alkaline metal identification by a flame analysis demonstrated that the isolated active compound was sodium glutamate. Although commercial L-sodium glutamate showed the same strong pulses in the identical assay, unnatural sodium D-glutamate did not afford such pulse at all. This unambiguously suggests that the interaction of the amino acid with the plant tissue was strictly diastereoselective at the molecular level. From Albizzia julibrissin, two compounds were isolated as active principles, one of which was identified as 5-hydroxypipecolic acid and other's structure still remains to be determined. These studies provide the first example to suggest that measuring the electric pulses produced by M.pudica could be utilized as a method for screening biologically important compounds in plant kingdom.