Glutamate induces series of action potentials and a decrease in circumnutation rate in Helianthus annuus

Reports concerning the function of glutamate (Glu) in the electrical and movement phenomena in plants are scarce. Using the method of extracellular measurement, we recorded electrical potential changes in the stem of 3-week-old Helianthus annuus L. plants after injection of Glu solution. Simultaneously, circumnutation movements of the stem were measured with the use of time-lapse images. Injection of Glu solution at millimolar (200, 50, 5 mM) concentrations in the basal part of the stem evoked a series of action potentials (APs). The APs appeared in the site of injection and in different parts of the stem and were propagated acropetally and/or basipetally along the stem. Glu injection also resulted in a transient, approximately 5-h-long decrease in the stem circumnutation rate. The APs initiated and propagating in the sunflower stem after Glu injection testify the existence of a Glu perception system in vascular plants and suggest its involvement in electrical, long-distance signaling. Our experiments also demonstrated that Glu is a factor affecting circumnutation movements.