CONTROL OF PHLOEM UNLOADING BY ACTION-POTENTIALS IN MIMOSA

In the sensitive plant, Mimosa pudica, action potentials arise when the leaves are touched and they trigger a sudden decrease in turgor of the pulvinar motor cells, which causes the leaf to close. These potentials may travel through the phloem and they appear to influence pulvinar phloem unloading after stimulation. Mature leaves were exposed to (CO2)-C-14 and phloem translocation was observed by autoradiography. In unstimulated pulvini, labeled photoassimilates were restricted to the phloem. However, after stimulation, the C-14-label appeared to be concentrated in the extensor region of the motor cortex. Since stimulation elicits an action potential, it is suggested that it also triggers phloem unloading of sucrose in the pulvini.