Weak Mechanical Stimulation Causes Hyperpolarisation in Root Cells of Lepidium

Abstract: In order to study the effect of mechanical stimulation on the membrane potential (E_m) of roots of Lepidium sativum L., the roots were subjected to pulses of perfusion medium expelled from a micropipette positioned 1 mm from the root surface at the level of the elongation zone. On the opposite side of the root, a microelectrode was inserted into rhizodermal or cortical cells of the elongation zone to record the membrane potential during such a pulse. A medium pulse elicited a fast transient hyperpolarisation of up to ?38 mV, reaching a peak approx. 1 min after the start of a pulse. Both degassing the medium and increasing the buffer strength had no effect on the magnitude of the pulse-induced hyperpolarisation. Covering the roots with Parafilm, and thereby preventing an exchange of medium in the vicinity of the root during a pulse, while still providing a mechanical stimulus, also did not abolish the response. We conclude that Lepidium roots are capable of perceiving extremely weak mechanical stimuli (less than 1 mN) which induce rapid transient hyperpolarisations of the plasma membrane.