Weak mechanical stimulation causes hyperpolarisation in root cells of Lepidium

In order to study the effect of mechanical stimulation on the membrane potential (Era) 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 rhizoderreal 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.