Cold- and menthol-evoked membrane potential changes in the moss Physcomitrella patens: influence of ion channel inhibitors and phytohormones.

Microelectrode measurements carried out on leaf cells from Physcomitrella patens revealed that a sudden temperature drop and application of menthol evoked two types of different-shaped membrane potential changes. Cold stimulation evoked spike-type responses. Menthol depolarized the cell membrane with different rates. When it reached above 1mVs(-1), the full response was recorded. Characteristic for the full responses was also a few-minute plateau of the membrane potential recorded after depolarization. The influence of inhibitors of calcium channels (5mM Gd3+), potassium channels (5 mM Ba2+), chloride channels (200 mu M Zn2+, 50 mu M niflumic acid) and proton pumps (10 mu M DES), an activator of calcium release from intracellular stores (Sr2+), calcium chelation (by 400 mu M EGTA) and phytohormones (50 mu M auxin, 50 mu M abscisic acid (ABA), 500 mu M salicylic acid) on cold- and menthol-evoked responses was tested. Both responses are different in respect to the ion mechanism: cold-evoked depolarizations were influenced by Ba2+ and DES; in turn, menthol-evoked potential changes were most effectively blocked by Zn2+. Moreover, the effectiveness of menthol in generation of full responses was reduced after administration of auxin or ABA, i.e. phytohormones known for their participation in responses to cold and regulation of proton pumps. The effects of DES indicated that one of the main conditions for generation of menthol-evoked responses is inhibition of the proton pump activity. Our results indicate that perception of cold and menthol by plants proceeds in different ways due to the differences in ionic mechanism and hormone dependence of cold- and menthol-evoked responses.