Light- and dark-induced action potentials inPhyscomitrella patens

Abstract

Glass microelectrodes were inserted into Physcomitrella patens gametophyte leaves and action potentials (APs) were recorded in response to sudden illumination as well as after darkening, i.e., when the dark-induced membrane depolarization crossed a threshold. Application of 5 mM La 3+ (a calcium channel inhibitor), 10 mM TEA + (a potassium channel inhibitor) and increased free Ca 2+ resulted in a loss of excitability. Lack of Ca 2+ in the external medium did not prevent APs from occurring. It was concluded that during light-dark-induced excitation of Physcomitrella patens, APs might rely upon calcium influxes from the intracellular compartments. APs were not blocked by the proton pump inhibitors (DES, DCCD), although the resting potential (RP) diminished significantly.

Generation of action potential-type changes in response to darkening and illumination as indication of the plasma membrane proton pump status in Marchantia polymorpha

“…The amplitudes of APs evoked by illumination and darkening are similar and relatively constant, but the halftimes are different, i.e., light-induced APs are characterised by several times shorter half-time than APs evoked by darkening (Ermolayeva et al 1996;Koselski et al 2008). In the range of subthreshold values, electrical responses of the moss cells to light-dark transitions are opposite and symmetrical to the responses evoked by light stimulation, i.e., illumination evokes transient depolarisation first and then long-lasting hyperpolarisation, while darkening causes fast hyperpolarisation followed by long-lasting depolarisation (Ermolayeva et al 1996;Koselski et al 2008).…”

“…Taking into account the repolarisation features mentioned above and the fact that the threshold value of the intensity and time of illumination preceding darkening (refractory period) was hard to establish, we regarded AP dark -like responses as not being typical action potentials. Interestingly, generation of AP dark and/or AP dark -like after darkening and persistent depolarisation was observed in the moss P. patens (Koselski et al 2008), but not in the liverwort C. conicum . The dark-induced AP dark in M. polymorpha was characterised by a several times shorter half-time (10-s range) than AP dark registered in P. patens (10-min range) (Koselski et al 2008).…”

“…Interestingly, generation of AP dark and/or AP dark -like after darkening and persistent depolarisation was observed in the moss P. patens (Koselski et al 2008), but not in the liverwort C. conicum . The dark-induced AP dark in M. polymorpha was characterised by a several times shorter half-time (10-s range) than AP dark registered in P. patens (10-min range) (Koselski et al 2008). In M. polymorpha cells, illumination, in contrast to darkening, always evoked typical action potentials for the threshold and higher light intensities or generator potentials (GPs) for subthreshold light stimuli depending on the light intensity values.…”

“…Gametophyte cells of P. patens generate APs both in response to illumination and darkening (Koselski et al 2008). The amplitudes of APs evoked by illumination and darkening are similar and relatively constant, but the halftimes are different, i.e., light-induced APs are characterised by several times shorter half-time than APs evoked by darkening (Ermolayeva et al 1996;Koselski et al 2008).…”

“…However, to date, there has been no report about the characteristics of electrical signals in M. polymorpha gamethophyte cells. Simultaneously, there are reports about intracellular investigations conducted on another liverwort Conocephalum conicum (Dziubińska et al 1983;Favre et al 1999b;Król et al 2007;Zawadzki and Trębacz 1985) and on the moss Physcomitrella patens, a species that is phylogenetically related to liverworts and regarded as a model system in plant functional genomics (Decker et al 2006;Reski 1999) and electrophysiology (Ermolayeva et al 1996(Ermolayeva et al , 1997Koselski et al 2008Koselski et al , 2013Koselski et al , 2015. Conocephalum conicum displays excitability to various stimuli, such as light (Król and Trębacz 1999;Trębacz and Zawadzki 1985;Trębacz et al 1989a), cold (Król et al 2003;Kupisz and Trebacz 2011), wounding (Favre et al 1999a), and direct current (DC) (Dziubińska et al 1983;Król and Trębacz 1999;Paszewski et al 1982).…”