Ionic mechanism and role of phytochrome-mediated membrane depolarisation in caulonemal side branch initial formation in the moss Physcomitrella patens

Elena Petroff, Dale Sanders, Eva Johannes

Research output: Contribution to journalArticle

35 Citations (Scopus)

Abstract

In caulonemal filaments of the moss Physcomitrella patens (Hedw.), red light triggers a phytochrome-mediated transient depolarisation of the plasma membrane and the formation of side branch initials. Three-electrode voltage clamp and ion flux measurements were employed to elucidate the ionic mechanism and physiological relevance of the red-light-induced changes in ion transport. Current-voltage analyses indicated that ion channels permeable to K+ and Ca2+ are activated at the peak of the depolarisation. Calcium influx evoked by red light coincided with the depolarisation in various conditions, suggesting the involvement of voltage-gated Ca2+ channels. Respective K+ fluxes showed a small initial influx followed by a dramatic transient efflux. A role of anion channels in the depolarising current is suggested by the finding that Cl- efflux was also increased after red light irradiation. In the presence of tetraethylammonium (10 mM) or niflumic acid (1 μM), which block the red-light-induced membrane depolarisation and ion fluxes, the red-light-promoted formation of side branch initials was also abolished. Lanthanum (100 μM), which inhibits K+ fluxes and part of the initial Ca2+ influx activated by red light, reduced the development of side branch initials in red light by 50%. The results suggest a causal link between the red-light-induced ion fluxes and the physiological response. The sequence of events underlying the red-light-triggered membrane potential transient and the role of ion transport in stimulus-response coupling are discussed in terms of a new model for ion-channel interaction at the plasma membrane during signalling.

Original languageEnglish
Pages (from-to)109-118
Number of pages10
JournalPlanta
Volume201
Issue number2
DOIs
StatePublished - 1 Jan 1997

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Bryopsida
Phytochrome
Bryophyta
Physcomitrella patens
phytochrome
red light
mosses and liverworts
Light
Membranes
calcium
Ion Transport
ion channels
ion transport
Ions
ions
Ion Channels
plasma membrane
Niflumic Acid
Cell Membrane
Lanthanum

Keywords

  • Depolarisation
  • Ion transport
  • Physcomitrella
  • Phytochrome
  • Signal transduction

Cite this

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Ionic mechanism and role of phytochrome-mediated membrane depolarisation in caulonemal side branch initial formation in the moss Physcomitrella patens. / Petroff, Elena; Sanders, Dale; Johannes, Eva.

In: Planta, Vol. 201, No. 2, 01.01.1997, p. 109-118.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Ionic mechanism and role of phytochrome-mediated membrane depolarisation in caulonemal side branch initial formation in the moss Physcomitrella patens

AU - Petroff, Elena

AU - Sanders, Dale

AU - Johannes, Eva

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N2 - In caulonemal filaments of the moss Physcomitrella patens (Hedw.), red light triggers a phytochrome-mediated transient depolarisation of the plasma membrane and the formation of side branch initials. Three-electrode voltage clamp and ion flux measurements were employed to elucidate the ionic mechanism and physiological relevance of the red-light-induced changes in ion transport. Current-voltage analyses indicated that ion channels permeable to K+ and Ca2+ are activated at the peak of the depolarisation. Calcium influx evoked by red light coincided with the depolarisation in various conditions, suggesting the involvement of voltage-gated Ca2+ channels. Respective K+ fluxes showed a small initial influx followed by a dramatic transient efflux. A role of anion channels in the depolarising current is suggested by the finding that Cl- efflux was also increased after red light irradiation. In the presence of tetraethylammonium (10 mM) or niflumic acid (1 μM), which block the red-light-induced membrane depolarisation and ion fluxes, the red-light-promoted formation of side branch initials was also abolished. Lanthanum (100 μM), which inhibits K+ fluxes and part of the initial Ca2+ influx activated by red light, reduced the development of side branch initials in red light by 50%. The results suggest a causal link between the red-light-induced ion fluxes and the physiological response. The sequence of events underlying the red-light-triggered membrane potential transient and the role of ion transport in stimulus-response coupling are discussed in terms of a new model for ion-channel interaction at the plasma membrane during signalling.

AB - In caulonemal filaments of the moss Physcomitrella patens (Hedw.), red light triggers a phytochrome-mediated transient depolarisation of the plasma membrane and the formation of side branch initials. Three-electrode voltage clamp and ion flux measurements were employed to elucidate the ionic mechanism and physiological relevance of the red-light-induced changes in ion transport. Current-voltage analyses indicated that ion channels permeable to K+ and Ca2+ are activated at the peak of the depolarisation. Calcium influx evoked by red light coincided with the depolarisation in various conditions, suggesting the involvement of voltage-gated Ca2+ channels. Respective K+ fluxes showed a small initial influx followed by a dramatic transient efflux. A role of anion channels in the depolarising current is suggested by the finding that Cl- efflux was also increased after red light irradiation. In the presence of tetraethylammonium (10 mM) or niflumic acid (1 μM), which block the red-light-induced membrane depolarisation and ion fluxes, the red-light-promoted formation of side branch initials was also abolished. Lanthanum (100 μM), which inhibits K+ fluxes and part of the initial Ca2+ influx activated by red light, reduced the development of side branch initials in red light by 50%. The results suggest a causal link between the red-light-induced ion fluxes and the physiological response. The sequence of events underlying the red-light-triggered membrane potential transient and the role of ion transport in stimulus-response coupling are discussed in terms of a new model for ion-channel interaction at the plasma membrane during signalling.

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