Ionic mechanism and role of phytochrome-mediated membrane depolarisation in caulonemal side branch initial formation in the mossPhyscomitrella patens |
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Authors: | Elena Ermolayeva Dale Sanders Eva Johannes |
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Institution: | (1) The Plant Laboratory, Biology Department, University of York, PO Box 373, Y01 5YW York, UK;(2) Present address: Pharmacology Department, University of Cambridge, Tennis Court Road, CB2 IQJ Cambridge, UK |
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Abstract: | In caulonemal filaments of the mossPhyscomitrella 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 M), 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 M), 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.Abbreviations Ca2+]c
cytosolic free Ca2+
- I-V
current-voltage
- E
equilibrium potential
- Pr
red-light-absorbing phytochrome form
- Pr
far-red-light-absorbing phytochrome form
- SPQ
6-methoxy-l-(3-sulphonatopropyl)quinolinium
- TEA
tetraethylammonium |
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Keywords: | Depolarisation Ion transport Signal transduction Physcomitrella Phytochrome |
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