title: Sieve element Ca2+ channels as relay stations between remote stimuli and sieve tube occlusion in Vicia faba.
abstract: Damage induces remote occlusion of sieve tubes in Vicia faba by forisome dispersion, triggered during the passage of an electropotential wave (EPW). This study addresses the role of Ca2+ channels and cytosolic Ca2+ elevation as a link between EPWs and forisome dispersion. Ca2+ channel antagonists affect the initial phase of the EPW as well as the prolonged plateau phase. Resting levels of sieve tube Ca2+ of approximately 50 nM were independently estimated using Ca2+-selective electrodes and a Ca2+-sensitive dye. Transient changes in cytosolic Ca2+ were observed in phloem tissue in response to remote stimuli and showed profiles similar to those of EPWs. The measured elevation of Ca2+ in sieve tubes was below the threshold necessary for forisome dispersion. Therefore, forisomes need to be associated with Ca2+ release sites. We found an association between forisomes and endoplasmic reticulum (ER) at sieve plates and pore-plasmodesma units where high-affinity binding of a fluorescent Ca2+ channel blocker mapped an increased density of Ca2+ channels. In conclusion, propagation of EPWs in response to remote stimuli is linked to forisome dispersion through transiently high levels of parietal Ca2+, release of which depends on both plasma membrane and ER Ca2+ channels.
authors: Plant Cell Biology Research Group, Institute of General Botany, Justus-Liebig-University, D-35390 Giessen, Germany.
authors: Alexandra C U
authors: AC
authors: Furch
authors: Aart J E
authors: AJ
authors: van Bel
authors: Mark D
authors: MD
authors: Fricker
authors: Hubert H
authors: HH
authors: Felle
authors: Maike
authors: M
authors: Fuchs
authors: Jens B
authors: JB
authors: Hafke
mesh_terms: D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D004594:Electrophysiology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D009543:Nifedipine / Q000494:pharmacology; D052585:Phloem / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D010940:Plant Proteins / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology; D031307:Vicia faba / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D010940:Plant Proteins; D014700:Verapamil; D009543:Nifedipine; D002118:Calcium