title: Sieve elements caught in the act.
abstract: Phloem is a puzzling plant tissue owing to the unique natural defence responses of the sieve elements to any kind of mechanical manipulation. Recent non-invasive studies have enabled real-time observation of events in intact sieve tubes, including mass transport, sieve-pore sealing and conformational changes of structural proteins. These studies further highlighted the importance of the symplasmic setting for development and functioning of the sieve elements. Exchange of macromolecules between companion cells and sieve elements is indispensable for the survival of the sieve element, but also seems to be involved in long-distance communication. How the branched plasmodesmata between sieve element and companion cell function as corridors for the passage of macromolecules is an intriguing but unresolved story.
authors.affiliation: Institute General Botany, Justus-Liebig University Giessen, Senckenbergstrasse 17, 35390, Giessen, Germany. aart.v.bel@bot1.bio.uni-giessen.de
authors.forename: Aart J E
authors.initials: AJ
authors.lastname: van Bel
authors.forename: Katrin
authors.initials: K
authors.lastname: Ehlers
authors.forename: Michael
authors.initials: M
authors.lastname: Knoblauch
mesh_terms: D001692:Biological Transport; D007365:Intercellular Junctions / Q000502:physiology* / Q000648:ultrastructure; D008854:Microscopy, Electron; D010940:Plant Proteins / Q000378:metabolism; D018514:Plant Structures / Q000502:physiology* / Q000648:ultrastructure; D011523:Protoplasts / Q000502:physiology* / Q000648:ultrastructure; D018749:RNA, Plant / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology
chemical_list: D010940:Plant Proteins; D018749:RNA, Plant