The neck constriction in plasmodesmata : Evidence for a peripheral sphincter-like structure revealed by fixation with tannic acid

摘要: Simple plasmodesmata between mesophyll and bundle sheath cells in actively expanding leaves of Salsola kali L. roots Epilobium hirsutum are shown to possess specialized structures, called sphincters, around their neck regions. The sphineters made visible by the combined effects tannic acid heavy metal staining; they localized just outside that area plasmalemma, which forms collar entrance each plasmodesmos. This localization corresponds a very active plasmodesmos/olasmalemma complex (i.e. enzyme activity and/or presence strongly reducing substances).Evidence is presented these ring structures structural equivalents hypothetical sphincters performing some valve function; i.e. participating control rates directions symplastic transport solutes through plasmodesmata. middle layer plasmalemma region composed closely-packed, globular subunits appearing negative contrast. Apparently, correspond particle clusters observed at plasmodesmatal freeze-fracture preparations. They appear similar animal tight junctions, possible function providing electrical coupling via low resistance junctions plant discussed.