title: Microtubule distribution in gravitropic protonemata of the moss Ceratodon.
abstract: Tip cells of dark-grown protonemata of the moss Ceratodon purpureus are negatively gravitropic (grow upward).  They possess a unique longitudinal zonation:  (1) a tip group of amylochloroplasts in the apical dome, (2) a plastid-free zone, (3) a zone of significant plastid sedimentation, and (4) a zone of mostly non-sedimenting plastids.  Immunofluorescence of vertical cells showed microtubules distributed throughout the cytoplasm in a mostly axial orientation extending through all zones.  Optical sectioning revealed a close spatial association between microtubules and plastids.  A majority (two thirds) of protonemata gravistimulated for > 20 min had a higher density of microtubules near the lower flank compared to the upper flank in the plastid-free zone.  This apparent enrichment of microtubules occurred just proximal to sedimented plastids and near the part of the tip that presumably elongates more to produce curvature.  Fewer than 5% of gravistimulated protonemata had an enrichment in microtubules near the upper flank, whereas 14% of vertical protonemata were enriched near one of the side walls.  Oryzalin and amiprophos-methyl (APM) disrupted microtubules, gravitropism, and normal tip growth and zonation, but did not prevent plastid sedimentation.  We hypothesize that a microtubule redistribution plays a role in gravitropism in this protonema.  This appears to be the first report of an effect of gravity on microtubule distribution in plants.
authors.affiliation: Institut für Allgemeine Botanik, Universität Mainz.
authors.forename: J
authors.initials: J
authors.lastname: Schwuchow
authors.forename: F D
authors.initials: FD
authors.lastname: Sack
authors.forename: E
authors.initials: E
authors.lastname: Hartmann
mesh_terms: D002451:Cell Compartmentation; D003624:Darkness; D004136:Dinitrobenzenes / Q000494:pharmacology; D006112:Gravitation; D018522:Gravitropism / Q000187:drug effects / Q000502:physiology*; D006540:Herbicides / Q000494:pharmacology; D008868:Microtubule Proteins / Q000037:antagonists & inhibitors; D008870:Microtubules / Q000187:drug effects* / Q000502:physiology*; D009578:Nitrobenzenes; D009946:Organothiophosphorus Compounds / Q000494:pharmacology; D059828:Plant Cells; D063245:Plant Development; D010944:Plants / Q000187:drug effects; D018087:Plastids / Q000502:physiology; D013424:Sulfanilamides
chemical_list: D004136:Dinitrobenzenes; D006540:Herbicides; D008868:Microtubule Proteins; D009578:Nitrobenzenes; D009946:Organothiophosphorus Compounds; D013424:Sulfanilamides; C017823:amiprophos methyl; C012465:oryzalin