Mechanism for formation of the secondary wall thickening in tracheary elements: Microtubules and microfibrils of tracheary elements ofPisum sativumL. andCommelina communisL. and the effects of amiprophosmethyl

摘要

Arrangements of microfibrils (MFs) and microtubules (MTs) were examined in tracheary elements (TEs) ofPisum sativumL. andCommelina communisL. by production of replicas of cryo-sections, and by immunofluorescence microscopy, respectively. The secondary wall thickenings of TEs ofPisumandCommelinaroots have pitted and latticed patterns, respectively. Most MFs in the pitted thickening ofPisumTEs retain a parallel alignment as they pass around the periphery of pits. However, some groups of MFs grow into the pits but then terminate at the edge of the thickening, indicating that cellulose-synthase complexes are inactivated in the plasma membrane under the pit. Microtubules of TEs of bothPisumandCommelinaare localized under the secondary thickening and few MTs are detected in the areas between wall thickenings. In the presence of the MT-disrupting agent, amiprophosmethyl, cellulose and hemicellulose, which is specific to secondary thickening, are deposited in deformed patterns in TEs ofPisumroots,Pisumepicotyls andCommelinaroots. This indicates that the localized deposition of hemicellulose as well as cellulose involves MTs. The deformed, but heterogeneous pattern of secondary thickening is still visible, indicating that MTs are involved in determining and maintaining the regular patterns of the secondary thickening but not the spatial heterogeneous pattern of the wall deposition. A working hypothesis for the formation of the secondary thickening is proposed.