INTERPHASE AND PREPROPHASE MICROTUBULE ORGANIZATION IN SOME POLARIZEDCELL-TYPES OF THE LIVERWORT MARCHANTIA-PALEACEA BERT

The organization of interphase and preprophase-prophase microtubules w as studied in photosynthetic filament mother cells (PFMCs), photosynth etic filament cells (PFCs), mucilage papilla mother cells (MPMCs) and mucilage papillae (MP) of Marchantia paleacea Bert. These cell types e xhibit polarized growth resulting, (a) in the formation of cell outgro wths followed by asymmetrical division (PFMCs and MPMCs), or (b) in th e development of a tubular cell shape (PFCs and MP). The above cell ty pes display an interphase cortical microtubule ring perpendicular to t he axis of growth. In PFMCs and MPMCs it resides at the base of the ce ll outgrowth, while in PFCs and MP it has a median location. This micr otubule ring is involved in the deposition of transverse, circumferent ially aligned, cellulose microfibrils, defines the site where cell pro trusion formation occurs and affects cell morphogenesis. In differenti ated MP microtubules are rearranged in longitudinal or oblique cortica l arrays. PFCs and MP also contain a prominent system of endoplasmic m icrotubules which may be involved in cytoplasmic polarization. In PFMC s, PFCs and MPMCs the interphase microtubule ring seems to function as a preprophase microtubule band (PPB). In the asymmetrically dividing PFMCs and MPMCs the PPB is complete but in symmetrically dividing PFCs it may be interrupted. The cell plate meets the parent wall at sites adjacent to the PPB cortical zone. These observations reveal further p eculiarities in cortical microtubule organization and particularly in the PPBs of M. paleacea. Possible factors underlying the formation of complete or interrupted PPBs are discussed.