THE ORIENTATION AND LOCALIZATION OF CORTICAL MICROTUBULES IN DIFFERENTIATING CONIFER TRACHEIDS DURING CELL EXPANSION

Arrays of cortical microtubules (MTs) on radial walls in differentiati ng tracheids of Taxus cuspidata were randomly oriented when primary wa lls formed. The orientation of MTs changed progressively from longitud inal to transverse as cells expanded. During formation of primary wall s, MTs in differentiating tracheids disappeared locally at sites of fu ture intertracheal bordered pits. In further differentiated tracheids, circular bands of MTs were observed around the edges of developing bo rdered pits.