CHANGES IN THE ARRANGEMENT OF MICROTUBULES AND MICROFIBRILS IN DIFFERENTIATING CONIFER TRACHEIDS DURING THE EXPANSION OF CELLS

The arrangements of microtubules and the cellulose microfibrils of radial walls in tracheids of Abies sachalinensis Masters during the expansion of cells were examined by immunofluorescence and field-emission scanning electron microscopy. The radial diameter of tracheids increased to three to four times that of cambial initial cells. Microfibrils on the innermost surface of primary walls of conifer tracheids at early stages were not well ordered and most of the microfibrils were oriented longitudinally. As each cell expanded, microfibrils in the process of deposition were still not well ordered but their orientation changed from longitudinal to transverse. When cell expansion ceased, microfibrils were well ordered and oriented transversely. Cortical microtubules showed a change in orientation similar to that of the microfibrils. These results indicate that the orientation of cortical microtubules is correlated with that of microfibrils as they are being laid down and with cell morphogenesis in conifer tracheids.