Autoradiographic study of mannan incorporation into the growing cell walls of Saccharomyces cerevisiae.

The incorporation of mannan labeled by d-[1-(3)H]mannose into the growing cell walls of Saccharomyces cerevisiae has been followed by means of high-resolution autoradiography. The results show that, in the very first stage of budding, when the shape of the bud is nearly spherical, the new mannan is incorporated uniformly over the whole surface of the emerging bud. Later on, as the bud growth proceeds, the polarized tip growth predominates. In the maturation phase of bud growth, when the size of the bud is about two-thirds that of the mother cell, again a considerable incorporation of the labeled substrate over the whole bud surface was observed. The cell wall of the mother cell remained largely unlabeled. These facts indicate that the ellipsoidal shape of the cell walls in S. cerevisiae is the result of the combination of polarized tip growth and nonpolarized spherical extension.