Ultrastructural changes during development, release, and germination of monospores of Tilopteris mertensii (Tilopteridales, Phaeophyta)

Abstract Monospores of Tilopteris mertensii (Turner in Smith) Kutzing are formed singly or in small groups at the base of young lateral branches. The differentiation of their mother cells involves a significant increase of cell volume, cytoplasmic density, and organelle number. An active perinuclear Golgi apparatus releases numerous vesicles, contributing to the deposition of additional layers, probably mucilaginous, on the inner face of the cell wall. Application of anti-tubulin immunofluorescent label in studies of apolar spores reveals many microtubule (MT) bundles radiating from the centrosomal area, which lies close to a large, spherical, centrally located nucleus. After monospore release and settlement, the polar axis is established and the spores germinate. Polarization is expressed by several cytological changes. The centrosome and nucleus migrate to the rhizoidal pole. The nucleus becomes lobed and develops a sharp protrusion toward the pole; the centrosome is positioned close to this region. The...