A MORPHOLOGICAL STUDY OF BUD INITIATION IN THE BROWN ALGA SPHACELARIA FURCIGERA*^†

Abstract

SUMMARYBud initiation and development in Sphacelaria furcigera involves the de-differentiation of a quiescent axial cell. This entails loss of cytoplasmic vacuoles and an increase in cytoplasmic mass and density. Cytoplasmic pressure in conjunction with a loosening ofthe outer longitudinal cell wall contributes to the formation of a bud protrusion. Incorporation of new cell wall material into the outer longitudinal cell wall allows the continued expansion of the bud protrusion. Pre-mitotic migration of the nucleus to a point midway between the axial mother cell and the protruding bud initial is followed by the reappearance of cytoplasmic vacuoles within the basal portion of the axial mother cell. Karyokinesis soon follows with the formation of two daughter nuclei. The deposition of a cross wall between the two nuclei results in an unequal cell division. The bud cell, typically meristematic in nature, is non-vacuolated and rich in organelles whereas the sister axial cell is highly vacuolated, poor in organelles and behaves like a quiescent axial cell.

A Histochemical Study of Bud Initiation in the Brown Alga Sphacelaria Furcigera*

“…The results of the histochemical tests seem then to correlate well with our previous electron microscopic observations (Burns et al, 1981) in which cell wall layers CWl, CW3 and CWO were found to be primarily composed of amorphous material (fucans) and cell wall layers CW2, CW4, and CWI to be primarily composed of oriented microfibrils (alginates). Bud initiation appears to be characterized by a weakening/loosening ofthe cell wall in the vicinity of the bud protrusion and by a reduction in the number of cell wall layers from four to two during subsequent expansion (Burns et al, 1981). The reduction to two cell wall layers during bud expansion is probably related to an increase in cell wall pliability, a condition that is far more suitable for cellular growth and morphogenesis.…”

“…1) identical to that observed with the transmission electron microscope (Burns et al, 1981). At the onset of bud initiation, four distinct layers are recognized.…”

“…Histochemical studies of S.furcigera revealed a distinctive layered pattern within the outer cell wall of both the basal and apical portion of the protruding bud initial comparable to that observed with the electron microscope (Burns et al, 1981). Histochemical staining (see Table 1) indicates that the cell wall layers CWl, CW3, and CWO are composed primarily of sulphated polysaccharides (fucans) while acidic polysaccharides (alginates) seem to predominate in cell wall layers CW2, CW4, and CWI (Fig.…”

“…2(b)], suggesting that the major role of this layer may be to strengthen the newly formed cell wall. Support for this idea comes from the observation that this layer is composed primarily of oriented microfibrils (alginates) and also from the fact that CWO can be damaged/ruptured without affecting the integrity of the bud initial (Burns et a/., 1981).…”

“…It is generally accepted that the fibrillar material corresponds to the alginates and the amorphous material to the fucans (McCully, 1965(McCully, , 1968Novotny and Forman, 1975). Our previous electron microscopic study of bud initiation and development in the brown alga Sphacelaria furcigera Kiitz (Burns, Oliveira and Bisalputra, 1981), revealed that the cell wall was also composed of fibrillar material embedded in an amorphous matrix. The distribution of fibrillar material was not homogenous and four distinct ' morphological' layers were recognized in the outer longitudinal cell wall prior to bud initiation.…”