ULTRASTRUCTURAL STUDIES OF BROWN ALGAL NUCLEI

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Abstract
The nuclei of four brown algae (Dictyota, Padina, Zonaria, and Dictyopteris) have been studied using sectioning and freeze‐etching techniques. A comparison of the results obtained with those of earlier workers suggests that nuclear structure may be similar throughout the Phaeophyta. Freeze etching has revealed striking bands of nuclear pores and arrays of particles within the nuclear envelope membrane, which are reported for the first time. Particular attention has been given to nuclei in experimentally manipulated cells of Zonaria, where changes in nucleolar size, nucleoplasmic staining, nuclear envelope configuration, and in the contents and extent of the perinuclear cytoplasm were found to occur. These changes appear to be related to whether the apical cells and nuclei were active, dormant, or in the process of division. The Zonaria nucleus may control the arrangements of microtubules, cellular membranes, and organelles seen in the apical cells of this brown alga.