Ultrastructural changes in the storage cells of the pyloric caeca of the sea star Asterias rubens L during the reproductive cycle
Den Besten, P.J.; Van Donselaar, E.G.; Voogt, P.A.; Herwig, H.J.
Netherlands Journal of Zoology 44(1-2): 65-76
At six week time intervals between August and June, samples were taken from the pyloric cacca of female sea stars, Asterias rubens, in order to study the ultrastructural organization of the storage cells. In August, at the start of the phase of gonadal growth, the storage cells are characterized by the presence of a large number of storage granules, an elaborate RER in the perinuclear region, and lipid droplets located in the basal part of the cells. The strongly dilated cisternae of the RER are filled with a fine granular glycoproteinous material. From October onwards, during the phase of gonadal growth, the size of the RER gradually decreases, while the Golgi system becomes increasingly active. The Golgi system produces dense-core vesicles which accumulate near the basal membrane, indicating that their content is transferred to the mesenterial connective tissue layer. From December onwards the number of storage granules decreases and their content becomes more electron-lucent, suggesting a remobilization of stored material. In April-May, just before spawning, the Golgi system is strongly reduced and remaining elements of RER and storage granules are found in autophagic vacuoles. In June, one month after spawning, the cells again have an elaborate RER and numerous storage granules, indicating that new reserves have been built up already. No morphological evidence has been found for a release of nutrients from the caeca by destruction of complete storage cells. It is concluded that the reduction of pyloric cacca weight during the gonadal development is caused by a gradual release of substrates from storage granules, RER and lipid droplets, resulting in a decrease in cell volume.