Adipogranular cells from the mantle tissue of Mytilus edulis L. II. Seasonal changes in the distribution of dispersed cells in a preformed Percoll density gradient

Abstract

Seasonal changes in the number of adipogranular (ADG) cells in mantle tissue dispersions of Mytilus edulis L. showed a decline in cell numbers during gametogenesis (October–March) as the storage tissue was replaced by gonadal cells. The data for cell counts agreed well with previously described changes in the mantle volume fraction occupied by ADG cells. The distribution of dispersed cells in preformed Percoll density gradients showed two distinct peaks at high and low density, respectively. Adipogranular cells undergo controlled autolysis in which protein and glycogen reserves are mobilized for gamete formation (Bayne et al., 1982). Early in the seasonal cycle (October–December) the ADG cells exhibited a distinct peak at high density with very few low-density ADG cells. The number of high-density ADG cells then declined (January–April), being particularly rapid during the later stages of gametogenesis. The fact that, under the light microscope, few recognizable ADG cells appeared in the low-density fraction suggests that autolysis once initiated is rapid and complete. Ultrastructural studies showed that the low-density fraction included many ADG cells in the final stages of regression. Other cells observed in this fraction were macrophages and, during early summer, new amoebocytic cells.