| Popis: |
The activity of ornithine decarboxylase (ODC) and levels of polyamines were measured in the testes of Asterias vulgaris ncollected throughout an annual spermatogenic cycle. Samples of the testes were prepared for light and electron microscopy to observe the associated changes in the cytology of germinal cells. The specific activity of ODC increased at the onset of testicular growth, decreased during the coldest period of the winter when testicular growth was minimal, and increased again early in the spring when testes grew maximally. Increased activity of ODC resulted in increased levels of polyamines and was correlated with either mitotic or meiotic germinal cell divisions, or both. Spermine levels were always greater than putrescine, followed by spermidine. Highest levels of polyamine synthesis coincided with the onset of spermatogonial proliferation during the fall and with the period of meiotic differentiation and spermiogenesis in the spring. Mid-summer (July) testes were small (0.3n0.5 gonad index (GI)) and contained amitotic spermatogonia arrested in G 1 nof the cell cycle. Mitotic and pre-meiotic testes (October/November) increased slightly in size (0.3n1.4 GI) and contained actively dividing spermatogonia, most of which differentiated into primary spermatocytes. Testes from February and March were large (1n6.75 GI), but the proliferative status of their spermatogonia and primary spermatocytes varied. Spermatogonia and primary spermatocytes from early February testes were not dividing. In testes obtained in March, both spermatogonial mitosis and meiosis of spermatocytes resumed, coincident with increased field water temperatures. |
