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- W2046706750 abstract "The principal events in spermatogenesis, in particular those occurring in the final stage in which the isodiametric spermatocyte is transformed into the helical spermatozoid, are described. The origin of the blepharoplast remains obscure, but its subsequent development is now well known. Firm information is still lacking concerning the manner of growth of the microtubular ribbon and flagella, and the nature of the forces shaping the nucleus. The spermatozoid of Pteridium has much in common with those of other archegoniates, and there are significant parallels with the motile cells of chaetophoralean algae. Oogenesis involves extensive cytochemical changes, as well as ultrastructural ones, extending over three cell generations. The mature egg contains relatively large amounts of cytoplasmic deoxyribo- and ribo-nucleic acids, part of the latter informational in nature. Considerable autophagy, including partial elimination of cytoplasmic organelles, occurs early in oogenesis. Termination of this stage is marked by the secretion of an acetolysis-resistant membrane around the maturing egg, completing its isolation from the gametophyte. Maturation also involves nucleolar activity, bodies of nucleolar origin entering nuclear evaginations. Most evaginations are sac-like; others, formed by an overarching sheet of nucleus, hood-like. The fate of the evaginations is problematical. Some may become free and differentiate into mitochondria or plastids. The contents of the egg nucleus remain less dense than the cytoplasm and the chromatin highly dispersed. Only very few eggs are viable at fertilization. The manner of syngamy is not yet clear. Immersion of the male gamete in the female cytoplasm causes freeing of the nucleus from the microtubular ribbon, and reconstitution of its envelope. It now falls into irregular loops within the funnel formed by the coiled ribbon. Orientation of this funnel such that the anterior end of the male nucleus contacts the female is probably essential for karyogamy. Following the formation of an orifice, the male chromatin moves into the female nucleus. The male nuclear envelope is probably resorbed, and the other parts of the spermatozoid eventually digested. The special egg membrane becomes incorporated into the common wall between the gametophyte and zygote, and may prevent the transference of complex molecules." @default.
- W2046706750 created "2016-06-24" @default.
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- W2046706750 date "1976-07-01" @default.
- W2046706750 modified "2023-09-23" @default.
- W2046706750 title "Gametogenesis and fertilization in Pteridium" @default.
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- W2046706750 doi "https://doi.org/10.1111/j.1095-8339.1976.tb02012.x" @default.
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