ABSTRACT
Pteridophytes are spore-bearing vascular plants. They are considered to be transitional taxa between bryophytes and seed plants. Pteridophytes are usually divided into ferns (macrophyll pteridophytes) and fern allies (microphyll pteridophytes) according to the traditional viewpoint. Recent phylogenetic investigations revealed a basal dichotomy within vascular plants, separating the lycophytes from other vascular plants (the euphyllophytes) (Smith et al. 2006). Thus, the euphyllophytes comprise two clades: the spermatophytes (seed plants) and ferns (the monilophytes), which have about 9000 species, including horsetails, whisk ferns, and all eusporangiate and leptosporangiate ferns (Pryer et al. 2004). The ferns are divided into two categories according to the spore types: the homosporous ferns, which have homosporous spores, including all horsetails, whisk ferns, eusporangiate, and almost all the leptosporangiate ferns; and heterosporous ferns, which have large and small spores, and only include the Marsileaceae, Salviniaceae and Azollaceae. The ferns have independently-living gametophytes, also known as the prothallus. The gametophyte propagates by sexual reproduction, which includes spermatogenesis, oogenesis, fertilization and embryo development. The spermatogenesis has been studied in many aspects and with numerous species of ferns (Bell 1974, 1975; Bell et al. 1971; Bell and Duckett 1976; Doonan et al. 1986; Duckett 1973; Hoffman 1995; Myles and Hepler 1977; Kotenko 1990; Renzaglia and Garbary 2001). Spermatogenesis in ferns can usually be divided into two stages. The fi rst stage is from the initial spermatogenous cell to the spermatocytes (spermatid mother cell); and the second stage is the differentiation of the spermatocytes. The differentiation of the spermatocytesis a complex process, which includes a multilayered structure (MLS) and microtubular ribbon (MTR) that are formed de novo; mitochondrial fusion and nuclear shaping. And fi nally a spiral spermatozoid is formed. However, the oogenesis and fertilization are less reported. The present paper reports our recent investigations on the oogenesis and fertilization of ferns.
