Embryology of Ceratopteris richardii (Pteridaceae, tribe Ceratopterideae), with emphasis on placental development

Abstract

This comprehensive study of early embryology in Ceratopteris richardii combines light microscopy with the first ultrastructural evaluation of any pteridophyte embryo. Emphasis is placed on ontogeny of the foot and placental transfer cells. The embryology of C. richardii shares many similarities with that of other polypodiacious ferns while exhibiting distinctive division patterns. Formative embryonic stages have been reconstructed into three-dimensional models for ease of interpretation. The zygote divides perpendicular to the gametophyte plane and anterioposterior axis. This division establishes a prone embryological habit that maximizes rapid independent establishment of a leaf-root axis in a cordate gametophyte. After the formation of a globular eight-celled stage, initials of the first leaf, and root and shoot apical meristems are defined early by discrete formative divisions. Concomitantly, the foot expands and differentiates to transport nutrients from the gametophyte for the developing embryonic organs. Transfer cell wall ingrowth deposition begins in the gametophyte placental cells before the adjacent sporophyte cells just after the eight-celled stage. These observations provide an anatomical framework for future comparative developmental genetic studies of embryogenesis in free-sporing plants.

Overview of the morphology, anatomy, and ontogeny of Adiantum capillus‐veneris: An experimental system to study the development of ferns

“…As in pteridophytes, the foot of A. capillus‐veneris matures before the formation of the first leaf–root axis (Fig. : C; Johnson & Renzaglia, ).…”

“…Instead, the embryo follows the development of the foot as well as the first leaf and shoot apical meristem, although there are some differences in the differentiation time for different organs of the young embryo (Fig. ; Johnson & Renzaglia, ). As in pteridophytes, the foot of A. capillus‐veneris matures before the formation of the first leaf–root axis (Fig.…”

High-Efficiency Stable Transformation of the Model Fern Species Ceratopteris richardii via Microparticle Bombardment

“…Sexual reproduction in this species requires the presence of water and occurs through fusion of retained egg cells and motile sperm. The resultant diploid embryo develops within the gametophyte archegonium (Johnson and Renzaglia, 2008). Subsequent growth of the sporophyte occurs indeterminately through divisions of a tetrahedral shoot apical cell (Hou and Hill, 2002), the products of which establish both frond primordia and a shoot-derived root system, each with their own associated apical cells (Hou and Hill, 2004).…”

Comparative development of the sporophyte–gametophyte junction in six moss species

“…A placental space containing crushed cells between the sporophyte and gametophyte is present not only in mosses but also in many liverworts and certain tracheophytes, while it is absent in hornworts and many tracheophytes (Gambardella and Ligrone 1987;Ligrone et al 1993;Hilger et al 2002;Duckett and Ligrone 2003;Johnson and Renzaglia 2008). This suggests a possibility that the sporophyte penetration accompanied with the degeneration of epigonium cells is a symplesiomorphic character state in land plants.…”