Developmental and Structural Section
Carmichael, Jeff .
Asexual embryogenesis in Rudbeckia fulgida..
Pseudogamy, whereby endosperm is formed by the fertilization of polar nuclei with a sperm but embryos develop apomictically, was demonstrated over fifty years ago in Rudbeckia. Unfortunately, embryo sac development and embryogenesis has not been thoroughly investigated in this group. This study incorporates a combination of microscopy techniques to examine early embryogenesis in Rudbeckia fulgida in attempt to further our understanding of the events, including the potential for pseudogamy, associated with seed development in this genus. Ovules are tenuinucellate with a single well-defined megasporocyte. Megasporogenesis is tetrasporic and embryo sac development conforms to the Adoxa type. The mature embryo sac includes three antipodals, two of which degenerate. The remaining antipodal is elongate and closely resembles the egg cell. The mature egg cell is flanked by two synergids, both of which appear to degenerate even in the absence of fertilization. Only a single, large polar nucleus was observed in each embryo sac. Controlled pollinations reveal that embryos and cellular endosperm develop in self and cross-pollinations. However, there was no evidence (based on sectioned material and fluorescence visualization of pollen tubes) that pollen tubes ever deliver sperm to the embryo sac or that any type of fertilization takes place. Thus, seeds of R. fulgida are apomictic, but not pseudogamous. Collectively, these observations indicate that other members of Rudbeckia, especially those previously reported to be pseudogamous, should be carefully studied to confirm whether pseudogamy is indeed prevalent within this group.
1 - University of North Dakota, Biology, Starcher Hall, Grand Forks, North Dakota, 58202, USA
Presentation Type: Poster
Location: Special Event Center (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 12:30 PM