Developmental and Structural Section
Johnson, Gabriel , Lopez-Smith, Renee , Renzaglia, Karen S. .
Early embryology and placental transfer cell development in Ceratopteris richardii.
CERATOPTERIS richardii embryos were examined at various stages of development using light, fluorescence, and transmission electron microscopy. Like other leptosporangiate ferns, the initial divisions of the zygote produce four cells or quadrants, which are specified to develop into the foot, root, shoot, and first leaf. However, the pattern of development of the foot deviates slightly from this fixed quadrant model in that this embryonic organ derives from both the foot-initiating quadrant and the shoot-initiating quadrant. Distinct apical cells are formed within the root, shoot, and first leaf primordia. Proliferative divisions are initiated in the first leaf before the root and shoot. Concomitantly, the foot develops through proliferation and enlargement of cells that are in close contact with gametophytic cells; this junction between generations, the placenta, contains transfer cells with wall ingrowths. Three days following fertilization, cell wall ingrowths are visible only on the gametophyte side, while at eight days post fertilization, the wall labyrinth is more extensive in foot cells. Abundant polysomes and a scarcity of Golgi bodies suggest that mainly non-Golgi derived materials are contributed to walls during ingrowth formation. For example, aniline blue fluorescence identifies callose as a primary constituent in early cell wall ingrowths. This first anatomical and ultrastructural study of embryogenesis and transfer cell wall development in Ceratopteris provides a morphological context in which to interpret future developmental and molecular genetic studies on this model fern.
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1 - Southern Illinois University, Department of Plant Biology, 1125 Lincoln Drive, Carbondale, Illinois, 62901-6509, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 303/Bell Memorial Union
Date: Monday, July 31st, 2006
Time: 11:30 AM