Lopez-Smith, Renee , Renzaglia, Karen S. .
Does actin play a role in fertilization in Ceratopteris richardii?.
Prior to the advent of electron microscopy, exquisite drawings at the light microscope level provided fundamental information on fertilization in ferns. Since that time, few ultrastructural papers have been published concerning the union of motile male and non-motile female gametes in plants. Consequently, little is known about the subcellular entities involved in syngamy. To determine whether or not the cytoskeletal protein actin is necessary for fertilization in ferns, we conducted ultrastructural and experimental studies on Ceratopteris richardii. Swimming gametes of this fern contain a dense ridge that encircles the leading edge of the cell. Rhodamine-phalloidin localizations suggest that the ridge is actin-containing. Disruption of the integrity of the dense ridge after treatment with cytochalasin, an actin inhibitor, further suggests that actin is a component of the dense ridge. While in the archegonial neck, the dense ridge expands and contains numerous evenly-spaced filaments, ranging from 5-7 nm in diameter. Mature gametophytes of C. richardii were exposed to three treatments for fertilization; distilled water, distilled water containing DMSO and distilled water containing cytochalasin B and DMSO. Cultures were monitored and harvested when prominent embryos were visible. Gametophytes were examined in the light microscope and the percent of embryo-producing gametophytes was calculated for each treatment. Morphological data were collected in the light, scanning, and transmission electron microscopes. Gametophytes treated with the actin inhibitor produced significantly fewer embryos than those of the control group. This provides evidence that the presumed actin filaments of the dense ridge are involved in fertilization. We speculate that actin is necessary to anchor the sperm cell to the egg and ultimately to unite the two nuclei of the gametes.
1 - Southern Illinois University, Department of Plant Biology, 1125 Lincoln Drive, Carbondale, Illinois, 62901-6509, USA
Presentation Type: Paper
Location: Superior B (Cliff Lodge)
Date: Monday, August 2nd, 2004
Time: 3:15 PM