Submitted by Alexander GettyIn a previous lab, we inoculated petri dishes with Ceratopteris richardii (known as “C-fern”) spores. The C-fern is a species of aquatic fern native to the tropics, and is a popular “model organism” for lab use because it is easily cultured and has a fast life cycle. It is our goal today to find and follow one of the C-fern sperm cells on its journey. It will not be easy; these tiny, multi-flagellate cells are on a mission, moving very rapidly. They do not have much time, maybe 48 hours max to reach their target destination, before the solitary cell consumes all its resources and will die. Will the sperm make it? Will it fulfill its duty, and succeed in its sole purpose of existence? Ferns reproduce by first producing a spore by meiosis. These spores are dispersed, and generate the gametophyte body. The gametophytes of the C-fern may be either male, which are smaller, or hermaphrodite, which are 4-5 times larger and “mitten” shaped. Male gametophytes develop structures called antheridia which produce and disperse sperm cells. Hermaphrodites also have antheridia, but produce and disperse sperm less effectively. Instead, hermaphrodite gametophytes have a second structure called the archegonium, where the egg develops. In contact with water, male antheridia release their flagellate, swimming sperm on an epic journey to locate and penetrate the archegonia of the hermaphrodite C-fern gametophytes. If successful, this will fertilize the egg, and develop into the embryo of a new sporophyte body, which will then produce more spores and start the cycle again. Using a dissecting microscope, we examined our petri dishes and locate a few male and hermaphrodite C-fern gametophyte bodies. We will then transfer these to a slide with a drop of water for viewing under the compound microscope. The water should cause the male antheridia to release their sperm cells on their journey. The sperm of the C-fern is no easy prey, as I quickly find while trying to capture one on film. Not only are they tiny and quite quick, but they are also more or less translucent. For quite some time you will notice as I attempt to catch one of the sperm being released from the antheridia, with no luck. Some sperm is visible stuck between the gametophyte body and the cover slip, spinning in place, and then at the 3 minute mark we see one sperm break away and set off on a fantastic journey. Spinning around wildly, the sperm swims to and fro while I frantically try to keep it in view and in focus, only to eventually exhaust itself and stop. Ceratopteris richardii “C-fern” gametophyte at 400x magnification, showing first the male body with its antheridia, then eventually a free swimming sperm. Courtesy of Alexander Getty
0 Comments
|
AuthorContent is created by students participating in the Plant Structure course at Oregon State University for Winter 2017. Archives
March 2017
Categories
All
|