Benjamin Gutman
Project Topic / Abstract:
"Pollen Wall Morphology in Cabomba caroliniana (Cabombaceae): An Ontogenetic Study"
The Cabombaceae is one of three plant families of
waterlilies consisting of the two genera Brasenia and
Cabomba. Cabomba caroliniana Gray is commonly known as
fanwort and occurs in subtropical to temperate regions of
eastern North and South America. This species is cultivated
as a popular aquarium plant, but can also naturally occur as
an aquatic weed choking off recreational and agricultural
water ways. In addition to these economic factors, Cabomba,
along with other waterliles, is of considerable evolutionary
interest, because of its reputed position among the most
primitive angiosperms. Particularly useful phylogenetic
characters include pollen morphology and development. In
this presentation, the ontogeny of both pollen grains and
the pollen-producing organs, or anthers, are described using
scanning electron, transmission electron, and light
microscopy. Pollen was examined at stages progressing from
undifferentiated sporogenous tissue to fully mature pollen
grains. The ontogenetic timing of the following events were
documented: differentiation of microspore mother cells,
appearance of a callose wall, division into tetrads,
formation of an aperture and apertural membrane, and
formation of ectexine, endexine and intine. The development
of an unusual series of microchannels throughout the
ectexine was also evaluated. Regarding anther development,
the concurrent ontogenetic features that were studied
include: number and size of anther wall layers, appearance
of endothecial thickenings, changes in tapetum morphology,
and timing of tapetum dissociation. Significantly, an
amoeboid type of tapetum was observed for the first time.
Furthermore, this is the first study to utilize electron
microscopy in an investigation of pollen development in
either Cabomba or any other member of the family. The new
ontogenetic data are discussed as they relate to
phylogenetic interpretations of this important group of
aquatic angiosperms.
Presentations:
1996 National Conference on Undergraduate
Research (Asheville, NC)
1996 Truman Undergraduate Research
Symposium (Kirksville, MO)
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