LUCAS, JESSICA R.* AND KAREN S. RENZAGLIA. Department of Plant Biology, Southern Illinois University, Carbondale, IL 62901. - Anatomy, ultrastructure and physiology of hornwort stomata: an evaluation of homology.
Stomata are integral to water transport in plants because evaporation
of water throught the stomatal pore draws water through the water
conducting tissue. This pore also enables gas exchange, especially
carbon dioxide entrance. Among bryophytes, stomata are restricted to
sporophytes of mosses and three hornwort genera. This study of the
anatomy and ultrastructure of the stomata in Phaeoceros and
Folioceros was undertaken to evaluate homology of stomata among
basal embryophytes. Light microscope studies indicate that the
reniform guard cells of hornworts contain a large vacuole, one to two
starch-filled plastids and a peripheral nucleus. Compared to other
epidermal cells, the guard cells walls are thickened, especially
adjacent to the pore. Transmission electron microscopy revealed that
the pronounced cell wall is of three layers, each containing parallel
microfibrils oriented in different directions. Intercellular spaces
are found internal to the stomata in the assimilative cells. Such
evidence, combined with the fact that other epidermal cells lack
chloroplasts, implies that hornwort stomata function in gas exchange.
To evaluate whether or not these stomata open and close as a result of
osmotic changes, we have performed histochemical studies on potassium
and organic ion sequestration in guard cells. The role of stomata in
transpiration will be evaluated in regards to water transport through
the sporophyte. Comparisions will be made with stomata of lycophytes
and mosses.
Key words: Anthocerotaceae, homology, stomata