Anatomy, Ultrastructure and Physiology of Hornwort Stomata
by Lucas J. R. (2000)
Jessica Regan Lucas, Southern Illinois University Carbondale
in Honors Theses. Paper 136 –
The development of hornwort stomata is very simple. This is indicated by the single longitudinal division of the guard cell precursor, pectinous ledges, lack of subsidiary cells, and lack of radial micellation. Gas exchange seems to be a likely function of hornwort stomata, but the absence of vascular tissue makes water transport improbable. Histochemical stains for malate and potassium indicate that guard cells localize ions for a short time- after the differentiation of the epidermis and before spore dispersal.
Diurnal guard cell movements do not occur in hornworts. Neither dehydration or ABA treatment effects the guard cells in respect to movement. It is still unclear whether or not hornwort stomata are homologous to stomata of vascular plants. The prominent chloroplast, the localization of ions, and the role of stomata in gas exchange suggest that anthocerote stomata are related to those of other embryophytes.
However, the lack of vascular tissue and stomatal movement counter the homologous theory. Also in opposition to this paradigm is the distinct wall structure of hornwort guard cells. A multilayered wall and ledges of pectin have only been reported for a few other plants. In the future to elucidate the homology of these structures, the effect of ABA should further be studied. Also the guard cells’ ability to transport ions, which is essential for movement, should be determined.