KOBIYAMA, YUKI. Department of Plant Biology, Southern Illinois University, Carbondale, IL 62901-6509 USA. - Diversity of central strand structure in the Metzgeriidae.
In spite of the common misconception of bryophytes as nonvascular
plants, many detailed studies have demonstrated conducting strands in
mosses and liverworts. The ultrastructure of the water-conducting
cells in Metzgeriidean liverworts, such as Symphyogyna and
Pallavicinia, have been well described by Smith (1966), Frey et
al. (1996), and Ligrone and Duckett (1996). Central strands in
different taxa of Metzgeriidean liverworts, in fact, show different
levels of cell differentiation. The purpose of this investigation is
to describe the structure of central strand cells in several simple
thalloid liverworts, including Jensenia, Hattorianthus,
Cavicularia, and Calycularia. Studies with optical and
electron microscopy show that both the rhizome and the thallus midrib
of Jensenia possess a central strand which is composed of thick
walled, small diameter cells. SEM study shows that these cells possess
numerous, oblong shaped pits on the inner surface of the wall and are
connected by oblique end walls. These central strand cells of
Jensenia are, in fact, structurally very similar to those in
Symphyogyna. The massive midrib of Hattorianthus
possesses two central strands. The cells in the strand are smaller in
diameter than surrounding cells and have brownish coloration. SEM
study shows that end walls of some specialized parenchyma cells in
Hattorianthus possess numerous small pits which seem to be of
plasmodesmatal origin. The genus Cavicularia possesses three
differentiated central strands in the midrib. The cells in the strand
are smaller in diameter, but do not possess any wall thickenings. The
cells of the thick, conspicuous midrib of Calycularia are
filled with many starch grains, but there is no differentiated central
strand. Continuing studies, using TEM and histochemistry, will focus
on the internal structure and function of these cells.
Key words: central strand anatomy, liverworts, pits, SEM