Developmental and Structural Section
Rogers, Cassandra E. , Blackwell, Andrew J. , Renzaglia, Karen S. .
Sperm cell architecture in two liverworts.
The immense somatic structural diversity that characterizes liverworts is also evident in sperm cell architecture. Although similar to other bryophytes in the possession of a two flagella, cylindrical nucleus, anterior and posterior mitochondria, and a starch-filled plastid, sperm cells of liverworts show remarkable variability in size and number of coils. In this ultrastructural study, mature sperm cells were examined in Sphaerocarpos (Marchantiopsida) and Pellia (Jungermanniopsida). These genera represent the extremes in male gamete size and structural complexity. From images taken on the electron microscope, three-dimensional, color drawings of gametes from both plants were constructed. The minute male gametes of Sphaerocarpos coil 1.5 revolutions and are approximately 22.0 μm in length with an average diameter of 4.5 μm. At 3.5 coils and a maximum diameter of 9.0 μm, the sperm cells of Pellia are nearly 100 μm in length and are the largest of any known bryophyte. Basal bodies are dimorphic in both liverworts. The short, anterior basal body is positioned in front on the right-hand side with the longer, posterior basal body farther back on the left. Exceedingly long ventral triplets of the posterior basal body in Pellia gametes position the posterior flagellum one half revolution (>12.0 μm) from the front of the cell. Basal body staggering is minimal in Sphaerocarpos, with both flagella emerging within 1.0 μm of the leading edge of the cell. The nucleus is a narrow, compacted cylinder in both taxa, with the substantially longer nucleus of Pellia correlated with greater genome size. Comparisons of sperm cell architecture with other liverworts reveal that gamete structure is relatively conserved in the marchantiopsid liverworts, while most of the variability exists in the Haplomitriopsida and Jungermanniopsida.
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1 - Southern Illinois University, Department of Plant Biology, 1125 Lincoln Drive, Carbondale, Illinois, 62901-6509, USA
Presentation Type: Oral Paper
Date: Monday, August 15th, 2005
Time: 4:15 PM