Bryological and Lichenological Section/ABLS
Mansouri, Katayoun , Renzaglia, Karen S. .
Ultrastructure and diversity in the generative apex of liverworts.
Across the morphologically diverse liverworts, there are four distinct apical cells geometries that are responsible for growth of the gametophyte: lenticular, tetrahedral, wedge-shaped and hemidiscoid. The leafy and thalloid growth forms are correlated with these geometries in a way that apical derivatives (merophytes) typically give rise to a leaf or leaf-like structure. In this study apical meristems of Treubia, Haplomitrium, Metzgeria conjugata, Bazzania trilobata, Pellia epiphylla, Sphaerocarpos texanus, representing five of the major clades of liverworts and three apical cell geometries, were examined in the light, scanning and transmission electron microscopes. Apical cells and their immediate derivatives (merophytes) were examined for general cytological features. In addition, plasmodesmatal ultrastructure and density were recorded for apical cell and merophyte walls. For example, M. conjugata has a lenticular apical cell, with dense cytoplasm containing poorly-differentiated plastids, spherical mitochondria, Golgi bodies, vesicles, rough endoplasmic reticulum and ribosomes. Apical cell walls are abundantly traversed by simple plasmodesmata that average 47 per μm-2. The first wall produced in immediate apical derivatives averages 34 plasmodesmata per μm-2. Plasmodesmatal density rapidly decreases from 21 per μm-2 to no more than 11 per μm-2 in the third and fourth divisions. No secondary, H-shaped or branched plasmodesmata were seen in this or any of the liverworts examined. This first ultrastructural study of liverwort apices provides evidence that the apical cell contains abundantly more plasmodesmata than derivatives, supporting the concept that this cell not only produces merophytes but also is responsible for coordinating morphogenetic events.
Log in to add this item to your schedule
1 - Southern Illinois University Carbondale, Plant Biology, Life Science II 459, Carbondale, IL, 62901, USA
2 - Southern Illinois University, Department of Plant Biology, 1125 Lincoln Drive, Carbondale, Illinois, 62901-6509, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 28th, 2008
Time: 9:30 AM