Bryological and Lichenological Section/ABLS
Long, Joel A. , Renzaglia, Karen S. .
An ultrastructural study of sporogenesis in Notothylas..
Because spores are key innovations in land colonization, elucidating the process of sporogenesis in basal land plants is critical to understanding embryophyte diversification. This study provides the first detailed ultrastructural description of sporogenesis in a hornwort. Sporophytes of Notothylas orbicularis were examined using SEM, TEM, light and fluorescence microscopy. Progressive stages of spore differentiation are visible in longitudinal section. After being cleaved from a basal meristem, the rounded spore mother cells (SMCs) have thin walls, are highly vacuolated, and possess a single starch-laden plastid with few thylakoids. The plastid undergoes two synchronized divisions producing four plastids that migrate to the meiotic poles. Concomitantly, the SMC wall thickens with deposition of fibrillar wall material resulting in cytoplasmic lobes that are contained within a spherical wall. Following meiosis, spore wall development begins with the deposition of intersporal wall, which is laid done simultaneously along tetrahedral planes that separate the four haploid cells. Young tetrads are approximately the same size as the sporocytes. As tetrads nearly double in size, a primexine is deposited around the circumference of each spore. Spore wall patterning is determined by the production of a thin homogenous electron-dense layer on the outside of the primexine. Sporopollenin is then systematically deposited from the outside inward, filling the primexine in all wall regions except the trilete mark and equatorial girdle. Following the deposition of sporopollenin, a loosely fibrillar intine is laid down. Differentiation is completed with the compaction of a thin layer of spore mother cell wall on the outside of the spore. Mature spores are trilete with vermiculate ornamentation.
1 - Southern Illinois University, Department of Plant Biology, 1125 Lincoln Drive, Carbondale, Illinois, 62901-6509, USA
Presentation Type: Paper
Location: Ballroom 3 (Cliff Lodge)
Date: Monday, August 2nd, 2004
Time: 3:15 PM