Ultrastructure of Sporogenesis in a Moss, Ditrichum pallidum I. Meiotic Prophase

Publisher Website
Google Scholar
Abstract
The ultrastructure of meiotic prophase in a moss is described for the 1st time. Six stages based on light and electron microscopic observations of D. pallidum are recognized. Premeiotic sporocytes encased in a polysaccharide layer, which persists through spore formation, are released into the spore chamber by lysis of the archesporial cell walls. Synaptinemal complexes (SCs) form. Nuclei containing well-developed SCs migrate to the sporocyte periphery and assume the acentric bouquet appearance. Pachytene nuclei return to a more central position. Nuclei enter a diffuse stage with chromatin relaxed; cytoplasmic furrows produce 4 lobes in tetrahedral arrangement; microtubules appear and proliferate around the plastid in each of the 4 lobes and finally ensheath the nucleus. The nuclear membrane is disassociated; chromatin recondenses into chromosomes and kinetochore-microtubule attachments form. Although no novel structures were associated with spindle formation and orientation, microtubules were 1st observed in the region of the plastids. Only plastid behavior, i.e., 2 successive divisions resulting in 4 plastids positioned in the 4 lobes just prior to the onset of meiosis, parallels the phenomenon of precocious cytoplasmic lobing.