ULTRASTRUCTURAL ASPECTS OF SPOROGENESIS IN A FERN, PTERIDIUM-AQUILINUM (L) KUHN

The meiotic process of sporogenesis in Pteridium is accompanied by a regular cycle of ultrastructural events. These include the dedifferentiation and redifferentiation of organelles, and the elimination and restoration of ribosomes. Although similar in nature to corresponding stages in other land plants, sporogenesis in Pteridium provides several unique features.During prophase the plastids pass through a stage during which no envelope can be resolved at the periphery of the stroma. They appear to survive this period and there is no evidence that plastid lineage is broken from primary archesporium to spore. The plastid cycle is accompanied by the presence of the iron-protein complex phytoferritin.The repopulation of the spore cytoplasm with ribosomes, following the prophase elimination, is achieved through the agency of nucleoloid-like bodies. These bodies, however, are not synthesized within the nucleus, but form within membrane-bound regions of the early prophase cytoplasm.Prophase is also characterized by the development of nuclear vacuoles, expansions of the perinuclear space, which progressively ramify through the karyoplasm prior to the dissolution of the nuclear envelope at metaphase I.The significance of these events, their similarities with, and differences from, comparable stages of meiosis in other plants are discussed. © 1979, Annals of Botany Company.