The Gametophyte-Sporophyte Junction in Land Plants

The chapter presents a comparative analysis of the placenta in land plants. The gametophyte–sporophyte junction is termed as the placental region. Systematic survey of bryophytes, pteridophytes, and placental analogues in seed plants are also explained. The gametophyte–sporophyte junctions in bryophyte groups are distinguished by the presence or absence of cell wall labyrinths in the placental cells, cell wall structure, shape, and arrangement of wall ingrowths and plastid morphology. Two stages of sporophyte development, the pre–meiotic stage and post–meiotic stage are discussed. Studies carried out by using the representatives of bryophyte groups namely mosses, liverworts, and anthocerotes are explained. The chapter also explains characteristic features of placenta like the distribution of transfer cells, distribution of wall ingrowth and time of ingrowth for different organisms belonging to mosses and liverworts. Cytoplasmic features of placental cells like shape, membrane system, plastoglobuli, and starch for sporophyte and gametophyte in mosses and liverworts are described. The anthocerotes are distinguished based on cytological, anatomical, and developmental characteristics. The taxonomic significance of placenta in bryophytes and the implications on phylogeny are also discussed. Differences in the placental regions, cell wall ingrowths, and intercellular spaces between bryophytes and pteridophytes are explained. These differences are related to the transient nature of sporophytic dependence on the gametophyte in pteridophytes. Transfer cell morphology has been described at every site of solute exchange via the apoplast of angiosperms.