| Abstract: | Plasmodesmata are occluded when Funaria chloronemata are fragmented by the development of tmema cells (TCs). The TC deposits a new wall layer along the cross wall toward the neighbouring non-sister cell (NC). This wall layer cuts off the plasmodesmata and its connection with the cross wall is soon lost. The plasmodesmata become isolated when the NC forms a new wall layer along the former cross wall. At the end of TC development, before its disintegration, the sister cell (SC) also deposits a new wall layer along the cross wall toward the TC, cutting off the plasmodesmata. For some time the plasmalemma of the plasmodesmata remains connected to the NC or the TC, whereas the desmotubule soon disappears. Relicts of the plasmalemma remain even after the isolation of the plasmodesmata and the disintegration of the TC. During the decay of the plasmodesmata, a cylinder of electron-dense material is frequently formed along the border of the plasmodesmatal channel. This may extend over the surface of the cell wall. Eventually, the plasmodesmatal channel is filled with wall material. Callose is only observed around functional plasmodesmata and does not seem to play a role in their occlusion. |
