Ultrastructural Aspects and Possible Origin of Cytoplasmic Channels Providing Intercellular Connection in Vegetative Tissues of Anthers1

Cytoplasmic channel represents a huge intercellular connection other than plasmodesma. They are proposed to play an essential role in controlling cell-to-cell trafficking of macromolecules. The present study ultrastructurally examined the occurrence, structure, and formation of this intercellular path in somatic tissues of wheat, tobacco, and onion anthers as well as their differences from those present in anther generative tissue. It was shown that cytoplasmic channels existed not only in the pollen mother cells, but also in both epidermis and vascular parenchyma of the anthers. In somatic tissues, they appeared as plasmallema-lined tubes 400–750 nm wide filled with nuclear or cytoplasmic material, the latter including cytoplasmic matrix, ribosomes, and filamentous structures. Their biogenesis seems to result from the thinning of the local portions of cell wall containing multiple plasmodesmata and the fusion of plasmodesmata in such regions induced by the wall-digesting enzymes released by nearby located vesicles. In contrast to the channels existing in the pollen mother cells of tobacco, the cytoplasmic channels in the epidermal or vascular parenchyma cells of wheat, onion, and tobacco anthers usually do not appear in groups, but are single. Perhaps this is the way for nuclear material to migrate from cell to cell via a single channel and then form a single chromatin spherical body in the adjoining cell. An individual cell could not accept the nuclear material from another cell while extruding its own to the third cell. Cell-to-cell migration of organelles through the cytoplasmic channels was not shown in the somatic tissues.