Abstract:

Cytoplasmic bridge, as a broader cellular connection structure, exists in plants from Volvox to higher plants, but has been subjected to less investigation as compared to plasmodesmata. It has been speculated that the structure may be related to the synchronization of cell division and development during the microsporegenesis and spermatogenesis. During spermatogenesis in bryophytes, the spermatogenous cells are divided into several domains within an antheridium, and their divisions are synchronous. However, their cellular connection system has not been investigated systematically. In this study, we undertook an ultrastructural examination of the structure and dynamics of the intercellular connection system during the spermatogenesis in Funaria hygrometrica Hedw. The result revealed that within each individual domain, synchronously dividing spermatogenous cells were connected with each other by numerous cytoplasmic bridges, which were absent in the walls between different domains. The plasmodesmata connected spermatogenous cells with the cells of jacket layer, and also existed between the jacket layer cells, but absent in the walls between the developing spermatogenous cells. At the late stage of the antheridial development, as the cell wall began to degrade, all of the spermatid cells within an antheridium seem connected with each other by the expanded cytoplasmic bridges. The cytoplasmic bridges retained to the late stage of spermatid’s differentiation, and finally, the spermatids synchronously differentiated into spermatozoids. The different internal structures, biogenesis mechanisms and distribution between the plasmodesmata and cytoplasmic bridges suggest that they may play distinct roles during the development of antheridia.

Key words: cytoplasmic bridges, plasmodesmata, spermatogenesis, Funaria hygrometrica