Connective structures between tapetal cells and spores in Lycophyta and pollen grains in angiosperms — A review

This article is a review of research and accumulated information about connective structures between, respectively, microspores in the locular space in anthers of angiosperms and the spores in the megasporangia of Lycophyta, as well as a comparison between these structures. The most extraordinary conclusion, if our interpretations of the results are correct, is that the reason for the great number of exine components and the great complexity of the micro- and mega-spore walls is that each exine unit structure acts as a plasmodesma and that each spore unit directs a wick-component to the cytoplasm. Pollen grains and spores that are literally covered by plasmodesmata or plasmodesmatal equivalents may be expected to grow and develop rapidly. These connections are believed to be routes of transport for substances between tapetal cells and the plasma membrane and cytoplasm in both pollen grains and spores. In Selaginella, “wicks” which are plasmodesmata equivalents extend from tapetal cells to exospore units and further to plasma membrane and megaspore cytoplasm. In angiosperm pollen grains plasmodesmata equivalents extend from the tapetum into and through exine and into the cytoplasm passing through the core of exine units (tufts), but in spores (e.g., Selaginella) the strand-like wicks traverse the space between the components of the exospore and the megaspore cytoplasm. These structures were successfully fixed with ruthenium red and Alcian blue, which tend to stabilize polysaccharides and glycoprotein as well as contrasting the components of the exine and exospore transfer systems.