Sporangiogenesis in Three Genera of the Saprolegniaceae. II. Primary Spore Initial to Secondary Spore Initial Stage

Abstract

The ultrastructure of primary and secondary spore initial stages are described in five species of Saprolegniaceae. In Dictyuchus anomalus, D. pseudodictyon and B. minutandra, radially-oriented nuclei in sporangia retract from their peripheral position. Wall vesicles appear in the region of cytoplasm between these nuclei and the sporangium wall. Astral microtubules are concentrated in this zone, but are apparently not physically linked to wall vesicles. Cleavage of spores involves coalescence of cleavage, wall, and dense-body vesicles into a reticulate network of furrows. During the homogeneous stage mitochondria are radially oriented around pre-basal bodies. There are no K1 bodies present in these isolates at this time. Cyst walls are deposited around the spores. Secondary spore initials of the three isolates mentioned above plus those of Dictyuchus carpophorus and encysted primary spores of Achlya debaryana are potentially motile, for they contain portions of the flagellum microtubule rootlet systems and K2 bodies.