FUSION, SUBSEQUENT SWELLING AND FINAL DISSOLUTION OF THE APICAL WALLS OF THE PROGAMETANGIA OF RHIZOPUS SEXUALIS (SMITH) CALLEN: AN ELECTRON MICROSCOPE STUDY

Abstract

SUMMARYConjugating progametangia of Rhizopus sexualis rapidly enlarge and become flattened at the apical zone of contact. The walls over this zone fuse immediately, lose their separate identity and form a single plate. The fusion wall then thickens by gelatinization and swelling: there is no evidence of deposition of secondary wall material. The plasmalemmas on either side of the fusion wall become wrinkled and enclose pockets of electron transparent material along the sides adjacent to the wall. Vesicles and later lomasome-like masses are seen in a few of these pockets. Numerous small vesicles are present in the adjacent zones of cytoplasm on either side of the wall; some may be seen attached to the plasmalemmas. The wall then thins from the centre of the plate outwards but remains in being until after the gametangia have been delimited by new septa. Cell fusion then takes place by the development at the centre of the fusion wall of a hole which enlarges rapidly until the whole of the plate is dissolved. The evidence from electron micrographs suggests that the dissolution process is entirely chemical and that both matrix and microfibrillar skeleton are dissolved enzymatically while still enclosed in the plasmalemma.

Cell Wall Formation in the Saprolegniales: Cytoplasmic Vesicles Underlying Developing Walls

“…Similarly, the germ tube must break out of the encysted spore and the sporangium wall must be breached to release the zoospores of Dictyuchus sterile. This suggests that wall-degrading enzymes must be considered as possible components of the wall vesicles in these areas, and also in the hyphae in view of the work on Achlya by Thomas & Mullins (1969) and Rhizopus by Hawker & Gooday (1969). The darker vesicles in P1.…”

Septal involvement in nuclear migration inSchizophyllum commune

“…Similar structures in Rhizopus sexualis are associated with the dissolution of the fusion walls in the progametangia (Hawker and Gooday, 1968). These bodies have als0 been associated either with cell wall and septum synthesis, or septal dissolution in other fungi (Scannerini, 1967).…”