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Abstract:
Scanning electron microscopy and freeze-etching/cleaving have been employed to examine events in the synchronized development of gametophytic germlings of the aquatic Phycomycete Allomyces macrogynus. Motile spores were induced to start synchronized development and the sequence of surface changes associated with the encystment process was studied. Time course studies show that small vesicles (apparently blebbed off from the gamma-particles) start to accumulate on the surface of the plasma membrane after 6 min of synchronized growth at the same time as the first cell wall material can be detected. The vesicles increase in number during encystment. After 15 min of synchronized growth the number of vesicles decrease and after 20 min of growth no vesicle can be observed on the cell surface. During this period the cell surface appears increasingly smooth, probably due to cell wall formation. In freeze-etching/cleaving electron micrographs from this period, both intact and what appear to be ruptured vesicles outside the cell surface, can be observed. The intact vesicle has a characteristic surface pattern presumably of membrane particles. This surface view of the encystment processes supports the hypothesis that the gamma-particles through gamma vesicle formation participate in the cell wall synthesis during encystment in Allomyces.
Insights
During encystment, Allomyces macrogynus gametophytic germlings show surface changes. Gamma vesicles form and contribute to cell wall synthesis, supporting a key hypothesis.
Area of Science:
- Mycology
- Cell Biology
- Developmental Biology
Background:
- The aquatic Phycomycete Allomyces macrogynus undergoes synchronized development.
- Understanding the early events of gametophytic germling development is crucial for fungal biology.
Purpose of the Study:
- To investigate the surface changes during synchronized encystment of Allomyces macrogynus gametophytic germlings.
- To elucidate the role of gamma-particles and gamma vesicles in cell wall formation during encystment.
Main Methods:
- Scanning electron microscopy (SEM) was used to observe surface morphology.
- Freeze-etching/cleaving electron microscopy provided high-resolution views of membrane structures.
- Time-course studies tracked developmental events from synchronized spore germination.
Main Results:
- Small vesicles, originating from gamma-particles, accumulated on the plasma membrane starting at 6 minutes, coinciding with initial cell wall material detection.
- Vesicle numbers peaked during encystment and subsequently decreased, with the cell surface becoming smoother.
- Electron micrographs revealed intact and ruptured vesicles outside the cell, displaying distinct surface patterns.
Conclusions:
- The observed vesicle dynamics support the hypothesis that gamma-particles, via gamma vesicle formation, are integral to cell wall synthesis during Allomyces macrogynus encystment.
- This study provides critical ultrastructural evidence for the mechanism of cell wall construction in developing fungal spores.