The Ultrastructure and Development of Sporangia In Gilbertella Persicaria

A bird's-eye view of the endoplasmic reticulum in filamentous fungi

SUMMARYThe endoplasmic reticulum (ER) is one of the most extensive organelles in eukaryotic cells. It performs crucial roles in protein and lipid synthesis and Ca2+ homeostasis. Most information on ER types, functions, organization, and domains comes from studies in uninucleate animal, plant, and yeast cells. In contrast, there is limited information on the multinucleate cells of filamentous fungi, i.e., hyphae. We provide an analytical review of existing literature to categorize different types of ER described in filamentous fungi while emphasizing the research techniques and markers used. Additionally, we identify the knowledge gaps that need to be resolved better to understand the structure-function correlation of ER in filamentous fungi. Finally, advanced technologies that can provide breakthroughs in understanding the ER in filamentous fungi are discussed.

Fine structure and development of the zygospore of Rhizopus sexualis (Smith) Callen

The development of the zygospore of Rhizopus sexualis (Smith) Callen was followed by light microscopy, transmission electron microscopy and scanning electron microscopy. Details of all stages, including dissolution of the fusion wall, delimitation of the gametangia by septa, and formation of the complex wall of the zygospore are described and illustrated. Changes in number, form and distribution of the organelles and the behaviour of the nuclei are described. The probable function of the cytoplasmic organelles and the possible mechanisms controlling development are discussed.

The development and application of ultrastructural research in mycology

Electron microscopy has contributed a great deal to the field of mycology. Fungal ultrastructure has been, and continues to be, a key research element in the study of spore development and germination, host-pathogen interactions, nuclear behavior, and studies of subcellular organelles and organization linking structure and function. Since the earliest research in transmission electron microscopy in the 1950s, mycologists have kept pace with the developments in all areas of electron microscopy and have used them to great advantage in generating fine structural information on fungi. These recent developments include the use of scanning electron microscopy in the 1960s, X-ray microanalysis, cryopreservation and immunoelectron microscopy in the 1970s and 1980s. All of these techniques will continue to provide mycologists with the means to gain morphological and analytical data at the ultrastructural level.

Altered expression of chitin synthetase activity and biochemical changes in the cell wall in a developmental mutant of Phycomyces

The Phycomyces developmental mutant S356 elaborates spores which show a much poorer viability and a higher affinity for Calcofluor White than the wild-type spores. Protease-activated extracts of the mutant spores showed higher levels of chitin synthetase activity than the parental strain-derived spores. High levels of enzyme activity in the mutant extracts, but not in the corresponding wild-type extracts, could be detected in the absence of an exogenous protease. The high basal active chitin synthetase is not the result of activation by endogeneous proteases during cell breakage since protease inhibitors did not reduce, but rather increased, the activity levels. The analysis of cell wall composition in the mutant spores revealed significant changes in the proportion of uronic acids and protein but not in chitin. The mutant phenotype is discussed in relation to the developmental stage at which the alterations connected with cell wall metabolism occurred.

Guanine plus cytosine content of the DNA of Coccidioides immitis

The mole per cent guanine plus cytosine was determined for DNA extracted from Coccidioides immitis to add information pertinent to the taxonomy of this zoopathogenic fungus. Four strains of C. immitis, three in the mycelial phase, one in the spherule/endospore phase yielded guanine plus cytosine in the narrow range of 49.41 to 49.61 mole percent. These values are lower than those for ascomycetes that mimic the arthroconidial form of C. immitis, higher than those for ascomycetous yeasts, but closer to those of 'transition zone' or basidiomycetous yeasts.

Ultrastructure of the sporangiospore of Piptocephalis unispora (Mucorales)

Sporangiospore structure in Piptocephalis unispora Benjamin was studied using light microscopy, freeze-etching, scanning and transmission electron microscopy, and compared with that of other members of the Mucorales. A merosporangial wall, plasmalemmal invaginations, and wall protuberances were demonstrated in sections and their possible significance discussed.

Ultramicroscopic structure of Intrasporangium calvum (Actinomycetales)

The electron microscopic observation of vesicles formed by Intrasporangium calvum revealed that they do not contain spores. It thus seems that these vesicles should not be called sporangia. Isolation and study of three other strains of actinomycetes forming similar vesicles indicated that such structures can be formed by actinomycetes with very different properties. The taxonomic value of vesicle formation in actinomycetes is questioned.