Fine structure of mycota

Lomasomes and Other Fungal Plasma Membrane Macroinvaginations Have a Tubular and Lamellar Genesis

The plasma membrane of filamentous fungi forms large-sized invaginations, which are either tubes or parietal vesicles. Vesicular macroinvaginations at the ultrastructural level correspond to classical lomasomes. There is an assumption that vesicular macroinvaginations/lomasomes may be involved in macrovesicular endocytosis. The original aim of this study was to test for the presence of macroendocytosis in xylotrophic basidiomycetes using time-lapse and Z-stacks fluorescent microscopic technologies. However, the results were unexpected since most of the membrane structures labeled by the endocytic tracer (FM4-64 analog) are various types of plasma membrane macroinvaginations and not any endomembranes. All of these macroinvaginations have a tubular or lamellar genesis. Moreover, under specific conditions of a microscopic preparation, the diameter of the tubes forming the macroinvaginations increases with the time of the sample observation. In addition, the morphology and successive formation of the macroinvaginations mimic the endocytic pathway; these invaginations can easily be mistaken for endocytic vesicles, endosomes, and vacuole-lysosomes. The paper analyzes the various macroinvagination types, suggests their biological functions, and discusses some features of fungal endocytosis. This study is a next step toward understanding complex fungal physiology and is a presentation of a new intracellular tubular system in wood-decaying fungi.

Biochemical, genetic and ultrastructural defects in a mitochondrial mutant (ER-3) of Neurospora crassa with senescence phenotype

The structural and functional abnormalities in a new respiratory deficient, mitochondrial senescence mutant ER-3 of Neurospora crassa are described. The mitochondrial mutant, which grows at a rate of only 10% of that of the wild type, was found deficient in all three cytochromes, and completely lacking in cytochromes aa3. Cytochrome oxidase activity in the mutant mitochondria was only about 5% of the wild type mitochondria. However, the total whole cell respiration rate of the mutant was 33% greater than that of the wild type, while the cyanide-resistant respiration rates were equal. The results of inhibitor studies clearly demonstrate that the mutant possesses a defect in one or more components of the terminal oxidase. Electron microscopic examination of whole cell sections and subsequent morphometric analysis revealed a significant (33%) reduction in membrane surface density of mitochondrial cristae in the mutant as compared with the wild type. Results of genetic and heterokaryon analyses indicate the location of mutation (ER-3) in the mitochondrial DNA. It is concluded that the senescence mutant ER-3 possesses a defect in the terminal portion of the mitochondrial respiratory apparatus. These results are consistent with previous analyses of mitochondrial DNA populations, and support the notion that obligately aerobic eukaryotic cells deficient in mitochondrial respiration necessarily exist as a result of stable heteroplasmosis and that defects in mitochondria lead to senescence in Neurospora mutant ER-3.

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.

FINE STRUCTURE OF THE AGARICUS CARPOPHORE

The fine structure in the carpophore of the mushroom, Agaricus campestris, was studied with the electron microscope. The stipe consists of two types of cells (i) fundamental and (ii) long and thread-like. The pileus contains only the first type. The tramal cells of the gills are more elongated than broad, regularly arranged, and rich in cytoplasmic contents. The cross wall of the hyphal cells shows a conspicuous pore apparatus with dark septal swellings encased in the plasma membrane. The nuclear membranes are differentiated early during nuclear division and are highly alveolated around the interphase nucleus. In the maturing basidium, the mitochondria increase in number by division of pre-existing ones, and thus become small with few cristae. Numerous vacuoles appear in the upper portion of the basidium. Oil globules are also produced in the mature basidium but were not observed during the early stages of development of the basidium or in any other part of the carpophore. The young basidium has food reserve which is granular in nature. The basidiospore contains numerous large oil globules, few mitochondria, scanty endoplasmic reticulum, and a wall of three well-defined layers.