Germ Tube Wall Research Articles

Cell Walls of Germinating Uredospores

Synthesis of germ tube wall is a major quantitative event during germination penetration of fungi on host plants, but little is known of germ tube composition or metabolic regulation. Sonic oscillation was used to separate germ tubes from germinating uredospores of Uromyces phaseoli var. typica. Uniformly (14)C-labeled wall fractions from both structures were prepared by repeated low speed centrifugation and extraction with polar and nonpolar solvents. Based on amino acid analysis, approximately 6 and 16% of the carbon from uredospore and germ tube walls, respectively, was present in amino acids readily accessible to protease. Covalent linkages between amino acid and carbohydrate of walls was indicated by analysis of fragments prepared by mild hydrolytic procedures and separated by column chromatography and paper electrophoresis. The existence of protein in wall structures may resolve some previous uncertainty about the occurrence of protein biosynthesis during germination of rust fungi. Glucose, mannose, and glucosamine were the only carbohydrate components identified in both germ tubes and uredospore walls but different percentages were observed (germ tubes 28: 16: 16; uredospore 6: 36: 6). In germ tubes, most of the glucosamine was present in linkages hydrolyzed only by strong acid treatment, suggesting chitin-like polymers. In uredospore walls, glucosamine appears to be associated with red uredospore pigment which has properties similar to those of a melanin. Approximately 20% of the carbon in walls could not be identified with known compounds, partially because of degradation during the analytical procedures.

Ultrastructural changes during germination of Geotrichum candidum arthrospores

The dormant arthrospore in Geotrichum candidum has three, possibly four, layers making up the spore wall. Nuclei, mitochondria, free ribosomes, fragments of endoplasmic reticulum, various small vacuoles, and particles of glycogen were observed within the protoplasm. During germination a new layer of wall material forms between the original spore wall and the cytoplasm. This new layer is confined to the region where germ-tube emergence occurs and is continuous with the germ-tube wall. After germ-tube emergence vesicles were seen at the apices of germlings. Another feature of germination was an apparent increase in the amount of endoplasmic reticulum, some of which appears to assume the function of the Golgi apparatus.

A structural comparison of cyst and germ tube wall inPhytophthora palmivora

An electron microscopic analysis of germinating cysts ofPhytophthora palmivora involving freeze-etching, thin sectioning, and replica techniques reveals that both cyst and hyphal wall comprise a two-phase system with a fibrillar and an amorphous component. The cyst wall is fibrillar throughout with the fibrils tightly interwoven and embedded in an amorphous matrix on the internal side of the wall. The hyphal wall consists of a fibrillar inner layer with the fibrils lightly covered by some amorphous material and an amorphous outer layer devoid of any fibrillar material. Both cyst and germ tube walls are wholly or partially covered by a fluffy coat of variable thickness. In the zone of germ tube emergence cyst wall and germ tube wall overlap and are tightly apposed. Thus, the germ tube wall is not a simple extension of the cyst wall but a new structural entity separated from the cyst wall by a thin line of demarcation.

Ultrastructure of Dormant and Germinating Conidia of Aspergillus Nidulans

The cell wall of dry, dormant conidia of Aspergillus nidulans is three-layered. The wall of hydrated conidia is five-layered and the germ tube wall is continuous with the innermost layer. The outer...

Phospholipids in the Uredospores of Uromyces phaseoli

Utilizing paper, thin layer and gas chromatography, the phospholipids of dormant and germinating spores have been isolated and identified. The identifications were based upon agreements of retardation factor values between the unknowns and reference compounds and their derivatives. Quantitative analysis of components, color reactions and specific labeling experiments were also used to support certain identifications. At least three, and usually more, criteria were used for each phospholipid that was definitively identified.The major phospholipids of Uromyces phaseoli are phosphatidylcholine and phosphatidylethanolamine. Diphosphatidylglycerol, or cardiolipin, phosphatidylinositol, and another phosphoinositide were present as minor components. In germinating spores, phosphatidylmonomethylethanolamine, phosphatidyldimethylethanolamine, phosphatidylserine, and phosphatidic acid were detected in trace amounts. The presence of these common intermediates in the biosynthesis of phospholipids indicates that phospholipid synthesis is active during the germination process. Except for the absence of phosphatidylglycerol, the types of phospholipids present are similar to the host plant. Germ tube wall preparations were found to contain phosphatidylcholine and phosphatidylethanolamine in about the same proportion as that observed in resting spores, while the proportion of diphosphatidylglycerol was about three times higher. An unidentified phosphorous-containing lipid was also a significant component of the total phospholipids extracted from germ tube walls.

Fine structure and physiology of conidial germination in Aspergillus fumigatus

The fine structure of Aspergillus fumigatus conidia at successive stages of germination is described. Spore swelling is accompanied by a stretching and disintegration of the outer wall layer of the spore, nuclear division, increase in the number of mitochondria and the formation of a vacuole from endoplasmic reticulum. The inner spore wall gives rise to the germ-tube wall by growing out through the remains of the outer wall. Spore swelling is dependent upon an external supply of assimilable carbon compounds. Percentage germination at a fixed incubation time is much reduced by total lack of nutrients and is more influenced by the level of external carbon than by that of external nitrogen compounds.

Fine Structure of Spore Germination in Botrytis cinerea

SUMMARY The ultrastructure of germinating Botrytis cinerea conidia was studied using three different fixatives. Good fixation and embedment of dormant spores was achieved. The wall of the dormant spore was composed of two layers. During germination three new wall layers were formed between the original wall and the cytoplasm; the inner two layers were continuous around the spore cytoplasm whilst the third was formed only near the point of germ-tube emergence and was continuous with the germ-tube wall. The conidial wall increased in thickness from 263 to 339 nm. during germination. It was calculated that, as a result of spore swelling alone, the dormant spore wall would decrease in thickness from 263 to 178 nm. An apical corpuscle was observed in the germ-tube wall during germination.

Fine-structural Changes during Germination of Conidia of Penicillium griseofulvum Dierckx

Conidia of Penicillium griseofulvum Dierckx have been examined by electron-microscopy at a series of stages throughout the course of germination. The conidia have two-layered walls but during germination a third, inner wall layer appears which may be quite distinct or rather indistinct according to the composition of the germination medium. The germ-tube wall is continuous with this third spore-wall layer only. Ungerminated conidia contain a nucleus and mitochondria. During swelling mitochondria increase in size and become lobed, endoplasmic reticulum becomes visible, and vacuoles are formed. Septa formed in germ-tubes are perforate and have Woronin bodies associated with them. The structural changes during germination can be correlated with changes in physiological behaviour of the germinating conidia.

Wall fibrils ingerminating sporangiospores of Gilbertella persicaria (Mucorales)

In germinated sporangiospores of Gilbertella persicaria, negatively contrasted fibrils, 20–70 A diam, are seen in thin sections of the inner vegetative wall that is continuous with the germ tube wall. The fibrils are randomly oriented in a loose network in this wall and in the germ tube wall. Germ tubes have an additional surface layer of fine, positively contrasted fibrils which appear as a nap-like coating on the hyphae. Patterns of wall fibril orientation are not revealed by transverse sections of spore and germ tube walls, whereas oblique and tangential sections are favorable for examining cell wall architecture in situ. Staining patterns show textural and compositional differences among various wall layers.

Structure and differentiation of the cell wall of Phytophthora palmivora: cysts, hyphae and sporangia.

Walls from cysts, hyphae and sporangia of Phytophthora palmivora consist chiefly (ca. 90% dry wt) of β-glucans with 1,3-, 1,4- and 1,6-links. The glucans are predominatly β-1,3-linked but there are significant differences in the relative proportion of 1,3-, 1,6- and 1,4-linked glucosyl residues among the three wall types. There are also differences in protein content, susceptibility to degradation by various β-glucanases, and surface texture. The isolated cyst wall consists solely of a thin fabric of long, tightly interwoven, randomly oriented microfibrils. Both inner and outer surfaces of the cyst wall are distinctly microfibrillar. The hyphal wall has two different textures; the internal surface is distinctly microfibrillar while the external surface is non-fibrillar. In a germinated cyst, there is a zone of demarcation where the microfibrils of the cyst wall disappear into the smooth outer texture of the germ tube wall. An exo-β-1,3-glucanase preferentially removed the amorphous material of the outer surface of the germ tube leaving exposed a continuous microfibrillar fabric from cyst to hyphal tube. Conceivably, the textural and structural differentiation of the cell wall may play a decisive role in cellular morphogenesis.

Protein and Ribonucleic Acid Synthesis during Germination of Uredospores

Existing evidence suggests that there is no net synthesis of protein during germination of spores of some obligate parasites. The problem was reinvestigated with enzymatic hydrolysis, rather than acid hydrolysis or solubility properties, to estimate changes in protein and RNA. Procedures are detailed for the use of uniformly labeled (14)C-uredospores for the isolation and quantitative assay of amino acids and nucleosides resulting from hydrolysis.During early stages of germination in the absence of exogenous substrates, nucleosides derived enzymatically from RNA do not increase nor does the base composition vary. The bases of the free nucleotide pool, although varying in concentration from the RNA bases, also remain constant during this time. After 16 or 24 hours, bases from both sources decrease appreciably, and the decline is correlated with leakages to the external medium.In contrast to previous reports, amino acids released by proteases increased 20 to 25% during the first 3 to 5 hours of germination but decreased after 16 to 24 hours. The results suggest that spores of obligate parasites have a functional protein synthetic system which is involved in germination. Previous negative findings may have resulted from a lack of specificity in the analytic procedures employed, coupled with the possibility that protein or amino acid is associated with the walls of spores and the walls of germ tubes.

Emergence of the aeciospore germ tubes of Cronartium coleosporioides (=Peridermium stalactiforme) as observed by scanning electron microscope

Germ tubes of Cronartium coleosporioides Arth. (= Peridermium stalactiforme Arth. and Kern) emerged between processes through short irregular slits. Germ tube walls were folded when they emerged and expanded after the emergence.

Electron microscopy of spore germination and cell wall formation in Mucor rouxii

The fine structure of ungerminated and aerobically germinated sporangiospores of Mucor rouxii was compared. The germination process may be divided into two stages: I, spherical growth; II, emergence of a germ tube. In both stages, germination is growth in its strictest sense with overall increases in cell organelles; e.g., the increase in mitochondria is commensurate with the overall increase in protoplasmic mass. Noticeable changes occurring during germination are the disappearance of electron-dense lipoid bodies, formation of a large central vacuole and, most strikingly, formation of a new cell wall. Unlike many other fungi, M. rouxii does not germinate by converting the spore wall into a vegetative wall. Instead, as in other Mucorales, a vegetative wall is formed de novo under the spore wall during germination stage I. This new wall grows out, rupturing the spore wall, to become the germ tube wall. Associated with the apical wall of the germ tube is an apical corpuscle previously described. The vegetative wall exhibits a nonlayered, uniformly microfibrillar appearance in marked distinction to the spore wall which is triple-layered, with two thin electron dense outer layers, and a thick transparent inner stratum. The lack of continuity between the spore and vegetative walls is correlated with marked differences in wall chemistry previously reported. A separate new wall is also formed under the spore wall during anaerobic germination leading to yeast cell formation. On the other hand, in the development of one vegetative cell from another, such as in the formation of hyphae from yeast cells, the cell wall is structurally continuous. This continuity is correlated with a similarity in chemical composition of the cell wall reported earlier.

Fine structure of quiescent and germinating aeciospores of Cronartium fusiforme.

Aeciospores of the long-cycle heteroecious rust fungus, Cronartium fusiforme, were found to have an extremely thick cell wall with striking spicules protruding from it. The wall was readily degraded by commercial chitinase, but spicules were unaffected. Quiescent spores contained two nuclei with distinct nuclear membranes possessing many pores. Numerous membrane-bounded lipid bodies were found both in wild-type orange and in white mutant aeciospores. An abundance of irregularly ovoid mitochondria was present in quiescent spores. After glutaraldehydeosmium fixation, the surface of the mitochondria appeared to be covered with ribosomes or microtubules in a paracrystalline array, whereas after permanganate fixation only smooth outer mitochondrial membranes were noted. The latter fixative revealed abundant vesicular endoplasmic reticulum in the spore. Spores incubated at 20 C on agar produced one to five distinct germ tubes within 65 to 180 min. These thin-walled tubes exhibited varying degrees of branching, and reached a total hyphal length of 300 to 500 mu prior to rupturing. Emergence of germ tubes took place through a pore in the spore wall and appeared to be mainly a physical flowing of cytoplasm from the spore into the germ tube without division of nuclei or other cell organelles. On completion of germination, the protoplasm of the germ tube contained both nuclei and nearly all of the other spore contents. Mitochondria had smooth outer membranes, were greatly elongated, and possessed distinct longitudinal cristae. A limited amount of rough endoplasmic reticulum was arranged parallel to the germ tube wall. Other organelles seen in germ tubes were lipid bodies, concentric membrane figures, and numerous ribosomes. Lipid bodies appeared smaller and fewer in number than in quiescent spores.

Fusion Of Uredospore Germ Tubes in Puccinia graminis

Rodenhiser and Hurd-Karrer1, working with Puccinia graminis tritici, observed the fusion of spherical ‘fusion bodies’ produced by certain germ tubes with germ tubes of other uredospores. They noted that “the body envelopes the contacted hypha as would a viscous drop”; in some cases dissolution of the germ tube wall at the point of contact was seen. In one case movement of the granular contents of the hypha with which contact was made into the fusion body was observed. The work of Nelson, Wilcoxson and Christensen2 provided genetical evidence for fusion between germ tubes, but although they observed fusions they gave no cytological details.