Shigeyasu Akai

Histochemical observation of the halo on the epidermal cell wall of barley leaves attacked by Erysiphe graminis hordei

Histochemical characters of the halo on the epidermal cell wall of barley leaves attacked byErysiphe graminis hordei were investigated with light microscope. The area corresponding to the halo showed reduced intensity of stain reactions for cuticle, pectin and cellulose, especially at the penetration point. From the several histochemical reactions, it was concluded that reducing substances with aldehyde groups (such as hexose), pentoses and possibly uronic acids occur in the halo. According to these results, it can be concluded that the halo is caused by the degeneration of the epidermal cell wall by the fungal enzymes.

Histochemical changes of the epidermal cell wall of barley leaves infected by erysiphe graminis hordei

Chemical changes in the epidermal cell wall of barley leaves attacked byErysiphe graminis hordei were investigated by means of histochemical techniques and electron microscope. A very narrow area in the cuticle which was not stained by Sudan III was detected around the penetration point of this fungus. This is to indicate that the cuticle was changed either enzymatically or mechanically at the penetration point. According to the procedures using zinc-chloriodide and Schiffs reagent, it was obvious that the area of cellulose layer corresponding to the halo changed chemically, which suggested that the halo was attributable to the degeneration of the cellulose layer by the fungal enzyme, probably the cellulase. Electron micrographs showed that the cell wall around the penetration point was prominently electron dense and indicated an enzymic degeneration of the host cell wall.

Effect of the host-specific toxin from Alternaria kikuchiana on the ultrastructure of plasma membranes of cells in leaves of Japanese pear☆

Abstract Alternaria kikuchiana , causal fungus of the black spot disease of Japanese pear, produces a host-specific toxin (AK-toxin) which caused immediate changes in permeability of susceptible leaf tissues. The first obvious change in ultrastructure of susceptible cells in the vascular bundle sheath and in the mesophyll was an invagination of plasma membranes, evident by 1 h after exposure. There were still more invaginated plasma membranes by 3 and 6 h after exposure, when a high percentage of susceptible cells showed such changes. There was no obvious effect of toxin on cellular organelles of susceptible leaves after 1, 3 and 6 h of treatment; the organelles appeared to be normal even in cells with invagination of plasma membranes. After 10 h of toxin exposure, leaf cells were necrotic, but the cellular membrane systems still maintained much of their original structures. The degeneration that was evident may have been from secondary effects of toxin. The spaces between susceptible cell walls and invaginated membranes contained many lomasome-like vesicles, membrane fragments and darkly stained materials. Rolands staining method indicated that the vesicles were fragments from invaginated plasma membranes. However, ultrastructural changes in unit membranes of invaginated plasma membranes were not observed. Cells of resistant leaf tissues were not affected by toxin. These results are compatible with the hypothesis that the plasma membrane is the site of an initial effect of AK-toxin.

An electron microscopic observation on the germination of conidia of Colletotrichum lagenarium

On the electron microscopy of germinating fungal spores, HAWKER & ABBOTT (1963) observed the germination of sporangiospores of Rhizopus, and HAWKER & HENDY (1963) and BUCKLEY et al. (1966) examined the sections of germinating and ungerminating conidia of Botrytis cinema. In germinating conidia of Botrytis they found some structures which have not been observed before germination. When conidia of Botrytis germinate they elongate germ tubes considerably. In our experiments with Colletotrichum lagenarium, however, nearly all conidia (about 90 %) produced appressoria immediately after germination, and only about 10 °/o germinated by having distinct germ tubes. From various studies, there are abundant informations on the mechanism of appressorium formation, but we still lack definite theory as to its formation. In this paper the writers described results of our observation on the structure of germinating conidia and the process of appressorium formation. A grateful acknowledgement is made to Mr. M. FUKUTOMI for the technical advice and assistance given us, and to Dr. H. YASVMORI, Gunma Forest Experiment Station for providing us with the strain of the fungus used in this experiment.

Relation of Temperature to Germination of Conidia and Appressorium Formation in Colletotrichum Lagenarium

The relation of temperature to germination of conidia and appressorium formation in Colletotrichum lagenarium is discussed. The optimum temperature for germination of conidia is from 20 to 32 C, and 20 to 26 C was the optimum for appressorium formation. Conidia that germinated at 32 C seemed to lose the ability to form appressoria. All conidia kept at 32 C for 2-12 hr germinated, but they did not form appressoria.

Electron microscopic observation of cell wall structure during appressorium formation in Colletotrichum lagenarium

The formation of cell walls during the appressorium formation inColletotrichum lagenarium was observed by electron microscope on the materials prepared by replicas and sectioning. The outer layer of conidia cell walls ruptured at the time of germination and the inner layer bulged out to form a germ tube. The germ tubes and primordia of appressoria had smooth surface and were consisted of one-layered cell wall. However, as the appressorium matured, the electron dense materials appeared on the outer surface of the cell wall which grew into granules. These granules are believed to form the outer layer of appressoria. The under side of the appressorium in contact with the glass surface showed a round pore.

The electron microscopic observation of haustoria of Erysiphe graminis hordei

The fine structure of haustoria ofErysiphe graminis hordei was studied using samples fixed with 3 per cent KMnO4 or 2 per cent OsO4. The cell wall of the infected leaves of barley seedlings was extremely electron-dense around the penetration point of this fungus. This may be due to chemical change of components in cell wall by the enzymatic action of the fungus. The cell wall was invaginated towards the cytoplasm at the point of penetration and formed a sheath around the infection hypha. Unknown electron-dense substances were accumulated around the infection hypha outside the sheath. The haustorial cell wall was surrounded with encapsulation and distinguished clearly from the cytoplasm of epidermal cell. The cell wall of the haustorium was very thin and electron-transparent, when compared with that of conidia and hyphae. A septum with a septal pore was observed between the infection hypha and the haustorium. Besides the nucleus, mitochondria, endoplasmic reticula and the like, many kinds of vesicles and specific coiled membraneous structure were found in the haustorium. The origin and the function of the encapsulation remain obscure. Die Feinstruktur von Haustorien vonErysiphe graminis hordei war untersucht, indem Stücke mit 3 % KMnO4 oder 2 % OsO4 fixiert worden sind. Die Zellwand der infizierten Blätter der Gerstenkeimlinge war elektron-dicht um die Eindringungsstelle des Pilzes. Dies mag die Folge der chemischen Veränderung der Komponenten in der Zellwand durch die enzymatische Wirkung des Pilzes sein. Die Zellwand war an der Eindringungsstelle zum Zytoplasma gebogen und hat eine Hülle um die Infektionshyphe gebildet. Unbekannte, elektron-dichte Substanzen waren um die Infektionshyphe außerhalb der Hülle angesammelt. Die Haustorialzellwand war abgegrenzt und war vom Zytoplasma der Epidermalzelle unterscheidbar. Die Zellwand des Haustoriums war dünn und elektron-durchsichtig im Vergleich mit denen der Konidien und Hyphen. Ein Septum mit einer Septalpore war zwischen der Infektionshyphe und dem Haustorium beobachtet. Neben dem Nucleus, Mitochondrien, endoplasmatischen Netz sind mancherlei Blister, spezifische, eingerollte Membranstruktur im Haustorium gefunden worden. Die Herkunft und die Funktion dieser Strukturen blieb ungeklärt.

An electron microscopic observation of conidium and hypha of Erysiphe graminis hordei

The fine structure of conidia and hyphae ofErysiphe graminis hordei, attacking leaves of barley, were investigated. The cell walls of conidia and hyphae were relatively thin and consisted of two layers, the inner and outer layers. The surface of conidia was not smooth and the thickness of cell walls was irregular. A nucleus, mitochondria, endoplasmic reticula and vacuoles in plasma were identified. The vacuoles in conidia were tightly packed with fine granules. Such granules in vacuoles, however, were not observed in hyphal cells. A lamellar structure was located in conidia, but not in hyphal cells. This structure may be specific in conidia of this fungus, but its function is not yet known. Many glycogen granules were observed in endoplasm of conidia, which were scattered or congregated in groups. In hyphae, however, they were extremely few. Hyphal septa were connected directly with the inner layer of cell walls. These had simple septal pore. The Woronin bodies were detected in the endoplasm in the vicinity of hyphal septa.

Fine structure of antheridia and oogonia of Phytophthora macrospora, the downy mildew fungus of rice plants

In the present paper fine structure of antheridium and oogonium ofPhytophthora macrospora (Sacc.)S. Ito etI. Tanaka, the downy mildew fungus of rice plants was discussed. Before the fertilization some nuclei and a large number of mitochondria were scattered in the cytoplasm of the antheridium. Many lipid granules were observed in the peripheral region, but vacuoles did not appear at this stage of antheridium. Many mitochondria were associated in the neighborhood of the fertilization pore. The wall at the pore was very thin, but the wall surrounding the pore was slightly swollen towards the inside. In the oogonium, many nuclei, mitochondria and cytoplasmic matrix were observed at the peripheral part. A large number of lipid granules was found in the oogonium, but they were more numerous in the peripheral region. The vacuoles developed as the oogonium matured. They were enveloped by tonoplast and contained vacuolar matrix. Many electron dense granules were in contact with the tonoplast or free in the vacuoles, and they were larger in the central part. As stated above, wall at the fertilization pore was thin. However, the oogonial wall surrounding the pore swelled protruding into the oogonium. An electron-dense layer was recognized between the antheridial and oogonial wall, and the walls of both the organs were closely in contact with each other.

An observation on fine structure of conidia of sphaerotheca pannosa (wallr.) lév. attacking leaves of roses

Fine structures of conidia ofSphaerotheca pannosa, the causal fungus of powdery mildew of rose plants were investigated. The cell wall of conidia was relatively thin and consisted of two layers. Nuclei, mitochondria, endoplasmic reticula and vacuoles were identified in the conidia, and there were many unknown vesicles just inside the plasma membrane. Usually the conidia were uninucleate, but before the germination the nucleus divided into two. Vacuole held a number of osmiophilic globules which were located along the tonoplast, and in large magnifications they appeared as aggregation of small electron-transparent globules when fixed with KMnO4 solution. In a germ tube one large mitochondrion and many endoplasmic reticula were found.