Maria Bassi

ULTRASTRUCTURAL CYTOPLASMIC CHANGES OF LIVER CELLS AFTER REVERSIBLE AND IRREVERSIBLE ISCHEMIA.

Abstract The ultrastructural alterations caused by temporary ischemia have been studied in liver parenchymal cells of fasted and fed rats. Ischemia was induced by ligation or clamping of the liver pedicle. Samples of liver were taken 15, 30, 60, and 120 minutes after ligation, and also 2 hours after the re-establishment of blood circulation in the liver lobes after previous ischemia. The first alterations caused by ischemia are changes in the plasma membrane, with disappearance of the microvilli at the sinusoidal border, formation of a number of vacuoles in the sinusoidal region, and disappearance of the intramitochondrial dense granules. By prolonging the duration of ischemia, mitochondria swell, the endoplasmic reticulum becomes fragmented and dilated, the microvilli of the bile canaliculi become swollen and greatly distorted, and the number of microbodies increases. In fasted animals these alterations appear earlier than in fed animals. All these changes are reversible if the duration of ischemia is not longer than 60 minutes; 2 hours after the re-establishment of blood circulation the cells have regained their normal appearance. But if ischemia lasts 120 minutes, the cells lose their capacity of recovery, and 2 hours after the re-establishment of blood circulation most of them are verging on necrosis. No specific lesion appears in relation to the death of liver cells subjected to ischemia. The limit of irreversibility is reached through a progressive deterioration of different cellular structures, and death appears as the outcome of many defects in subcellular organization that have passed the stage of compensatory repair.

Some ultrastructural and cytochemical observations on Chinese cabbage leaves infected with cauliflower mosaic virus

Abstract In leaves of Chinese cabbage infected with cauliflower mosaic virus (CaMV), inclusion bodies, made of amorphous material and virus particles, were found in the cytoplasm of most parenchyma cells of the mesophyll and veins, and also in epidermal cells. Most of the virus particles appeared as empty shells, and only a few had an electron dense core. Enzymatic digestions demonstrated that the amorphous material that constitutes the bulk of the inclusion bodies is proteinaceous. The main cellular alterations were deeply lobated nuclei and enlarged nucleoli, swollen mitochondria, formation of cell wall extrusions containing one or more plasmodesma-like channels, presence of masses of convoluted tubules or vesicles along the cell wall.

Modifications of the vascular bundle ultrastructure in the resistant zone around necrotic lesions induced by tobacco mosaic virus

Abstract The modifications that the vascular bundles undergo in the “resistant zone” surrounding TMV-induced necrotic lesions were studied by electron microscopy. It was found that, at a distance of about 1 mm from the lesions, the sieve plate pores and the plasmodesmata connecting the sieve elements with their companion cells were occluded by a callose-like substance. Nearer to the lesions, the tracheids were partially or totally occluded by plugs of electron-dense material, and the xylem parenchyma cells produced thickenings in their walls. The plugs in the tracheid lumen were not digested by pectinase or pronase, and were not preferentially stained by ruthenium red. They were markedly labelled after phenylalanine 3 H uptake, and it is suggested that one of their main constituents might be phenolic compounds.

State and function of liver polysomes during recovery from ischemia

Abstract The reestablishment of blood supply to the liver lobes which have suffered ischemia is followed by an increase in protein synthesis only if ischemia did not last longer than 60 minutes. The increase is accompanied by the recovery of a normal polyribosomal pattern. Treatment of the rats with actinomycin D does not prevent this restoration. In the early phase of the reestablishment of circulation there is a sudden formation of monomers. These monosomes respond well to polyuridylic acid (poly-U) in vitro . The monosome formation can be prevented by treatment of the animal with cycloheximide. Treatment with cycloheximide also prevents the disappearance of the polysomal shoulder during ischemia. The results support the hypothesis that the lowering of the polysomal shoulder and the formation of monosomes are not the effect of ribonuclease action, but the consequence of an interference with recycling of ribosomes on mRNA. The recovery of a normal polysomal pattern after ischemia does not depend on the synthesis of new mRNA.

Cell wall protrusions induced by cauliflower mosaic virus in Chinese cabbage leaves: A cytochemical and autoradiographic study

Abstract The mesophyll cells of Chinese cabbage leaves systemically infected with cauliflower mosaic virus (CaMV) often show outgrowths of their cell walls, which are generally traversed by one or more canals and sometimes assume the aspect of long tubules. By means of specific staining of the plasmalemma with a phosphotungstic-chromic acid solution (PTA), it was demonstrated that these tubular protrusions are lined by plasmalemma not only on the outside, but also on the inside, and that they should be considered as plasmodesma-related structures. By autoradiographic methods it was shown that the cell wall protrusions become heavily labeled after glucose- 3 H administration. The rest of the cell wall remains almost unlabeled. Thus, CaMV induces the deposition of cell wall material only in preferential sites. After phenylalanine- 3 H administration, no label was found in cell wall protrusions, showing that no lignification occurs in these structures.

An electron microscopy study of the penetration of tobacco mosaic virus into leaves following experimental inoculation

Abstract Leaves of Vigna sinensis were inoculated with tobacco mosaic virus (TMV) by gently rubbing their surface with a suspension of virus particles mixed with Carborundum powder. The modifications induced by this treatment on the leaf surface and in the epidermal cells were studied on replicas of the leaf surface and in ultrathin sections of the leaf. On the leaf surface scratchings and a great number of TMV particles were detected; some of the TMV particles were attached to the surface in vertical position. In the epidermal cells, as seen in sections, the external cell wall showed blebs under the cuticle. It is inferred that the rubbing of the leaf surface favors the implantation of some virus particles on the cuticle, and that the alterations of the cell wall provide an easy way of penetration of the particles into the epidermal cells.

Ultrastructural alterations induced by rice tungro virus in rice leaves.

Abstract Particles of rice tungro virus (RTV) were found in phloem parenchyma and companion cells. The most relevant alterations found in these cells were viroplasms and tubular inclusions. Virus particles, viroplasms and tubular inclusions were never observed in mesophyll parenchyma cells. However, the latter contained altered chloroplasts with taillike protrusions and an accumulation of heavy amounts of starch.

A submicroscopical study of leaves of alfalfa, Basil, and tobacco experimentally infected with lucerne mosaic virus

SummaryThe leaves of three species of plants (Medicago sativa L.,Ocymum basilicum L., andNicotiana tabacum L., cv.Samsun), previously infected with lucerne mosaic virus (LMV), were studied in the electron microscope. In the leaves ofM. sativa andO. basilicum the infection was systemic, while in the leaves ofN. tabacum the infection was local. In all the three species LMV particles were always detected only in the cytoplasm. Apart from the presence of virus particles in the cytoplasm, no ultrastructural alterations were found inM. sativa andN. tabacum. InO. basilicum, the green leaf areas did not show any prominent alterations, while the yellow leaf areas showed marked alterations of the chloroplasts. In these, the lamellar system was scarcely developed, and the few thylakoids tended to fragment, curl and disappear. In the chloroplast stroma, there was an abnormal development of filamentous structures, resembling the stromacentre.

Osservazioni preliminari al microscopio elettronico a scansione sulle ornamentazioni delle spore di Russula

Abstract Preliminary observations on spore ornementation of Russula, as seen in the scanning electron microscope. — The spores of 16 species of Russula have been examined in the scanning electron microscope, as a preliminary attempt to see if an accurate examination of the spore surface at the ultrastructural level could reveal details of ornamentation which might be useful for the classification of the many species of this genus. The examination, carried out both on fixed and unfixed specimens, has demonstrated that the spore shape is always round or slightly elliptic, and that the obnormal forms as previously described are probably artifacts. Five main types of ornamentation have been described: single wart-like and single finger-like Protrusion, wart- or finger-like protrusions interconnected by thin ridges, and thick, short « papillae » together with large ridges that run along large tracts of the spore circumference. The type of ornamentation was a constant character in each species.

Tipo e frequenza delle ornamentazioni delle spore di russula osservate al microscopio elettronico a scansione

Abstract Type and frequency of spore ornamentation of Russula, as revealed by scanning electron microscopy. – The spores of 30 species of Russula have been examined by scanning electron microscopy. The following characters have been considered: shape of spores, type of ornamentation, and frequency of the ornaments per unit area. The ornamentation frequency data have been elaborated statistically by variance analysis and Duncans test. It has been demonstrated that these characters alone do not always allow a clear-cut discrimination of the species. However, it seems that they can be used together in the elaboration of a dichotomic key which may help to clarify some controversial points in the classification of the species of Russula.