Search results for "Ultrastructure"

Early stages of test formation in larva of Ascidia malaca (Tunicata, Ascidiacea): ultrastructural and cytochemical investigations.

2003

Abstract The swimming larvae of ascidians are entirely covered by a hyalin coat called tunic, or test. This covering consists of two cuticular layers, C 1 and C 2 , which surround an inner compartment composed of an amorphous hyalin matrix with numerous fibrils dispersed inside. Data from the literature agree on the key role played by the cells of the larval ectodermic layer in the synthesis and secretion of larval test components. In the present article are reported ultrastructural and cytochemical investigations made during test formation in the swimming larva of Ascidia malaca . Besides confirming the role played by ectodermic cells during the early stages of test formation, the investig…

Ultrastructural changes of sparkling wine lees during long-term aging in real enological conditions.

2012

Ultrastructural changes of lees of three series of sparkling wines produced using the traditional method during long-term aging (4 years) were assessed by high-pressure freezing in combination with transmission electron microscopy. The stratified structure of the cell wall disappeared throughout aging. After 18 months, the microfibrous material of the cell wall appeared more diffuse and the amorphous midzone of the inner wall layer was progressively degraded. From 30 months onward, the cell wall consisted of a tangled structure of fibers. In spite of these changes, the cell wall of yeasts remained unbroken at 48 months of wine aging. Cell membrane breakage was observed for the first time in…

New insights into the regulatory mechanisms of ppGpp and DksA on Escherichia coli RNA polymerase-promoter complex

2015

The stringent response modulators, guanosine tetraphosphate (ppGpp) and protein DksA, bind RNA polymerase (RNAP) and regulate gene expression to adapt bacteria to different environmental conditions. Here, we use Atomic Force Microscopy and in vitro transcription assays to study the effects of these modulators on the conformation and stability of the open promoter complex (RPo) formed at the rrnA P1, rrnB P1, its discriminator (dis) variant and lambda pR promoters. In the absence of modulators, RPo formed at these promoters show different extents of DNA wrapping which correlate with the position of UP elements. Addition of the modulators affects both DNA wrapping and RPo stability in a promo…

Chloroplast morphology and pyrenoid ultrastructural analyses reappraise the diversity of the lichen phycobiont genus Trebouxia (Chlorophyta)

2022

Abstract Trebouxiophyceae is a wide class of green algae comprising coccoid and elliptic unicells, filaments, blades and colony-forming species that occur in diverse terrestrial and aquatic environments. Within this class, the genus Trebouxia Puymaly is among the most widespread lichen phycobionts worldwide. However, the 29 formally described species based on the combination of morphological traits and genetic diversity woefully underrepresented the overall species-level diversity recognized in the genus. In Trebouxia, reliable differentiation and characterization of the species-level lineages can be achieved by studying the diversity of key diagnostic features of pyrenoid ultrastructure an…

Ultrastructure

1973

Crystalloid lysozyme inclusions in Paneth cells of vitamin A-deficient rats.

1990

The effect of vitamin A-deficiency on jejunal Paneth cells in rats was investigated. Crystalloid particles were observed in secretion granules of Paneth cells from 6 out of 8 rats with vitamin A-deficiency. The particles were similar to those found in Paneth cells under other experimental conditions. Using an immuno-electron-microscopic technique we demonstrated a clear lysozyme immunoreactivity of these particles. In 2 vitamin A-deficient rats tubular structures have been detected in addition to the crystalloid particles. Crystalloid particles or tubular structures were not detectable in a control group of 8 vitamin A-supplemented rats. The morphological alterations of Paneth cells may be …

Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition)

2016

Seuls les 100 premiers auteurs dont les auteurs INRA ont été entrés dans la notice. La liste complète des auteurs et de leurs affiliations est accessible sur la publication.; International audience; In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues…

Ultrastructure of the conus arteriosus ofScyliorhinus stellaris

1989

The functional morphology of the fourth chamber of the fish heart, the bulbus arteriosus, differs in teleosts and elasmobranchs. In elasmobranchs, this chamber is referred to as the conus arteriosus because its wall is made up of myocardial tissue in addition to elastic tissue. As a result of this feature, the function of the conus is very specialized. We report the basic ultrastructure of the wall of the conus arteriosus in the elasmobranch Scyllium stellare. The wall consists of three layers: the outer epicardial, the middle myocardial, and the inner endocardial layer. The outer layer is composed of the visceral pericardium consisting of cuboidal mesothelial cells, beneath which numerous …

Effects of tributyltin(IV) chloride exposure on early embryonic stages ofCiona intestinalis:In vivo and ultrastructural investigations

1993

The effects of tributyltin(IV) chloride (TBT chloride) solutions on ascidian embryos of Ciona intestinalis have been tested at different stages of development. It has been observed, in vivo, that TBT chooride inhibited cleavage of fertilized eggs and of embryo blastomeres giving rise to cellular masses that are not delimited by plasma membrane. Electron-dense precipitates of TBT chloride, probably as inorganic tin, have been observed by transmission electron microscopy in the egg cytoplasm of cellular masses. The same type of precipitate was present also inside the mitochondria, whose structure appeared to be highly modified. These ultrastructure aspects are indicative of a degenerative pro…

The complex life-cycle of a polymorphic prokaryote epibiont of the photosynthetic bacterium Chromatium weissei

1993

In natural populations of the anaerobic phototrophic bacterium Chromatium weissei, many cells support a prokaryotic epibiont. This epibiont appears in several forms, all from the life cycle of a single species. A typical epibiont consists of one to five flattened coccoid cells stacked one above the other, perpendicular to the C. weissei surface. The cells at the proximal and distal ends of the stack are 0.6 μm in diameter and 0.8 μm in length; mid-stack cells are slightly shorter. A typical three or four cell stack is 2 μm in length. Small mesosome-like inclusions in the distal cell are involved in the development of ‘droplet’ shaped cells which are released from the end of each stack. Thes…