Effect of fucoidan from brown alga <Emphasis Type="Italic">Fucus evanescens</Emphasis> on a formation of TMV-specific inclusions in the cells of tobacco leaves

The effect of fucoidan (1.3; 1.4-α-L-fucan), a sulfated polysaccharide from the brown alga Fucus evanescens on the formation of specific granular and tubular inclusions induced by tobacco mosaic virus (TMV) and consisted presumably of the virus-coded protein components of the viral replicase was investigated in the TMV-infected leaves of tobacco (Nicotiana tabacum L.). In four days after inoculation of the leaves with a TMV preparation (1 mg/ml), the signature of infection in a presence of fucoidan (1 mg/ml) was a preferential formation of intracellular granular inclusions, which were related to early stages of the virus reproduction. When infected leaves were not treated with fucoidan, their cells contained mainly tubular inclusions, which were presumably formed from the granular ones on the last stages of the infection process. These observations demonstrated that fucoidan delayed the development of the TMV-induced infection.     

Effects of selenium on growth and ultrastructure of the marine unicellular alga <Emphasis Type="Italic">Dunaliella salina</Emphasis> (Chlorophyta)

This study examines the effects of selenium in concentrations of 0.01, 0.5, 1, 5, and 10 mg/liter on the growth and ultrastructure of the microalga Dunaliella salina. Selenium in concentrations of 0.01 and 0.5 mg/liter stimulated cell population growth, while the number of ultrastructural alterations was the same as in the control cells. At a selenium concentrations of 1 mg/liter, cell population growth slightly decreased by the end of the experiment, and there was some increase in the number of cells with damaged organoids and in the number of completely destroyed cells. As well, the excretory function of cell vacuoles was suppressed, and the autophagic activity of these vacuoles was activated to destroy the cytoplasm and nucleus. Concentrations of 5 and 10 mg/liter were toxic to D. salina, suppressing cell population growth and promoting extensive destructive changes. The threshold concentration of selenium for D. salina was 1 mg/liter, which is 1000 times greater than the maximum permissible concentration (MPC). The fact that the microalga was able to survive for several days in this concentration is indicative of its high resistance to selenium.     

Ultrastructural Study of Relationships between Germinal Bodies and Mitochondria in Apostichopus japonicus (Echinodermata: Holothuroidea) and Pleuronectes asper (Teleostei: Pleuronectidae)

The relationships between germinal bodies and mitochondria were studied in the holothurian Apostichopus japonicus and the flounder Pleuronectes asper using TEM. In the gonial cells of both species the mitochondria are arranged around germinal bodies and are in contact with the latter. A gradual disappearance of the outer membrane is found in the mitochondria that interact with the germinal substance. Later on, dispersion of the globules of the mitochondrial matrix containing mitochondrial cristae occurs. It is supposed that the substance of the mitochondrial matrix takes part in the development and functioning of the germinal plasm in both invertebrates and vertebrates.     

Effect of chitosan on tobacco mosaic virus(TMV) accumulation,hydrolase activity,and morphological abnormalities of the viral particles in leaves of N. tabacum L. cv. Samsun

The effect of chitosan on the development of infection caused by Tobacco mosaic virus(TMV) in leaves of Nicotiana tabacum L. cv. Samsun has been studied. It was shown that the infectivity and viral coat protein content in leaves inoculated with a mixture of TMV(2 μg/mL) and chitosan(1 mg/mL) were lower in the early period of infection(3 days after inoculation), by 63% and 66% respectively, than in leaves inoculated with TMV only. Treatment of leaves with chitosan 24 h before inoculation with TMV also caused the antiviral effects, but these were less apparent than when the virus and polysaccharide were applied simultaneously. The inhibitory effects of the agent decreased as the infection progressed. Inoculation of leaves with TMV together with chitosan considerably enhanced the activity of hydrolases(proteases, RNases) in the leaves, in comparison with leaves inoculated with TMV alone. Electron microscope assays of phosphotungstic acid(PTA)-stained suspensions from infected tobacco leaves showed that, in addition to the normal TMV particles(18 nm in diameter, 300 nm long), these suspensions contained abnormal(swollen, "thin" and "short") virions. The highest number of abnormal virions was found in suspensions from leaves inoculated with a mixture of TMV and chitosan. Immuno-electron microscopy showed that "thin" virus particles, in contrast to the particles of normal diameter, lost the ability to bind to specific antiserum. It seems that the chitosan-induced activation of hydrolases stimulates the intracellular degradation of TMV particles and hence hydrolase activation may be considered to be one of the polysaccharide-mediated cellular defense mechanisms that limit virus accumulation in cells.     

Resorption of Gametes in the Testes of the Sea Star <Emphasis Type="Italic">Asterina pectinifera</Emphasis> (Mueller et Troschel, 1842)

The process of resorption of spermatozoa is described in the testes of the starfish Asterina pectinifera. It is shown that the mode of resorption of the male gametes in this species is different from that in the starfish Asterias vulgaris (see Walker [17, 18]), A. amurensis, and Aphelasterias japonica (see Kasyanov et al. Original Russian Text Copyright © 2005 by Biologiya Morya, Kalachev, Reunov.     

Phagocytic Activity of Accessory Cells in the Gonad of the Sea Urchin <Emphasis Type="Italic">Strongylocentrotus nudus</Emphasis>

The ultrastructural mechanism of postspawning sperm resorption in the testes of the sea urchin Strongylocentrotus nudus is described. Two types of phagosomes (containing sperm and containing residual bodies) are formed in the cytoplasm of nutritive phagocytes. The phagosomes fuse with electron-dense globules, and their contents are gradually destroyed. Afterward, phagosomes are transformed into electron-transparent vacuoles, which are finally compressed by the surrounding cytoplasm.     

Chitosan antiviral activity: Dependence on structure and depolymerization method

Enzymatic (the action of lysozyme) and chemical (the action of hydrogen peroxide) hydrolysis of chitosans with various degree of acetylation (DA)—25, 17, and 1.5%—was performed. Purification and fractioning of the hydrolysis products were performed using dialysis, ultrafiltration, and gel-penetrating chromatography. Low-molecular (LM) derivatives of the polysaccharide with molecular masses from 17 to 2 kDa were obtained. The study of their antiviral activity against the tobacco mosaic virus (TMV) showed that these samples inhibited the formation of local necroses induced by the virus for 50–90%. The antiviral activity of the LM chitosans significantly increased with the lowering of their polymerization degree. Furthermore, the products of the enzymatic hydrolysis possessed lower activity than the chitosan samples obtained as a result of chemical hydrolysis. It was revealed that the exhibition of the antiviral activity weakly depended on the degree of acetylation of the samples.     

A subset of cells in tobacco mosaic virus (TMV)-induced local lesions in <Emphasis Type="Italic">Datura stramonium</Emphasis> leaves are tolerant to TMV

Ultrastructural examination of tobacco mosaic virus-induced local lesions growing in Datura stramonium leaves is carried out. It is demonstrated that, in the central area of the lesions, the cell response to viral invasion is not uniform. Most cells exhibited an acute hypersensitive reaction (HR) and underwent rapid and complete necrosis. However, some cells, despite considerable virus accumulation and immediate contact with completely collapsed cells, maintained a certain degree of structural integrity. Analysis performed showed that the proportion of collapsed and uncollapsed cells in the lesion centre 3 to 5 days after infection essentially did not change. These data suggest that the absence of HR in some cells in the lesion centre is not due to an early stage of infection but is likely caused by cell tolerance of the virus.     

Structures related to the germ plasm in mouse

This report presents data from ultrastructural and morphometric studies on the germinal-body-like structures, nuage, nuage-mitochondrial clusters and chromatoid bodies in 4.5-day embryo cells and spermatogenic cells of the laboratory mouse Mus musculus. In the 4.5-day embryo cells the germinal-body-like structures that, according to previous data, arise by condensation of mitochondria in Graafian oocytes, were found not to undergo any ultrastructural alterations. In spermatogonia the germinal-body-like structures presumably were transformed into nuage that functioned as 'intermitochondrial cement' binding the mitochondrial clusters. In primary spermatocytes mitochondria aggregated by nuage were found with large vacuoles containing membraneous conglomerates that were obviously excreted by organelles into the cytoplasm. The chromatoid bodies that arose in spermatocytes and finally disintegrated in the posterior part of late spermatids seemed not to be implicated in the pathway of the germinal-body-like structure. The dispersion of chromatoid bodies was noted to be accompanied by excretion of membraneous conglomerates by late spermatid mitochondria. The spermatozoa were not found to contain either the germinal-body-like structures or any other germ-plasm-related structures.     

The ultrastructural patterns of germinal and yolk granules in oocytes and embryonic cells of the holothurian Apostichopus japonicus

The yolk germinal granules in oocytes and embryonic cells of Apostichopus japonicus were studied by transmission electron microscopy. Analysis of the features of synthesis and utilization of yolk granules made it possible to reveal ultrastructural criteria to distinguish between granules of the forming and utilized yolk, and germinal granules. Based on these findings, the authors suppose that identification of germ plasm elements in oocytes and embryonic cells of A. japonicus is quite possible with ultrastructural analysis only, and does not require utilizing molecular markers.