Formation Of Enlarged Cells Research Articles

Effect of photosensitisers on growth and morphology of Phytophthora citrophthora coupled with leaf bioassays in pear seedlings

The phytopathogenic oomycetes of the genus Phytophthora cause devastating economic losses worldwide.<br />Naphthodianthrone compounds, present in plant extracts of buckwheat and Saint John’s wort act as photosensitiser<br />agents and exhibit antimicrobial activity against a number of pathogens. In this study, we investigated the potential<br />inhibitory effects of fagopyrin and hypericin on Phytophthora citrophthora (R.E. Sm. & E.H. Sm.) Leonian 1906, the<br />main causal agent of rot diseases in deciduous trees. Fagopyrin had the highest inhibitory effect in the colony growth<br />at a concentration of 2% of a stock solution (3 mg/mL), inducing clubbed hyphae with round tips. Notably, hypericin<br />also inhibited the radial colony growth and increased the hyphal branching at the subapical region, while also promoting<br />the formation of enlarged cells with irregular shapes growing collectively as biofilm-like structures. In terms of the<br />mycelial dry weight, although both photosensitisers had considerable inhibitory effects, the fagopyrin treatment was<br />most effective. Leaf bioassays showed that under dark conditions the photosensitiser pre-treated zoospores formed a<br />dense, but aberrant, mycelial growth with penetration defects. In contrast, when the zoospore production was performed<br />under light conditions, the zoospores failed to cause necrotic lesions and penetration events implying that their<br />virulence was impaired. These findings shed light on the biological effects of fagopyrin and hypericin in the regulation<br />of the mycelial growth, morphology and pathogenicity of P. citrophthora.

Reduction of Tubulin Expression in Angomonas deanei by RNAi Modifies the Ultrastructure of the Trypanosomatid Protozoan and Impairs Division of Its Endosymbiotic Bacterium

In the last two decades, RNA interference pathways have been employed as a useful tool for reverse genetics in trypanosomatids. Angomonas deanei is a nonpathogenic trypanosomatid that maintains an obligatory endosymbiosis with a bacterium related to the Alcaligenaceae family. Studies of this symbiosis can help us to understand the origin of eukaryotic organelles. The recent elucidation of both the A.deanei and the bacterium symbiont genomes revealed that the host protozoan codes for the enzymes necessary for RNAi activity in trypanosomatids. Here, we tested the functionality of the RNAi machinery by transfecting cells with dsRNA to a reporter gene (green fluorescent protein), which had been previously expressed in the parasite and to α-tubulin, an endogenous gene. In both cases, protein expression was reduced by the presence of specific dsRNA, inducing, respectively, a decreased GFP fluorescence and the formation of enlarged cells with modified arrangement of subpellicular microtubules. Furthermore, symbiont division was impaired. These results indicate that the RNAi system is active in A.deanei and can be used to further explore gene function in symbiont-containing trypanosomatids and to clarify important aspects of symbiosis and cell evolution.

DISTRIBUTION ANALYSIS OF ENLARGED CELLS DERIVED FROM GROUPER SLEEPY DISEASE IRIDOVIRUS (GSDIV) INFECTED HUMPBACK GROUPER Cromileptes altivelis

Characteristic of Megalocytivirus infection has been known to produce formation of inclusion body bearing cells (IBCs) on internals organs of fish predominantly on spleen and kidney. Megalocytivirus that infected grouper is known as Grouper Sleepy Disease Iridovirus (GSDIV). This study was conducted to answer the effect of entry sites of GSDIV on distribution of enlarged cells formed on the internal organs of humpback grouper Cromileptes altivelis. Enlarged cells were observed histologically under the light microscope on spleen, head kidney, trunk kidney, liver, gill, heart, stomach, intestine, muscle and brain. Entry sites were designated to intramuscularly injection, intraperitoneally injection, dipped gill and inoculum added feed. Enlarged cells were formed on spleen, head kidney, trunk kidney, liver, gill, heart, stomach, muscle, except on intestine and brain. All the entry sites resulted in formation of enlarged cells on spleen, head kidney, trunk kidney, liver, heart. Spleen and head kidney were the most frequent observed organ. These results suggested that distribution of enlarged cells were not affected by the entry site of GSDIV.

Restoration of proliferation ability with increased genomic instability from Rad2p-induced mitotic catastrophe in Saccharomyces cerevisiae

Yeast RAD2, a counterpart of human XPG, is an essential gene for nucleotide excision repair. Rad2p is an endonuclease that incises the 3′ side of a DNA damaged lesion. However, over-expression of Rad2p provokes cell growth arrest, resulting in mitotic catastrophe as evidenced by formation of enlarged cells and micro-nucleation. Interestingly, the effect of Rad2p on cell growth arrest is not caused by its endonuclease activity, and it has been suggested that Rad2p might be involved in cell cycle regulation. Mitotic catastrophe mainly results in cell death but also functions as a survival mechanism. Using RAD2, we show that some yeast cells growth-arrested by Rad2p-induced mitotic catastrophe regain their ability to proliferate mainly because some Rad2p-induced polyploid cells produce haploid cells with normal cell cycles. Rad2p over-expression also causes increased mutagenesis and the cells with recovered proliferative ability exhibit increased genomic instability, which in turn decreases Rad2p expression. From these results it is inferred that Rad2pinduced polyploid cells undergo increased genetic rearrangement resulting in production of haploid cells.

Transcriptional Regulation of the Heterocyst Patterning Gene patA from Anabaena sp. Strain PCC 7120

The filamentous cyanobacterium Anabaena sp. strain PCC 7120 forms a periodic pattern of nitrogen-fixing heterocysts when grown in the absence of combined nitrogen. PatA is necessary for proper patterning of heterocysts along filaments. In this study, apparent transcriptional start points (tsps) were identified at nucleotides -305, -614, and -645 relative to the translational start site (-305, -614, and -645 tsps). Transcriptional reporter fusions were used to show that transcription from the -305 tsp was induced in all cells of filaments in response to nitrogen deprivation, required hetR for induction, and increased in a patA mutant. Transcription from -614/-645 tsp reporter fusions was spatially regulated and occurred primarily in cells that would become heterocysts. Complementation of a patA mutant strain by alleles encoding substitutions in, or deletion of, the putative phosphoacceptor C-terminal domain indicates that the PATAN domain can function independently of the C-terminal domain of PatA. Localization of a ring of PatA-GFP at sites of cell division, as well as the formation of enlarged cells with altered cell morphology when patA was overexpressed, suggests that PatA may participate in cell division.

Surface‐related Changes of Fusing Phytophthora Zoospores

AbstractZoospores of Phytophthora spp. were fused and then regenerated using a technique previously described. At various points in the fusion and regeneration processes, components of spore surfaces were immunolabelled with specific monoclonal antibodies. Changes in the antigenic properties of spore surfaces during these events were monitored by fluorescence microscopy. Additional, surface‐related processes of the phenomena were monitored by electron microscopy, in the presence of lithium ions and polyethylene glycol, zoospores aggregated into clumps and began to fuse. During this time, zoospores retained their reniform shape and antibodies reacted only with plasma membrane‐bound antigenic components that are characteristic of the zoosporic state. Immuno‐labelling of cell wall occurred only after the fusion solution was replaced with a regeneration solution. As expected, the fusion and the asynchronous regeneration process resulted in the formation of enlarged cells with enlarged or multiple nuclei.

Use of the elzone particle counter to monitor morphological changes in bacteria associated with endospore germination and direct viable counting

A novel approach to the measurement of endospore germination was investigated using Thermoactinomyces vulgaris as a model organism. The method employed an Elzone particle counter to monitor spore development from activation to outgrowth. The advantages of using this technique over microscopic or spectrophotometric techniques include the ease of monitoring germination and the facility to determine the relative frequencies of different germination stages in the bacterial population. Peaks in histograms showing population size distribution at hourly intervals over a 5-h incubation period correspond to the various germination stages. The potential of the particle counter to measure changes in bacterial size in contexts other than germination was also assessed. Direct viable counting by the method of Kogure et al. was applied to Escherichia coli and the formation of enlarged cells was monitored by means of the instrument. Shifts in the frequency of different cell sizes within the total cell population over a 7-h incubation period were detected easily. The Elzone particle counter and similar instruments save time and offer alternative methods for microbiological investigations.

Morphological changes of conidiophores and mycelium of some hyphomycetes.

The formation of enlarged cells and other abnormalities of mycelium and conidiophores occurring inAspergillus flavus Link,Penicillium chrysogenum Thom,Penicillium notatum Westling,Penicillium variabile Sopp.,Scopularipsis brevicaulis Bainier,Fusarium moniliforme Sheld.,Botrytis cinera Pers. ex Fr.,Botrytis allii Rud.,Humicola brunnea var.africana Fass. andTritirachium heimii var.grisea Fass. under the influence of uranium acetate, radioactive sediment from Přibram mines (uranium mines in Přibram, Bohemia), fungicidal compounds (fungizon, fungistatin, nitrofungin), antibiotic nystatin and antifungal bacteriumBacillus subtilis Cohn emend. Prazmowski were investigated. Enlarged phialides or phialides with extended orifices and collarettes and occasionally a conversion of phialides to spherical enlarged cells were observed inAspergillus flavus grown on a Sabouraud agar supplemented with uranium acetate. InPenicillium chrysogenum some conidiophores were completely reduced to enlarged cells. Less abnormalities were observed on the Czapek-Dox agar. The radioactive sediment as a component of malt agar caused either complete reduction of conidiophores inAspergillus flavus to dichotomously branched hyphae or sometimes only an enlargement of phialides. The antifungal effect ofBacillus subtilis was demonstrated in all studied strains. Enlarged cells instead of whole conidiophores were formed under the influence of the bacterium. This effect was observed inBotrytis allii, Botrytis cinerea and to a lesser extent inPenicillium notatum, Aspergillus flavus andFusarium moniliforme. The enlarged cells could still germinate and can be considered as reduced conidiophores. The used fungicidal compounds and the antibiotic nystatin inhibited to a certain degree the studied strains, however, their application did not bring about any abnormalities of mycelium and conidiophores.