Effect of Viral Infection on the Ultrastructural Organization of Black Currant Leaf Tissue Cells

Abstract

One of the significant reserves for further increasing the yield of berry crops is to protect them from pests and diseases. Among the latter, viral ones are especially dangerous. Therefore, methods of virus diagnostics and especially electron microscopy are of great importance, which makes it possible to see viral particles, determine their shape, size, localization in tissues, and identify anomalies in affected plant cells. Objective. To conduct a comparative study of healthy and diseased blackcurrant leaves in order to determine the degree of influence of the two viruses on the anatomical structure of organelles and inclusions, which can be used in the diagnosis and identifi cation of viruses affecting plants. Methods. The material was blackcurrant plants with symptoms of reversion and green speckles, which are detected visually when examining the plantings of this crop. The morphology of viral particles, the anatomical structure of organelles, and inclusions were studied using the method of electron microscopy of ultrathin sections. Detected ultrastructural changes in cells can be used as diagnostic signs when identifying viruses. Also, viruses were identified by external signs and biological testing. Results. The study of ultrathin sections of leaf tissue and abnormal petals of the blackcurrant flower with symptoms of reversion revealed a bacillus-visible virus (Blackcurrant reversion virus) from the Rabdoviridae family, which is easy to identify due to its large size and appearance, in which it differs from similar features in ordinary cellular components. Typical locations of virus particles are the cytoplasm, nucleus, and perinuclear zone. The size of viral particles on ultrathin sections was 271±7.19 nm long and 78±2.31 nm in diameter. According to electron microscopic methods of studying artificially infected plants of Chenopodium quinoa, an inoculum of affected blackcurrant leaves, virions of Cucumis virus 1 Smith were observed in cells, which were freely located in the cytoplasm of the cell interspersed with ribosomes. Individual areas of the cytoplasm with a high virus concentration were also found in the affected parenchymal cells. Zones surrounded by a double membrane differ in the size and degree of virus saturation. When studying the pathogen morphology in the native preparations, the viral particles had a spherical shape with smparticles showed that they had an average size of 29.6±0.59 nm. During the study of the ultrastructure of blackcurrant plant cells affected by Cucumis virus 1. Smith, myelin-like bodies were found not only in the cytoplasm of affected cells but also in the extra-plasma space. Analysis of the morphology of chloroplasts of blackcurrant plants affected by green speckles and reversion shows that chloroplasts with outgrowths and cup-shaped formations are present in many cells. Under various viral infections, there is a wide variety of mitochondria’s shapes: they are elongated, cup- or club-like, etc. At the same time, their internal structure changes as well. We found that at the stage of the neurotization of a Nicotiana tabacum leaf infected with Cucumis virus 1. Smith, the peroxisome matrix is intensively filled with crystalline inclusions that have an electron-dense surface or are a system of rods with different configurations in the form of rectangles and trapezoids. They completely fill the entire matrix. During the development of viral pathology in the cells of diseased plants, destructive processes also cover the nucleus. As a rule, it takes on a lobed or radially elongated shape. Among the viruses we studied, the Blackcurrant reverse virus causes this trait the most. This may be due to the fact that this virus, accumulated in large quantities, exerts mechanical pressure on the nuclei and thereby accelerates the process of their deformation. A peculiar sign of changes in the nucleus ultrastructure is the content of viral particles. Of the viruses we studied, blackcurrant reversal virus particles were the most common in the nucleus nucleoplasm and perinuclear zone. Conclusions. The intracellular development of viruses and their use of energy systems and components of plant cells for their reproduction lead to signifi cant morphological and structural changes in the latter. In particular, electron microscopic studies of ultrathin tissue sections of diseased blackcurrant plants in comparison with healthy ones revealed the forms of the nucleus, mitochondria, and plastids modified under the infl uence of viral infection, namely Blackcurrant reverse and Cucumber mosaic viruses. Chloroplasts noticeably swelled without the existing content of starch grains, and clumping or the absence of gran thylakoids was observed. Plastids with a highly reduced membrane system were found. The results of studies have shown that the species affiliation of the virus does not cause specific changes in the morphology and structure of mitochondria. Their structural transformations under the influence of the viruses under study were the same: changes in shape and swelling, expansion of crists and a decrease in their number, a decrease in the electron density of their matrix, and so on. It was found that in the nuclei of cells infected with the Blackcurrant reverse virus, chromatin forms small, interconnected granular lumps located in different zones of the matrix. When studying ultrathin sections of Nicotiana tabacum leaf infected with Cucumis virus 1. Smith, rather specific crystal inclusions that fill the entire matrix were detected by the peroxisome. If external anomalies are detected in the form of mosaics, spots that can be caused by many pathogens in the absence of mechanical transmission of the pathogen, it is advisable to use the method of electron microscopy of ultrathin sections.