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The interaction of plants with certain types of parasites leads to the formation of galls, organised structures that create the habitat of the parasite, caused by an abnormal proliferation of host plant's cells under the influence of growth regulators, secreted by the parasite, or by the plant itself under the influence of the parasite. Arthropods, mites in particular, are the largest group of gall-inducing phytoparasites, but the mechanisms of their interaction with plants remain virtually unexplored. The interaction of the gall-inducing eriophyoid mite Fragariocoptes setiger with Fragaria viridis plants was used as a model gall-mite system where data were obtained on the changes in the histological structure of F. viridis leaf blades under the influence of the mites as well as F. viridis gene expression during gall formation. For histological purposes, gall formation was split into four stages with each corresponding to the age of the gall as well as to specific changes that occur during that period. A dramatic change of adaxial-abaxial polarity of the lamina throughout the four stages was observed. Moreover, qRT-PCR analysis of F. viridis gene expression in the developing gall revealed changes in the expression levels of certain meristem-specific genes, as well as the genes that determine adaxial-abaxial polarity and signalling of phytohormones. Petersburg State University and the resource centre of the Komarov Botanical Institute of RAS.

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Stomatal rings are structural elements of stomata of some flowering plants, being found in various groups of eudicots. The presence of a stomatal ring on a stoma does not depend on stomatal complex types, dimensions of stomata or their density. The guard cells of these stomata lie on the subsidiary cells. The location of the outer ledges on the outer tangential walls of the guard cells and the position of the stomatal rings on the guard cell walls around the outer ledges or on the outer ledges themselves are also among the characteristic features of these stomata. To elucidate the role of the stomatal rings we applied modelling using the finite-element method. The modelling has shown that the outer ledges prevent movements of the outer tangential walls of the guard cells and stimulate movements of the inner tangential walls and the immersion of the opening stomatal pore in the epidermis. Stomatal rings can enhance this effect. They also prevent the movements of the outer ledges and the widening of the stomatal aperture between them during stoma opening. This type of stomata occurs in evergreen plants growing in diverse conditions.

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The cork warts on leaves of plants appear to be a response to mechanical injuries or pathogen penetrations. Many of Gnetum species regularly form cork warts on leaf surfaces and stems. We have searched anatomy, morphology and development of cork warts and also estimated evaluation of probable influence to its origin by phylloplane fungi. Leaves of two species of Gnetaceae family G. gnemon and G. montanum have been investigated for anatomical and morphological studies of cork warts and for mycological research. Herbarial specimens of 13 Gnetum species have been searched. We have successfully extracted 15 species of phylloplane ascomycetes that appear to influence negatively on continuity of leaf epidermis and being able to existing as parasites as well. The most frequent species were Cladosporium cladosporioides which became a dominant indicating 100% of frequency index and representatives of Fusarium and Phoma genera. The frequency index of latter numbered 36 and 20% correspondingly. Five species of Penicillium ascomycetes were also determined as frequent. Cork warts have been found in 13 species of Gnetum that grow in natural environment. Cells in local areas of epidermis and subepidermal layers proliferate periclinally during cork wart development in leaves of G. gnemon and G. montanum. As a result, the layer of high compactly packaged cells emerges. Tannins inside cell compartments and suberinization of cell walls were indicated for cork warts. It emphasizes a defensive function of the structures. Cork warts appear to originate like "Patches" on the surfaces of leaves of evergreen gnetum plants.