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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.

According to a common hypothesis, some of the epidermal structural features in the leaves of tracheidbearing plants "offset" low specific conductivity of vesselless wood. The data concerning this issue is contradictory, which can be explained by the fact that leaf water relations depend not only on the epidermis structure, but also on the structure of other leaf tissues. In the current study we aimed to evaluate the diversity of water transport systems in the leaves of tracheid-bearing woody plants in the temperate rainforest of south-central Chile. For this purpose, we collected leaves of four Podocarpaceae and two Winteraceae species in natural habitats, examined their leaf anatomy using light and transmission electron microscopy, measured the quantitative characters and analyzed the data using principal component analysis. Leaves of the studied species differ in the mesophyll and xylem anatomy. Four species have features that accelerate water transport through the leaf tissues via the apoplast (Prumnopitys andina), accessory transfusion tissue (Podocarpus saligna) and a network of veins (Drimys species). On the contrary, the leaves of Saxegothaea conspicua and Podocarpus nubigena accumulate water in water-storage tissue (hydrenchyma), but their ecology suggest that hydrenchyma is not an adaptation to environmental conditions. The obtained data indicate the existence of different ways of water delivery to the photosynthetic tissue in the leaves of vesselless plants. In the case of insufficient water supply through the tracheids, hydrenchyma is likely to maintain hydration of the leaves.

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