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The study is aimed at the induction of systemic disease resistance by a local oxidative burst caused by inhibition of plant antioxidant enzymes. A possible involvement of ROS was ascertained. Inhibitors of superoxide dismutase and catalase, respectively, diethyldithiocarbamate (DDC) and aminotriazole (AT) were applied to the fist (local) true leaf of cucumber seedlings (Cucumis sativus L.). When the second and third (systemic) leaves developed, they were inoculated with spores of the virulent fungus Cladosporium cucumerinum Ell. et Arth. causing cucurbit scab. The inhibitors at concentrations nontoxic to leaves or spores greatly reduced the disease symptoms on the systemic leaves. The inhibition of both enzymes was confirmed, and increased superoxide production was found in the chemically treated local leaf. In case of a treatment with water, diffusates of the healthy systemic leaves stimulated spore germination, and those of infected systemic leaves were ineffective. Treatment of the local leaf with any compound systemically suppressed the aforementioned stimulation in the healthy counterpart and provided fungitoxicity in the infected one. Both antifungal effects were abolished by diffusate boiling, suggesting protein involvement. Meanwhile, the effects were insensitive to antioxidants and, apparently, independent of reactive oxygen. DDC and AT did not promote salicylic acid accumulation in infected systemic leaves; presumably, the disease control did not represent systemic acquired resistance. It is suggested that both inhibitors induce some kind of systemic resistance through the local oxidative burst caused by inhibition of antioxidant enzymes. The systemic implementation of the resistance may include antifungal effects. [ABSTRACT FROM AUTHOR]

New data on the micromorphology, histochemistry, and fluorescence of colleters on leaf structures at different stages of development (leaf blade, stipules, and petiole) of Mespilus germanica L. are presented. Colleters are found on the tips of the teeth of both young and mature leaf blades and stipules, less often on the petioles. The leaf veins approach the leaf tooth, but no vascularization was found in the colleter. On leaf structures inside the bud, young colleters were observed in the form of finger-shaped or rounded outgrowths consisting of isodiametric cells. Mature colleters are multicellular secretory structures that have a head on a short stalk. The central part of the head consists of densely packed parenchymal cells, which are surrounded by radially elongated palisade-like secretory cells covered with a cuticle. The main secretion process of the colleter falls on the period of active growth of leaf structures. The secreted substances accumulated in the intercellular spaces of the palisade-like cells of the head and then were released outside in the form of translucent vesicles. The secretion products were released when the cuticle was ruptured and spread over the surface of the head and tooth of the leaf blade and stipules. After the end of secretion, the sizes of the head of the colleter decreased, and an abscission zone appeared in the cells of the colleter stalk, along the border of which a fracture occurred when the head fell off. Histochemical analysis of the contents of the colleter showed the presence of polysaccharides, especially at a young age, substances of a phenolic nature and lipids at a more mature age. In the fluorescence spectrum of young leaf colleter secretion, a peak at 671-672 nm was observed upon excitation at 405 and 473 nm. The obtained data on Mespilus germanica L. colleter can be used in the taxonomy of Pyrinae and Rosaceae., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

On example of Dienia ophrydis (J. Köenig) Seidenf (Orchidaceae), we have described a new type of embryogenesis of orchids — Dienia-type, which is differs from Liparis-type learned earlier in the tribe Malaxideae. Embryogenesis of Dienia-type is characterized by 1) the development of a single-celled suspensor formed by cb-derivative, 2) linear arrangement of germ cells in the tetrad stage, 3) the special structure of the embryo in the stages of tetrads and octants (l, lR, m, ci, cb), and 4) the absence of ci and cb cell division. The convergent similarity of embryogenesis of Dienia- and Caryophyllaceae-types is proposed. A number of specific for D. ophrydis structures of embryo sac and embryo, including «petassum», «fitting» and «suspensor coat» are described for the first time. Petassum represents remains of the cell walls of pollen tube, and perhaps of filamentous apparatus of synergids, plugging the micropyle side of the fertilized embryo sac. The only cell of suspensor has a specific appendix («fitting»), that connects it with the embryo itself. There is «suspensor coat» which surrounds the only suspensor cell, including «fitting», but does not extend to the basal cells of the embryo itself.

Cytokine-regulated growth of germs' roots and hypocotyls was investigated on a background of modeled oxidative outbreak caused by the stress from exogenous hydrogen peroxide. Germs of rape (1-d old) and tomato (56-d old) in Petri dishes with solutions containing substances under study were subjected to 24-48 hour incubation in the dark. Exogenous zeatin inhibited growth; in different tests treatment with H2O2 brought about both acceleration and inhibition of root and hypocotyl growth. The combined use of two substances deformed concentration curves. Hydrogen peroxide concentration of 100 microM without cytokines inhibited growth of tomato root significantly, whereas application of 0.003-0.01 and 0.9 microM of zeatin intensified root growth. The series of zeatin concentration-effect curves obtained for rape roots and hypocotyls with gradually increasing H2O2 concentration included the inhibition curve (w/o H2O2), curve with predominant growth stimulation and reliable maximum (1 microM of H2O2), intermediate shape curves (0.3 and 3.3-10 microM). Hence, biological life support systems should be designed with consideration for variability of effects of physiologically active substances under conditions of stress.

Physiologically active substances are considered as a potential component of plant cultivation technologies for biological life support systems. In spacelight, plant reactions to growth-regulating agents may be changed by the specific stress factors such as microgravity, radiation, and trace admixtures in cabin air. Complex character of the concentration dependence of PAS efficiency and consequent variability generate a need to optimize plant growth regulating technologies in order to stabilize the wanted effect. Pattern of the concentration dependence of zeatin and tidiazurone effects on roots and hypocotyls growth was analyzed in rape germs. 24-hour Brassica napus germs grown in the dark in thermostat at 24 degrees C were transferred to Petri dishes with solutions of cytokinins under study for continued incubation under the same conditions for the next 24 hours. Roots and hypocotyls were measured. Zeatin concentration curve for roots was multiphase and, in addition to the general trend towards greater inhibition with increase of phyto-hormone concentration and had clearly defined minimum and maximum. The dependence of root growth inhibition on tidiazurone concentration also was not monotonic and had a distinct similarity with the zeatin curve. Gradual increase of tidiazurone concentration used in combination with zeatin brought about a predictable gradual twist of the zeatin curve; however, in most of the instances no additive cytokinin effect was observed. A supposition can be made that PAS interaction with the phytohormone regulation system may be a factor in variability of activity of these substances.

Scanning electronic microscopy was used to investigate the regularities of growth direction of infectious structures and colonies of the agent of powdery mildew of wheat Erysiphe graminis f. sp. tritici. The growth of appressoria with normal morphology in wheat leaves occurs predominantly along the long axis of the cell. Most anomalous appressoria grow perpendicularly. Treatment with zeatin changes the ratio of the directions of growth of normal appressoria and hyphae of the colonies. The dependence of these parameters and of the surficial density of colonies on the concentration of phytohormone is monophasic. The hypothesis is suggested that the strategy of selection of the direction of growth of infectious structures on leaves with an anisotropic surface depends on the most probable position of the receptor cell and the action of cytokinins on their participation in redistribution of nutrients between the infected and noninfected cells of the host plant.

Using methods of light and electron scanning microscopy, development and infection structures differentiation of the causal organism of wheat powdery mildew, Erysiphe graminis DC. f. sp. tritici March., was investigated under influence of exogenous zeatin. It has been shown for the first time that physiologically active materials, in particular, cytokinin type phytohormons affect on the dimensions of halo revealed at the site of pathogen penetration by cytochemical staining. Treatment with zeatin influenced conidia germination and pathogen growth at the ectophytic stage. Dose response dependence of zeatin for number of mature colonies of pathogen (6 days after an infection) has been presented by multiphase curve with two maxima (1 and 3 microM) and minimum (1.5 microM). Similar curves have been received for the number of normal appressoria and the diameters of the large halo that possibly shows the existence of factors affecting both parameters, and the final number of pathogen colonies, as well. The obtained data demonstrate that multiphase dose response curve for development of the causal organism of powdery mildew under effect of cytokinins is originated from the factors acting at early stages of pathogenesis.

Under consideration are some questions concerning participation of lectins in the plant pathogenesis, including their role in the recognition of microbes and elicitors, and as a protective agent limiting pathogenic growth and displacements. "Classical" lectins also probably play an important role in these processes along with lectin-like receptor kinases. The principal features of those "classical" lectins are their relativly high concentration in the plant tissues, monosaccharide specificity, and limited number of the isolecin forms. Therefore, in supposing their participation in the biological recognition, it is needed to clarify how does a limited number of lectins with a limited number of carbohydrate groups can provide recognition of a potentially huge number of pathogens. This task can be fulfilled by recognition of carbohydrate residues peculiar to a particular microbe group by the "classical" lectins. These recognition processes are similar to acivity of the animal inherited immune system responsible for a rapid primary protection even in animals with well developed antibody system. A mechanism widening the carbohydrate specificity of the carbohydrate-binding center includes interaction with hydrophobic substituents in a carbohydrate residue, as well as lectin modular organization allowing for regulation of lectin binding with oligo- and polysaccharides. The free lectins effect on the microbe growth in both plants and animals. Such an action may be inhibiting in pathogenesis, while in the case of symbiotic relations, the lectin can bear signal that readdresses metabolism of a future symbiont. So, lectins seem to serve as natural deciphering device for information contained in the carbohydrate polymers, and reading of this information is the main lectin function in the cell.

The content of wheat germ agglutinin (WGA) in hydrogen peroxide-treated seedlings was studied by indirect competitive enzyme-linked immunosorbent assay. WGA content in roots showed a transitory increase: at 10 mM hydrogen peroxide, maximum level was observed after 2 h; at 1 mM hydrogen peroxide, the maximum occurred 2 or 24 h after the treatment. Lectin induction by hydrogen peroxide is viewed as an element of a feedback mechanism limiting the operation of defense responses during pathogenetic processes.

We studied the dynamics of abscisic acid and cytokinins content in wheat-aegilops lines and their parental forms affected by powdery mildew. Lines 95/99i and 56/99i demonstrated the types of resistance untypical of the soft wheat Rodina and Aegilops speltoides k-389 but typical of Ae. speltoides Tausch from other natural habitats. A relative stability of the hormonal balance in the course of the infection was demonstrated for lines 95/99i and Ae. speltoides k-389 highly resistant to the pathogen penetration. Line 56/99i was sensitive to the penetration; however, a subsequent prolonged hypersensitive response eliminated pathogen colonies surrounded by necrotic areas. A correlation between disbalanced hormonal metabolism of cytokinins and low resistance to the infection has been revealed for 56/99i line and Rodina cultivar. Free form of abscisic acid was revealed in the intact plants of the parental forms. Bound form of this hormone was revealed in the infected plants of lines 95/99i and 56/99i as well as of Ae. speltoides k-389, which seems to be a marker of their different stress resistance according to the phenotypic manifestation of powdery mildew.

The activities of lectins and peroxidase and lignin content were studied in the perilesional area of leaves in two tobacco species (Nicotiana tabacum L., cultivar Samsun NN, and N. glutinosa L.) inoculated with tobacco mosaic virus. The development of hypersensitivity response proved to be accompanied by a complex spatial and temporal distribution of lectin activity. The area 5-9 mm away from the lesion center was characterized by the highest activity of loosely bound membrane lectins eluted with 0.05% Triton X-100. In the fraction of tightly bound membrane lectins (eluted with 0.5% detergent), lectin activity decreased during the first two days but increased on day 4 after inoculation. The activity of loosely bound membrane lectins increased in the leaf areas distant from the lesion. Two-phase dynamics in the interlesional area were also observed for lectin activity in the tightly bound membrane fraction (decrease on day 2 days and increase on day 4 after inoculation) and for peroxidase activity (increase on day 2 days and decrease on day 4). The relationship between the dynamics and spatial distribution of lectins in the perilesional area and the possible involvement of these proteins in pathogen-induced changes in photosynthesis are discussed.

We studied the changes in lectin activity in tobacco leaf disc and potato tubers treated with polysaccharides (chitosan, glucomannan, and dextran sulfate), enzymes (cellulase and pectinase), or monosaccharides (glucose and glucosamine). All studied substances changed lectin activity to a certain extent(significantly or as a trend). The number of membrane lectins in the chloroplasts (tobacco leaf discs) usually considerably decreased immediately after the treatment (1-2 days) but increased later (2-4 days). Generally, an increased lectin activity predominated in potato tubers treated with the inducers. The enzymes increased lectin activity during the whole observation period (5 days). A pronounced antiviral activity was observed in the hypersensitive tobacco-tobacco mosaic virus system only after treatment with chitosan and glucomannan.

We studied the role of phytohormones: zeatin, kinetin, and abscisic acid, in the regulation of development of the conidial inoculum of Erysiphe cichoracearum DC. f. phlogis Jacz. and E. graminis DC. f. hordei Marchal. When the pathogen conidia were in direct contact with phytohormones, the intensity of their germination significantly increased. In the presence of cytokinins, the amount of normal appressoria decreased and that of abnormal growth tubes increased. On the phlox leaves treated with cytokinins, the intensity of germination of the conidia increased, as compared to the control, while abscisic acid exerted the opposite effect. The treatment of barley leaves with cytokinins did not affect markedly the development of conidial inoculum, as compared to the control, while abscisic acid significantly decreased the intensity of germination of the conidia. On the leaves of different Phlox species, the degree of germination of the conidial negative correlated with their resistance against the powdery mildew. The role of cytokinins in pathogenesis of biotrophic fungi is discussed.