[Characteristics of wheat powdery mildew growth along and across the longitudinal axis of a leaf under the action of exogenous zeatin].

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.

[Influence of exogenous cytokinins on dynamics of development and differentiation of infection structure of the causal organism of wheat powdery mildew].

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.

[Characteristics of halo formation during pathogenesis as a response of cereal epidermal cells to penetration of powdery mildew pathogens]. / Osobennosti formirovaniia galo v protsesse patogeneza kak otvetnaia reaktsiia épidermal'nykh kletok zlakov na proniknovenie vozbuditelei muchnistoi rosy.

A cytophysiological study was carried out of the functional status of a halo as a response of the host plant to contact with a powdery mildew pathogen. Interactions of the powdery mildew causative agents with barley, wheat, wheat-wheat-grass hybrids, wheat-aegilops lines, and aegilops with different genotypic resistance lead to the expression of haloes during pathogens, which are induced by infection pegs of the primary growth tubes appressoria, and hyphal lobes. Haloes are visualized using cytochemical reactions to proteins and scanning electron microscopy. The observed differences in the size of haloes and intensity of their staining (uniform or zonal) are related, to a great extent, to individual reactions of the plant cell at the penetration site and, to a lesser extent, to the level of genotypic resistance. An analysis of electron microscopy and cytochemistry studies suggests that the halo as a physiologically active zone is localized at the level of the plant cell plasmalemma. Active taxis of the cell organelles to the site of infection during the formation of a halo suggests that some kind of informational signals to changes in the cell metabolism are spread from the halo zone, which lead to compatible or incompatible interactions.