Influence of Phytohormones on Development of Conidial Inoculum of Causative Agents of the Phlox and Barley Powdery Mildew

We studied the role of phytohormones: zeatin, kinetin, and abscisic acid, in the regulation of development of the conidial inoculum of Erysiphe cichoracearumDC. f. phlogisJacz. and E. graminisDC. f. hordeiMarchal. 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 Phloxspecies, 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.     

Inhibitors of Antioxidant Enzymes Systemically Protect Cucumber Plants from Scab

Russian Journal of Plant Physiology - 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...     

Inducible lectins and plant resistance to pathogens and abiotic stress

Lectin concentration (activity) increases in plant tissues upon infection by pathogens, in response to abiotic stress, as well as during growth and development of tissues. Such a broad range of events accompanied by accumulation of lectins is indicative of their involvement in regulation of integral processes in plant cells. Data concerning the role of lectins in regulation of oxidative stress and stress-induced cytoskeleton rearrangements are presented.     

Lectins and the problem of phitopatogene recognition by a host plant

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.     

Induction of Phytohemagglutinin Activity by Arachidonic Acid in in vitro Potato Plants

Tube-grown potato (Solanum tuberosum L., cv. Nevskii) plants treated with arachidonic acid (AA) were used as a model to study the activity of phytohemagglutinins (PHA) during induction of the plant antiviral defense system. Plant treatment with 10^–8 M AA and also their inoculation with potato viruses X, Y, and M resulted in the increased activity of PHAs in potato shoots. The inducer of antiviral resistance behaved as a modulator of the PHA activity providing for its various levels during the development of viral infection. During the development of AA-induced systemic resistance, the level of phytohemagglutinin activity did not essentially depend on the nature of the viral pathogen. We suggested that the mechanism of AA-induced plant antiviral defense was connected with changes in the PHA activity.     

Effect of Plant Oligoadenylates on Viral Infection and Antistress and Growth-Regulating Properties in Potato Plants Grown in vitro

Biological properties of plant oligoadenylates (POA) were studied in in vitro grown potato (Solanum tuberosum L.) plants. POA were synthesized by ATP polymerization in the presence of an enzyme preparation isolated from leaves of wild potato Solanum chacoense Bitt. treated with resistance inducers. The concentration of viral antigen was determined by the method of immunoenzyme analysis. In the course of virus elimination by the apical meristem method, pretreatment of potato tuber sprouts with POA increased the survival rate of meristem explants and, in several cultivars, enhanced morphogenesis and increased the yield of virus-free regenerants. Prolonged application of POA in the nutrient medium for microcutting of potato tube plants infected in vitro with X-, S-, and M-viruses increased their height due to internode lengthening. The effect of this treatment on virus reproduction was ambiguous: various combinations of virus species, the duration of growth on POA-containing media, and POA concentration resulted in either statistically significant inhibition or a significant enhancement of virus reproduction. Possible mechanisms of the antistress effect of POA, in connection with their effect on virus reproduction, are discussed.     

The Dynamics of Abscisic Acid and Cytokinins Content in the Leaves of Wheat–Aegilops Lines and Their Parental Forms Affected by Powdery Mildew

We studied the dynamics of abscisic acid and cytokinins content in wheat–aegilops lines and their parental forms affected by powdery mildew. Lines 95/99 ⁱ and 56/99 ⁱ 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 95/99 ⁱ and Ae. speltoides k-389 highly resistant to the pathogen penetration. Line 56/99 ⁱ 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 56/99 ⁱ 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 95/99 ⁱ and 56/99 ⁱ 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.     

Features of the embryonic development of <Emphasis Type="Italic">Dienia ophrydis</Emphasis> (Orchidaceae)

A new Dienia type of the embryogenesis of orchid plants differing from the Liparis type, earlier observed for the tribe Malaxideae, has been described in Dienia ophrydis (J. Köenig) Seidenf. (Orchidaceae). The Dienia-type embryogenesis is characterized by the following features: (1) development of a single-celled suspensor formed by a cb-derivative, (2) linear arrangement of embryo cells at the tetrad stage, (3) atypical origin of some tiers, and (4) no divisions of the ci and cb cells. A hypothesis about the convergent similarity between the Dienia and Caryophyllaceae types of embryogenesis has been proposed. A number of embryo sac and embryo structures typical for D. ophrydis, including “petassum,” “fitting,” and “suspensor mantle,” have been first described. A “petassum” represents the remains of cell walls of the pollen tube and probably the filamentous apparatus of synergids sealing the micropyle side of a fertilized embryo sac. The sole suspensor cell has a special appendix (“fitting”), which connects it to the embryo. The suspensor and the fitting are surrounded by a special envelope (“suspensor mantle”), which does not cover the basal cell of the embryo (ci).     

Changes in Lectin Activity in Plants Treated with Resistance Inducers

We studied the changes in lectin activity in tobacco leaf discs and potato tubers treated with polysaccharides (chitosan, glucomannan, and dextran sulfate), enzymes (cellulase and pectinase), or monosaccharides (glucose and glucosamine). All these substances changed lectin activity to a certain extent (significantly or as a tendency). The content of membrane lectins in the chloroplasts (tobacco leaf discs) usually decreased considerably immediately after the treatment (1–2 days) but increased later (2–4 days). Generally, a higher lectin activity was characteristic of 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.