R. M. Khairullin

Chitin-specific peroxidases in plants.

The activity of various plant peroxidases and the ability of their individual isoforms to bind chitin was studied. Some increase in peroxidase activity was observed in crude extracts in the presence of chitin. Activated peroxidases of some species fell in the fraction not sorbed on chitin and those of other species can bind chitin. Only anionic isoperoxidases from oat (Avena sativa), rice (Oryza sativa), horseradish (Armoracia rusticana), garden radish (Raphanus sativus var. radicula), peanut (Arachis hypogaea), and tobacco (Nicotiana tabacum Link et Otto) were sorbed on chitin. Both anionic and cationic isoforms from pea (Pisum sativum), galega (Galega orientalis), cucumber (Cucumis sativus), and zucchini (Cucurbita pepo L.) were sorbed on chitin. Peroxidase activation under the influence of chitin was correlated to the processes that occur during hypersensitive reaction and lignification of sites, in which pathogenic fungus penetrates into a plant. The role of chitin-specific isoperoxidases in inhibition of fungal growth and connection of this phenomenon with structural characteristics of isoperoxidases are also discussed.

Chitooligosaccharide-Induced Activation of o-Phenylenediamine Oxidation by Wheat Seedlings in the Presence of Oxalic Acid

A method for determination of oxidation of phenolic compounds by intact wheat seedlings using o-phenylenediamine (OPD) was developed. The reaction is initiated by the addition of oxalic acid to the incubation medium. It is suggested that an endogenous peroxidase and hydrogen peroxide formed during oxidation of oxalic acid by endogenous oxalate oxidase are involved in OPD oxidation. Treatment of plants with chitooligosaccharides (1-10 mg/liter) with acetylation degree of 65% and molecular masses of 5-10 kD significantly activated OPD oxidation by wheat seedlings.

Involvement of phytohormones in the development of interaction between wheat seedlings and endophytic Bacillus subtilis strain 11BM

Wheat (Triticum aestivum L., cv. Kazakhstanskaya 10) seedling growth activation by the endophytic 11BM strain of the bacterium Bacillus subtilis Cohn and the involvement of phytohormones in this process were studied. At the concentration used, bacteria enhanced wheat root and shoot growth as compared to control. Biotests demonstrated auxin-, cytokinin-, and gibberellin-like activities of the endophyte, but the result depended on the way of experiment performing. When wheat seeds were treated with the spores of B. subtilis 11BM strain, the concentrations of IAA and ABA increased transiently in the roots and shoots of the seedlings. The involvement of IAA oxidase in the plant response to inoculation with bacteria was shown; it was accompanied by a decrease in enzyme activity, which occurred later than auxin accumulation. It was concluded that observed changes in the hormonal status of wheat plants under the influence of the endophytic bacterial strain may be one of the mechanisms for seedling growth stimulation.

The effect of chitooligosaccharides on hydrogen peroxide production and anionic peroxidase activity in wheat coleoptiles

We studied the effects of chitooligosaccharides (ChOS) with a mol wt of 5 kD, the degree of acetylation of 65%, and the concentrations from 0.01 to 100 mg/l on the content of hydrogen peroxide in incubation medium and the activity of anionic peroxidase (pI ∼ 3.5) in the segments of wheat (Triticum aestivum) coleoptiles. H2O2 production and peroxidase activity were found to be dependent on the ChOS concentration. After 3 h of incubation, the highest H2O2 level in medium was observed at 0.01 mg/l ChOS, whereas after 6h, at 1 mg/l. After 3 h of incubation, ChOS suppressed peroxidase activity. After 6 h of incubation, high ChOS concentrations enhanced peroxidase activity. IAA favored H2O2 accumulation in medium and suppressed anionic peroxidase. The involvement of ChOS in the control of the level of reactive oxygen species and anionic peroxidase activity in plant cells is suggested.

Plant growth-promoting bacteria in regulation of plant resistance to stress factors

The review considers the mechanisms underlying the ability of plant growth-promoting bacteria (PGPB) to enhance plant tolerance to biotic and abiotic stresses. The improved tolerance is determined by a number of microbiological factors such as: supply of mineral nutrients; production of hormones and signaling metabolites; syntheses of antibiotics, biosurfactants, siderophores, chitinases, glucanases, proteases and lipases and other defence proteins; and induction of plant systemic resistance to pathogens and herbivores. Possible mechanisms of interactions in the plant–PGPB–pathogen (pest) system are considered. The PGPB may exert their role either directly, through elimination of harmful organisms by antimicrobial substances and hydrolytic enzymes, or indirectly, through activation of host defense systems and the induction of systemic resistance. New approaches to the design of broad-spectrum biopesticides on the basis of PGPB are considered.

The activity of peroxidase in various cell fractions of wheat plants infected with Septoria nodorum berk.

The activities of peroxidase isoforms and hydrogen peroxide content in leaf cuttings of wheat (Triticum aestivum L., cv. Diamant) resistant to Septoria blotch were studied during aging and following the infection with Septoria nodorum Berk. The differential activation of peroxidase isoforms was regulated by hydrogen peroxide level in the tissue. At early stages of fungus development in plant tissues, the decrease in the activities of soluble, membrane and ion-bound fractions of peroxidase elevated the level of hydrogen peroxide in infected tissues and rapidly activated peroxidase isoforms in infected tissues as compared to the aging ones even before disease symptoms appeared. The anionic peroxidases, which were first to respond to the pathogen, seem to stand for wheat resistance to fungal infections and the protection of leaf tissues from oxidative stress.

Luminol-Dependent Chemiluminescence Analysis of Chitooligosaccharide-Induced Rapid Production of Hydrogen Peroxide by Intact Wheat Seedlings

The feasibility of a luminol-dependent chemiluminescence analysis of hydrogen peroxide production by intact wheat seedlings using a KhL-003 chemiluminometer was determined. It was shown that the minimal H2O2 concentration that can be detected in a 0.5-ml sample with this instrument is 0.125 µM. Analysis of biological activity of a mixture of chitooligosaccharides with molecular masses from 5 to 10 kD and acetylation degree of 65% demonstrated that, at a concentration of 1 µg/ml, they induce rapid overproduction of H2O2 in roots of 3-day-old wheat seedlings.

Increasing Triticum aestivum tolerance to cadmium stress through endophytic strains of Bacillus subtilis

Impact of inoculation of wheat seeds with endophytic strains of B. subtilis bacterium on revealing cadmium phytotoxicity of the plants was investigated. It was shown that, in the presence of Cd in the plants whose seeds were inoculated with the above bacteria, the activities of catalase and peroxidase and the content of nonprotein thiols were increased, while an intensity of lipid peroxidation decreased. Moreover, inoculation of plant seeds with the bacteria contributed to lowering the metal content in plant shoots.

Activity of trypsin inhibitors in wheat seedlings exposed to pathogenic fungus Tilletia caries and phytohormones

We compared the effect of common bunt (caused by fungus Tilletia caries Tul.) and treatment with phytohormones IAA, ABA, and cytokinins (CK) on the activity of trypsin inhibitors (TI) in wheat seedlings. The experiments were conducted with pathogen-susceptible species of wheat Triticum aestivum L. (cv. Zhnitsa) and resistant species T. timopheevii Zhuk. (accession k-58666 from the collection of All-Russian Institute of Plant Industry). In the resistant wheat, the fungus elevated the activity of TI and the content of CK, whereas in the susceptible wheat, it induced accumulation of IAA. In the seedlings of wheat T. aestivum, TI activity increased under the effect of CK, same as upon the action of pathogen. ABA briefly increased the activity of TI, whereas IAA did not considerably affect it. It was concluded that among the investigated hormones, CK play a leading role in the regulation of defense responses of wheat plants involving TI.

Cadmium and Nickel Toxicity for Sinapis alba Plants Inoculated with Endophytic Strains of Bacillus subtilis

We studied the effect of cadmium and nickel on Sinapis alba L. plants inoculated with endophytic strains of Bacillus subtilis. It was shown that treatment of S. alba seeds with endophytic strains of bacteria B. subtilis improves plant resistance to the toxic effect of cadmium and nickel and reduces manifestation of oxidative stress in the presence of higher levels of metal ions in the above-ground part of plants. Anti-stress effect and the ability of endophytic strains of B. subtilis to intensify uptake of cadmium and nickel ions by S. alba plants may be used for phytoextraction of heavy metals and stimulation of plant growth in contaminated areas.