S. V. Zinov'eva

[Modulation of plant resistance to diseases by water-soluble chitosan].

Low-molecular-weight water-soluble chitosan (5 kDa) obtained after enzymatic hydrolysis of native crab chitosan was shown to display an elicitor activity by inducing the local and systemic resistance of Solanum tuberosum potato and Lycopesicon esculentum tomato to Phytophthora infestans and nematodes, respectively. Chitosan induced the accumulation of phytoalexins in tissues of host plants; decreased the total content; changed the composition of free sterols producing adverse effects on infesters; activated chitinases, β-glucanases, and lipoxygenases; and stimulated the generation of reactive oxygen species. The activation of protective mechanisms in plant tissues inhibited the growth of taxonomically different pathogens (parasitic fungus Phytophthora infestans and root knot nematode Meloidogyne incognita).

Biochemical Aspects of Plant Interactions with Phytoparasitic Nematodes: A Review

The review summarizes reports on molecular aspects of interactions of phytoparasitic nematodes with plant hosts. Data on nematode secretions affecting plants (elicitors, toxins, products of parasitism genes, etc.) are analyzed and information flow pathways comprising all elements of the plant–parasite interaction (from elicitors to defense responses of plant cells) are described. Emphasis is placed on the mechanisms whereby plants are protected from nematode invasion (hypersensitivity reactions, apoptosis, phytoalexins, proteinase inhibitors, PR proteins, etc.). Consideration is given to genetic aspects of plant–parasite relationships. Promising practical approaches to defending plants from phytoparasitic nematodes developed based on the results of studies of molecular mechanisms of plant–parasite interactions are presented in the conclusion.

The role of salicylic acid in systemic resistance of tomato to nematodes.

The induced resistance of plants to phytopathogens can be expressed either locally (at the site of infection or treatment with the elicitor) or at a certain distance from the site of infection. The latter form of the protective response of plants has been termed systemic induced resistance (SIR) [1]. The development of resistance in tissues of vegetating plants after presowing treatment of the plant seeds with elicitors is a manifestation of SIR.

Correlation between the Structure of Plant Steroids and Their Effects on Phytoparasitic Nematodes

The effects of certain plant steroids (belonging to furostanol glycosides or glycoalkaloids) and α-ecdysone on growth and development of phytoparasitic nematodes were studied. It was shown using an experimental system including tomato Lycopersicon esculentum Mill. and root-knot nematode, Meloidogyne incognita Kofoid et White, that a steroid molecule exhibits significant nematicidal activity if it contains a carbohydrate moiety and an additional heterocycle in the steroid core. The maximum nematicidal activity is inherent in glycosides containing chacotriose as the carbohydrate moiety of the molecule. Some compounds tested in this work could be used for protecting plants against phytoparasitic nematodes.

Role of Isoprenoids in Plant Adaptation to Biogenic Stress Induced by Parasitic Nematodes (Review)

Parasitic nematodes are considered a biogenic stress factor in plants. The effects of various plant isoprenoids, including mono-, sesqui-, di-, and triterpenoids, sterols, and steroid glycosides, on parasitic nematodes are reviewed. Certain isoprenoids can be placed in the class of natural plant adaptogens.

Photosynthetic Pigments of Tomato Plants under Conditions of Biotic Stress and Effects of Furostanol Glycosides

The adaptogenic effect of furostanol glycosides (FG) on biosynthesis of photosynthetic pigments in tomato plants (Lycopersicon esculentum Mill.) was studied under conditions of biotic stress caused by root-knot nematode (Meloidogyne incognita Kofoid et White). Treatment of plants with 5 × 10–4 M FG was accompanied by an increase in the rate of biosynthesis of pigments (particularly, chlorophyll b and carotenoids), which was observed against the background of a decrease in the relative contribution of β-carotene and an increase in the relative contribution of pigments of the violaxanthin cycle (VXC) to the overall pool of carotenoids. It was suggested that FG stimulated phytoimmunity by shifting metabolism of carotenoids toward enhanced biosynthesis of VXC pigments. These pigments play a protective role and facilitate stabilization of the photosynthetic apparatus, which is particularly important under stress conditions.

PR proteins in plants infested with the root-knot nematode Meloidogyne incognita (Kofoid et White, 1919) Chitwood 1949.

Production of pathogenesis-related proteins (PR proteins) is an important protective response of plants to pathogenic factors. It was suggested [1, 2] that this group of plant-encoded inducible proteins is related to specific forms of resistance to pathogens and stresses. PR proteins isolated from tobacco plants infected with tobacco mosaic virus have been studied in most detail. These proteins are arbitrarily divided into five groups. The properties of hydrolytic proteins of groups 2 and 3 ( β -1,3-glucanases and chitinases) has been described most comprehensively [3]. There are grounds to assume that these enzymes fulfil at least two functions in plant disease control. First, they are capable of catalyzing degradation of cell walls of pathogenic agents, because β -1,3-glucanes and chitin are essential components of the pathogen cell walls [4, 5]. Second, these enzymes catalyze hydrolysis of the corresponding substrates, thereby releasing biologically active oligosaccharides (elicitors and suppressors) capable of regulating the immune status of plant tissues [6]. The content of PR proteins in healthy plant tissues is insignificant, and these proteins were found in healthy plants only at certain stages of development [7]. The process of the pathogen-induced production of PR proteins should be regarded as systemic, because these proteins are accumulated not only at the site of pathogen localization, but also in noninoculated parts of plant. The information about protective effects of PR proteins against parasitic nematodes is scarce and contradictory. Some authors reported an absence of induction of PR proteins in plants infested with the nematode [8]. On the other hand, it was shown that nematode infestation induces an increase in the activity of glucanase and chitinase. Although no quantitative correlation of the activity of the enzymes with the degree of plant resistance was found in [8–10], there is evidence for contribution of PR proteins to plant protection against parasitic nematodes [11]. The goal of this work was to study the role of β -1,3glucanase and chitinase in the interaction between cucumber ( Cucumis sativum L.) and the root-knot nematode Meloidogyne incognita (Kofoid et White, 1919) Chitwood 1949 race 1. The cucumber cultivar TSKh211 was used. The degree of plant damage was four points on an invasion scale. Water-soluble chitosan (molecular weight, 5 kD; degree of acetylation, 15%) at a concentration of 50 μ g/ml and ascorbic acid (AA; Sigma) at a concentration of 10 − 7 M were used as elicitors for modulating the immune status of plants [12]. Before planting into soil, cucumber seeds were treated for 2 h with aqueous solutions of AA and chitosan. The morphological and physiological states of the nematodes and plants were assessed 40 days after infestation of roots. The chitinase and glucanase activities in cucumber leaves and roots were measured 21 days after infestation as described in [13, 14]. Colloid chitin (10 mg/ml) and laminarin (2 mg/ml) were used as substrates of chitinase and β -1,3-glucanase, respectively. The specific activity was expressed in μ mol of the reaction product per min per mg protein. The β -1,3-glucanase and chitinase reaction products were glucose and N-acetylglucoosamine, respectively. The results shown in Table 1 indicate that treatment with either of the elicitors caused a decrease in the degree of infestation of cucumber roots with nematodes. This decrease correlated with an acceleration of plant growth and an increase in the weight of their aboveground organs. It should be noted that chitosan was a more effective suppressor of nematodes than AA. For example, treatment with chitosan or AA caused a threefold or only a 13% decrease in the number of cucumber root knots, respectively. The effect of chitosan on nematode development was particularly notable. Indeed, at the end of the experiment, mature female nematodes were entirely absent in plants treated with chitosan, whereas in plants treated with AA, the number of mature female nematodes was no less than 40% GENERAL BIOLOGY

The immunocorrection properties of 1-->3-beta-glucans in the interaction of plants of the family solanaceae with phytopathogens.

Certain parasitic fungi are also sources of β -glucans. It was shown earlier by Ayers et al. [3] that metabolites of Phytophthora megasperma var. soja contained hepta1 → 3 ; 1 → 6 β -D-glucan, an elicitor of soybean defense mechanisms. The elicitor activity is observed if the heptaglucoside molecule contains three terminal glucose residues, two specifically oriented branches, and 1 → 6 β bonds in the main backbone chain of the elicitor.

Effect of furastanol glycosides of Dioscorea on lipid peroxidation in tomatoes infected with gall nematode.

The adaptogenic effect of furostanol glycosides of Dioscorea deltoidea Wall on plants was first observed by us in tomatoes and cucumbers infected with the gall nematode. Phytonematodes cause stress in plants, which leads to significant disturbances in homeostasis in the cell, related to changes in the structure of biological membranes. Furostanol glycosides induced certain biochemical changes in tomato plants under the conditions of biotic stress, induced by the parasitic nematodes Meloidogyne incognita Kofoid et White, which facilitated the development of immunity to phytopathogens in plants [1, 2].