The Fungicide Tetramethylthiuram Disulfide Negatively Affects Plant Cell Walls, Infection Thread Walls, and Symbiosomes in Pea (Pisum sativum L.) Symbiotic Nodules

Impact of Argemone mexicana L. on tomato plants infected with Phytophthora infestans

Background

Fungal diseases can cause significant losses in the tomato crop. Phytophthora infestans causes the late blight disease, which considerably affects tomato production worldwide. Weed-based plant extracts are a promising ecological alternative for disease control.

Methods

In this study, we analyzed the plant extract of Argemone mexicana L. using chromatography-mass spectrometry analysis (GC-MS). We evaluated its impact on the severity of P. infestans, as well as its effect on the components of the antioxidant defense system in tomato plants.

Results

The extract from A. mexicana contains twelve compounds most have antifungal and biostimulant properties. The findings of the study indicate that applying the A. mexicana extract can reduce the severity of P. infestans, increase tomato fruit yield, enhance the levels of photosynthetic pigments, ascorbic acid, phenols, and flavonoids, as well as decrease the biosynthesis of H2O2, malondialdehyde (MDA), and superoxide anion in the leaves of plants infected with this pathogen. These results suggest that using the extract from A. mexicana could be a viable solution to control the disease caused by P. infestans in tomato crop.

Effects of Elevated Temperature on Pisum sativum Nodule Development: I-Detailed Characteristic of Unusual Apical Senescence

Despite global warming, the influence of heat on symbiotic nodules is scarcely studied. In this study, the effects of heat stress on the functioning of nodules formed by Rhizobium leguminosarum bv. viciae strain 3841 on pea (Pisum sativum) line SGE were analyzed. The influence of elevated temperature was analyzed at histological, ultrastructural, and transcriptional levels. As a result, an unusual apical pattern of nodule senescence was revealed. After five days of exposure, a senescence zone with degraded symbiotic structures was formed in place of the distal nitrogen fixation zone. There was downregulation of various genes, including those associated with the assimilation of fixed nitrogen and leghemoglobin. After nine days, the complete destruction of the nodules was demonstrated. It was shown that nodule recovery was possible after exposure to elevated temperature for 3 days but not after 5 days (which coincides with heat wave duration). At the same time, the exposure of plants to optimal temperature during the night leveled the negative effects. Thus, the study of the effects of elevated temperature on symbiotic nodules using a well-studied pea genotype and Rhizobium strain led to the discovery of a novel positional response of the nodule to heat stress.

Effects of Elevated Temperature on Pisum sativum Nodule Development: II-Phytohormonal Responses

High temperature is one of the most important factors limiting legume productivity. We have previously shown the induction of senescence in the apical part of nodules of the pea SGE line, formed by Rhizobium leguminosarum bv. viciae strain 3841, when they were exposed to elevated temperature (28 °C). In this study, we analyzed the potential involvement of abscisic acid (ABA), ethylene, and gibberellins in apical senescence in pea nodules under elevated temperature. Immunolocalization revealed an increase in ABA and 1-aminocyclopropane-1-carboxylic acid (ACC, the precursor of ethylene biosynthesis) levels in cells of the nitrogen fixation zone in heat-stressed nodules in 1 day of exposure compared to heat-unstressed nodules. Both ABA and ethylene appear to be involved in the earliest responses of nodules to heat stress. A decrease in the gibberellic acid (GA3) level in heat-stressed nodules was observed. Exogenous GA3 treatment induced a delay in the degradation of the nitrogen fixation zone in heat-stressed nodules. At the same time, a decrease in the expression level of many genes associated with nodule senescence, heat shock, and defense responses in pea nodules treated with GA3 at an elevated temperature was detected. Therefore, apical senescence in heat-stressed nodules is regulated by phytohormones in a manner similar to natural senescence. Gibberellins can be considered as negative regulators, while ABA and ethylene can be considered positive regulators.

Effect of Triazole Fungicides Titul Duo and Vintage on the Development of Pea (Pisum sativum L.) Symbiotic Nodules

Triazole fungicides are widely used in agricultural production for plant protection, including pea (Pisum sativum L.). The use of fungicides can negatively affect the legume-Rhizobium symbiosis. In this study, the effects of triazole fungicides Vintage and Titul Duo on nodule formation and, in particular, on nodule morphology, were studied. Both fungicides at the highest concentration decreased the nodule number and dry weight of the roots 20 days after inoculation. Transmission electron microscopy revealed the following ultrastructural changes in nodules: modifications in the cell walls (their clearing and thinning), thickening of the infection thread walls with the formation of outgrowths, accumulation of poly-β-hydroxybutyrates in bacteroids, expansion of the peribacteroid space, and fusion of symbiosomes. Fungicides Vintage and Titul Duo negatively affect the composition of cell walls, leading to a decrease in the activity of synthesis of cellulose microfibrils and an increase in the number of matrix polysaccharides of cell walls. The results obtained coincide well with the data of transcriptomic analysis, which revealed an increase in the expression levels of genes that control cell wall modification and defense reactions. The data obtained indicate the need for further research on the effects of pesticides on the legume-Rhizobium symbiosis in order to optimize their use.

Bioremediation of tetramethyl thiuram disulfide and resource utilization of natural rubber wastewater by WR-2 Bacillus-dominated microbial community

Tetramethyl thiuram disulfide (TMTD), an emerging pollutant with ecotoxicity and accumulation in rubber wastewater, is directly discharged by factories into the surrounding soil to save costs, and this disrupts the nearby ecosystem. In this study, an efficient bioremediation microbial community (WR-2) dominated by Bacillus was acclimatized and isolated from soil contaminated by rubber wastewater. After passing through the metabolic process of WR-2, the ecotoxic TMTD decomposes within 14 days. In the pot experiment, WR-2 not only completed the bioremediation of contaminated soil but also significantly improved the crop growth conditions and the product quality. These results show that WR-2 has broad application prospects in the bioremediation of soil contaminated by rubber wastewater. It also provides a theoretical framework for the resource utilization of the effluent at the end of the initial rubber processing.

Biological activity of soybean seed lectin at the spraying of Glycine max plants against the background of seed treatment with pesticide containing fipronil, thiophanate-methyl, pyraclostrobin as active substances and rhizobial bacterization

Preparations for protecting plants, particularly those with fungicidal activity, continue to be relevant in agricultural production. They are used to effectively combat phytopathogens and ensure high yield of cultivated plants. However, they are among the anthropogenic factors which impose a heavy chemical load on ecosystems. Data about the effects of pesticides on physiological parameters of plants are essential for understanding the main regulatory mechanisms as preconditions to the phytotoxic state of compounds, as well as greater substantial understanding of the functional condition and implementation of adaptive potential of plants during and post stress. An important and relevant task – both practically and theoretically in the conditions of action of fungicide on seeds - is studying the possibilities of application of phytolectines as biologically active compounds with broad spectrum of action, including fungicidal effect, for spraying legumes in order to stabilize their development, ensure effective functioning of legume-rhizobial symbioses and cause fuller realization of productive potential against the background of decrease in chemical pressure on agrocenoses. Therefore, we aimed to evaluate the biological activity of soybean seed lectin (according to the parameters of productivity and functional activity of soybean-rhizobial symbiosis) at the spraying of Glycine max (L.) Merr. plants against the background of seed treatment of pesticide, Standak Top with fungicidal and insecticidal actions on the day of sowing and inoculation with Bradyrhizobium japonicum 634b. We used physiological, biochemical, microbiological and statistical methods of studies. We determined that Standak Top, applied on soybeans that were afterwards inoculated with rhizobia, exerted negative tendency on formation of vegetative mass by plants at the beginning of vegetation, though in the following phases of ontogenesis, their development and productivity reached the level of the control. Nitrogenase activity of symbiosis and the condition of photosynthetic pigment complex (content of chlorophyll and carotenoids and their ratio) were at the level or significantly lower than in the control plants. After spraying soybeans with lectin (without use of the fungicide) in the phase of development of two true leaves, there occurred significant increase in functional activity of the symbiotic system (according to total nitrogenase activity of symbiosis, higher by 1.91 and 1.79 times compared with the controls with inoculation and inoculation + fungicide) and the content of photosynthetic pigments (chlorophylls were higher by 1.12–1.45 times, carotenoids by 1.14–1.39 times) and development of strong leaf apparatus (by 1.33–1.42 times). This caused highest level of realization (by 13.9% and 10.1% higher compared with the controls with inoculation and inoculation + fungicide) of productive potential of cultivated plants. After spraying plants with soybean lectin against the background of use of fungicide, notable and reliable increases occurred in the level of absorption of molecular nitrogen (by 1.72 and 1.52 times according to total activity of symbiosis, compared with the controls with inoculation and inoculation + fungicide), content of chlorophyll (1.25–1.64 times) and carotenoids (1.12–1.42 times) in leaves of soybean, and also plants were actively developing during vegetation (1.12–1.40 times), producing yield that exceeded by 12.8% and 9.1% the controls with inoculation and inoculation + fungicide. Therefore, use of soybean seed lectin for spraying plants against the background of seed treatment of pesticide Standak Top on day of sowing can stabilize and even increase the level of realization of symbiotic and productive potential of soybean-rhizobial symbiosis compared both with the control (inoculation with rhizobia) and the variant with treatment of seeds (rhizobia + fungicide). This indicates on the perspectives of further studies of biological activity of phytolectins aiming at decreasing chemical pressure on ecosystems by leveling out or decreasing the negative impact of chemical means of protection on the plants and symbiosis.

The Regulation of Pea (Pisum sativum L.) Symbiotic Nodule Infection and Defense Responses by Glutathione, Homoglutathione, and Their Ratio

In this study, the roles of glutathione (GSH), homoglutathione (hGSH), and their ratio in symbiotic nodule development and functioning, as well as in defense responses accompanying ineffective nodulation in pea (Pisum sativum) were investigated. The expression of genes involved in (h)GSH biosynthesis, thiol content, and localization of the reduced form of GSH were analyzed in nodules of wild-type pea plants and mutants sym33-3 (weak allele, "locked" infection threads, occasional bacterial release, and defense reactions) and sym33-2 (strong allele, "locked" infection threads, defense reactions), and sym40-1 (abnormal bacteroids, oxidative stress, early senescence, and defense reactions). The effects of (h)GSH depletion and GSH treatment on nodule number and development were also examined. The GSH:hGSH ratio was found to be higher in nodules than in uninoculated roots in all genotypes analyzed, with the highest value being detected in wild-type nodules. Moreover, it was demonstrated, that a hGSHS-to-GSHS switch in gene expression in nodule tissue occurs only after bacterial release and leads to an increase in the GSH:hGSH ratio. Ineffective nodules showed variable GSH:hGSH ratios that correlated with the stage of nodule development. Changes in the levels of both thiols led to the activation of defense responses in nodules. The application of a (h)GSH biosynthesis inhibitor disrupted the nitrogen fixation zone in wild-type nodules, affected symbiosome formation in sym40-1 mutant nodules, and meristem functioning and infection thread growth in sym33-3 mutant nodules. An increase in the levels of both thiols following GSH treatment promoted both infection and extension of defense responses in sym33-3 nodules, whereas a similar increase in sym40-1 nodules led to the formation of infected cells resembling wild-type nitrogen-fixing cells and the disappearance of an early senescence zone in the base of the nodule. Meanwhile, an increase in hGSH levels in sym40-1 nodules resulting from GSH treatment manifested as a restriction of infection similar to that seen in untreated sym33-3 nodules. These findings indicated that a certain level of thiols is required for proper symbiotic nitrogen fixation and that changes in thiol content or the GSH:hGSH ratio are associated with different abnormalities and defense responses.

Structure and Development of the Legume-Rhizobial Symbiotic Interface in Infection Threads

The intracellular infection thread initiated in a root hair cell is a unique structure associated with Rhizobium-legume symbiosis. It is characterized by inverted tip growth of the plant cell wall, resulting in a tunnel that allows invasion of host cells by bacteria during the formation of the nitrogen-fixing root nodule. Regulation of the plant-microbial interface is essential for infection thread growth. This involves targeted deposition of the cell wall and extracellular matrix and tight control of cell wall remodeling. This review describes the potential role of different actors such as transcription factors, receptors, and enzymes in the rearrangement of the plant-microbial interface and control of polar infection thread growth. It also focuses on the composition of the main polymers of the infection thread wall and matrix and the participation of reactive oxygen species (ROS) in the development of the infection thread. Mutant analysis has helped to gain insight into the development of host defense reactions. The available data raise many new questions about the structure, function, and development of infection threads.