A dissection of the effects of ethylene, H2O2 and high irradiance on antioxidants and several genes associated with stress and senescence in tobacco leaves

Ethylene-Cytokinin Interaction Determines Early Defense Response of Wheat against Stagonospora nodorum Berk

Ethylene, salicylic acid (SA), and jasmonic acid are the key phytohormones involved in plant immunity, and other plant hormones have been demonstrated to interact with them. The classic phytohormone cytokinins are important participants of plant defense signaling. Crosstalk between ethylene and cytokinins has not been sufficiently studied as an aspect of plant immunity and is addressed in the present research. We compared expression of the genes responsible for hormonal metabolism and signaling in wheat cultivars differing in resistance to Stagonospora nodorum in response to their infection with fungal isolates, whose virulence depends on the presence of the necrotrophic effector SnTox3. Furthermore, we studied the action of the exogenous cytokinins, ethephon (2-chloroethylphosphonic acid, ethylene-releasing agent) and 1-methylcyclopropene (1-MCP, inhibitor of ethylene action) on infected plants. Wheat susceptibility was shown to develop due to suppression of reactive oxygen species production and decreased content of active cytokinins brought about by SnTox3-mediated activation of the ethylene signaling pathway. SnTox3 decreased cytokinin content most quickly by its activated glucosylation in an ethylene-dependent manner and, furthermore, by oxidative degradation and inhibition of biosynthesis in ethylene-dependent and ethylene-independent manners. Exogenous zeatin application enhanced wheat resistance against S. nodorum through inhibition of the ethylene signaling pathway and upregulation of SA-dependent genes. Thus, ethylene inhibited triggering of SA-dependent resistance mechanism, at least in part, by suppression of the cytokinin signaling pathway.

What is the Difference between the Response of Grass Pea (Lathyrus sativus L.) to Salinity and Drought Stress?—A Physiological Study

Understanding the mechanisms of plant tolerance to osmotic and chemical stress is fundamental to maintaining high crop productivity. Soil drought often occurs in combination with physiological drought, which causes chemical stress due to high concentrations of ions. Hence, it is often assumed that the acclimatization of plants to salinity and drought follows the same mechanisms. Grass pea (Lathyrus sativus L.) is a legume plant with extraordinary tolerance to severe drought and moderate salinity. The aim of the presented study was to compare acclimatization strategies of grass pea seedlings to osmotic (PEG) and chemical (NaCl) stress on a physiological level. Concentrations of NaCl and PEG were adjusted to create an osmotic potential of a medium at the level of 0.0, −0.45 and −0.65 MPa. The seedlings on the media with PEG were much smaller than those growing in the presence of NaCl, but had a significantly higher content percentage of dry weight. Moreover, the stressors triggered different accumulation patterns of phenolic compounds, soluble and insoluble sugars, proline and β-N-oxalyl-L-α,β-diamino propionic acid, as well as peroxidase and catalase activity. Our results showed that drought stress induced a resistance mechanism consisting of growth rate limitation in favor of osmotic adjustment, while salinity stress induced primarily the mechanisms of efficient compartmentation of harmful ions in the roots and shoots. Furthermore, our results indicated that grass pea plants differed in their response to drought and salinity from the very beginning of stress occurrence.

Can Ceylon Leadwort (Plumbago zeylanica L.) Acclimate to Lead Toxicity?-Studies of Photosynthetic Apparatus Efficiency

Ceylon leadwort (Plumbago zeylanica) is ornamental plant known for its pharmacological properties arising from the abundant production of various secondary metabolites. It often grows in lead polluted areas. The aim of presented study was to evaluate the survival strategy of P. zeylanica to lead toxicity via photosynthetic apparatus acclimatization. Shoots of P. zeylanica were cultivated on media with different Pb concentrations (0.0, 0.05, and 0.1 g Pb∙l⁻¹). After a four-week culture, the efficiency of the photosynthetic apparatus of plants was evaluated by Chl a fluorescence measurement, photosynthetic pigment, and Lhcb1, PsbA, PsbO, and RuBisCo protein accumulation, antioxidant enzymes activity, and chloroplast ultrastructure observation. Plants from lower Pb concentration revealed no changes in photosynthetic pigments content and light-harvesting complex (LHCII) size, as well as no limitation on the donor side of Photosystem II Reaction Centre (PSII RC). However, the activity and content of antioxidant enzymes indicated a high risk of limitation on the acceptor side of Photosystem I. In turn, plants from 0.1 g Pb∙l⁻¹ showed a significant decrease in pigments content, LHCII size, the amount of active PSII RC, oxygen-evolving complex activity, and significant remodeling of chloroplast ultrastructure indicated limitation of PSII RC donor side. Obtained results indicate that P. zeylanica plants acclimate to lead toxicity by Pb accumulation in roots and, depending on Pb concentration, by adjusting their photosynthetic apparatus via the activation of alternative (cyclic and pseudocyclic) electron transport pathways.

Effect of the host-specific toxin SnTOX3 from Stagonospora nodorum on ethylene signaling pathway regulation and redox-state in common wheat

The fungus Stagonospora nodorum Berk. is the causative agent of Septoria nodorum blotch (SNB) of wheat. The most important factors of Stagonospora nodorum virulence include numerous fungal necrotrophic effectors (NEs) encoded by SnTox genes. They interact with the matching products of host susceptibility genes (Snn). SnTox-Snn interactions are mirror images of classical gene-for-gene interactions and lead to the development of disease. We have studied the SnTox3-Snn3 interaction, resulting in the development of infection on leaves and formation of extensive lesions. The mechanism of SnTox3 action is likely to be linked to the regulation of redox metabolism and the influence on ethylene synthesis in the wheat plants, although the molecular mechanisms are not fully unveiled. To characterize the SnTox3-Snn3 interaction, we used S. nodorum isolates differing in the expression of the NEs genes SnTox3 (SnB (Tox3+), Sn4VD (Tox3–)) and two soft spring wheat (Triticum aestivum L.) cultivars, contrasting in resistance to the SNB agent and differing in the allelic composition of the susceptibility locus Snn3-B1: Kazakhstanskaya 10 (susceptible) and Omskaya 35 (resistant). We carried out a comparative assessment of the transcriptional activity patterns of genes responsible for ethylene biosynthesis (TaACS1, TaACО) and signaling pathway (TaEIL1, TaERF1) by real-time PCR and estimated the redox state of wheat plants infected with different isolates of S. nodorum by spectrometry. The induction of ethylene biosynthesis and signaling has been shown to result from gene-for-gene interaction between Snn3-B1 and SnTox3. The results of plant redox status estimation showed that ethylene inhibited accumulation of hydrogen peroxide in SnTox3-sensitive genotypes by regulating the operation of various pro-/antioxidant enzymes at the transcriptional and posttranslational levels. Our results suggest that NE SnTox3 influences ethylene biosynthesis and signaling, thereby regulating redox metabolism in infected wheat plants as necessary for successful host colonization at the initial phases of infection, which ultimately leads to extensive lesions due to fast pathogen reproduction.

Priming plant resistance by activation of redox-sensitive genes

Priming by natural compounds is an interesting alternative for sustainable agriculture, which also contributes to explore the molecular mechanisms associated with stress tolerance. Although hosts and stress types eventually determine the mode of action of plant-priming agents, it highlights that many of them act on redox signalling. These include vitamins thiamine, riboflavin and quercetin; organic acids like pipecolic, azelaic and hexanoic; volatile organic compounds such as methyl jasmonate; cell wall components like chitosans and oligogalacturonides; H₂O₂, etc. This review provides data on how priming inducers promote stronger and faster responses to stress by modulating the oxidative environment, and interacting with signalling pathways mediated by salycilic acid, jasmonic acid and ethylene. The histone modifications involved in priming that affect the transcription of defence-related genes are also discussed. Despite the evolutionary distance between plants and animals, and the fact that the plant innate immunity takes place in each plant cell, they show many similarities in the molecular mechanisms that underlie pathogen perception and further signalling to activate defence responses. This review highlights the similarities between priming through redox signalling in plants and in mammalian cells. The strategies used by pathogens to manipulate the host´s recognition and the further activation of defences also show similarities in both kingdoms. Moreover, phytochemicals like sulforaphane and 12-oxo-phytodienoic acid prime both plant and mammalian responses by activating redox-sensitive genes. Hence research data into the priming of plant defences can provide additional information and a new viewpoint for priming mammalian defence, and vice versa.

A sugarcane R2R3-MYB transcription factor gene is alternatively spliced during drought stress

MYB transcription factors of the R2R3-MYB family have been shown to play important roles in many plant processes. A sugarcane R2R3-MYB gene (ScMYB2) and its two alternative forms of transcript (ScMYB2S1 and ScMYB2S2) were identified in this study. The deduced protein of ScMYB2S1 is a typical plant R2R3-MYB protein, while ScMYB2S2 encodes a truncated protein. Real-time qPCR analysis revealed that ScMYB2S1 is suppressed under PEG-simulated drought stress in sugarcane, while ScMYB2S2 is induced at later treatment stage. A senescence symptom was observed when ScMYB2S1 was injected into tobacco leaves mediated by Agrobacterium, but no symptom for ScMYB2S2. Further investigation showed that the expression levels of 4 senescence-associated genes, NtPR-1a, NtNYC1, NtCAT3 and NtABRE, were markedly induced in tobacco leaves after ScMYB2S1-injection, while they were not sensitive to ScMYB2S2-injection. Moreover, MDA and proline were also investigated after injection. Similarly, MDA and proline levels were induced by ABA and ScMYB2S1, while inhibited by ScMYB2S2. We propose that ScMYB2, by alternatively splicing two transcripts (ScMYB2S1 and ScMYB2S2), is involved in an ABA-mediated leaf senescence signaling pathway and play positive role in respond to drought-induced senescence in sugarcane. The results of this study provide information for further research in sugarcane stress processes.

Absence of Cu-Zn superoxide dismutase BCSOD1 reduces Botrytis cinerea virulence in Arabidopsis and tomato plants, revealing interplay among reactive oxygen species, callose and signalling pathways

Plants activate responses against pathogens, including the oxidative burst. Necrotrophic pathogens can produce reactive oxygen species (ROS) that benefit the colonization process. Previously, we have demonstrated that tomato plants challenged with Botrytis cinerea accumulate ROS and callose, together with the induction of genes involved in defence, signalling and oxidative metabolism. Here, we studied the infection phenotype of the Δbcsod1 strain in both tomato and Arabidopsis plants. This mutant lacks bcsod1, which encodes Cu-Zn superoxide dismutase (SOD). This enzyme catalyses the conversion of superoxide ion ( O2-) into hydrogen peroxide (H₂ O₂ ). ROS play a protective role and act as signals in plants. Δbcsod1 displayed reduced virulence compared with wild-type B05.10 in both species. Plants infected with Δbcsod1 accumulated less H₂ O₂ and more O2- than those infected with B05.10, which is associated with an increase in the defensive polymer callose. This supports a major role of fungal SOD in H₂ O₂ production during the plant-pathogen interaction. The early induction of the callose synthase gene PMR4 suggested that changes in ROS altered plant defensive responses at the transcriptional level. The metabolites and genes involved in signalling and in response to oxidative stress were differentially expressed on Δbcsod1 infection, supporting the notion that plants perceive changes in ROS balance and activate defence responses. A higher O₂^- /H₂ O₂ ratio seems to be beneficial for plant protection against this necrotroph. Our results highlight the relevance of callose and the oxylipin 12-oxo-phytodienoic acid (OPDA) in the response to changes in the oxidative environment, and clarify the mechanisms that underlie the responses to Botrytis in Arabidopsis and tomato plants.

Cross Talk between H2O2 and Interacting Signal Molecules under Plant Stress Response

It is well established that oxidative stress is an important cause of cellular damage. During stress conditions, plants have evolved regulatory mechanisms to adapt to various environmental stresses. One of the consequences of stress is an increase in the cellular concentration of reactive oxygen species, which is subsequently converted to H2O2. H2O2 is continuously produced as the byproduct of oxidative plant aerobic metabolism. Organelles with a high oxidizing metabolic activity or with an intense rate of electron flow, such as chloroplasts, mitochondria, or peroxisomes are major sources of H2O2 production. H2O2 acts as a versatile molecule because of its dual role in cells. Under normal conditions, H2O2 immerges as an important factor during many biological processes. It has been established that it acts as a secondary messenger in signal transduction networks. In this review, we discuss potential roles of H2O2 and other signaling molecules during various stress responses.

Cross Talk between H2O2 and Interacting Signal Molecules under Plant Stress Response

It is well established that oxidative stress is an important cause of cellular damage. During stress conditions, plants have evolved regulatory mechanisms to adapt to various environmental stresses. One of the consequences of stress is an increase in the cellular concentration of reactive oxygen species, which is subsequently converted to H2O2. H2O2 is continuously produced as the byproduct of oxidative plant aerobic metabolism. Organelles with a high oxidizing metabolic activity or with an intense rate of electron flow, such as chloroplasts, mitochondria, or peroxisomes are major sources of H2O2 production. H2O2 acts as a versatile molecule because of its dual role in cells. Under normal conditions, H2O2 immerges as an important factor during many biological processes. It has been established that it acts as a secondary messenger in signal transduction networks. In this review, we discuss potential roles of H2O2 and other signaling molecules during various stress responses.

Cross Talk between H2O2 and Interacting Signal Molecules under Plant Stress Response

It is well established that oxidative stress is an important cause of cellular damage. During stress conditions, plants have evolved regulatory mechanisms to adapt to various environmental stresses. One of the consequences of stress is an increase in the cellular concentration of reactive oxygen species, which is subsequently converted to H2O2. H2O2 is continuously produced as the byproduct of oxidative plant aerobic metabolism. Organelles with a high oxidizing metabolic activity or with an intense rate of electron flow, such as chloroplasts, mitochondria, or peroxisomes are major sources of H2O2 production. H2O2 acts as a versatile molecule because of its dual role in cells. Under normal conditions, H2O2 immerges as an important factor during many biological processes. It has been established that it acts as a secondary messenger in signal transduction networks. In this review, we discuss potential roles of H2O2 and other signaling molecules during various stress responses.

Senescence, Stress, and Reactive Oxygen Species

Generation of reactive oxygen species (ROS) is one of the earliest responses of plant cells to various biotic and abiotic stresses. ROS are capable of inducing cellular damage by oxidation of proteins, inactivation of enzymes, alterations in the gene expression, and decomposition of biomembranes. On the other hand, they also have a signaling role and changes in production of ROS can act as signals that change the transcription of genes that favor the acclimation of plants to abiotic stresses. Among the ROS, it is believed that H₂O₂ causes the largest changes in the levels of gene expression in plants. A wide range of plant responses has been found to be triggered by H₂O₂ such as acclimation to drought, photooxidative stress, and induction of senescence. Our knowledge on signaling roles of singlet oxygen (¹O₂) has been limited by its short lifetime, but recent experiments with a flu mutant demonstrated that singlet oxygen does not act primarily as a toxin but rather as a signal that activates several stress-response pathways. In this review we summarize the latest progress on the signaling roles of ROS during senescence and abiotic stresses and we give a short overview of the methods that can be used for their assessment.