Mechanisms of ROS Regulation of Plant Development and Stress Responses

Plant developmental stage influences responses of Pinus strobiformis seedlings to experimental warming

Seedling emergence, survival, morphological and physiological traits, and oxidative stress resistance of southwestern white pine (Pinus strobiformis Engelm.) were studied in response to warming treatments applied during embryogenesis, germination, and early seedling growth. Daytime air temperature surrounding cones in tree canopies was warmed by +2.1°C during embryo development. Resulting seeds and seedlings were assigned to three thermal regimes in growth chambers, with each regime separated by 4°C to encompass the wide range of temperatures observed over space and time across the species' range, plus the effect of heat waves coupled with a high carbon emissions scenario of climate warming. The embryo warming treatment reduced percent seedling emergence in all germination and growth environments and reduced mortality of seedlings grown in the warmest environment. Warm thermal regimes during early seedling growth increased subsequent seedling resistance to oxidative stress and transpirational water use. Experimental warming during seed development, germination, and seedling growth affected seedling emergence and survival. Oxidative stress resistance, morphology, and water relations were affected only by warming imposed during germination and seedling growth. This work explores potential outcomes of climate warming on multiple dimensions of seedling performance and uniquely illustrates that plant responses to heat vary with plant developmental stage in addition to the magnitude of temperature change.

Ecotoxicological risk assessment of pentachlorophenol, an emerging DBP to plants: evaluation of oxidative stress and antioxidant responses

Chlorophenols are not only noticed in an effluvium of industries but also can emerge from the water treatment plants for domestic supply which poses a high threat for crop production and human health. Therefore, research on their risks to ecosystem and human health via ecotoxicological tests to derivate permissible environmental contaminant concentrations is necessary. The chlorophenols produced in the course of chlorination of potable water is an outcome of natural carboxylic acids/organic material and those chlorophenols occurred as emerging disinfection byproducts (EDBPs). Among chlorophenols, pentachlorophenol (PCP) has been recently identified as one of the important EDBPs. The main objective was to evaluate the PCP-induced genotoxicity and the oxidative damage in two plant species, i.e., Allium cepa and Vigna radiata. Genotoxicity of PCP was examined at three selected concentrations based on EC₅₀ (half-maximal effective concentrations) values in both the plants along with the defense mechanism. EC₅₀ value for A. cepa and V. radiata was 0.7 mg/L and 35 mg/L. Root length inhibition, DNA laddering, lipid peroxidation, H₂O₂ content, and antioxidant enzymatic assays evaluated revealed a dose-dependent response. PCP influenced defense enzyme glutathione peroxidase (GPX) and ascorbate peroxidase (APX) action in both plants and showed deprivement of catalase (CAT) with the increase of PCP concentrations. PCP-invaded toxicity management by these plants implied that A. cepa is more sensitive than V. radiata regarding PCP-induced toxicity.

Effect of different copper oxide particles on cell division and related genes of soybean roots

In this study, soybean (Glycine max) seeds were cultured in distilled water. When the roots were about 2 cm, they were separately treated with copper oxide bulk particles (CuO BPs) suspensions and copper oxide nanoparticle (CuO NPs) suspensions in different concentrations (2, 5 and 10 mg L-1) for 24 h and 48 h. Results showed that different concentrations of CuO BPs suspensions had little effect on the structure and cell division of meristematic zone. After CuO NPs treatment, Cu content increased in the roots, accompanied by high reactive oxygen species, malondialdehyde and relative electrical conductivity. CuO NPs significantly inhibited the growth of soybean roots over exposure time and the concentration. The destruction of CuO NPs occurred first in the promeristem, and then in the primary meristem of the meristematic zone. The meristematic cells of roots showed vacuolization, the nuclei swelled and deformed. After 10 mg L-1 CuO NPs treatment for 48 h, the mitotic index of root cells decreased by 14.28%, and the micronucleus rate increased by 14.33‰. Some cell division genes, such as GmCYCB1; 2, GmCYCU4; 1, GmCYCA1; 1, GmCYCP3; 1, GmCYCD3; 1 and CDC20; 1 were up-regulated or down-regulated with CuO NPs treatments.

β-Sitosterol differentially regulates key metabolites for growth improvement and stress tolerance in rice plants during prolonged UV-B stress

BACKGROUND

Elevated ultraviolet-B (UV-B) radiation is potentially deleterious to many organisms specifically crop plants and has become a global challenge. Rice is an exceptionally important staple food which is grown worldwide, and many efforts have been done recently to improve rice varieties against UV-B stress. This current study aims to investigate the effects of exogenous application of β-sitosterol (βSito) on growth improvement and tolerance level of rice plants against prolonged UV-B stress. The physiological and metabolic responses were evaluated in rice plants not supplemented with βSito (Nβ) and those supplemented with βSito (Sβ).

RESULTS

The Nβ and Sβ plants were grown under non-stress (ns) and under prolonged UV-B stress (uvs) conditions and termed as Nβ^ns, Sβ^ns and Nβ^uvs, Sβ^uvs, respectively. The application of βSito contributes positively under non-stress and specifically to UV-B stress in terms of improving numerous physiological parameters associated with growth and development such as shoot and root length, RWC, whole plant biomass, chlorophyll pigments, and photosynthetic-related parameters (Pn, Gs, Tr, WUEi, Fv/Fm, and NPQ) in Sβ compared with Nβ plants. Moreover, enhanced oxidative stress tolerance of Sβ^uvs vs. Nβ^uvs plants under stress was attributed to low levels of ROS and substantial trigger in activities of antioxidant enzymes (SOD, POD, CAT, and APX). Metabolic analysis was performed using GC-TOFMS, which revealed higher accumulation of several key metabolites including organic acids, sugars, amino acids, and others in Sβ^uvs vs. Nβ^uvs plants, which were mainly reduced in Nβ plants under stress vs. non-stress conditions.

CONCLUSION

These results provide useful data regarding the important role of βSito on growth maintenance and modulation of several metabolites associated with osmotic and redox adjustments during UV-B stress tolerance in rice plants. Importantly, βSito-regulated plasticity could further be explored specifically in relation to different environmental stresses in other economically useful crop plants.

Polymorphism in the Chloroplast ATP Synthase Beta-Subunit Is Associated with a Maternally Inherited Enhanced Cold Recovery in Cucumber

Cucumber (Cucumis sativus L.) is a warm-season crop that is sensitive to chilling temperatures and a maternally inherited cold tolerance exists in the heirloom cultivar 'Chipper' (CH). Because the organelles of cucumber show differential transmission (maternal for chloroplast and paternal for mitochondrion), this cold tolerance is hypothesized to be chloroplast-associated. The goal of this research was to characterize the cold tolerant phenotype from CH and determine its genetic basis. Doubled haploid (DH) lines were produced from CH and cold susceptible cucumbers, reciprocal hybrids with identical nuclear genotypes were produced, and plants were subjected to cold treatments under lights at 4 °C for 5.5 h. Hybrid plants with CH as the maternal parent had significantly higher fresh and dry weights 14 days after cold treatment compared to the reciprocal hybrid, revealing an enhanced cold recovery phenotype maternally conferred by CH. Results from analyses of the nuclear transcriptome and reactive oxygen species (ROS) between reciprocal hybrids were consistent with the cold recovery phenotype. Sequencing of the chloroplast genome and transcriptome of the DH parents and reciprocal hybrids, respectively, revealed one maternally transmitted non-synonymous single nucleotide polymorphism (SNP) in the chloroplast F₁F_O-ATP synthase (CF₁F_O-ATPase) beta-subunit gene (atpB) of CH which confers an amino acid change from threonine to arginine. Protein modeling revealed that this change is located at the interface of the alpha- and beta-subunits in the CF₁F_O-ATPase complex. Polymorphisms in the CF₁F_O-ATPase complex have been associated with stress tolerances in other plants, and selection for or creation of polymorphic beta-subunit proteins by chloroplast transformation or gene editing could condition improved recovery from cold stress in plants.

Oxidative signalling in seed germination and early seedling growth: an emerging role for ROS trafficking and inter-organelle communication

Underground early development of higher plants includes two distinct developmental processes, seed germination and then skotomorphogenesis, a mechanism which favours elongation of the hypocotyl and helps the seedling to find light. Interestingly, both processes, which are regulated by plant hormones, have been shown to depend on reactive oxygen species metabolism and to be related to mitochondrial retrograde signalling. Here we review the recent outcomes in this field of research and highlight the emerging role of ROS communication between organelles and cell compartments. We point out the role of mitochondria as an environmental and developmental sensor organelle that regulates ROS homeostasis and downstream events and we propose future directions of research that should help better understanding the roles of ROS in germination and seedling emergence.

Redox and low-oxygen stress: signal integration and interplay

Plants are aerobic organisms relying on oxygen to serve their energy needs. The amount of oxygen available to sustain plant growth can vary significantly due to environmental constraints or developmental programs. In particular, flooding stress, which negatively impacts crop productivity, is characterized by a decline in oxygen availability. Oxygen fluctuations result in an altered redox balance and the formation of reactive oxygen/nitrogen species (ROS/RNS) during the onset of hypoxia and upon re-oxygenation. In this update, we provide an overview of the current understanding of the impact of redox and ROS/RNS on low-oxygen signaling and adaptation. We first focus on the formation of ROS and RNS during low-oxygen conditions. Following this, we examine the impact of hypoxia on cellular and organellar redox systems. Finally, we describe how redox and ROS/RNS participate in signaling events during hypoxia through potential post-translational modifications (PTMs) of hypoxia-relevant proteins. The aim of this update is to define our current understanding of the field and to provide avenues for future research directions.

Ozone responses in Arabidopsis: beyond stomatal conductance

Tropospheric ozone (O3) is a major air pollutant that decreases yield of important crops worldwide. Despite long-lasting research of its negative effects on plants, there are many gaps in our knowledge on how plants respond to O3. In this study, we used natural variation in the model plant Arabidopsis (Arabidopsis thaliana) to characterize molecular and physiological mechanisms underlying O3 sensitivity. A key parameter in models for O3 damage is stomatal uptake. Here we show that the extent of O3 damage in the sensitive Arabidopsis accession Shahdara (Sha) does not correspond with O3 uptake, pointing toward stomata-independent mechanisms for the development of O3 damage. We compared tolerant (Col-0) versus sensitive accessions (Sha, Cvi-0) in assays related to photosynthesis, cell death, antioxidants, and transcriptional regulation. Acute O3 exposure increased cell death, development of lesions in the leaves, and decreased photosynthesis in sensitive accessions. In both Sha and Cvi-0, O3-induced lesions were associated with decreased maximal chlorophyll fluorescence and low quantum yield of electron transfer from Photosystem II to plastoquinone. However, O3-induced repression of photosynthesis in these two O3-sensitive accessions developed in different ways. We demonstrate that O3 sensitivity in Arabidopsis is influenced by genetic diversity given that Sha and Cvi-0 developed accession-specific transcriptional responses to O3. Our findings advance the understanding of plant responses to O3 and set a framework for future studies to characterize molecular and physiological mechanisms allowing plants to respond to high O3 levels in the atmosphere as a result of high air pollution and climate change.

The Effects of Plant-Associated Bacterial Exopolysaccharides on Plant Abiotic Stress Tolerance

Plant growth-promoting rhizobacteria (PGPR) are beneficial soil microorganisms that can stimulate plant growth and increase tolerance to biotic and abiotic stresses. Some PGPR are capable of secreting exopolysaccharides (EPS) to protect themselves and, consequently, their plant hosts against environmental fluctuations and other abiotic stresses such as drought, salinity, or heavy metal pollution. This review focuses on the enhancement of plant abiotic stress tolerance by bacterial EPS. We provide a comprehensive summary of the mechanisms through EPS to alleviate plant abiotic stress tolerance, including salinity, drought, temperature, and heavy metal toxicity. Finally, we discuss how these abiotic stresses may affect bacterial EPS production and its role during plant-microbe interactions.

Molecular Cloning and Functional Characterization of Heat Stress-Responsive Superoxide Dismutases in Garlic (Allium sativum L.)

Superoxide dismutases (SODs) are key antioxidant enzymes that can detoxify the superoxide radicals generated by various stresses. Although various plant SODs have been suggested to improve stress tolerance, SODs in garlic, an economically important vegetable grown worldwide, remain relatively unknown. In this study, we found that heat stress strongly induced the activities of Cu/ZnSODs, FeSODs, and MnSODs in garlic leaves. In addition, we cloned four garlic SODs (AsSODs) and suggest that heat stress-increased SOD activity was reflected at least by the induction of these AsSODs. The results of the agro-infiltration assay suggested that the cloned AsSODs encoded functional SOD enzymes belonging to the Cu/ZnSOD and MnSOD families. As a first step toward understanding the enzymatic antioxidant system in garlic plants, our results provide a solid foundation for an in-depth analysis of the physiological functions of the AsSOD family.

Transcriptome Analysis of Arabidopsis thaliana Plants Treated with a New Compound Natolen128, Enhancing Salt Stress Tolerance

Salinity stress is a major threat to agriculture and global food security. Chemical priming is a promising approach to improving salinity stress tolerance in plants. To identify small molecules with the capacity to enhance salinity stress tolerance in plants, chemical screening was performed using Arabidopsis thaliana. We screened 6400 compounds from the Nagoya University Institute of Transformative Bio-Molecule (ITbM) chemical library and identified one compound, Natolen128, that enhanced salinity-stress tolerance. Furthermore, we isolated a negative compound of Natolen128, namely Necolen124, that did not enhance salinity stress tolerance, though it has a similar chemical structure to Natolen128. We conducted a transcriptomic analysis of Natolen128 and Necolen124 to investigate how Natolen128 enhances high-salinity stress tolerance. Our data indicated that the expression levels of 330 genes were upregulated by Natolen128 treatment compared with that of Necolen124. Treatment with Natolen128 increased expression of hypoxia-responsive genes including ethylene biosynthetic enzymes and PHYTOGLOBIN, which modulate accumulation of nitric oxide (NO) level. NO was slightly increased in plants treated with Natolen128. These results suggest that Natolen128 may regulate NO accumulation and thus, improve salinity stress tolerance in A. thaliana.

Regulation of ascorbate-glutathione cycle by exogenous nitric oxide and hydrogen peroxide in soybean roots under arsenate stress

The role of nitric oxide (NO) and hydrogen peroxide (H2O2) is well known for regulating plant abiotic stress responses. However, underlying mechanisms are still poorly understood. Therefore, the present study investigated the involvement of NO and H2O2 signalling in the regulation of arsenate toxicity (AsV) in soybean roots employing a pharmacological approach. Results show that AsV toxicity declined root length and biomass due to greater As accumulation in the cell wall and cellular organelles. Arsenate induced cell death due to enhanced levels of reactive oxygen species, lipid and protein oxidation and down-regulation in ascorbate-glutathione cycle and redox states of ascorbate and glutathione. These results correlate with lower endogenous level of NO. Interestingly, addition of L-NAME increased AsV toxicity. However, addition of SNP reverses effect of L-NAME, suggesting that endogenous NO has a role in mitigating AsV toxicity. Exogenous H2O2 also demonstrated capability of alleviating AsV stress, while NAC reversed the protective effect of H2O2. Furthermore, DPI application further increased AsV toxicity, suggesting that endogenous H2O2 is also implicated in mitigating AsV stress. SNP was not able to mitigate AsV toxicity in the presence of DPI, suggesting that H2O2 might have acted downstream of NO in accomplishing amelioration of AsV toxicity.

Proteome analysis of bermudagrass stolons and rhizomes provides new insights into the adaptation of plant stems to aboveground and underground growth

As an important perennial warm-season turfgrass species, bermudagrass (Cynodon dactylon L.) forms underground-growing rhizomes and aboveground-growing stolons simultaneously, making it a fast propagating clonal plant with strong regeneration ability. In the current study, we compared the internode proteomes of rhizomes and stolons at the same developmental stage in the bermudagrass cultivar Yangjiang using iTRAQ. The results indicated that 228 protein species were differentially accumulated in the two specialized stems. In agreement with the different contents of starch, chlorophyll, anthocyanin and H₂O₂ in the two types of stems, photosynthesis and flavonoid biosynthesis were enriched with differentially accumulated protein species (DAPs) in stolons, whereas starch and sucrose metabolism, glycolysis, and H₂O₂ metabolism were enriched with DAPs in rhizomes. Burying stolons in the soil resulted in the gradual degradation of chlorophyll and anthocyanin, accumulation of starch, and increment of H₂O₂, which is similar to the physiological characteristics of rhizomes. These results collectively revealed that stolons and rhizomes of bermudagrass have significant differences at the proteome level and light might play important regulatory roles in the discrepancy of the proteome profiles and specialization of the two stems, providing new insights into the adaptation of plant stems to aboveground and underground growth. BIOLOGICAL SIGNIFICANCE: As two types of specialized stems that grow underground and aboveground respectively, rhizomes and stolons play important roles in overwintering and ecological invasion of many perennial and clonal plants. However, because rhizomes and stolons rarely coexist in single plant species, the differences between the two stems remain unclear at the molecular level. In this study, through an iTRAQ comparative proteomic analysis, we reported the identification of 228 differentially accumulated protein species (DAPs) in rhizomes and stolons of bermudagrass for the first time. We found that the 228 DAPs were interconnected to form protein networks in regulating diverse cellular activities and biochemical reactions. We also observed that stolons growing underground showed similar physiological activities and DAP expression as those of underground-growing rhizomes, suggesting that light might play important regulatory roles in the specialization of stolons and rhizomes. These results expanded our understanding of the mysterious adaption of plant stems to different growth conditions.

Isolation and Identification of Two Potent Phytotoxic Substances from Afzelia xylocarpa for Controlling Weeds

Phytotoxic substances released from plants are considered eco-friendly alternatives for controlling weeds in agricultural production. In this study, the leaves of Afzelia xylocarpa (Kurz) Craib. were investigated for biological activity, and their active substances were determined. Extracts of A. xylocarpa leaf exhibited concentration-dependent phytotoxic activity against the seedling length of Lepidium sativum L., Medicago sativa L., Phleum pratense L., and Echinochloa crus-galli (L.) P. Beauv. Bioassay-guided fractionation of the A. xylocarpa leaf extracts led to isolating and identifying two compounds: vanillic acid and trans-ferulic acid. Both compounds were applied to four model plants using different concentrations. The results showed both compounds significantly inhibited the model plants’ seedling length in a species-dependent manner (p < 0.05). The phytotoxic effects of trans-ferulic acid (IC50 = 0.42 to 2.43 mM) on the model plants were much greater than that of vanillic acid (IC50 = 0.73 to 3.17 mM) and P. pratense was the most sensitive to both compounds. In addition, the application of an equimolar (0.3 mM) mixture of vanillic acid and trans-ferulic acid showed the synergistic effects of the phytotoxic activity against the root length of P. pratense and L. sativum. These results suggest that the leaves of A. xylocarpa and its phytotoxic compounds could be used as a natural source of herbicides.

cROStalk for Life: Uncovering ROS Signaling in Plants and Animal Systems, from Gametogenesis to Early Embryonic Development

This review explores the role of reactive oxygen species (ROS)/Ca2+ in communication within reproductive structures in plants and animals. Many concepts have been described during the last years regarding how biosynthesis, generation products, antioxidant systems, and signal transduction involve ROS signaling, as well as its possible link with developmental processes and response to biotic and abiotic stresses. In this review, we first addressed classic key concepts in ROS and Ca2+ signaling in plants, both at the subcellular, cellular, and organ level. In the plant science field, during the last decades, new techniques have facilitated the in vivo monitoring of ROS signaling cascades. We will describe these powerful techniques in plants and compare them to those existing in animals. Development of new analytical techniques will facilitate the understanding of ROS signaling and their signal transduction pathways in plants and mammals. Many among those signaling pathways already have been studied in animals; therefore, a specific effort should be made to integrate this knowledge into plant biology. We here discuss examples of how changes in the ROS and Ca2+ signaling pathways can affect differentiation processes in plants, focusing specifically on reproductive processes where the ROS and Ca2+ signaling pathways influence the gametophyte functioning, sexual reproduction, and embryo formation in plants and animals. The study field regarding the role of ROS and Ca2+ in signal transduction is evolving continuously, which is why we reviewed the recent literature and propose here the potential targets affecting ROS in reproductive processes. We discuss the opportunities to integrate comparative developmental studies and experimental approaches into studies on the role of ROS/ Ca2+ in both plant and animal developmental biology studies, to further elucidate these crucial signaling pathways.

Betaine Aldehyde Dehydrogenase (BADH) vs. Flavodoxin (Fld): Two Important Genes for Enhancing Plants Stress Tolerance and Productivity

Abiotic stresses, mainly salinity and drought, are the most important environmental threats that constrain worldwide food security by hampering plant growth and productivity. Plants cope with the adverse effects of these stresses by implementing a series of morpho-physio-biochemical adaptation mechanisms. Accumulating effective osmo-protectants, such as proline and glycine betaine (GB), is one of the important plant stress tolerance strategies. These osmolytes can trigger plant stress tolerance mechanisms, which include stress signal transduction, activating resistance genes, increasing levels of enzymatic and non-enzymatic antioxidants, protecting cell osmotic pressure, enhancing cell membrane integrity, as well as protecting their photosynthetic apparatus, especially the photosystem II (PSII) complex. Genetic engineering, as one of the most important plant biotechnology methods, helps to expedite the development of stress-tolerant plants by introducing the key tolerance genes involved in the biosynthetic pathways of osmolytes into plants. Betaine aldehyde dehydrogenase (BADH) is one of the important genes involved in the biosynthetic pathway of GB, and its introduction has led to an increased tolerance to a variety of abiotic stresses in different plant species. Replacing down-regulated ferredoxin at the acceptor side of photosystem I (PSI) with its isofunctional counterpart electron carrier (flavodoxin) is another applicable strategy to strengthen the photosynthetic apparatus of plants under stressful conditions. Heterologous expression of microbially-sourced flavodoxin (Fld) in higher plants compensates for the deficiency of ferredoxin expression and enhances their stress tolerance. BADH and Fld are multifunctional transgenes that increase the stress tolerance of different plant species and maintain their production under stressful situations by protecting and enhancing their photosynthetic apparatus. In addition to increasing stress tolerance, both BADH and Fld genes can improve the productivity, symbiotic performance, and longevity of plants. Because of the multigenic and complex nature of abiotic stresses, the concomitant delivery of BADH and Fld transgenes can lead to more satisfying results in desired plants, as these two genes enhance plant stress tolerance through different mechanisms, and their cumulative effect can be much more beneficial than their individual ones. The importance of BADH and Fld genes in enhancing plant productivity under stress conditions has been discussed in detail in the present review.

Identification of Ipomoea batatas anti-cancer peptide (IbACP)-responsive genes in sweet potato leaves

IbACP, Ipomoea batatas anti-cancer peptide, a sixteen-amino-acid peptide isolated from sweet potato leaves, is capable of mediating a rapid alkalinization of growth media in plant suspension cells. However, the biological roles of IbACP as a defense peptide have not been studied. The objective of this study was to investigate the effect of IbACP on the accumulation of reactive oxygen species (ROS) and the expression of the defense-related genes. IbACP treatment of sweet potato leaves resulted in marked accumulation of both superoxide ion (O₂^-) and hydrogen peroxide (H₂O₂). The activity of peroxidase (POD) was significantly enhanced by IbACP treatment, suggesting that high levels of POD antioxidant activity may be used to scavenge the excess H₂O₂ in sweet potato plants. The IbACP-related genes were identified by suppression subtractive hybridization (SSH), and were then classified and assigned to the following categories: defense, development, metabolism, signaling, gene expression, and abiotic stress. H₂O₂ acts as a second messenger for gene activation in some of the IbACP-triggered gene expressions. These results demonstrated that IbACP is part of an integrated strategy for genetic regulation in sweet potato. Our work highlights the function of IbACP and its potential use for enhancing stress tolerance in sweet potato, in an effort to improve our understanding of defense-response mechanisms.

Genes related to redox and cell curvature facilitate interactions between Caulobacter strains and Arabidopsis

Bacteria play an integral role in shaping plant growth and development. However, the genetic factors that facilitate plant-bacteria interactions remain largely unknown. Here, we demonstrated the importance of two bacterial genetic factors that facilitate the interactions between plant-growth-promoting (PGP) bacteria in the genus Caulobacter and the host plant Arabidopsis. Using homologous recombination, we disrupted the cytochrome ubiquinol oxidase (cyo) operon in both C. vibrioides CB13 and C. segnis TK0059 by knocking out the expression of cyoB (critical subunit of the cyo operon) and showed that the mutant strains were unable to enhance the growth of Arabidopsis. In addition, disruption of the cyo operon, metabolomic reconstructions, and pH measurements suggested that both elevated cyoB expression and acid production by strain CB13 contribute to the previously observed inhibition of Arabidopsis seed germination. We also showed that the crescent shape of the PGP bacterial strain C. crescentus CB15 contributes to its ability to enhance plant growth. Thus, we have identified specific genetic factors that explain how select Caulobacter strains interact with Arabidopsis plants.

Stress-induced reactive oxygen species compartmentalization, perception and signalling

Reactive oxygen species (ROS) are essential for life and are involved in the regulation of almost all biological processes. ROS production is critical for plant development, response to abiotic stresses and immune responses. Here, we focus on recent discoveries in ROS biology emphasizing abiotic and biotic stress responses. Recent advancements have resulted in the identification of one of the first sensors for extracellular ROS and highlighted waves of ROS production during stress signalling in Arabidopsis. Enzymes that produce ROS, including NADPH oxidases, exhibit precise regulation through diverse post-translational modifications. Discoveries highlight the importance of both amino- and carboxy-terminal regulation of NADPH oxidases through protein phosphorylation and cysteine oxidation. Here, we discuss advancements in ROS compartmentalization, systemic ROS waves, ROS sensing and post-translational modification of ROS-producing enzymes and identify areas where foundational gaps remain.

A Plant Based Modified Biostimulant (Copper Chlorophyllin), Mediates Defense Response in Arabidopsis thaliana under Salinity Stress

To date, managing salinity stress in agriculture relies heavily on development of salt tolerant plant varieties, a time-consuming process particularly challenging for many crops. Plant based biostimulants (PBs) that enhance plant defenses under stress can potentially address this drawback, as they are not crop specific and are easy to apply in the field. Unfortunately, limited knowledge about their modes of action makes it harder to utilize them on a broader scale. Understanding how PBs enhance plant defenses at cellular and molecular levels, is a prerequisite for the development of sustainable management practices utilizing biostimulants to improve crop health. In this study we elucidated the protective mechanism of copper chlorophyllin (Cu-chl), a PB, under salinity stress. Our results indicate that Cu-chl exerts protective effects primarily by decreasing oxidative stress through modulating cellular H₂O₂ levels. Cu-chl treated plants increased tolerance to oxidative stress imposed by an herbicide, methyl viologen dichloride hydrate as well, suggesting a protective role against various sources of reactive oxygen species (ROS). RNA-Seq analysis of Cu-chl treated Arabidopsis thaliana seedlings subjected to salt stress identified genes involved in ROS detoxification, and cellular growth.

Effects of Maternal Environment on Seed Germination and Seedling Vigor of Petunia × hybrida under Different Abiotic Stresses

Seed germination and seedling vigor can be affected by environmental cues experienced by the mother plant. However, information about how the maternal environment affects seed quality is scarce in ornamental plants. This study aimed to investigate the effects of two different maternal environments on the seed germination and seedling vigor of Petunia × hybrida under a variety of abiotic stresses. Petunia mother plants were grown in either a greenhouse during the summer months or an indoor controlled-temperature-and-light environment. Collected seeds were subjected to external stressors, including polyethylene glycol (PEG), sodium chloride (NaCl), high temperature, and abscisic acid (ABA), to determine seed germination percentage and seedling vigor. Results indicated that seeds harvested from the mother plants grown in a controlled environment germinated better than seeds harvested from the mother plants grown in the greenhouse when suboptimal germination conditions were applied. Additionally, the seedlings from the controlled maternal environment performed better in both ABA and salinity stress tests than the greenhouse seedlings. Interestingly, the greenhouse seedlings displayed less reactive oxygen species (ROS) damage and lower electrolyte leakage than the controlled environment seedlings under dehydration stress. The difference in germination and seedling vigor of seeds from the two different maternal environments might be due to the epigenetic memory inherited from the mother plants. This study highlighted the strong impact of the maternal environment on seed germination and seedling vigor in Petunia and may assist in high-quality seed production in ornamental plants.

Roles of Plant Growth-Promoting Rhizobacteria (PGPR) in Stimulating Salinity Stress Defense in Plants: A Review

To date, soil salinity becomes a huge obstacle for food production worldwide since salt stress is one of the major factors limiting agricultural productivity. It is estimated that a significant loss of crops (20-50%) would be due to drought and salinity. To embark upon this harsh situation, numerous strategies such as plant breeding, plant genetic engineering, and a large variety of agricultural practices including the applications of plant growth-promoting rhizobacteria (PGPR) and seed biopriming technique have been developed to improve plant defense system against salt stress, resulting in higher crop yields to meet human's increasing food demand in the future. In the present review, we update and discuss the advantageous roles of beneficial PGPR as green bioinoculants in mitigating the burden of high saline conditions on morphological parameters and on physio-biochemical attributes of plant crops via diverse mechanisms. In addition, the applications of PGPR as a useful tool in seed biopriming technique are also updated and discussed since this approach exhibits promising potentials in improving seed vigor, rapid seed germination, and seedling growth uniformity. Furthermore, the controversial findings regarding the fluctuation of antioxidants and osmolytes in PGPR-treated plants are also pointed out and discussed.

Functional Characterization of PsnNAC036 under Salinity and High Temperature Stresses

Plant growth and development are challenged by biotic and abiotic stresses including salinity and heat stresses. For Populus simonii × P. nigra as an important greening and economic tree species in China, increasing soil salinization and global warming have become major environmental challenges. We aim to unravel the molecular mechanisms underlying tree tolerance to salt stress and high temprerature (HT) stress conditions. Transcriptomics revealed that a PsnNAC036 transcription factor (TF) was significantly induced by salt stress in P. simonii × P. nigra. This study focuses on addressing the biological functions of PsnNAC036. The gene was cloned, and its temporal and spatial expression was analyzed under different stresses. PsnNAC036 was significantly upregulated under 150 mM NaCl and 37 °C for 12 h. The result is consistent with the presence of stress responsive cis-elements in the PsnNAC036 promoter. Subcellular localization analysis showed that PsnNAC036 was targeted to the nucleus. Additionally, PsnNAC036 was highly expressed in the leaves and roots. To investigate the core activation region of PsnNAC036 protein and its potential regulatory factors and targets, we conducted trans-activation analysis and the result indicates that the C-terminal region of 191-343 amino acids of the PsnNAC036 was a potent activation domain. Furthermore, overexpression of PsnNAC036 stimulated plant growth and enhanced salinity and HT tolerance. Moreover, 14 stress-related genes upregulated in the transgenic plants under high salt and HT conditions may be potential targets of the PsnNAC036. All the results demonstrate that PsnNAC036 plays an important role in salt and HT stress tolerance.

Plant Defense Responses to Biotic Stress and Its Interplay With Fluctuating Dark/Light Conditions

Plants are subjected to a plethora of environmental cues that cause extreme losses to crop productivity. Due to fluctuating environmental conditions, plants encounter difficulties in attaining full genetic potential for growth and reproduction. One such environmental condition is the recurrent attack on plants by herbivores and microbial pathogens. To surmount such attacks, plants have developed a complex array of defense mechanisms. The defense mechanism can be either preformed, where toxic secondary metabolites are stored; or can be inducible, where defense is activated upon detection of an attack. Plants sense biotic stress conditions, activate the regulatory or transcriptional machinery, and eventually generate an appropriate response. Plant defense against pathogen attack is well understood, but the interplay and impact of different signals to generate defense responses against biotic stress still remain elusive. The impact of light and dark signals on biotic stress response is one such area to comprehend. Light and dark alterations not only regulate defense mechanisms impacting plant development and biochemistry but also bestow resistance against invading pathogens. The interaction between plant defense and dark/light environment activates a signaling cascade. This signaling cascade acts as a connecting link between perception of biotic stress, dark/light environment, and generation of an appropriate physiological or biochemical response. The present review highlights molecular responses arising from dark/light fluctuations vis-à-vis elicitation of defense mechanisms in plants.

Cryptochrome 1a depends on blue light fluence rate to mediate osmotic stress responses in tomato

The participation of plant cryptochromes in water deficit response mechanisms has been highlighted in several reports. However, the role of tomato (Solanum lycopersicum L.) cryptochrome 1a (cry1a) in the blue light fluence-dependent modulation of the water deficit response remains largely elusive. The tomato cry1a mutant and its wild-type counterpart were grown in water (no stress) or PEG₆₀₀₀ (osmotic stress) treatments under white light (60 μmol m^-2 s^-1) or from low to high blue light fluence (1, 5, 10, 15 and 25 μmol m^-2 s^-1). We first demonstrate that under nonstress conditions cry1a regulates seedling growth by mechanisms that involve pigmentation, lipid peroxidation and osmoprotectant accumulation in a blue light-dependent manner. In addition, we further highlighted under osmotic stress conditions that cry1a increased tomato growth by reduced malondialdehyde (MDA) and proline accumulation. Although blue light is an environmental signal that influences osmotic stress responses mediated by tomato cry1a, specific blue light fluence rates are required during these responses. Here, we show that CRY1a manipulation may be a potential biotechnological target to develop a drought-tolerant tomato variety. Nevertheless, the complete understanding of this phenomenon requires further investigation.

Cerium uptake, translocation and toxicity in the salt marsh halophyte Halimione portulacoides (L.), Aellen

Halimione portulacoides plants were exposed to dissolved cerium (Ce) in a hydroponic medium for five days. Ce accumulation in plants followed the metal's increase in the medium although with a very low translocation factor (TF < 0.01) between roots and shoots. Ce median concentrations in roots were 586, 988 and 1103 μg/g (dry wt.), while in shoots the median values reached 1.9, 3.5 and 10.0 μg/g (dry wt.), for plants exposed to 300, 600 and 1200 μg/L of Ce, respectively. No significant differences occurred in the length of roots and shoots among treatment groups, albeit plants exposed to the highest Ce concentration showed a clear loss of turgor pressure on the fifth day. An increase of hydrogen peroxide and malondialdehyde levels were observed in the plant shoots at 1200 μg/L of Ce. The highest concentration also triggered an answer by the shoots' antioxidant enzymes with a decrease in the activity of superoxide dismutase and an increase in peroxidase. However, no significant change in catalase activity was observed, compared to the control group, which may indicate that peroxidase played a more crucial role against the oxidative stress than catalase. Combined results indicate that H. portulacoides was actively responding to a toxic effect imposed by this higher Ce concentration. Nevertheless, changes in normal environmental conditions, may increase the bioavailability of Ce, while in areas where acid mine drainage may occur, the highest Ce concentration tested in this study may be largely exceeded, placing the sustainability of halophytes and estuarine marshes at risk.

Physio-biochemical and molecular assessment of Iron (Fe2+) toxicity responses in contrasting indigenous aromatic Joha rice cultivars of Assam, India

Iron (Fe) toxicity is one of the major abiotic stresses which limits the yield of lowland rice. This study aims to investigate the physiological, biochemical, and molecular aspects of two contrasting aromatic Joha rice, viz., Keteki and Kola Joha of Assam. Oxidative damage caused due to Fe²⁺ toxicity was quantitatively determined. Fe²⁺ toxicity in the growth medium increases the level of ROS and anti-oxidative enzyme activity. Along with the aforementioned damage caused due to Fe²⁺ toxicity, chlorophyll content decreases in both the rice varieties. Detection of Fe³⁺ and Fe²⁺ was also conducted by Perls' Prussian and Turnbull blue method, respectively. In addition, spectrophotometric quantification of Fe²⁺ was determined by 2, 2'-Bipyridyl (Bpy). Above 2.5 mM, Fe²⁺ toxicity was found to be lethal in rice seedlings affecting their total growth and biomass. Gene expression analysis of iron-regulated transporter 1 (OsIRT1), Yellow Stripe-Like 15 (OsYSL15), and ferritin 1 (OsFer1) revealed the differential gene expression over a time period of Fe²⁺ toxicity. Our study suggested that the different parameters which are considered here can be helpful for the better understanding of how aromatic Joha rice performed under Fe²⁺ toxicity which can also help to reveal broader aspects that how gene players are involved in the iron homeostasis mechanism in Joha rice in coming future.

Characterizing the putative mitogen-activated protein kinase (MAPK) and their protective role in oxidative stress tolerance and carbon assimilation in wheat under terminal heat stress

Wheat, being sensitive to terminal heat, causes drastic reduction in grain quality and yield. MAPK cascade regulates the network of defense mechanism operated inside plant system. Here, we have identified 21 novel MAPKs through gel-based proteomics and RNA-seq data analysis. Based on digital gene expression, two transcripts (transcript_2834 and transcript_8242) showing homology with MAPK were cloned and characterized from wheat (acc. nos. MK854806 and KT835664). Transcript_2834 was cloned in pET28a vector and recombinant MAPK protein of ∼40.3 kDa was isolated and characterized to have very high in-vitro kinase activity under HS. Native MAPK showed positive correlation with the expression of TFs, HSPs, genes linked with antioxidant enzyme (SOD, CAT, GPX), photosynthesis and starch biosynthesis pathways in wheat under HS. Wheat cv. HD3086 (thermotolerant) having higher expression and activity of MAPK under HS showed significant increase in accumulation of proline, H2O2, starch, and granule integrity, compared with BT-Schomburgk (thermosusceptible).

Chitin nanofibers trigger membrane bound defense signaling and induce elicitor activity in plants

The present study demonstrated that chitin-based nanofibers (CNFs) trigger the chitinase genes (PGIP1 and CaChi2), while elevating salicylic acid that can protect plants against pathogens. Cross-talk between this genetic induction and salicylic-acid-mediated immune response was also observed, which may arm a plant against multiple pathovars. Crab and mushroom based CNFs were synthesized by electrospinning and ball milling techniques. Plants (mung bean, Vigna radiata) (pepper, Capsicum annuum) were pre-inoculated with CNFs and treated with the pathogens Scrolotium rolfsii for pepper and Macrophomina phaseolina for mung bean and shrimp-based CNFs were used as a control. Treated plants had elevated levels of chitinase genes in response to CNFs at inoculation concentrations <10 mg/mL both in soil and media, to protect them against the pathogenic fungal disease. After 24 h of exposure to the pathogens, qRT-PCR showed genes class II chitinase gene (CaChi2) and polygalacturonase inhibitor protein 1 (PGIP1) to be up-regulated in both root and shoot at 0.1 and 1 mg/mL of inoculation, respectively. The ball milled mushroom CNFs were sufficient to trigger the membrane based enzymes with less diameter (≥15 nm) to be most efficient versus others. In vitro analysis showed IC₅₀ of ball milled mushroom CNFs to be most efficient in limiting the growth of fungal biomass. Further trigger-like effects were prominent in reducing pathogenic fungal spread in both species.

Recapitulation of the Function and Role of ROS Generated in Response to Heat Stress in Plants

In natural ecosystems, plants are constantly exposed to changes in their surroundings as they grow, caused by a lifestyle that requires them to live where their seeds fall. Thus, plants strive to adapt and respond to changes in their exposed environment that change every moment. Heat stress that naturally occurs when plants grow in the summer or a tropical area adversely affects plants' growth and poses a risk to plant development. When plants are subjected to heat stress, they recognize heat stress and respond using highly complex intracellular signaling systems such as reactive oxygen species (ROS). ROS was previously considered a byproduct that impairs plant growth. However, in recent studies, ROS gained attention for its function as a signaling molecule when plants respond to environmental stresses such as heat stress. In particular, ROS, produced in response to heat stress in various plant cell compartments such as mitochondria and chloroplasts, plays a crucial role as a signaling molecule that promotes plant growth and triggers subsequent downstream reactions. Therefore, this review aims to address the latest research trends and understandings, focusing on the function and role of ROS in responding and adapting plants to heat stress.

Nitric oxide, other reactive signalling compounds, redox, and reductive stress

Nitric oxide (NO) and other reactive nitrogen species (RNS) are key signalling molecules in plants, but they do not work in isolation. NO is produced in cells, often increased in response to stress conditions, but many other reactive compounds used in signalling are generated and accumulate spatially and temporally together. This includes the reactive oxygen species (ROS), such as hydrogen peroxide (H2O2), and hydrogen sulfide (H2S). Here, the interactions with such other reactive molecules is briefly reviewed. Furthermore, along with ROS and H2S, NO will potentially contribute to the overall intracellular redox of the cell. However, RNS will exist in redox couples and therefore the influence of the cellular redox on such couples will be explored. In discussions of the aberrations in intracellular redox it is usually oxidation, so-called oxidative stress, which is discussed. Here, we consider the notion of reductive stress and how this may influence the signalling which may be mediated by NO. By getting a more holistic view of NO biology, the influence on cell activity of NO and other RNS can be more fully understood, and may lead to the elucidation of methods for NO-based manipulation of plant physiology, leading to better stress responses and improved crops in the future.

Nutrient Imbalance of the Host Plant for Larvae of the Pale Grass Blue Butterfly May Mediate the Field Effect of Low-Dose Radiation Exposure in Fukushima: Dose-Dependent Changes in the Sodium Content

The pale grass blue butterfly Zizeeria maha is sensitive to low-dose radioactive pollution from the Fukushima nuclear accident in the field but is also highly tolerant to radioactive cesium (¹³⁷Cs) in an artificial diet in laboratory experiments. To resolve this field-laboratory paradox, we hypothesize that the butterfly shows vulnerability in the field through biochemical changes in the larval host plant, the creeping wood sorrel Oxalis corniculata, in response to radiation stress. To test this field-effect hypothesis, we examined nutrient contents in the host plant leaves from Tohoku (mostly polluted areas including Fukushima), Niigata, and Kyushu, Japan. Leaves from Tohoku showed significantly lower sodium and lipid contents than those from Niigata. In the Tohoku samples, the sodium content (but not the lipid content) was significantly negatively correlated with the radioactivity concentration of cesium (¹³⁷Cs) in leaves and with the ground radiation dose. The sodium content was also correlated with other nutrient factors. These results suggest that the sodium imbalance of the plant may be caused by radiation stress and that this nutrient imbalance may be one of the reasons that this monophagous butterfly showed high mortality and morphological abnormalities in the field shortly after the accident in Fukushima.

Tolerance to excess moisture in soybean is enhanced by over-expression of the Glycine max Phytoglobin (GmPgb1)

Excess moisture in the form of waterlogging or full submergence can cause severe conditions of hypoxia or anoxia compromising several physiological and biochemical processes. A decline in photosynthetic rate due to accumulation of ROS and damage of leaf tissue are the main consequences of excess moisture. These effects compromise crop yield and quality, especially in sensitive species, such as soybean (Glycine max.). Phytoglobins (Pgbs) are expressed during hypoxia and through their ability to scavenge nitric oxide participate in several stress-related responses. Soybean plants over-expressing or suppressing the Pgb1 gene GmPgb1 were generated and their ability to cope with waterlogging and full submergence conditions was assessed. Plants over-expressing GmPgb1 exhibited a higher retention of photosynthetic rate during waterlogging and survival rate during submergence relative to wild type plants. The same plants also had lower levels of ROS due to a reduction in expression of Respiratory Burst Oxidase Homologs (RBOH), components of the NADPH oxidase enzyme, and enhanced antioxidant system characterized by higher expression of catalases (CAT) and superoxide dismutase (SOD), as well as elevated expression and activity of ascorbate peroxidase (APX). Plants over-expressing GmPgb1 also exhibited an expression pattern of aquaporins typical of excess moisture resilience. This was in contrast to plants downregulating GmPgb1 which were characterized by the lowest photosynthetic rates, higher ROS signal, and reduced expression and activities of many antioxidant enzymes. Results from these studies suggest that GmPgb1 exercises a protective role during conditions of excess moisture with similar mechanisms operating during waterlogging and submergence.

Toxicity of insecticidal proteins from entomopathogenic bacteria to Galleria mellonella larvae

Entomopathogenic bacteria have great potential in insect control in the agricultural production because they produce a large variety of protein toxins that can kill their hosts by damaging the insect midgut. However, the mechanisms on how these toxins or specific insecticidal proteins act on insects are very diverse and elusive. Here we select Galleria mellonella larvae as the host to explore the effects of insecticidal proteins on the activities of three protective enzymes (SOD, POD, and CAT) and on the morphology of the midgut tissues. As a result, the activities of the three enzymes consistently increased and then decreased when the host was injected with the insecticidal proteins from the entomopathogenic bacterium Enterobacter cloacae. Moreover, the microscopy analysis showed that tissues, cells, and organelles of the host midgut are all diseased after uptake of the insecticidal proteins. Remarkably, the protein toxins contributed to the deformation of the midgut, blackening of the midgut surface, dissolution of cell membrane, shrinkage of cell nucleus, and chromatin condensation. Our findings will advance the explanation of G. mellonella pathogenesis caused by the insecticidal proteins.

Cryptochrome 1a of tomato mediates long-distance signaling of soil water deficit

Although the blue light photoreceptors cryptochromes mediate the expression of genes related to reactive oxygen species, whether cryptochrome 1a (cry1a) regulates local and long-distance signaling of water deficit in tomato (Solanum lycopersicum L.) is unknown. Thus the cry1a tomato mutant and its wild-type (WT) were reciprocally grafted (WT/WT; cry1a/cry1a; WT/cry1a; cry1a/WT; as scion/rootstock) or grown on their own roots (WT and cry1a) under irrigated and water deficit conditions. Plant growth, pigmentation, oxidative stress, water relations, stomatal characteristics and leaf gas exchange were measured. WT and cry1a plants grew similarly under irrigated conditions, whereas cry1a plants had less root biomass and length and higher tissue malondialdehyde concentrations under water deficit. Despite greater oxidative stress, cry1a maintained chlorophyll and carotenoid concentrations in drying soil. Lower stomatal density of cry1a likely increased its leaf relative water content (RWC). In grafted plants, scion genotype largely determined shoot and root biomass accumulation irrespective of water deficit. In chimeric plants grown in drying soil, cry1a rootstocks increased RWC while WT rootstocks maintained photosynthesis of cry1a scions. Manipulating tomato CRY1a may enhance plant drought tolerance by altering leaf pigmentation and gas exchange during soil drying via local and long-distance effects.

Alleviatory effects of Silicon on the morphology, physiology, and antioxidative mechanisms of wheat (Triticum aestivum L.) roots under cadmium stress in acidic nutrient solutions

Silicon (Si), as a quasi-essential element, has a vital role in alleviating the damaging effects of various environmental stresses on plants. Cadmium (Cd) stress is severe abiotic stress, especially in acidic ecological conditions, and Si can demolish the toxicity induced by Cd as well as acidic pH on plants. Based on these hypotheses, we demonstrated 2-repeated experiments to unfold the effects of Si as silica gel on the root morphology and physiology of wheat seedling under Cd as well as acidic stresses. For this purpose, we used nine treatments with three levels of Si nanoparticles (0, 1, and 3 mmol L⁻¹) derived from sodium silicate (Na₂SiO₃) against three concentrations of Cd (0, 50, and 200 µmol L⁻¹) in the form of cadmium chloride (CdCl₂) with three replications were arranged in a complete randomized design. The pH of the nutrient solution was adjusted at 5. The averages of three random replications showed that the mutual impacts of Si and Cd in acidic pH on wheat roots depend on the concentrations of Si and Cd. The collective or particular influence of low or high levels of Si (1 or 3 mM) and acidic pH (5) improved the development of wheat roots, and the collective influence was more significant than that of a single parallel treatment. The combined effects of low or high concentrations of Cd (50 or 200 µM) and acidic pH significantly reduced root growth and biomass while increased antioxidants, and reactive oxygen species (ROS) contents. The incorporation of Si (1 or 3 mmol L⁻¹) in Cd-contaminated acidic nutrient solution promoted the wheat root growth, decreased ROS contents, and further increased the antioxidants in the wheat roots compared with Cd single treatments in acidic pH. The demolishing effects were better with a high level of Si (3 mM) than the low level of Si (1 Mm). In conclusion, we could suggest Si as an effective beneficial nutrient that could participate actively in several morphological and physiological activities of roots in wheat plants grown under Cd and acidic pH stresses.

Defining the Cell Wall, Cell Cycle and Chromatin Landmarks in the Responses of Brachypodium distachyon to Salinity

Excess salinity is a major stress that limits crop yields. Here, we used the model grass Brachypodium distachyon (Brachypodium) reference line Bd21 in order to define the key molecular events in the responses to salt during germination. Salt was applied either throughout the germination period ("salt stress") or only after root emergence ("salt shock"). Germination was affected at ≥100 mM and root elongation at ≥75 mM NaCl. The expression of arabinogalactan proteins (AGPs), FLA1, FLA10, FLA11, AGP20 and AGP26, which regulate cell wall expansion (especially FLA11), were mostly induced by the "salt stress" but to a lesser extent by "salt shock". Cytological assessment using two AGP epitopes, JIM8 and JIM13 indicated that "salt stress" increases the fluorescence signals in rhizodermal and exodermal cell wall. Cell division was suppressed at >75 mM NaCl. The cell cycle genes (CDKB1, CDKB2, CYCA3, CYCB1, WEE1) were induced by "salt stress" in a concentration-dependent manner but not CDKA, CYCA and CYCLIN-D4-1-RELATED. Under "salt shock", the cell cycle genes were optimally expressed at 100 mM NaCl. These changes were consistent with the cell cycle arrest, possibly at the G1 phase. The salt-induced genomic damage was linked with the oxidative events via an increased glutathione accumulation. Histone acetylation and methylation and DNA methylation were visualized by immunofluorescence. Histone H4 acetylation at lysine 5 increased strongly whereas DNA methylation decreased with the application of salt. Taken together, we suggest that salt-induced oxidative stress causes genomic damage but that it also has epigenetic effects, which might modulate the cell cycle and AGP expression gene. Based on these landmarks, we aim to encourage functional genomics studies on the responses of Brachypodium to salt.

Linking jasmonates with vitamin E accumulation in plants: a case study in the Mediterranean shrub Cistus albidus L

Jasmonic acid positively modulates vitamin E accumulation, but the latter can also partly influence the capacity to accumulate the jasmonic acid precursor, 12-oxo-phytodienoic acid, in white-leaved rockrose (Cistus albidus L.) plants growing in their natural habitat. This study suggests a bidirectional link between chloroplastic antioxidants and lipid peroxidation-derived hormones in plants. While vitamin E is well known for its antioxidant properties being involved in plant responses to abiotic stress, jasmonates are generally related to biotic stress responses in plants. Studying them in non-model plants under natural conditions is crucial for the knowledge on their relationship, which will help us to better understand mechanisms and limits of stress tolerance to implement better conservation strategies in vulnerable ecosystems. We studied a typical Mediterranean shrub, white-leaved rockrose (Cistus albidus) under natural conditions during three winters and we analyzed both α and γ-tocopherol, and the three main jasmonates forms 12-oxo-phytodienoic acid (OPDA), jasmonic acid (JA), and jasmonoyl-isoleucine (JA-Ile). We found that JA contents positively correlated with vitamin E accumulation, most particularly with γ-tocopherol, the precursor of α-tocopherol (the most active vitamin E form). This finding was confirmed by exogenous application of methyl jasmonate (MeJA) in leaf discs under controlled conditions, which increased γ-tocopherol when applied at 0.1 mM MeJA and α-tocopherol at 1 mM MeJA. Furthermore, a complementary meta-analysis study with previously published reports revealed a positive correlation between JA and vitamin E, although this relationship turned to be strongly species specific. A strong negative correlation was observed, however, between total tocopherols and OPDA (a JA precursor located in chloroplasts). This antagonistic effect was observed between α-tocopherol and OPDA, but not between γ-tocopherol and OPDA. It is concluded that (i) variations in jasmonates and vitamin E due to yearly, inter-individual and sun orientation-driven variability are compatible with a partial regulation of vitamin E accumulation by jasmonates, (ii) vitamin E may also exert a role in the modulation of the biosynthesis of OPDA, with a much smaller effect, if any, on other jasmonates, and (iii) a trade-off in the accumulation of vitamin E and jasmonates might occur in the regulation of biotic and abiotic stress responses in plants.

Improved of growth and phytostabilization potential of lead (Pb) in Glebionis coronaria L. under the effect of IAA and GA3 alone and in combination with EDTA by altering biochemical attributes of stressed plants

This study evaluated the effect of EDTA, IAA and GA₃ alone and in combination in improving plant growth, Pb accumulation, and management of effective mechanisms associated with alleviation of Pb-induced adverse effect in Glebionis coronaria L. grown on industrial area in Alexandria. In this regards, 10-week-old plants were subjected to IAA and GA₃ as a foliar spray and EDTA was supplied in two doses 50 and 200mgkg^-1 soil. EDTA significantly reduced the plant growth and dry biomass, whereas GA₃ and IAA foliar spray increased growth significantly when compared with control (uncontaminated soil). In combined treatments of EDTA + GA₃ +IAA, the biomass was restored, which shows that GA₃ and IAA did compensate the negative effect of EDTA on plant growth and increased the Pb uptake significantly into roots. There were high GSH contents parallel with the increase of glutathione-S-transferase activity and induction of the antioxidant enzymes (SOD, CAT, APX, GR) as well as oxidized glutathione and ascorbic acid contents in leaves and roots when compared to control plants. This study suggests that G. coronaria is promising species for decontamination of Pb -contaminated soil and the application of EDTA together with IAA and GA₃ could be a useful strategy for enhancing the phytostabilization capability of Glebionis coronaria L. to eliminate Pb from contaminated soils. Novelty statement: The objective of this paper is to investigate the physiological performance of Glebionis coronaria as a new native for phytoremediation by phytostabilization mechanism of Pb after treatment with EDTA and phytohormones. Chemical additives of EDTA and GA₃ as well as IAA are promising alternatives to provide added benefits due to their individual credentials in improving the overall phytostabilization effectiveness and better immobilization efficiency in treating Pb contaminated soils by altering biochemical attributes of stressed plants. Currently these additives are not employed widely in large-scale field implementations, so field applications of these additives using Glebionis coronaria are essential for Phytoremediation of Pb-contaminated soils.

Transcription Factors as the "Blitzkrieg" of Plant Defense: A Pragmatic View of Nitric Oxide's Role in Gene Regulation

Plants are in continuous conflict with the environmental constraints and their sessile nature demands a fine-tuned, well-designed defense mechanism that can cope with a multitude of biotic and abiotic assaults. Therefore, plants have developed innate immunity, R-gene-mediated resistance, and systemic acquired resistance to ensure their survival. Transcription factors (TFs) are among the most important genetic components for the regulation of gene expression and several other biological processes. They bind to specific sequences in the DNA called transcription factor binding sites (TFBSs) that are present in the regulatory regions of genes. Depending on the environmental conditions, TFs can either enhance or suppress transcriptional processes. In the last couple of decades, nitric oxide (NO) emerged as a crucial molecule for signaling and regulating biological processes. Here, we have overviewed the plant defense system, the role of TFs in mediating the defense response, and that how NO can manipulate transcriptional changes including direct post-translational modifications of TFs. We also propose that NO might regulate gene expression by regulating the recruitment of RNA polymerase during transcription.

Overexpression of bacterial katE gene improves the resistance of modified tomato plant against Fusarium oxysporum f. sp. lycopersici

Tomato (Solanum lycopersicum L.) yield is severely affected by Fusarium fungal disease. To improve the resistance of tomato against Fusarium oxysporum f. sp. lycopersici (FOL), Escherichia coli katE gene was transformed into two tomato cultivars, namely Castle Rock and Super strain B, via Agrobacterium tumefaciens; the transformation efficiency was 5.6% and 3.5%, respectively. The integration of the katE gene into T₀, T₁, and T₂ transgenic tomato lines was confirmed using PCR. In addition, DNA dot blot technique confirmed the integration of the katE gene into T₂ transgenic tomato lines. The RT-PCR analysis confirmed that the katE gene could be expressed normally in the T₂ modified lines. Under artificial infection with FOL, the non-modified plants exhibited more severe fungal disease symptoms than those observed in katE overexpression (OE) lines. Our analysis showed that the levels of three defense enzymes, namely superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), were increased during transgenic T₂ generation pre-treated with FOL. The bioassay of modified lines revealed that an average of 52.56% of the modified Castle Rock cultivar and 50.28% of the modified Super Strain B cultivar showed resistance under Fusarium infection. These results clearly indicate that the modified tomato plants, in which the katE gene was overexpressed, became more resistant to the infection by FOL than the wild-type plants. Our study has proven that the overexpression of the E. coli katE gene in the OE lines could be utilized to develop and improve the resistance against fungal diseases in the modified crops.

Abscisic Acid-Induced Stomatal Closure: An Important Component of Plant Defense Against Abiotic and Biotic Stress

Abscisic acid (ABA) is a stress hormone that accumulates under different abiotic and biotic stresses. A typical effect of ABA on leaves is to reduce transpirational water loss by closing stomata and parallelly defend against microbes by restricting their entry through stomatal pores. ABA can also promote the accumulation of polyamines, sphingolipids, and even proline. Stomatal closure by compounds other than ABA also helps plant defense against both abiotic and biotic stress factors. Further, ABA can interact with other hormones, such as methyl jasmonate (MJ) and salicylic acid (SA). Such cross-talk can be an additional factor in plant adaptations against environmental stresses and microbial pathogens. The present review highlights the recent progress in understanding ABA's multifaceted role under stress conditions, particularly stomatal closure. We point out the importance of reactive oxygen species (ROS), reactive carbonyl species (RCS), nitric oxide (NO), and Ca²⁺ in guard cells as key signaling components during the ABA-mediated short-term plant defense reactions. The rise in ROS, RCS, NO, and intracellular Ca²⁺ triggered by ABA can promote additional events involved in long-term adaptive measures, including gene expression, accumulation of compatible solutes to protect the cell, hypersensitive response (HR), and programmed cell death (PCD). Several pathogens can counteract and try to reopen stomata. Similarly, pathogens attempt to trigger PCD of host tissue to their benefit. Yet, ABA-induced effects independent of stomatal closure can delay the pathogen spread and infection within leaves. Stomatal closure and other ABA influences can be among the early steps of defense and a crucial component of plants' innate immunity response. Stomatal guard cells are quite sensitive to environmental stress and are considered good model systems for signal transduction studies. Further research on the ABA-induced stomatal closure mechanism can help us design strategies for plant/crop adaptations to stress.

Light and Temperature Shape the Phenylpropanoid Profile of Azolla filiculoides Fronds

Azolla is a genus of floating freshwater ferns. By their high growth and N₂ fixation rates, Azolla species have been exploited for centuries by populations of South-east Asia as biofertilizers in rice paddies. The use of Azolla species as a sustainable plant material for diverse applications, such as feeding, biofuel production, and bioremediation, has encountered a growing interest over the last few years. However, high levels of feed deterrent flavonoids in their fronds have discouraged the use of these ferns as a sustainable protein source for animal consumption. Additionally, information on how and to what extent environmental determinants affect the accumulation of secondary metabolites in these organisms remains poorly understood. Moving from these considerations, here, we investigated by an untargeted metabolomics approach the profiles of phenylpropanoid compounds in the fronds of Azolla filiculoides sampled under control and pigment-inducing stress conditions. In parallel, we assayed the expression of essential structural genes of the phenylpropanoid pathway by quantitative RT-PCR. This study provides novel information concerning A. filiculoides phenylpropanoid compounds and their temporal profiling in response to environmental stimuli. In particular, we show that besides the already known 3-deoxyanthocyanidins, anthocyanidins, and proanthocyanidins, this fern can accumulate additional secondary metabolites of outstanding importance, such as chemoattractants, defense compounds, and reactive oxygen species (ROS) scavengers, and crucial as dietary components for humans, such as dihydrochalcones, stilbenes, isoflavones, and phlobaphenes. The findings of this study open an opportunity for future research studies to unveil the interplay between genetic and environmental determinants underlying the elicitation of the secondary metabolites in ferns and exploit these organisms as sustainable sources of beneficial metabolites for human health.

Titanium Application Increases Phosphorus Uptake Through Changes in Auxin Content and Root Architecture in Soybean (Glycine Max L.)

Phosphorus (P) is an essential macronutrient needed for plant growth, development, and production. A deficiency of P causes a severe impact on plant development and productivity. Several P-based fertilizers are being used in agriculture but limited uptake of P by the plant is still a challenge to be solved. Titanium (Ti) application increases the nutrient uptake by affecting the root growth; however, the role of Ti in plant biology, specifically its application under low light and phosphorus stress, has never been reported. Therefore, a pot study was planned with foliar application of Ti (in a different concentration ranging from 0 to 1,000 mg L^-1) under different light and P concentrations. The result indicated that under shade and low P conditions the foliar application of Ti in different concentrations significantly improves the plant growth parameters such as root length, root surface area, root dry matter, and shoot dry matters. The increase was observed to be more than 100% in shade and low P stressed soybean root parameter with 500 mg L^-1 of Ti treatment. Ti was observed to improve the plant growth both in high P and low P exposed plants, but the improvement was more obvious in Low P exposed plants. Auxin concentration in stressed and healthy plant roots was observed to be slightly increased with Ti application. Ti application was also observed to decrease rhizosphere soil pH and boosted the antioxidant enzymatic activities with an enhancement in photosynthetic efficiency of soybean plants under shade and P stress. With 500 mg L^-1 of Ti treatment, the photosynthetic rate was observed to improve by 45% under shade and P stressed soybean plants. Thus, this work for the first time indicates a good potential of Ti application in the low light and P deficient agricultural fields for the purpose to improve plant growth and development parameters.

The role of signal production and transduction in induced resistance of harvested fruits and vegetables

Postharvest diseases are the primary reason causing postharvest loss of fruits and vegetables. Although fungicides show an effective way to control postharvest diseases, the use of fungicides is gradually being restricted due to safety, environmental pollution, and resistance development in the pathogen. Induced resistance is a new strategy to control postharvest diseases by eliciting immune activity in fruits and vegetables with exogenous physical, chemical, and biological elicitors. After being stimulated by elicitors, fruits and vegetables respond immediately against pathogens. This process is actually a continuous signal transduction, including the generation, transduction, and interaction of signal molecules. Each step of response can lead to corresponding physiological functions, and ultimately induce disease resistance by upregulating the expression of disease resistance genes and activating a variety of metabolic pathways. Signal molecules not only mediate defense response alone, but also interact with other signal transduction pathways to regulate the disease resistance response. Among various signal molecules, the second messenger (reactive oxygen species, nitric oxide, calcium ions) and plant hormones (salicylic acid, jasmonic acid, ethylene, and abscisic acid) play an important role in induced resistance. This article summarizes and reviews the research progress of induced resistance in recent years, and expounds the role of the above-mentioned signal molecules in induced resistance of harvested fruits and vegetables, and prospects for future research.

The Roles of Peptide Hormones and Their Receptors during Plant Root Development

Peptide hormones play pivotal roles in many physiological processes through coordinating developmental and environmental cues among different cells. Peptide hormones are recognized by their receptors that convey signals to downstream targets and interact with multiple pathways to fine-tune plant growth. Extensive research has illustrated the mechanisms of peptides in shoots but functional studies of peptides in roots are scarce. Reactive oxygen species (ROS) are known to be involved in stress-related events. However, recent studies have shown that they are also associated with many processes that regulate plant development. Here, we focus on recent advances in understanding the relationships between peptide hormones and their receptors during root growth including outlines of how ROS are integrated with these networks.

Dampening the DAMPs: How Plants Maintain the Homeostasis of Cell Wall Molecular Patterns and Avoid Hyper-Immunity

Several oligosaccharide fragments derived from plant cell walls activate plant immunity and behave as typical damage-associated molecular patterns (DAMPs). Some of them also behave as negative regulators of growth and development, and due to their antithetic effect on immunity and growth, their concentrations, activity, time of formation, and localization is critical for the so-called "growth-defense trade-off." Moreover, like in animals, over accumulation of DAMPs in plants provokes deleterious physiological effects and may cause hyper-immunity if the cellular mechanisms controlling their homeostasis fail. Recently, a mechanism has been discovered that controls the activity of two well-known plant DAMPs, oligogalacturonides (OGs), released upon hydrolysis of homogalacturonan (HG), and cellodextrins (CDs), products of cellulose breakdown. The potential homeostatic mechanism involves specific oxidases belonging to the family of berberine bridge enzyme-like (BBE-like) proteins. Oxidation of OGs and CDs not only inactivates their DAMP activity, but also makes them a significantly less desirable food source for microbial pathogens. The evidence that oxidation and inactivation of OGs and CDs may be a general strategy of plants for controlling the homeostasis of DAMPs is discussed. The possibility exists of discovering additional oxidative and/or inactivating enzymes targeting other DAMP molecules both in the plant and in animal kingdoms.

The Biosynthesis of Phenolic Compounds is an Integrated Defence Mechanism to Prevent Ozone Injury in Salvia officinalis

Specialized metabolites constitute a major antioxidant system involved in plant defence against environmental constraints, such as tropospheric ozone (O₃). The objective of this experiment was to give a thorough description of the effects of an O₃ pulse (120 ppb, 5 h) on the phenylpropanoid metabolism of sage, at both biochemical and molecular levels. Variable O₃-induced changes were observed over time among the detected phenylpropanoid compounds (mostly identified as phenolic acids and flavonoids), likely because of their extraordinary functional diversity. Furthermore, decreases in the phenylalanine ammonia-lyase (PAL), phenol oxidase (PPO), and rosmarinic acid synthase (RAS) activities were reported during the first hours of treatment, probably due to an O₃-induced oxidative damage to proteins. Both PAL and PPO activities were also suppressed at 24 h from the beginning of exposure, whereas enhanced RAS activity occurred at the end of treatment and at the recovery time, suggesting that specific branches of the phenolic pathways were activated. The increased RAS activity was accompanied by the up-regulation of the transcript levels of genes like RAS, tyrosine aminotransferase, and cinnamic acid 4-hydroxylase. In conclusion, sage faced the O₃ pulse by regulating the activation of the phenolic biosynthetic route as an integrated defence mechanism.