ROS-mediated abiotic stress-induced programmed cell death in plants

Humic acids induce a eustress state via photosynthesis and nitrogen metabolism leading to a root growth improvement in rice plants

Chemical eustressors induce a eustress state "positive stress" increasing the resistance and improve the plant growth. The potentiality of humic acids (HA) to act as a eustressor has been scarcely explored. The present study aims to evaluate how HA with different structural characteristics induce differently, a eustress state in rice plants through the regulation of photosynthesis. The photosynthetic performance index showed an initial eustress state in plant by HA application characterized by reduction in photosynthesis followed by an increase in photosynthetic efficiency. The HA as a chemical eustressor triggering changes in plant metabolism indicate that the interaction of HA with root system induces a roots growth stimulus preceded by an initial positive stress. The eustress caused by HA is differentiated and is related to its chemical-physics characteristics. The HAVC, with a predominance of C_Alkyl-(O,N), C_Alkyl-di-O, C_Aromatic-O structures and greater polarity, stimulated the accumulation of N-NO₃^- and of soluble sugars in the sheath, increase carbohydrates content in the root and the root emission, resulting in higher total biomass production. The HASOIL, with a predominance of C_COOH-(H,R), C_Alkyl-O, C_Aromatic-H,R structures and greater hydrophobicity caused a decrease in N-NH₄⁺ and N-amine. The HARN, with a predominance of C_Alkyl-O, C_Alkyl-H,R, and CO, characterized by average polarity, caused an increase in photosynthetic pigment and N-NH₄⁺ content. These results are keys to understand that quality of soil organic matter is related to plant development and that HA are efficient proxies for elucidate its function in natural environments.

The interplay of hydraulic failure and cell vitality explains tree capacity to recover from drought

Global climatic models predict an increment in the frequency and intensity of drought events, which have important consequences on forest dieback. However, the mechanisms leading to tree mortality under drought conditions and the physiological thresholds for recovery are not totally understood yet. This study aimed to identify what are the key physiological traits that determine the tree capacity to recover from drought. Individuals of a conifer (Pseudotsuga menziesii M.) and an angiosperm (Prunus lusitanica L.) species were exposed to drought and their ability to recover after rehydration monitored. Results showed that the actual thresholds used for recovery from drought based on percentage loss of conductance (PLC) (i.e., 50% for conifers, 88% for angiosperms) do not provide accurate insights about the tree capacity for surviving extreme drought events. On the contrary, differences in stem relative water content (RWC_Stem ) and the level of electrolytes leakage (EL) were directly related to the capacity of the trees to recover from drought. This was the case for the conifer species, P. menziesii, for which higher RWC_Stem and lower EL values were related to the recovery capacity. Even if results showed a similar trend for the angiosperm P. lusitanica as for the conifers, differences between the two traits were much more subtle and did not allow an accurate differentiation between trees able to recover and those that were not. RWC_Stem and EL could work as indicators of tree capacity to recover from drought for conifers but more studies are required to confirm this observation for angiosperms.

The biotechnological importance of the plant-specific NAC transcription factor family in crop improvement

Climate change, malnutrition, and food insecurity are the inevitable challenges being faced by the agriculture sector today. Plants are susceptible to extreme temperatures during the crucial phases of flowering and seed development, and elevated carbon levels also lead to yield losses. Productivity is also affected by floods and droughts. Therefore, increasing plant yield and stress tolerance are the priorities to be met through novel biotechnological interventions. The contributions of NAC genes towards enhancing plant survivability under stress is well known. Here we focus on the potential of NAC genes in the regulation of abiotic stress tolerance, secondary cell wall synthesis, lateral root development, yield potential, seed size and biomass, ROS signaling, leaf senescence, and programmed cell death. Once naturally tolerant candidate NAC genes have been identified, and the nature of their association with growth and fitness against multi-environmental stresses has been determined, they can be exploited for building inherent tolerance in future crops via transgenic technologies. An update on the latest developments is provided in this review, which summarizes the current understanding of the roles of NAC in the establishment of various stress-adaptive mechanisms in model and food crop plants.

Central Metabolism in Mammals and Plants as a Hub for Controlling Cell Fate

Significance: The importance of oxidoreductases in energy metabolism together with the occurrence of enzymes of central metabolism in the nucleus gave rise to the active research field aiming to understand moonlighting enzymes that undergo post-translational modifications (PTMs) before carrying out new tasks. Recent Advances: Cytosolic enzymes were shown to induce gene transcription after PTM and concomitant translocation to the nucleus. Changed properties of the oxidized forms of cytosolic glyceraldehyde 3-phosphate dehydrogenase, and also malate dehydrogenases and others, are the basis for a hypothesis suggesting moonlighting functions that directly link energy metabolism to adaptive responses required for maintenance of redox-homeostasis in all eukaryotes. Critical Issues: Small molecules, such as metabolic intermediates, coenzymes, or reduced glutathione, were shown to fine-tune the redox switches, interlinking redox state, metabolism, and induction of new functions via nuclear gene expression. The cytosol with its metabolic enzymes connecting energy fluxes between the various cell compartments can be seen as a hub for redox signaling, integrating the different signals for graded and directed responses in stressful situations. Future Directions: Enzymes of central metabolism were shown to interact with p53 or the assumed plant homologue suppressor of gamma response 1 (SOG1), an NAM, ATAF, and CUC transcription factor involved in the stress response upon ultraviolet exposure. Metabolic enzymes serve as sensors for imbalances, their inhibition leading to changed energy metabolism, and the adoption of transcriptional coactivator activities. Depending on the intensity of the impact, rerouting of energy metabolism, proliferation, DNA repair, cell cycle arrest, immune responses, or cell death will be induced. Antioxid. Redox Signal. 34, 1025-1047.

Combined effects of water stress and salinity on growth, physiological, and biochemical traits in two walnut genotypes

Due to its great economic value, walnut (Juglans regia L.) has received increasing attention during recent years. However, water stress and salinity limit walnut growth, production, and quality. We employed two walnut genotypes, precocious walnut, and late-bearing walnut, to investigate their growth, photosynthetic capacity, non-structural carbohydrate contents, Cl^- allocation, reactive oxygen species (ROS) accumulation, and osmotic regulation under water stress, salinity, and their combination. We found that late-bearing walnut showed higher total biomass and net photosynthetic rate, higher activities of antioxidant enzymes, higher osmoregulation, and lower ROS accumulation than precocious walnut under stressful conditions. In addition, late-bearing walnut restricted salt transport and allocated more Cl^- into roots, whereas precocious walnut allocated more Cl^- into leaves when exposed to salinity stress. These data collectively demonstrated that late-bearing walnut possesses better stress tolerance under water stress, salinity, and especially under their combination. Such knowledge of genotype-specific responses and tolerances to water stress and salinity is important for walnut plantation management under increasing drought and aggravated soil salinization occurring with climate change.

Modular Assembly of Ordered Hydrophilic Proteins Improve Salinity Tolerance in Escherichia coli

Most late embryogenesis abundant group 3 (G3LEA) proteins are highly hydrophilic and disordered, which can be transformed into ordered α-helices to play an important role in responding to diverse stresses in numerous organisms. Unlike most G3LEA proteins, DosH derived from Dinococcus radiodurans is a naturally ordered G3LEA protein, and previous studies have found that the N-terminal domain (position 1–103) of DosH protein is the key region for its folding into an ordered secondary structure. Synthetic biology provides the possibility for artificial assembling ordered G3LEA proteins or their analogues. In this report, we used the N-terminal domain of DosH protein as module A (named DS) and the hydrophilic domains (DrHD, BnHD, CeHD, and YlHD) of G3LEA protein from different sources as module B, and artificially assembled four non-natural hydrophilic proteins, named DS + DrHD, DS + BnHD, DS + CeHD, and DS + YlHD, respectively. Circular dichroism showed that the four hydrophile proteins were highly ordered proteins, in which the α-helix contents were DS + DrHD (56.1%), DS + BnHD (53.7%), DS + CeHD (49.1%), and DS + YLHD (64.6%), respectively. Phenotypic analysis showed that the survival rate of recombinant Escherichia coli containing ordered hydrophilic protein was more than 10% after 4 h treatment with 1.5 M NaCl, which was much higher than that of the control group. Meanwhile, in vivo enzyme activity results showed that they had higher activities of superoxide dismutase, catalase, lactate dehydrogenase and less malondialdehyde production. Based on these results, the N-terminal domain of DosH protein can be applied in synthetic biology due to the fact that it can change the order of hydrophilic domains, thus increasing stress resistance.

The Effect of SP/NK1R on the Expression and Activity of Catalase and Superoxide Dismutase in Glioblastoma Cancer Cells

Introduction

Glioblastoma is the most malignant brain tumor with different therapeutic protocols, including surgery, radiotherapy, and chemotherapy. Substance P (SP), a peptide released by sensory nerves, increases cellular excitability by activating the neurokinin-1 receptor (NK1R) in several human tumor cells. Aprepitant is a potent and long-lasting NK1R antagonist, considered a new agent for inhibiting proliferation and induction of apoptosis in malignant cells. This study aimed to evaluate the effects of the SP/NK1R system on the expression and activity of catalase and superoxide dismutase (SOD) in the glioblastoma U87 cancer cell line.

Methods

Cytotoxicity was measured by the resazurin test, 24 hours after treatment, with increasing aprepitant concentrations. The production of reactive oxygen species (ROS) was also measured 24 hours after treatment with SP and aprepitant. Enzymes activity of catalase and SOD was measured using the corresponding assay kits. Real-time PCR also measured their expression.

Results

Aprepitant significantly reduced the viability of U87 cells in a concentration-dependent manner. ROS production was significantly reduced, and the activity of catalase and SOD increased after treatment with aprepitant. The expression of catalase and SOD enzymes also increased significantly in the presence of aprepitant.

Conclusion

The present study showed that aprepitant inhibited SP's oxidizing effects via inducing the antioxidant effects of catalase and SOD in the U87 cell line. Therefore, this drug might be introduced as a potential candidate for controlling glioblastoma cancer in animal models and clinical trials.

SPL36 Encodes a Receptor-like Protein Kinase that Regulates Programmed Cell Death and Defense Responses in Rice

Lesion mimic mutants spontaneously produce disease spots in the absence of biotic or abiotic stresses. Analyzing lesion mimic mutants' sheds light on the mechanisms underlying programmed cell death and defense-related responses in plants. Here, we isolated and characterized the rice (Oryza sativa) spotted leaf 36 (spl36) mutant, which was identified from an ethyl methanesulfonate-mutagenized japonica cultivar Yundao population. spl36 displayed spontaneous cell death and enhanced resistance to rice bacterial pathogens. Gene expression analysis suggested that spl36 functions in the disease response by upregulating the expression of defense-related genes. Physiological and biochemical experiments indicated that more cell death occurred in spl36 than the wild type and that plant growth and development were affected in this mutant. We isolated SPL36 by map-based cloning. A single base substitution was detected in spl36, which results in a cysteine-to-arginine substitution in SPL36. SPL36 is predicted to encode a receptor-like protein kinase containing leucine-rich domains that may be involved in stress responses in rice. spl36 was more sensitive to salt stress than the wild type, suggesting that SPL36 also negatively regulates the salt-stress response. These findings suggest that SPL36 regulates the disease resistance response in rice by affecting the expression of defense- and stress-related genes.

Reassessing the role of ion homeostasis for improving salinity tolerance in crop plants

Soil salinity is a constraint for major agricultural crops leading to severe yield loss, which may increase with the changing climatic conditions. Disruption in the cellular ionic homeostasis is one of the primary responses induced by elevated sodium ions (Na⁺ ). Therefore, unraveling the mechanism of Na⁺ uptake and transport in plants along with the characterization of the candidate genes facilitating ion homeostasis is obligatory for enhancing salinity tolerance in crops. This review summarizes the current advances in understanding the ion homeostasis mechanism in crop plants, emphasizing the role of transporters involved in the regulation of cytosolic Na⁺ level along with the conservation of K⁺ /Na⁺ ratio. Furthermore, expression profiles of the candidate genes for ion homeostasis were also explored under various developmental stages and tissues of Oryza sativa based on the publicly available microarray data. The review also gives an up-to-date summary on the efforts to increase salinity tolerance in crops by manipulating selected stress-associated genes. Overall, this review gives a combined view on both the ionomic and molecular background of salt stress tolerance in plants.

Ferroptosis in plants: triggers, proposed mechanisms, and the role of iron in modulating cell death

Regulated cell death plays key roles during essential processes throughout the plant life cycle. It takes part in specific developmental programs and maintains homeostasis of the organism in response to unfavorable environments. Ferroptosis is a recently discovered iron-dependent cell death pathway characterized by the accumulation of lipid reactive oxygen species. In plants, ferroptosis shares all the main hallmarks described in other systems. Those specific features include biochemical and morphological signatures that seem to be conserved among species. However, plant cells have specific metabolic pathways and a high degree of metabolic compartmentalization. Together with their particular morphology, these features add more complexity to the plant ferroptosis pathway. In this review, we summarize the most recent advances in elucidating the roles of ferroptosis in plants, focusing on specific triggers, the main players, and underlying pathways.

Integrated RNA-seq and Proteomic Studies Reveal Resource Reallocation towards Energy Metabolism and Defense in Skeletonema marinoi in Response to CO2 Increase

Rising atmospheric CO2 concentrations are causing ocean acidification (OA) with significant consequences for marine organisms. Because CO2 is essential for photosynthesis, the effect of elevated CO2 on phytoplankton is more complex and the mechanism is poorly understood. Here we applied RNA-seq and iTRAQ proteomics to investigate the impacts of CO2 increase (from ∼400 to 1000 ppm) on the temperate coastal marine diatom Skeletonema marinoi We identified 32,389 differentially expressed genes (DEGs) and 1,826 differentially expressed proteins (DEPs) from elevated CO2 conditions, accounting for 48.5% of total genes and 25.9% of total proteins we detected, respectively. Elevated pCO2 significantly inhibited the growth of S marinoi, and the 'omic' data suggested that this might be due to compromised photosynthesis in the chloroplast and raised mitochondrial energy metabolism. Furthermore, many genes/proteins associated with nitrogen metabolism, transcriptional regulation, and translational regulation were markedly up-regulated, suggesting enhanced protein synthesis. In addition, S marinoi exhibited higher capacity of ROS production and resistance to oxidative stress. Overall, elevated pCO2 seems to repress photosynthesis and growth of S marinoi, and through massive gene expression reconfiguration induce cells to increase investment in protein synthesis, energy metabolism and antioxidative stress defense, likely to maintain pH homeostasis and population survival. This survival strategy may deprive this usually dominant diatom in temperate coastal waters of its competitive advantages in acidified environments.Importance Rising atmospheric CO2 concentrations are causing ocean acidification with significant consequences for marine organisms. Chain-forming centric diatoms of Skeletonema is one of the most successful groups of eukaryotic primary producers with widespread geographic distribution. Among the recognized 28 species, S. marinoi can be a useful model for investigating the ecological, genetic, physiological, and biochemical characteristics of diatoms in temperate coastal regions. In this study, we found that the elevated pCO2 seems to repress photosynthesis and growth of S. marinoi, and through massive gene expression reconfiguration induce cells to increase investment in protein synthesis, energy metabolism and antioxidative stress defense, likely to maintain pH homeostasis and population survival. This survival strategy may deprive this usually dominant diatom in temperate coastal waters of its competitive advantages in acidified environments.

Downstream Signalling from Molecular Hydrogen

Molecular hydrogen (H2) is now considered part of the suite of small molecules that can control cellular activity. As such, H2 has been suggested to be used in the therapy of diseases in humans and in plant science to enhance the growth and productivity of plants. Treatments of plants may involve the creation of hydrogen-rich water (HRW), which can then be applied to the foliage or roots systems of the plants. However, the molecular action of H2 remains elusive. It has been suggested that the presence of H2 may act as an antioxidant or on the antioxidant capacity of cells, perhaps through the scavenging of hydroxyl radicals. H2 may act through influencing heme oxygenase activity or through the interaction with reactive nitrogen species. However, controversy exists around all the mechanisms suggested. Here, the downstream mechanisms in which H2 may be involved are critically reviewed, with a particular emphasis on the H2 mitigation of stress responses. Hopefully, this review will provide insight that may inform future research in this area.

Abiotic Stress and Reactive Oxygen Species: Generation, Signaling, and Defense Mechanisms

Climate change is an invisible, silent killer with calamitous effects on living organisms. As the sessile organism, plants experience a diverse array of abiotic stresses during ontogenesis. The relentless climatic changes amplify the intensity and duration of stresses, making plants dwindle to survive. Plants convert 1-2% of consumed oxygen into reactive oxygen species (ROS), in particular, singlet oxygen (1O2), superoxide radical (O2•-), hydrogen peroxide (H2O2), hydroxyl radical (•OH), etc. as a byproduct of aerobic metabolism in different cell organelles such as chloroplast, mitochondria, etc. The regulatory network comprising enzymatic and non-enzymatic antioxidant systems tends to keep the magnitude of ROS within plant cells to a non-damaging level. However, under stress conditions, the production rate of ROS increases exponentially, exceeding the potential of antioxidant scavengers instigating oxidative burst, which affects biomolecules and disturbs cellular redox homeostasis. ROS are similar to a double-edged sword; and, when present below the threshold level, mediate redox signaling pathways that actuate plant growth, development, and acclimatization against stresses. The production of ROS in plant cells displays both detrimental and beneficial effects. However, exact pathways of ROS mediated stress alleviation are yet to be fully elucidated. Therefore, the review deposits information about the status of known sites of production, signaling mechanisms/pathways, effects, and management of ROS within plant cells under stress. In addition, the role played by advancement in modern techniques such as molecular priming, systems biology, phenomics, and crop modeling in preventing oxidative stress, as well as diverting ROS into signaling pathways has been canvassed.

A novel glycine-rich domain protein, GRDP1, functions as a critical feedback regulator for controlling cell death and disease resistance in rice

Lesion mimic mutants constitute a valuable genetic resource for unraveling the signaling pathways and molecular mechanisms governing the programmed cell death and defense responses of plants. Here, we identified a lesion mimic mutant, spl-D, from T-DNA insertion rice lines. The mutant exhibited higher accumulation of H2O2, spontaneous cell death, decreased chlorophyll content, up-regulation of defense-related genes, and enhanced disease resistance. The causative gene, OsGRDP1, encodes a cytosol- and membrane-associated glycine-rich domain protein. OsGRDP1 was expressed constitutively in all of the organs of the wild-type plant, but was up-regulated throughout plant development in the spl-D mutant. Both the overexpression and knockdown (RNAi) of OsGRDP1 resulted in the lesion mimic phenotype. Moreover, the intact-protein level of OsGRDP1 was reduced in the spotted leaves from both overexpression and RNAi plants, suggesting that the disruption of intact OsGRDP1 is responsible for lesion formation. OsGRDP1 interacted with an aspartic proteinase, OsAP25. In the spl-D and overexpression plants, proteinase activity was elevated, and lesion formation was partially suppressed by an aspartic proteinase inhibitor. Taken together, our results reveal that OsGRDP1 is a critical feedback regulator, thus contributing to the elucidation of the mechanism underlying cell death and disease resistance.

Signaling Toward Reactive Oxygen Species-Scavenging Enzymes in Plants

Reactive oxygen species (ROS) are signaling molecules essential for plant responses to abiotic and biotic stimuli as well as for multiple developmental processes. They are produced as byproducts of aerobic metabolism and are affected by adverse environmental conditions. The ROS content is controlled on the side of their production but also by scavenging machinery. Antioxidant enzymes represent a major ROS-scavenging force and are crucial for stress tolerance in plants. Enzymatic antioxidant defense occurs as a series of redox reactions for ROS elimination. Therefore, the deregulation of the antioxidant machinery may lead to the overaccumulation of ROS in plants, with negative consequences both in terms of plant development and resistance to environmental challenges. The transcriptional activation of antioxidant enzymes accompanies the long-term exposure of plants to unfavorable environmental conditions. Fast ROS production requires the immediate mobilization of the antioxidant defense system, which may occur via retrograde signaling, redox-based modifications, and the phosphorylation of ROS detoxifying enzymes. This review aimed to summarize the current knowledge on signaling processes regulating the enzymatic antioxidant capacity of plants.

Piriformospora indica augments arsenic tolerance in rice (Oryza sativa) by immobilizing arsenic in roots and improving iron translocation to shoots

Arsenic (As) toxicity can be a hazardous threat to sustainable agriculture and human health. Piriformospora indica (P. indica), as a beneficial endophytic fungus, is involved in the plant tolerance to stressful conditions. Here, the biochemical and molecular responses of rice plants to As (50 μM) phytotoxicity and P. indica inoculation as well as the role of P. indica in improving rice adaptation to As stress were evaluated. The results showed that As stress reduced chlorophylls content, chlorophyll fluorescence yield (Fv/Fm), electron transport rate (ETR) and growth. However, P. indica restored chlorophyll content and growth. P. indica decreased the contents of methylglyoxal and malondialdehyde by improving the activity of enzymes involved in the glyoxalase pathway and modulating the redox state of the ascorbic acid-glutathione cycle, and consequently, increased the plant tolerance to As toxicity. P. indica, by downregulating Lsi2 expression (involved in As translocation to the shoot) and upregulating PCS1 and PCS2 expression (involved in As sequestration in vacuoles), immobilized As in the roots and reduced damage to photosynthetic organs. P. indica increased iron (Fe) accumulation in the shoot under As toxicity by upregulating the expression of IRO2, YSL2 and FRDL1 genes. The results of the present study augmented our knowledge in using P. indica symbiosis in improving the tolerance of rice plants against As toxicity for sustainable agriculture.

Phototropin 1 and 2 Influence Photosynthesis, UV-C Induced Photooxidative Stress Responses, and Cell Death

Phototropins are plasma membrane-associated photoreceptors of blue light and UV-A/B radiation. The Arabidopsis thaliana genome encodes two phototropins, PHOT1 and PHOT2, that mediate phototropism, chloroplast positioning, and stomatal opening. They are well characterized in terms of photomorphogenetic processes, but so far, little was known about their involvement in photosynthesis, oxidative stress responses, and cell death. By analyzing phot1, phot2 single, and phot1phot2 double mutants, we demonstrated that both phototropins influence the photochemical and non-photochemical reactions, photosynthetic pigments composition, stomata conductance, and water-use efficiency. After oxidative stress caused by UV-C treatment, phot1 and phot2 single and double mutants showed a significantly reduced accumulation of H₂O₂ and more efficient photosynthetic electron transport compared to the wild type. However, all phot mutants exhibited higher levels of cell death four days after UV-C treatment, as well as deregulated gene expression. Taken together, our results reveal that on the one hand, both phot1 and phot2 contribute to the inhibition of UV-C-induced foliar cell death, but on the other hand, they also contribute to the maintenance of foliar H₂O₂ levels and optimal intensity of photochemical reactions and non-photochemical quenching after an exposure to UV-C stress. Our data indicate a novel role for phototropins in the condition-dependent optimization of photosynthesis, growth, and water-use efficiency as well as oxidative stress and cell death response after UV-C exposure.

Insights into Plant Programmed Cell Death Induced by Heavy Metals-Discovering a Terra Incognita

Programmed cell death (PCD) is a process that plays a fundamental role in plant development and responses to biotic and abiotic stresses. Knowledge of plant PCD mechanisms is still very scarce and is incomparable to the large number of studies on PCD mechanisms in animals. Quick and accurate assays, e.g., the TUNEL assay, comet assay, and analysis of caspase-like enzyme activity, enable the differentiation of PCD from necrosis. Two main types of plant PCD, developmental (dPCD) regulated by internal factors, and environmental (ePCD) induced by external stimuli, are distinguished based on the differences in the expression of the conserved PCD-inducing genes. Abiotic stress factors, including heavy metals, induce necrosis or ePCD. Heavy metals induce PCD by triggering oxidative stress via reactive oxygen species (ROS) overproduction. ROS that are mainly produced by mitochondria modulate phytotoxicity mechanisms induced by heavy metals. Complex crosstalk between ROS, hormones (ethylene), nitric oxide (NO), and calcium ions evokes PCD, with proteases with caspase-like activity executing PCD in plant cells exposed to heavy metals. This pathway leads to very similar cytological hallmarks of heavy metal induced PCD to PCD induced by other abiotic factors. The forms, hallmarks, mechanisms, and genetic regulation of plant ePCD induced by abiotic stress are reviewed here in detail, with an emphasis on plant cell culture as a suitable model for PCD studies. The similarities and differences between plant and animal PCD are also discussed.

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.

Brassinosteroid and hydrogen peroxide improve photosynthetic machinery, stomatal movement, root morphology and cell viability and reduce Cu- triggered oxidative burst in tomato

Brassinosteroids and hydrogen peroxide (H₂O₂) are extensively used to combat several environmental factors, including heavy metal stress in plants, but their cumulative impact on the maintenance of copper (Cu) homeostasis in plants could not be dissected at elevated level. This study was executed to explore the roles of 24-epibrassinolide (EBL; foliar) and H₂O₂ (root dipping) in resilience of tomato (Solanum lycopersicum L.) plants to Cu stress. The cumulative effect of EBL and H₂O₂ in tomato plants grown under Cu stress (10 or 100 mg kg^-1 soil) were assessed. Roots of 20 d old plants were submerged in 0.1 mM of H₂O₂ solution for 4 h and subsequently transplanted in the soil-filled earthen pots and at 30 day after transplantation (DAT), the plants were sprinkled with deionized water (control), and/or 10^-8 M EBL and plant performances were evaluated at 40 DAT. High Cu (100 mg kg^-1 soil) concentration considerably reduced photosynthetic efficacy, cell viability, and plant growth, and deformed chloroplast ultrastructure and root morphology with altered stomatal behavior, but boosted the activity of antioxidant enzymes, proline content and electrolyte leakage in the leaves of tomato. Moreover, EBL and H₂O₂ implemented through distinct modes improved photosynthetic efficiency, modified chloroplast ultrastructure, stomatal behavior, root structure, cell viability and production of antioxidants and proline (osmolyte) that augmented resilience of tomato plants to Cu stress. This study revealed the potential of EBL and H₂O₂ applied through distinct mode could serve as an effective strategy to reduce Cu-toxicity in tomato crop.

The regulatory framework of developmentally programmed cell death in floral organs: A review

Developmentally programmed cell death (dPCD) is a tightly controlled biological process. In recent years, vital roles of dPCD on regulating floral organ growth and development have been reported. It is well known that flower is an essential organ for reproduction and a turning point of plants' life cycle. Hence, uncovering the complex molecular networks which regulates dPCD processes in floral organs is utmost important. So far, our understanding of dPCD on floral organ growth and development is just starting. Herein, we summarize the important factors that involved in the tapetal degeneration, pollen tube rupture, receptive synergid cell death, nucellar degradation, and antipodal cell degradation. Meanwhile, the known factors that involved in transmitting tract formation and self-incompatibility-induced PCD were also introduced. Furthermore, the genes that associated with anther dehiscence and petal senescence and abscission were reviewed as well. The functions of various types of factors involved in floral dPCD processes are highlighted principally. The regulatory panorama described here can provide us some insights about flower-specific dPCD process.

Lipid Peroxide-Derived Reactive Carbonyl Species as Mediators of Oxidative Stress and Signaling

Oxidation of membrane lipids by reactive oxygen species (ROS) or O₂/lipoxygenase leads to the formation of various bioactive compounds collectively called oxylipins. Reactive carbonyl species (RCS) are a group of oxylipins that have the α,β-unsaturated carbonyl structure, including acrolein and 4-hydroxy-(E)-2-nonenal. RCS provides a missing link between ROS stimuli and cellular responses in plants via their electrophilic modification of proteins. The physiological significance of RCS in plants has been established based on the observations that the RCS-scavenging enzymes that are overexpressed in plants or the RCS-scavenging chemicals added to plants suppress the plants' responses to ROS, i.e., photoinhibition, aluminum-induced root damage, programmed cell death (PCD), senescence, abscisic acid-induced stomata closure, and auxin-induced lateral root formation. The functions of RCS are thus a key to ROS- and redox-signaling in plants. The chemical species involved in distinct RCS signaling/damaging phenomena were recently revealed, based on comprehensive carbonyl determinations. This review presents an overview of the current status of research regarding RCS signaling functions in plants and discusses present challenges for gaining a more complete understanding of the signaling mechanisms.

Salt-Induced Differences During the Gene Expression of Telomerase Enzyme in Sunflower

Background:

Salinity is one of the most important environmental stresses which reduces the nutrient uptake, growth and yield of crops including sunflower.

Objectives:

The aim of this study was evaluating the expression pattern of telomerase gene, TERT, in sunflower plants under salinity stress.

Materials and Methods:

Sunflower plants of both sensitive and resistant lines were grown in greenhouse and treated with different levels of NaCl (2, 5 and 8 dSm^-1). The expression pattern of TERT gene was evaluated at 8^th leaf stage 6, 12 and 24 hours post salt treatment using real time-PCR, since the effects of salt stress are eventually manifested in the leaves.

Results:

In both lines, salt-subjected plants showed reduced size and dried leaves, due to breakthrough of the growth. Compared to the control group, treated groups tended to indicate downregulated pattern of TERT gene expression.

Conclusions:

This study offers TERT as a new gene affected by salt stress when growth is arrested.

An Ascophyllum nodosum-Derived Biostimulant Protects Model and Crop Plants from Oxidative Stress

Abiotic stresses, which at the molecular level leads to oxidative damage, are major determinants of crop yield loss worldwide. Therefore, considerable efforts are directed towards developing strategies for their limitation and mitigation. Here the superoxide-inducing agent paraquat (PQ) was used to generate oxidative stress in the model species Arabidopsis thaliana and the crops tomato and pepper. Pre-treatment with the biostimulant SuperFifty (SF) effectively and universally suppressed PQ-induced leaf lesions, H₂O₂ build up, cell destruction and photosynthesis inhibition. To further investigate the stress responses and SF-induced protection at the molecular level, we investigated the metabolites by GC-MS metabolomics. PQ induced specific metabolic changes such as accumulation of free amino acids (AA) and stress metabolites. These changes were fully prevented by the SF pre-treatment. Moreover, the metabolic changes of the specific groups were tightly correlating with their phenotypic characteristics. Overall, this study presents physiological and metabolomics data which shows that SF protects against oxidative stress in all three plant species.

UVC light modulates vitamin C and phenolic biosynthesis in acerola fruit: role of increased mitochondria activity and ROS production

The effects of ultraviolet-C light (UVC) on vitamin C and phenolic compounds in acerola during postharvest storage were investigated in order to elucidate the mechanism inducing the antioxidant systems. The fruits, stored at 10 °C for 7 days after a hormetic UVC irradiation (two pulses of 0.3 J/cm²), showed significantly less degradation of vitamin C and phenolic compounds than the control without the UVC challenge. UVC activated the L-galactono-1,4-lactone dehydrogenase (GalDH), a key enzyme for vitamin C biosynthesis, and altered the composition of phenolic compounds, through phenolic biosynthesis, in acerola during postharvest storage. UVC also induced reactive oxygen species (ROS) productions at immediate (day 0) and late (day 7) times during postharvest storage through the mitochondrial electron transport chain and NADPH oxidase, respectively. Results suggest that UVC helps in the retention of vitamin C and phenolic content in acerola by altering ascorbic acid and phenolic metabolism through an increase in mitochondrial activity and a ROS-mediated mechanism. Data showed the beneficial effects of UVC on maintenance of nutraceutical quality in acerola during postharvest storage and supplied new insights into understanding the mechanism by which UVC irradiation enhance the antioxidant system in fruits.

Vacuolar processing enzyme translocates to the vacuole through the autophagy pathway to induce programmed cell death

The caspase-like vacuolar processing enzyme (VPE) is a key factor in programmed cell death (PCD) associated with plant stress responses. Growth medium lacking a carbon source and dark conditions caused punctate labeling of 35S::VPE1-GFP (StVPE1-GFP) in potato leaves. Under conditions of carbon starvation, VPE activity and PCD symptoms strongly increased in BY-2 cells, but to a much lesser extent in VPE-RNAi BY-2 cells. During extended exposure to carbon starvation, VPE expression and activity levels peaked, with a gradual increase in BY-2 cell death. Histological analysis of StVPE1-GFP in BY-2 cells showed that carbon starvation induces its translocation from the endoplasmic reticulum to the central vacuole through tonoplast engulfment. Exposure of BY-2 culture to the macroautophagy/autophagy inhibitor concanamycin A led to, along with an accumulation of autophagic bodies, accumulation of StVPE1-GFP in the cell vacuole. This accumulation did not occur in the presence of 3-methyladenine, an inhibitor of early-stage autophagy. BY-2 cells constitutively expressing RFP-StATG8IL, an autophagosome marker, showed colocalization with the StVPE1-GFP protein in the cytoplasm and vacuole. RNAi silencing of the core autophagy component ATG4 in BY-2 cells reduced VPE activity and cell death. These results are the first to suggest that VPE translocates to the cell vacuole through the autophagy pathway, leading to PCD.Abbreviations: ATG: autophagy related; CLP: caspase-like protease; HR: hypersensitive response; PCD: programmed cell death; St: Solanum tuberosum; VPE: vacuolar processing enzyme.

Cyclic AMP mediates heat stress response by the control of redox homeostasis and ubiquitin-proteasome system

Heat stress (HS), causing impairment in several physiological processes, is one of the most damaging environmental cues for plants. To counteract the harmful effects of high temperatures, plants activate complex signalling networks, indicated as HS response (HSR). Expression of heat shock proteins (HSPs) and adjustment of redox homeostasis are crucial events of HSR, required for thermotolerance. By pharmacological approaches, the involvement of cAMP in triggering plant HSR has been recently proposed. In this study, to investigate the role of cAMP in HSR signalling, tobacco BY-2 cells overexpressing the 'cAMP-sponge', a genetic tool that reduces intracellular cAMP levels, have been used. in vivo cAMP dampening increased HS susceptibility in a HSPs-independent way. The failure in cAMP elevation during HS caused a high accumulation of reactive oxygen species, due to increased levels of respiratory burst oxidase homolog D, decreased activities of catalase and ascorbate peroxidase, as well as down-accumulation of proteins involved in the control of redox homeostasis. In addition, cAMP deficiency impaired proteasome activity and prevented the accumulation of many proteins of ubiquitin-proteasome system (UPS). By a large-scale proteomic approach together with in silico analyses, these UPS proteins were identified in a specific cAMP-dependent network of HSR.

Remodeling of Root Growth Under Combined Arsenic and Hypoxia Stress Is Linked to Nutrient Deprivation

Root architecture responds to environmental stress. Stress-induced metabolic and nutritional changes affect the endogenous root development program. Transcriptional and translational changes realize the switch between stem cell proliferation and cell differentiation, lateral root or root hair formation and root functionality for stress acclimation. The current work explores the effects of stress combination of arsenic toxicity (As) and hypoxia (Hpx) on root development in Arabidopsis thaliana. As revealed previously, combined As and Hpx treatment leads to severe nutritional disorder evident from deregulation of root transcriptome and plant mineral contents. Both As and Hpx were identified to pose stress-specific constraints on root development that lead to unique root growth phenotype under their combination. Besides inhibition of root apical meristem (RAM) activity under all stresses, As induced lateral root growth while root hair density and lengths were strongly increased by Hpx and HpxAs-treatments. A dual stimulation of phosphate (Pi)-starvation response was observed for HpxAs-treated plant roots; however, the response under HpxAs aligned more with Hpx than As. Transcriptional evidence along with biochemical data suggests involvement of PHOSPHATE STARVATION RESPONSE 1; PHR1-dependent systemic signaling. Pi metabolism-related transcripts in close association with cellular iron homeostasis modulate root development under HpxAs. Early redox potential changes in meristematic cells, differential ROS accumulation in root hair zone cell layers and strong deregulation of NADPH oxidases, NADPH-dependent oxidoreductases and peroxidases signify a role of redox and ROS signaling in root architecture remodeling under HpxAs. Differential aquaporin expression suggests transmembrane ROS transport to regulate root hair induction and growth. Reorganization of energy metabolism through NO-dependent alternate oxidase, lactate fermentation, and phosphofructokinase seems crucial under HpxAs. TOR and SnRK-signaling network components were potentially involved in control of sustainable utilization of available energy reserves for root hair growth under combined stress as well as recovery on reaeration. Findings are discussed in context of combined stress-induced signaling in regulation of root development in contrast to As and Hpx alone.

Hydrogen sulfide negatively regulates cd-induced cell death in cucumber (Cucumis sativus L) root tip cells

BACKGROUND

Hydrogen sulfide (H₂S) is a gas signal molecule involved in regulating plants tolerance to heavy metals stress. In this study, we investigated the role of H₂S in cadmium-(Cd-) induced cell death of root tips of cucumber seedlings.

RESULTS

The results showed that the application of 200 μM Cd caused cell death, increased the content of reactive oxygen species (ROS), chromatin condensation, the release of Cytochrome c (Cyt c) from mitochondria and activated caspase-3-like protease. Pretreatment of seedlings with 100 μM sodium hydrogen sulfide (NaHS, a H₂S donor) effectively alleviated the growth inhibition and reduced cell death of root tips caused by Cd stress. Additionally, NaHS + Cd treatment could decrease the ROS level and enhanced antioxidant enzyme activity. Pretreatment with NaHS also inhibited the release of Cyt c from the mitochondria, the opening of the mitochondrial permeability transition pore (MPTP), and the activity of caspase-3-like protease in the root tips of cucumber seedling under Cd stress.

CONCLUSION

H₂S inhibited Cd-induced cell death in cucumber root tips by reducing ROS accumulation, activating the antioxidant system, inhibiting mitochondrial Cyt c release and reducing the opening of the MPTP. The results suggest that H₂S is a negative regulator of Cd-induced cell death in the root tips of cucumber seedling.

Reactive Oxygen Species and Abiotic Stress in Plants

Abiotic stresses cause plant growth inhibition, damage, and in the most severe cases, cell death, resulting in major crop yield losses worldwide. Many abiotic stresses lead also to oxidative stress. Recent genetic and genomics studies have revealed highly complex and integrated gene networks which are responsible for stress adaptation. Here we summarize the main findings of the papers published in the Special Issue “ROS and Abiotic Stress in Plants”, providing a global picture of the link between reactive oxygen species and various abiotic stresses such as acid toxicity, drought, heat, heavy metals, osmotic stress, oxidative stress, and salinity.

Programmed cell death (PCD) control in plants: New insights from the Arabidopsis thaliana deathosome

Programmed cell death (PCD) is a genetically controlled process that leads to cell suicide in both eukaryotic and prokaryotic organisms. In plants PCD occurs during development, defence response and when exposed to adverse conditions. PCD acts controlling the number of cells by eliminating damaged, old, or unnecessary cells to maintain cellular homeostasis. Unlike in animals, the knowledge about PCD in plants is limited. The molecular network that controls plant PCD is poorly understood. Here we present a review of the current mechanisms involved with the genetic control of PCD in plants. We also present an updated version of the AtLSD1 deathosome, which was previously proposed as a network controlling HR-mediated cell death in Arabidopsis thaliana. Finally, we discuss the unclear points and open questions related to the AtLSD1 deathosome.

Metabolic rearrangements in imbibed maize (Zea mays L) embryos in the presence of oxidative stressors

Cadmium (Cd) is a metal known to generate oxidative stress in plants and may be particularly harmful during germination. Herein, the growth and metabolic rearrangements of maize embryo axes subjected during the imbibition stage to Cd ions and other two well-known oxidative stressors, methyl viologen (MV) and hydrogen peroxide (H₂O₂), were assessed for 48 h. Similar decreases in embryo's length were detected for all stressed axes up to 48 h of imbibition. By this time, treated embryos revealed greater accumulation of reactive oxygen species (ROS) and increased levels of carbonylated and ubiquitinated proteins. The proteolytic activities were intensely enhanced in the treated axes, particularly at 48 h of imbibition, and several antioxidant enzymes were induced in most cases. NMR spectroscopy followed by principal component analysis (PCA) and hierarchical cluster analysis (HCA) showed that a large proportion of polar metabolites, mainly amino acids and organic acids, were decreased under stress conditions, while carbohydrates were increased at 48 h of imbibition, with significant increases in glucose and raffinose for treated embryos relatively to controls. We demonstrated that maize embryo axes were capable of shifting their metabolism to improve their antioxidant defense system, at the expense of their growth. Under these adverse conditions, proteolysis seems to play a key role by providing free amino acids needed for the de novo synthesis of defense-related proteins.

Transcriptional modulation of AREB-1 by CRISPRa improves plant physiological performance under severe water deficit

Plants are sessile organisms, which are vulnerable to environmental stresses. As such, plants have developed multiple molecular, physiological, and cellular mechanisms to cope with natural stressors. However, these environmental adversities, including drought, are sources of the main agribusiness problems since they interfere with plant growth and productivity. Particularly under water deprivation conditions, the abscisic acid-responsive element-binding protein AREB1/ABF2 plays an important role in drought stress response and physiological adaptation. In this investigation, we provide substantial confirmation for the role of AREB1/ABF2 in plant survival under severe water deficit using the CRISPR activation (CRISPRa) technique to enhance the AREB1 gene expression. In our strategy, the inactive nuclease dCas9 was fused with an Arabidopsis histone acetyltransferase 1, which improves gene expression by remodeling chromatin. The AREB1 overexpression promotes an improvement in the physiological performance of the transgenic homozygous plants under drought, which was associated with an increase in chlorophyll content, antioxidant enzyme activity, and soluble sugar accumulation, leading to lower reactive oxygen species accumulation. Finally, we found that the CRISPR-mediated up-regulation of AREB1 changes the abundance of several downstream ABA-inducible genes, allowing us to report that CRISPRa dCas9-HAT is a valuable biotechnological tool to improve drought stress tolerance through the positive regulation of AREB1.

Cell death resulted from loss of fumarylacetoacetate hydrolase in Arabidopsis is related to phytohormone jasmonate but not salicylic acid

Fumarylacetoacetate hydrolase (FAH) catalyzes the final step in Tyr degradation pathway essential to animals but not well understood in plants. Previously, we found that mutation of SSCD1 encoding Arabidopsis FAH causes cell death under short day, which uncovered an important role of Tyr degradation pathway in plants. Since phytohormones salicylic acid (SA) and jasmonate (JA) are involved in programmed cell death, in this study, we investigated whether sscd1 cell death is related to SA and JA, and found that (1) it is accompanied by up-regulation of JA- and SA-inducible genes as well as accumulation of JA but not SA; (2) it is repressed by breakdown of JA signaling but not SA signaling; (3) the up-regulation of reactive oxygen species marker genes in sscd1 is repressed by breakdown of JA signaling; (4) treatment of wild-type Arabidopsis with succinylacetone, an abnormal metabolite caused by loss of FAH, induces expression of JA-inducible genes whereas treatment with JA induces expression of some Tyr degradation genes with dependence of JA signaling. These results demonstrated that cell death resulted from loss of FAH in Arabidopsis is related to JA but not SA, and suggested that JA signaling positively regulates sscd1 cell death by up-regulating Tyr degradation.

Can Alternative Metabolic Pathways and Shunts Overcome Salinity Induced Inhibition of Central Carbon Metabolism in Crops?

The annual cost of lost crop production from exposure to salinity has major impacts on food security in all parts of the world. Salinity stress disturbs energy metabolism and knowledge of the impacts on critical processes controlling plant energy production is key to successfully breeding salt tolerant crops. To date, little progress has been achieved using classic breeding approaches to develop salt tolerance. The hope of some salinity researchers is that through a better understanding of the metabolic responses and adaptation to salinity exposure, new breeding targets can be suggested to help develop salt tolerant crops. Plants sense and react to salinity through a complex system of sensors, receptor systems, transporters, signal transducers, and gene expression regulators in order to control the uptake of salts and to induce tolerant metabolism that jointly leads to changes in growth rate and biomass production. During this response, there must be a balance between supply of energy from mitochondria and chloroplasts and energy demands for water and ion transport, growth, and osmotic adjustment. The photosynthetic response to salinity has been thoroughly researched and generally we see a sharp drop in photosynthesis after exposure to salinity. However, less attention has been given to the effect of salt stress on plant mitochondrial respiration and the metabolic processes that influence respiratory rate. A further complication is the wide range of respiratory responses that have been observed in different plant species, which have included major and minor increases, decreases, and no change in respiratory rate after salt exposure. In this review, we begin by considering physiological and biochemical impacts of salinity on major crop plants. We then summarize and consider recent advances that have characterized changes in abundance of metabolites that are involved in respiratory pathways and their alternative routes and shunts in terms of energy metabolism in crop plants. We will consider the diverse molecular responses of cellular plant metabolism during salinity exposure and suggest how these metabolic responses might aid in salinity tolerance. Finally, we will consider how this commonality and diversity should influence how future research of the salinity responses of crops plants should proceed.

Methyl jasmonate alleviates arsenic toxicity in rice

Methyl jasmonate improved yield of both rice varieties under arsenic toxicity by alleviating oxidative stress through increasing the activity of antioxidant enzymes and decreasing arsenic accumulation by modulating arsenic transporters. Human health and rice cultivation are threatened by arsenic (As) contamination. Methyl jasmonate (MJ), as a regulator of plant growth, plays an important role in response to environmental stresses. In the present study, the effects of MJ (0, 0.5 and 1 µM) on yield, biochemical and molecular traits of two rice varieties (T. hashemi and Fajr) under As treatments (0, 25 and 50 µM) were investigated. The results showed that As decreased chlorophyll content, chlorophyll fluorescence and biomass production; however, MJ improved photosynthetic pigments and plant growth. As also induced oxidative stress (H₂O₂ and MDA) in both rice varieties; however, MJ reduced the As-induced oxidative stress by regulating the activity of antioxidant enzymes and the ASA-GSH cycle. As treatment increased As accumulation in the roots and leaves, which is in line with the increased expression of Lsi1, Lsi2 and Lsi6 genes. However, MJ reduced As accumulation by decreasing the expression of Lsi1, Lsi2 and Lsi6. Fe translocation to leaves reduced under As treatments; while, MJ increased Fe accumulation in the leaves by increasing expression of FRDL1 and YSL2 transporters under As toxicity. As treatments, especially 50 μM, decreased yield and yield components of both rice varieties; however, MJ improved yield and yield components of both rice varieties. The findings of the present study indicate that MJ improved the growth and yield of both rice varieties under As toxicity by alleviating oxidative stress through increasing the activity of antioxidant enzymes and ASA-GSH cycle and decreasing As accumulation by modulating As transporters.

ROS Homeostasis in Abiotic Stress Tolerance in Plants

Climate change-induced abiotic stress results in crop yield and production losses. These stresses result in changes at the physiological and molecular level that affect the development and growth of the plant. Reactive oxygen species (ROS) is formed at high levels due to abiotic stress within different organelles, leading to cellular damage. Plants have evolved mechanisms to control the production and scavenging of ROS through enzymatic and non-enzymatic antioxidative processes. However, ROS has a dual function in abiotic stresses where, at high levels, they are toxic to cells while the same molecule can function as a signal transducer that activates a local and systemic plant defense response against stress. The effects, perception, signaling, and activation of ROS and their antioxidative responses are elaborated in this review. This review aims to provide a purview of processes involved in ROS homeostasis in plants and to identify genes that are triggered in response to abiotic-induced oxidative stress. This review articulates the importance of these genes and pathways in understanding the mechanism of resistance in plants and the importance of this information in breeding and genetically developing crops for resistance against abiotic stress in plants.

Crop Enhancement of Cucumber Plants under Heat Stress by Shungite Carbon

Heat stress negatively impacts plant growth and yield. The effects of carbon materials on plants in response to abiotic stress and antioxidant activity are poorly understood. In this study, we propose a new method for improving heat tolerance in cucumber (Cucumis sativus L.) using a natural carbon material, shungite, which can be easily mixed into any soil. We analyzed the phenotype and physiological changes in cucumber plants maintained at 35 °C or 40 °C for 1 week. Our results show that shungite-treated cucumber plants had a healthier phenotype, exhibiting dark green leaves, compared to the plants in the control soil group. Furthermore, in the shungite-treated plants, the monodehydroascorbate content (a marker of oxidative damage) of the leaf was 34% lower than that in the control group. In addition, scavengers against reactive oxygen species, such as superoxide dismutase, catalase, and peroxidase were significantly upregulated. These results indicate that the successive pre-treatment of soil with a low-cost natural carbon material can improve the tolerance of cucumber plants to heat stress, as well as improve the corresponding antioxidant activity.

Leaf isoprene and monoterpene emission distribution across hyperdominant tree genera in the Amazon basin

Tropical forests are acknowledged to be the largest global source of isoprene (C₅H₈) and monoterpenes (C₁₀H₁₆) emissions, with current synthesis studies suggesting few tropical species emit isoprenoids (20-38%) and do so with highly variable emission capacities, including within the same genera. This apparent lack of a clear phylogenetic thread has created difficulties both in linking isoprenoid function with evolution and for the development of accurate biosphere-atmosphere models. Here, we present a systematic emission study of "hyperdominant" tree species in the Amazon Basin. Across 162 individuals, distributed among 25 botanical families and 113 species, isoprenoid emissions were widespread among both early and late successional species (isoprene: 61.9% of the species; monoterpenes: 15.0%; both isoprene and monoterpenes: 9.7%). The hyperdominant species (69) across the top five most abundant genera, which make up about 50% of all individuals in the Basin, had a similar abundance of isoprenoid emitters (isoprene: 63.8%; monoterpenes: 17.4%; both 11.6%). Among the abundant genera, only Pouteria had a low frequency of isoprene emitting species (15.8% of 19 species). In contrast, Protium, Licania, Inga, and Eschweilera were rich in isoprene emitting species (83.3% of 12 species, 61.1% of 18 species, 100% of 8 species, and 100% of 12 species, respectively). Light response curves of individuals in each of the five genera showed light-dependent, photosynthesis-linked emission rates of isoprene and monoterpenes. Importantly, in every genus, we observed species with light-dependent isoprene emissions together with monoterpenes including β-ocimene. These observations support the emerging view of the evolution of isoprene synthases from β-ocimene synthases. Our results have important implications for understanding isoprenoid function-evolution relationships and the development of more accurate Earth System Models.

The LRXs-RALFs-FER module controls plant growth and salt stress responses by modulating multiple plant hormones

Salt stress is a major environmental factor limiting plant growth and productivity. We recently discovered an important new salt tolerance pathway, where the cell wall leucine-rich repeat extensins LRX3/4/5, the RAPID ALKALINIZATION FACTOR (RALF) peptides RALF22/23 and receptor-like kinase FERONIA (FER) function as a module to simultaneously regulate plant growth and salt stress tolerance. However, the intracellular signaling pathways that are regulated by the extracellular LRX3/4/5-RALF22/23-FER module to coordinate growth, cell wall integrity and salt stress responses are still unknown. Here, we report that the LRX3/4/5-RALF22/23-FER module negatively regulates the levels of jasmonic acid (JA), salicylic acid (SA) and abscisic acid (ABA). Blocking JA pathway rescues the dwarf phenotype of the lrx345 and fer-4 mutants, while disruption of ABA biosynthesis suppresses the salt-hypersensitivity of these mutants. Many salt stress-responsive genes display abnormal expression patterns in the lrx345 and fer-4 mutants, as well as in the wild type plants treated with epigallocatechin gallate (EGCG), an inhibitor of pectin methylesterases, suggesting cell wall integrity as a critical factor that determines the expression pattern of stress-responsive genes. Production of reactive oxygen species (ROS) is constitutively increased in the lrx345 and fer-4 mutants, and inhibition of ROS accumulation suppresses the salt-hypersensitivity of these mutants. Together, our work provides strong evidence that the LRX3/4/5-RALF22/23-FER module controls plant growth and salt stress responses by regulating hormonal homeostasis and ROS accumulation.

Ethylene: A Master Regulator of Salinity Stress Tolerance in Plants

Salinity stress is one of the major threats to agricultural productivity across the globe. Research in the past three decades, therefore, has focused on analyzing the effects of salinity stress on the plants. Evidence gathered over the years supports the role of ethylene as a key regulator of salinity stress tolerance in plants. This gaseous plant hormone regulates many vital cellular processes starting from seed germination to photosynthesis for maintaining the plants' growth and yield under salinity stress. Ethylene modulates salinity stress responses largely via maintaining the homeostasis of Na+/K+, nutrients, and reactive oxygen species (ROS) by inducing antioxidant defense in addition to elevating the assimilation of nitrates and sulfates. Moreover, a cross-talk of ethylene signaling with other phytohormones has also been observed, which collectively regulate the salinity stress responses in plants. The present review provides a comprehensive update on the prospects of ethylene signaling and its cross-talk with other phytohormones to regulate salinity stress tolerance in plants.

Effect of Arsenic Stress on Expression Pattern of a Rice Specific miR156j at Various Developmental Stages and Their Allied Co-expression Target Networks

In plants, arsenic (As) stress modulates metabolic cascades at various developmental stages by influencing the pattern of gene expressions mediated by small non-coding RNAs, especially Micro-RNAs, involved in the moderation of a myriad of cellular processes needed for plant adaptation upon oxidative stress. miR156j of miR156 gene family, involved mainly in the regulation of growth and development in plants. This study was designed to find out the role of arsenic toxicity on Osa-miR156j expression in all physiological growth stages. To better understand the functional role of Osa-miR156j in rice, we observed the expression in different developmental stages (seedlings, tillering and flowering) and various tissues of leaf, stem and root tissues (at 0, 24, 48, and 72 h) under 25 μM arsenite [As (III)] exposure. Additionally, using bioinformatic tools to target genes of Osa-miR156j and the potential co-expressed genes were explored at different development stages in the various tissues of rice under stress conditions. The expression of Osa-miR156j showed its temporal downregulation in various tissues in different developmental stages. Of note, the downregulation was more pronounced in root tissues at seedlings, tillering, and flowering stages during 0-72 h under arsenite exposure as compared to other tissues. Overall, the As stress altered the gene expression more prominently at seedlings developmental stage followed by flowering and tillering. Additionally, through the In silico approach, the target functions and presence of oxidative stress-responsive cis-acting regulatory elements/motifs also confirmed Osa-miR156j involvement in the regulation of arsenic stress in rice. The findings of this study demonstrate the prominent role of Osa-miR156j in rice under arsenite stress, which was found to modulate the metabolic activities in rice plants at different developmental stages, and thus it might be useful for the development of arsenic tolerant varieties.

The Mechanosensitive Ion Channel MSL10 Potentiates Responses to Cell Swelling in Arabidopsis Seedlings

The ability to respond to unanticipated increases in volume is a fundamental property of cells, essential for cellular integrity in the face of osmotic challenges. Plants must manage cell swelling during flooding, rehydration, and pathogen invasion-but little is known about the mechanisms by which this occurs. It has been proposed that plant cells could sense and respond to cell swelling through the action of mechanosensitive ion channels. Here, we characterize a new assay to study the effects of cell swelling on Arabidopsis thaliana seedlings and to test the contributions of the mechanosensitive ion channel MscS-like10 (MSL10). The assay incorporates both cell wall softening and hypo-osmotic treatment to induce cell swelling. We show that MSL10 is required for several previously demonstrated responses to hypo-osmotic shock, including a cytoplasmic calcium transient within the first few seconds, accumulation of ROS within the first 30 min, and increased transcript levels of mechano-inducible genes within 60 min. We also show that cell swelling induces programmed cell death within 3 h in a MSL10-dependent manner. Finally, we show that MSL10 is unable to potentiate cell swelling-induced death when phosphomimetic residues are introduced into its soluble N terminus. Thus, MSL10 functions as a phospho-regulated membrane-based sensor that connects the perception of cell swelling to a downstream signaling cascade and programmed cell death.

Proteome and transcriptome reveal the involvement of heat shock proteins and antioxidant system in thermotolerance of Clematis florida

Clematis florida Thun (CfT) is an ornamental and medicinal plant. It is a cold resistant but heat sensitive species and deserves to be further investigated to improve its adaptability to heat stress. Exploring the molecular mechanism potential via an omic-analysis constitutes a promising approach towards improving heat tolerance of CfT. Two CfT lines, heat resistance (HR) and heat sensitive (HS), with differential thermotolerance capacities were used for the integrative analyses of proteomics and transcriptomes. Transcriptomes analysis showed that various pathways were significantly enriched including plant hormone signal transduction and carbon fixation pathways in prokaryotes. Proteomics study revealed the enrichment of some other pathways comprising antioxidant activity and carbohydrates metabolism. Based on combined transcriptomes and proteomics analyses and following heat stress treatment, a total of 1724 annotated genes were overlapped between both CfT lines. Particularly, 84 differential expressed genes (DEGs) were overlapped in both CfT lines. Fifteen out of these 84 genes were up-regulated solely for HR line (PS) but not for HS one (SG). This strongly suggests a potential prominent role for these genes in the thermotolerance process in PS line. We corroborate that two Hsps (Hsp18 and Hsp70) out of 20 detected proteins with higher expression levels in PS than in SG based on either global transcripts or proteins levels. According to the transcriptomes and proteomics analyses, 6 proteins and their corresponding genes were found to be significantly abundant in HR line (PS). Data are available via ProteomeXchange with identifier PXD018192. The expressions levels of these 6 genes were checked also for both CfT lines to evaluate their potential contributions in the heat tolerance process. Thus, their expression levels were approximately 2~4 times higher in HR than in HS line. We provided as well a representative schematic model to highlight the key genes involved in ROS scavenging and photorespiratory pathway in CfT. This model could be helpful also in understanding the mechanism of heat tolerance in CfT.

The leaf extract of crofton weed (Eupatorium adenophorum) inhibits primary root growth by inducing cell death in maize root border cells

The extract of crofton weed (Eupatorium adenophorum) inhibits seed germination and weed growth; however, the physiological mechanisms underlying the effect of crofton weed extract on the modulation of seedling growth and root system development remain largely unclear. In this study, we investigated the effects of the leaf extract of crofton weed (LECW) on primary root (PR) growth in maize seedlings. Treatment with LECW markedly inhibited seed germination and seedling growth in a dose-dependent manner. Physiological analysis indicated that the LECW induced reactive oxygen species (ROS) accumulation in root tips, thereby leading to cell swelling and deformation both in the root cap and elongation zone of root tips, finally leading to cell death in root border cells (RBCs) and PR growth inhibition. The LECW also inhibited pectin methyl esterase (PME) activity, thereby decreasing the RBC number. Taken together, our results indicated that the LECW inhibited PR growth by inducing ROS accumulation and subsequent cell death in RBCs. The present study provides a better understanding of how the LECW modifies root system development and provides insight for evaluating the toxicity of crofton weed extracts in plants.

Gene expression and metabolic changes of Momordica charantia L. seedlings in response to low temperature stress

Low temperature is one of the abiotic factors limiting germination, growth and distribution of the plant in current plant-products industry, especially for the tropical vegetables in non-tropical area or other fields under cold temperature. Screening the plant with ability against cold temperature captured worldwide attention and exerted great importance. In our previous work, the anti-cold specie of Momordica Charantia L. seedlings was screened out. Yet, the molecular and physiological mechanisms underlying this adaptive process still remain unknown. This study was aimed to investigate adaption mechanism of anti-cold species of Momordica Charantia L. seedlings in genetical and metabolomics levels. Two species, cold-susceptible group (Y17) and cold-resistant group (Y54), were evaluated containing the indexes of malondialdehyde (MDA), hydrogen peroxide (H2O2), proline content, activities of antioxidant enzymes, metabolites changes and genes differentiation in plant tissues after cold treatment. It found that low temperature stress resulted in increased accumulation of MDA, H2O2 and proline content in two species, but less expressions in cold-resistant species Y54. As compared to Y17, cold-resistant species Y54 presented significantly enhanced antioxidant enzyme activities of POD (peroxidase), CAT (cataalase) and SOD (superoxide dismutase). Meanwhile, higher expressed genes encoded antioxidant enzymes and transcription factors when exposure to the low temperature were found in cold-resistant species Y54, and core genes were explored by Q-PCR validation, including McSOD1, McPDC1 and McCHS1. Moreover, plant metabolites containing amino acid, sugar, fatty acid and organic acid in Y54 were higher than Y17, indicating their important roles in cold acclimation. Meanwhile, initial metabolites, including amimo acids, polypeptides, sugars, organic acids and nucleobases, were apparently increased in cold resistant species Y54 than cold susceptible species Y17. Our results demonstrated that the Momordica Charantia L. seedlings achieved cold tolerance might be went through mobilization of antioxidant systems, adjustment of the transcription factors and accumulation of osmoregulation substance. This work presented meaning information for revealing the anti-cold mechanism of the Momordica Charantia L. seedlings and newsight for further screening of anti-cold species in other plant.

Role of Glycine max in improving drought tolerance in Zanthoxylum bungeanum

Intercropping may improve community stability and yield under climate change. Here, we set up a field experiment to evaluate the advantages of cultivating Z anthoxylum bungeanum with Capsicum annum, and Z. bungeanum with Glycine max as intercrops, compared with cultivating Z. bungeanum in monoculture. Effects of extreme drought stress conditions on morphological, physiological, and biochemical traits of the three crop species cultivated in the three contrasting planting systems were compared. Results showed that extreme drought conditions induced negative impacts on Z. bungeanum grown in monoculture, due to reduced growth and metabolic impairment. However, limited stomatal conductance, reduced transpiration rate (T_r), and increased water use efficiency, carotenoid content, catalase activity, and accumulation of soluble sugars in Z. bungeanum indicated its adaptive strategies for tolerance of extreme drought stress conditions. Compared with cultivation in monoculture, intercropping with C. annum had positive effects on Z. bungeanum under extreme drought stress conditions, as a result of improved crown diameter, leaf relative water content (LRWC), net photosynthetic rate, and proline content, while intercropping with G. max under extreme drought stress conditions increased net CO₂ assimilation rates, LRWC, T_r, and superoxide dismutase (SOD) activity. In conclusion, Z. bungeanum has an effective defense mechanism for extreme drought stress tolerance. Intercropping with G. max enhanced this tolerance potential primarily through its physio-biochemical adjustments, rather than as a result of nitrogen fixation by G. max.

Internal aeration and respiration of submerged tomato hypocotyls are enhanced by ethylene-mediated aerenchyma formation and hypertrophy

With the impending threat that climate change is imposing on all terrestrial ecosystems, the ability of plants to adjust to changing environments is, more than ever, a very desirable trait. Tomato (Solanum lycopersicum L.) plants display a number of responses that allow them to survive under different abiotic stresses such as flooding. We focused on understanding the mechanism that facilitates oxygen diffusion to submerged tissues and the impact it has on sustaining respiration levels. We observed that, as flooding stress progresses, stems increase their diameter and internal porosity. Ethylene triggers stem hypertrophy by inducing cell wall loosening genes, and aerenchyma formation seems to involve programmed cell death mediated by hydrogen peroxide. We finally assessed whether these changes in stem morphology and anatomy are indeed effective to restore oxygen levels in submerged organs. We found that aerenchyma formation and hypertrophy not only increase oxygen diffusion toward the base of the plant, but also result in an augmented respiration rate. We consider that this response is crucial to maintain adventitious root development under such conditions and, therefore, making it possible for the plant to survive when the original roots die.

Overexpression of wheat α-mannosidase gene TaMP impairs salt tolerance in transgenic Brachypodium distachyon

The TaMP gene from wheat encodes an α-mannosidase induced by salt stress that functions as negative regulator of salt tolerance in plants. Salt stress significantly affects growth and yield of crop plants. The α-mannosidases function in protein folding, trafficking, and endoplasmic reticulum-associated degradation in eukaryotic cells, and they are involved in abiotic stress tolerance in plants. Previously, we identified the α-mannosidase gene TaMP in wheat (Triticum aestivum). In this study, we investigated the function of TaMP in salt stress tolerance. TaMP expression was induced in wheat leaves by salt, drought, abscisic acid, and H₂O₂ treatments. Overexpressing TaMP in Brachypodium distachyon was associated with a salt-sensitive phenotype. Under salt stress, the overexpressing plants had reduced height, delayed growth status, low photosynthetic rate, decreased survival rate, and diminished yield. Moreover, the overexpression of TaMP aggravated the tendency for ions to become toxic under salt stress by significantly affecting the Na⁺ and K⁺ contents in cells. In addition, TaMP could negatively regulate salt tolerance by affecting the antioxidant enzyme system capacity and increasing the reactive oxygen species accumulation. Our study was helpful to understand the underlying physiological and molecular mechanisms of salt stress tolerance in plants.