Methylglyoxal: An Emerging Signaling Molecule in Plant Abiotic Stress Responses and Tolerance

A Metabolic Profiling Analysis Revealed a Primary Metabolism Reprogramming in Arabidopsis glyI4 Loss-of-Function Mutant

Methylglyoxal (MG) is a cytotoxic compound often produced as a side product of metabolic processes such as glycolysis, lipid peroxidation, and photosynthesis. MG is mainly scavenged by the glyoxalase system, a two-step pathway, in which the coordinate activity of GLYI and GLYII transforms it into D-lactate, releasing GSH. In Arabidopsis thaliana, a member of the GLYI family named GLYI4 has been recently characterized. In glyI4 mutant plants, a general stress phenotype characterized by compromised MG scavenging, accumulation of reactive oxygen species (ROS), stomatal closure, and reduced fitness was observed. In order to shed some light on the impact of gly4 loss-of-function on plant metabolism, we applied a high resolution mass spectrometry-based metabolomic approach to Arabidopsis Col-8 wild type and glyI4 mutant plants. A compound library containing a total of 70 metabolites, differentially synthesized in glyI4 compared to Col-8, was obtained. Pathway analysis of the identified compounds showed that the upregulated pathways are mainly involved in redox reactions and cellular energy maintenance, and those downregulated in plant defense and growth. These results improved our understanding of the impacts of glyI4 loss-of-function on the general reprogramming of the plant's metabolic landscape as a strategy for surviving under adverse physiological conditions.

The antioxidant defense and glyoxalase systems contribute to the thermotolerance of Heliotropium thermophilum

This study focused on the impact of the antioxidant defence and glyoxalase systems on extreme heat tolerance of the thermophilic plant Heliotropium thermophilum L. For this purpose, plants were exposed to 20, 40, 60 and 80±5°C soil temperature gradually for 15days under laboratory conditions. Our results showed that the hydrogen peroxide and superoxide levels of H. thermophilum were lower at 40±5°C and higher at 80±5°C compared with plants grown at 20±5°C. Some antioxidant enzyme activities tended to increase in plants at 40, 60 and 80±5°C compared with those at 20±5°C and the protein contents responsible for the antioxidant enzymes were in parallel with these enzyme activities. The contents of both reduced and oxidised ascorbate and glutathione rose with increasing temperature. Methylglyoxal level was lower at 40±5°C and higher at 80±5°C compared with plants grown at 20±5°C. Glyoxalase activities highly increased with rising of soil temperature from 20±5°C to 80±5°C. The results of this study suggest that differential modulations of enzymatic antioxidants and the increase in non-enzymatic antioxidants and glyoxalase activities can contribute to the development of the thermotolerance of H. thermophilum through the detoxification of reactive oxygen species and methylglyoxal.

What signals the glyoxalase pathway in plants?

Glyoxalase (GLY) system, comprising of GLYI and GLYII enzymes, has emerged as one of the primary methylglyoxal (MG) detoxification pathways with an indispensable role during abiotic and biotic stresses. MG homeostasis is indeed very closely guarded by the cell as its higher levels are cytotoxic for the organism. The dynamic responsiveness of MG-metabolizing GLY pathway to both endogenous cues such as, phytohormones, nutrient status, etc., as well as external environmental fluctuations (abiotic and biotic stresses) indicates that a tight regulation occurs in the cell to maintain physiological levels of MG in the system. Interestingly, GLY pathway is also manipulated by its substrates and reaction products. Hence, an investigation of signalling and regulatory aspects of GLY pathway would be worthwhile. Herein, we have attempted to converge all known factors acting as signals or directly regulating GLYI/II enzymes in plants. Further, we also discuss how crosstalk between these different signal molecules might facilitate the regulation of glyoxalase pathway. We believe that MG detoxification is controlled by intricate mechanisms involving a plethora of signal molecules.

Glutathione Metabolism in Plants under Stress: Beyond Reactive Oxygen Species Detoxification

Glutathione is an essential metabolite for plant life best known for its role in the control of reactive oxygen species (ROS). Glutathione is also involved in the detoxification of methylglyoxal (MG) which, much like ROS, is produced at low levels by aerobic metabolism under normal conditions. While several physiological processes depend on ROS and MG, a variety of stresses can dramatically increase their concentration leading to potentially deleterious effects. In this review, we examine the structure and the stress regulation of the pathways involved in glutathione synthesis and degradation. We provide a synthesis of the current knowledge on the glutathione-dependent glyoxalase pathway responsible for MG detoxification. We present recent developments on the organization of the glyoxalase pathway in which alternative splicing generate a number of isoforms targeted to various subcellular compartments. Stress regulation of enzymes involved in MG detoxification occurs at multiple levels. A growing number of studies show that oxidative stress promotes the covalent modification of proteins by glutathione. This post-translational modification is called S-glutathionylation. It affects the function of several target proteins and is relevant to stress adaptation. We address this regulatory function in an analysis of the enzymes and pathways targeted by S-glutathionylation.

Silicon assisted ameliorative effects of iron nanoparticles against cadmium stress: Attaining new equilibrium among physiochemical parameters, antioxidative machinery, and osmoregulators of Phaseolus lunatus

Currently, producing safe agricultural commodities from the crop plants cultivated in the soil with increasing heavy metal toxicity is a gigantic challenge in front of researchers. Heavy metals are absorbed and translocated in the crop plants and then transferred to every downstream consumer of the food chain, including humans, causing serious disorders and ailments. The current research presents a combined schematic application of iron nanoparticles (Fe-NPs) and/or silicon (Si), to mitigate cadmium (Cd) stress in Lima bean (Phaseolus lunatus). It was noted that Cd-induced toxicity curtailed growth, antioxidative machinery, glyoxalase system and nutrient uptake of the plants. Furthermore, the physiochemical features of Cd stressed plants, including carotenoids, chlorophyll, photochemical quenching, photosynthetic efficiency, and leaf relative water contents, were improved by the combined application of Si and Fe-NPs. Moreover, higher levels of malondialdehyde (MDA), methylglyoxal (MG), hydrogen peroxide (H₂O₂), and electrolyte leakage (EL) were observed in Cd stressed plants. Nevertheless, the independent treatment or combined application of Si and/or Fe-NPs attenuated the adversative effects of Cd on the aforementioned growth attributes. Furthermore, Si and Fe-NPs defended plants from the injurious effects of MG by improving the activities of the glyoxalase enzyme. The Si and Fe-NPs reduced Cd contents but at the same time improved uptake and accumulation of nutrients in treated plants exposed to the Cd regime. This study highlights that Si and Fe-NPs have enormous potential to mitigate Cd-induced phytotoxicity by declining Cd uptake and improving the growth attributes of plants if applied in combination.

Functional characterization and expression profiling of glyoxalase III genes in date palm grown under abiotic stresses

Methylglyoxal (MG), a by-product of various metabolic processes, including glycolysis, is a highly reactive cytotoxic metabolite. The level of MG in the cell is maintained at a non-toxic level via MG detoxification pathways such as the universal glyoxalase system, including glyoxalase I/II/III enzymes. Glyoxalase III (DJ-1) can breakdown MG to d-lactate in a single step without reducing glutathione (GSH). Elucidating the function of the DJ-1 gene family may provide further knowledge about its role in plants under abiotic stresses. Here, we characterize four glyoxalase III genes (PdDJ-1B1, PdDJ-1B2, PdDJ-1C, and PdDJ-1D) encoding the conserved DJ-1 domain in the genome of the date palm, a crop with high drought and salinity tolerance. The expression level of the PdDJ-1 genes increased in date palm leaves upon salinity treatment. In addition, overexpression of PdDJ-1 genes in Escherichia coli and the complementation in yeast hsp31Δ knockout mutant cells enhanced their growth rate and reduced the accumulation of reactive oxygen species (ROS) under MG and oxidative stress conditions as shown by the flow cytometry assay. Subcellular localization using confocal microscopy revealed the accumulation of PdDJ-1B1, PdDJ-1C, and PdDJ-1D in the chloroplast, whereas PdDJ-1B2 was localized to the cytosol. Remarkably, constitutive expression of the PdDJ-1C gene in Arabidopsis thaliana Columbia (Col-0) resulted in the generation of non-viable albino plants implying that PdDJ-1C plays a critical function in chloroplast development. These findings suggest that PdDJ-1 protein has an important function in MG-detoxification and maintaining the redox balance in date palm plants under abiotic stress conditions.

Transcriptome Profile Analysis of Arabidopsis Reveals the Drought Stress-Induced Long Non-coding RNAs Associated With Photosynthesis, Chlorophyll Synthesis, Fatty Acid Synthesis and Degradation

Long non-coding RNAs (lncRNAs) play an important role in the response of plants to drought stress. The previous studies have reported that overexpression of LEA3 and VOC could enhance drought tolerance and improve the oil content in Brassica napus and Arabidopsis thaliana, and most of the efforts have been invested in the gene function analysis, there is little understanding of how genes that involved in these important pathways are regulated. In the present study, the transcriptomic results of LEA3 and VOC over-expressed (OE) lines were compared with the RNAi lines, mutant lines and control lines under long-term and short-term drought treatment, a series of differentially expressed lncRNAs were identified, and their regulation patterns in mRNA were also investigated in above mentioned materials. The regulation of the target genes of differentially expressed lncRNAs on plant biological functions was studied. It was revealed that the mutant lines had less drought-response related lncRNAs than that of the OE lines. Functional analysis demonstrated that multiple genes were involved in the carbon-fixing and chlorophyll metabolism, such as CDR1, CHLM, and CH1, were regulated by the upregulated lncRNA in OE lines. In LEA-OE, AT4G13180 that promotes the fatty acid synthesis was regulated by five lncRNAs that were upregulated under both long-term and short-term drought treatments. The key genes, including of SHM1, GOX2, and GS2, in the methylglyoxal synthesis pathway were all regulated by a number of down-regulated lncRNAs in OE lines, thereby reducing the content of such harmful compounds produced under stress in plants. This study identified a series of lncRNAs related to the pathways that affect photosynthesis, chlorophyll synthesis, fatty acid synthesis, degradation, and other important effects on drought resistance and oil content. The present study provided a series of lncRNAs for further improvement of crop varieties, especially drought resistant and oil content traits.

Exogenous Potassium (K+) Positively Regulates Na+/H+ Antiport System, Carbohydrate Metabolism, and Ascorbate-Glutathione Cycle in H2S-Dependent Manner in NaCl-Stressed Tomato Seedling Roots

Potassium (K⁺) is one of the vital macronutrients required by plants for proper growth and blossoming harvest. In addition, K⁺ also plays a decisive role in promoting tolerance to various stresses. Under stressful conditions, plants deploy their defense system through various signaling molecules, including hydrogen sulfide (H₂S). The present investigation was carried out to unravel the role of K⁺ and H₂S in plants under NaCl stress. The results of the study show that NaCl stress caused a reduction in K⁺ and an increase in Na⁺ content in the tomato seedling roots which coincided with a lower H⁺-ATPase activity and K⁺/Na⁺ ratio. However, application of 5 mM K⁺, in association with endogenous H₂S, positively regulated the Na⁺/H⁺ antiport system that accelerated K+ influx and Na+ efflux, resulting in the maintenance of a higher K⁺/Na⁺ ratio. The role of K⁺ and H₂S in the regulation of the Na⁺/H⁺ antiport system was validated by applying sodium orthovanadate (plasma membrane H⁺-ATPase inhibitor), tetraethylammonium chloride (K⁺ channel blocker), amiloride (Na⁺/H⁺ antiporter inhibitor), and hypotaurine (HT, H₂S scavenger). Application of 5 mM K⁺ positively regulated the ascorbate–glutathione cycle and activity of antioxidant enzymes that resulted in a reduction in reactive oxygen species generation and associated damage. Under NaCl stress, K⁺ also activated carbohydrate metabolism and proline accumulation that caused improvement in osmotic tolerance and enhanced the hydration level of the stressed seedlings. However, inclusion of the H₂S scavenger HT reversed the effect of K⁺, suggesting H₂S-dependent functioning of K⁺ under NaCl stress. Therefore, the present findings report that K⁺, in association with H₂S, alleviates NaCl-induced impairments by regulating the Na⁺/H⁺ antiport system, carbohydrate metabolism, and antioxidative defense system.

Nitric oxide effectively curtails neck bending and mitigates senescence in isolated flowers of Calendula officinalis L

In recent years, there has been a considerable and renewed upsurge in research to ascertain the physiological and biochemical role of Nitric oxide (NO) in plants. The present investigation is focused to study the role of NO on neck bending associated with senescence and postharvest performance in isolated flowers of Calendula officinalis. The flower buds harvested at one day before anthesis stage were supplied with sodium nitroprusside (SNP) as a source of NO at different concentrations viz., 50, 100, 150 and 200 µM. A distinct set of flowers held in distilled water designated the control. The investigation revealed that SNP delayed the senescence in flowers of C. officinalis significantly manifested by prolonged longevity. The maximum longevity of 12 days was recorded in flowers supplemented with 100 µM SNP. The flowers held in distilled water (control) displayed early senescence symptoms and lasted for 6 days only. Our research suggested that improved flower longevity by SNP was commensurate with delayed neck bending, inhibition of bacterial growth in the vase, increased solution uptake, high membrane stability, besides an up-regulated activities of antioxidant enzymes in the tissue samples. In addition, the treated flowers exhibited increased content of  sugar fractions, total phenols and soluble proteins in the petal tissues compared to control. Further, 100 µM SNP was observed as most effective treatment and increased the longevity of flowers by 6 days. The concentration above 150 µM provoked early senescence compared to control, whereas concentration lower than 100 µM was less efficacious in improving the postharvest life and longevity of cut Calendula flowers.

Exogenous 3,3'-Diindolylmethane Improves Vanadium Stress Tolerance in Brassica napus Seedling Shoots by Modulating Antioxidant Enzyme Activities

3,3′-diindolylmethane (DIM) belongs to a family of indole glucosinolate compounds that have been shown to improve Brassica napus growth through the modulation of reactive oxygen species when applied exogenously. The B. napus cultivar AV Garnet was previously identified as a vanadium-sensitive cultivar. Therefore, in this study we investigated whether exogenous DIM could improve the vanadium tolerance of AV Garnet. We performed the following experiments: seed germination assessment, dry weight assessment, cell viability assay, chlorophyll content assay, malondialdehyde (MDA) assay, conjugated diene (CD) content assay, hydrogen peroxide (H₂O₂) content assay, superoxide (O₂⁻) content determination, methylglyoxal (MG) content determination, hydroxyl radical (·OH) concentration determination, ascorbate peroxidase (APX) activity assay, superoxide dismutase (SOD) activity assay, glyoxalase I (Gly I) activity assay, glutathione S-transferase (GST) activity assay and inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis for vanadium content determination. Under vanadium stress, exogenous DIM increased the seed germination percentage, shoot dry weight, cell viability and chlorophyll content. Exogenous DIM also led to a decrease in MDA, CD, H₂O₂, O₂⁻, MG and ·OH, under vanadium stress in the shoots. Furthermore, DIM application led to an increase in the enzymatic activities of APX, SOD, Gly I and GST under vanadium stress. Interestingly, under vanadium stress, DIM treatment did not alter vanadium content in B. napus shoots. Our results indicate that exogenous application of DIM can improve B. napus seedling shoot growth and biomass under vanadium stress by priming the antioxidant enzymes via reactive oxygen species (ROS) signaling.

The metabolite methylglyoxal-mediated gene expression is associated with histone methylglyoxalation

Methylglyoxal (MG) is a byproduct of glycolysis that functions in diverse mammalian developmental processes and diseases and in plant responses to various stresses, including salt stress. However, it is unknown whether MG-regulated gene expression is associated with an epigenetic modification. Here we report that MG methylglyoxalates H3 including H3K4 and increases chromatin accessibility, consistent with the result that H3 methylglyoxalation positively correlates with gene expression. Salt stress also increases H3 methylglyoxalation at salt stress responsive genes correlated to their higher expression. Following exposure to salt stress, salt stress responsive genes were expressed at higher levels in the Arabidopsis glyI2 mutant than in wild-type plants, but at lower levels in 35S::GLYI2 35S::GLYII4 plants, consistent with the higher and lower MG accumulation and H3 methylglyoxalation of target genes in glyI2 and 35S::GLYI2 35S::GLYII4, respectively. Further, ABI3 and MYC2, regulators of salt stress responsive genes, affect the distribution of H3 methylglyoxalation at salt stress responsive genes. Thus, MG functions as a histone-modifying group associated with gene expression that links glucose metabolism and epigenetic regulation.

Calcium-hydrogen sulfide crosstalk during K+-deficient NaCl stress operates through regulation of Na+/H+ antiport and antioxidative defense system in mung bean roots

Present investigation reports the role of calcium (Ca²⁺) and hydrogen sulfide (H₂S) crosstalk associated with Vigna radiata seedlings subjected to K⁺ deficient conditions under short-term (24 h) and long-term (72 h) NaCl stress. Perusal of the data reveals that under short-term NaCl stress an initial decline in K⁺ level led to the elevation in Ca²⁺ and H₂S levels along with improvement in antioxidant system and reduction in reactive oxygen species (ROS) production. Under long-term NaCl stress a further decline in K⁺ content was deleterious that led to a lower K⁺/Na⁺ ratio. This was followed by reduction in antioxidant system along with excessive accumulation of ROS and methylglyoxal content, and increased membrane damage. However, supplementation of the seedling roots with Ca²⁺ enhanced biosynthesis of H₂S through enhancing cysteine pool. The present findings suggest that synergistic action of Ca²⁺ and H₂S induced the activity of H⁺-ATPase that created H⁺ gradient which in turn induced Na⁺/H⁺ antiport system that accelerated K⁺ influx and Na⁺ efflux. All of these together contributed to a higher K⁺/Na⁺ ratio, activation of antioxidative defense system, and maintenance of redox homeostasis and membrane integrity in Ca²⁺-supplemented stressed seedlings. Role of Ca²⁺ and H₂S in the regulation of Na⁺/H⁺ antiport system was validated by the use of sodium orthovanadate (plasma membrane H⁺-ATPase inhibitor), tetraethylammonium chloride (K⁺ channel blocker), and amiloride (Na⁺/H⁺ antiporter inhibitor). Application of Ca²⁺-chelator EGTA (ethylene glycol-bis(b-aminoethylether)-N,N,N',N'-tetraacetic acid) and H₂S scavenger hypotaurine abolished the effect of Ca²⁺, suggesting the involvement of Ca²⁺ and H₂S in the alleviation of NaCl stress. Moreover, use of EGTA and HT also substantiates the downstream functioning of H₂S during Ca²⁺-mediated regulation of plant adaptive responses to NaCl stress. To sum up, present findings reveal the association of Ca²⁺ and H₂S signaling in the regulation of ion homeostasis and antioxidant defense during K⁺-deficient NaCl stress.

Hydrogen sulfide mitigates cadmium induced toxicity in Brassica rapa by modulating physiochemical attributes, osmolyte metabolism and antioxidative machinery

Hydrogen sulfide (H₂S) is helpful for maintaining plant growth under abiotic stresses. The current study elucidated the physiological and biochemical strategies by which sodium hydrosulfide (NaHS), a donor of H₂S, alleviated cadmium (Cd) toxicity in Brassica rapa. B. rapa plants growing under 50 mgkg^-1 Cd stress showed reduced leaf relative water contents (LRWC), photosynthetic pigments, total soluble proteins, minerals uptake, antioxidants and growth. Furthermore, enhanced accumulation of Cd contents caused augmentation in levels of electrolyte leakage (EL) and methylglyoxal (MG). Nevertheless, improved physiochemical parameters in B. rapa seedlings obtained from seeds primed with 1.5 mM NaHS resulted better phenotype, growth and biomass production in Cd stressed plants. Protective stimulus of H₂S regulated minerals and Cd homeostasis besides increased activity of antioxidants which decreased level of reactive oxygen species (ROS), EL, malondialdehyde (MDA) and MG in Cd regimes. Furthermore, H₂S treated seedlings exhibited reduction in Cd content and revealed an active participation in the indole acetic acid (IAA) mediated pathway during stress. The findings of current study propose that H₂S improved stress tolerance and mitigated Cd stress in B. rapa by modulating growth biomarkers and antioxidative system.

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.

Interplay among Oxidative Stress, Methylglyoxal Pathway and S-Glutathionylation

Reactive oxygen species (ROS) are produced constantly inside the cells as a consequence of nutrient catabolism. The balance between ROS production and elimination allows to maintain cell redox homeostasis and biological functions, avoiding the occurrence of oxidative distress causing irreversible oxidative damages. A fundamental player in this fine balance is reduced glutathione (GSH), required for the scavenging of ROS as well as of the reactive 2-oxoaldehydes methylglyoxal (MGO). MGO is a cytotoxic compound formed constitutively as byproduct of nutrient catabolism, and in particular of glycolysis, detoxified in a GSH-dependent manner by the glyoxalase pathway consisting in glyoxalase I and glyoxalase II reactions. A physiological increase in ROS production (oxidative eustress, OxeS) is promptly signaled by the decrease of cellular GSH/GSSG ratio which can induce the reversible S-glutathionylation of key proteins aimed at restoring the redox balance. An increase in MGO level also occurs under oxidative stress (OxS) conditions probably due to several events among which the decrease in GSH level and/or the bottleneck of glycolysis caused by the reversible S-glutathionylation and inhibition of glyceraldehyde-3-phosphate dehydrogenase. In the present review, it is shown how MGO can play a role as a stress signaling molecule in response to OxeS, contributing to the coordination of cell metabolism with gene expression by the glycation of specific proteins. Moreover, it is highlighted how the products of MGO metabolism, S-D-lactoylglutathione (SLG) and D-lactate, which can be taken up and metabolized by mitochondria, could play important roles in cell response to OxS, contributing to cytosol-mitochondria crosstalk, cytosolic and mitochondrial GSH pools, energy production, and the restoration of the GSH/GSSG ratio. The role for SLG and glyoxalase II in the regulation of protein function through S-glutathionylation under OxS conditions is also discussed. Overall, the data reported here stress the need for further studies aimed at understanding what role the evolutionary-conserved MGO formation and metabolism can play in cell signaling and response to OxS conditions, the aberration of which may importantly contribute to the pathogenesis of diseases associated to elevated OxS.

Mechanistic Insight of Allantoin in Protecting Tomato Plants Against Ultraviolet C Stress

Allantoin ((AT) a purine metabolite)-mediated ultraviolet C (UVC) stress mitigation has not been studied to date. Here, we reported the physicochemical mechanisms of UVC-induced stress in tomato (Solanum lycopersicum L.) plants, including an AT-directed mitigation strategy. UVC stress reduced plant growth and photosynthetic pigments. Heatmap and principal component analysis (PCA) revealed that these toxic impacts were triggered by the greater oxidative damage and disruption of osmolyte homeostasis. However, pre-treatment of AT noticeably ameliorated the stress-induced toxicity as evident by enhanced chlorophyll, soluble protein, and soluble carbohydrate contents in AT-pretreated UVC-stressed plants relative to only stressed plants leading to the improvement of the plant growth and biomass. Moreover, AT pre-treatment enhanced endogenous AT and allantoate content, phenylalanine ammonia-lyase, non-enzymatic antioxidants, and the enzymatic antioxidants leading to reduced oxidative stress markers compared with only stressed plants, indicating the protective effect of AT against oxidative damage. Moreover, PCA displayed that the protective roles of AT strongly associate with the improved antioxidants. On the other hand, post-treatment of AT showed less efficacy in UVC stress mitigation relative to pre-treatment of AT. Overall, this finding illustrated that AT pre-treatment could be an effective way to counteract the UVC stress in tomato, and perhaps in other crop plants.

Nitric oxide and hydrogen sulfide protect plasma membrane integrity and mitigate chromium-induced methylglyoxal toxicity in maize seedlings

The present study aims to analyse the potential crosstalk between nitric oxide (NO) and hydrogen sulfide (H₂S) in triggering resilience of maize (Zea mays L.) seedlings to hexavalent chromium (Cr VI). Exogenous application of 500 μM sodium nitroprusside (SNP, as a NO donor) or sodium hydrosulfide (NaHS, as a H₂S donor) to 9-day-old maize seedlings, countered a Cr (200 μM) -elicited reduction in embryonic axis biomass. Cr caused cellular membrane injury by enhancing the levels of superoxide and hydroxyl radicals as well as methylglyoxal, and 4-hydroxy-2-nonenal. The application of SNP or NaHS considerably improved the endogenous NO and H₂S pool, decreased oxidative stress and lipid peroxidation by suppressing lipoxygenase activity and improving some antioxidant enzymes activities in radicles and epicotyls. Radicles were more affected than epicotyls by Cr-stress with enhanced electrolyte leakage and decreased proton extrusion as indicated by lesser H⁺-ATPase activity. H₂S appeared to mitigate Cr toxicity through up-regulated H⁺-ATPase and glyoxalase pathways and by maintaining optimal GSH levels as downstream effects of ROS and MG suppression. Hence, H₂S-mediated the regeneration of GSH pool is associated with the attenuation of MG toxicity by enhancing S-lactoglutathione and D-lactate production. Taken together, our results indicate complementary roles for H₂S and GSH to strengthen membrane integrity against Cr stress in maize seedlings.

Effects of exogenous spermidine on antioxidants and glyoxalase system of lettuce seedlings under high temperature

In this research, the lettuce high-temperature-sensitive variety Beisan San 3 was used as a test material. The effects of exogenous spermidine (Spd) on membrane lipid peroxidation, the antioxidant system, the ascorbic acid-glutathione (AsA-GSH) system and the glyoxalase (Glo) system in lettuce seedlings under high-temperature stress were studied by spraying either 1 mM spermidine or ionized water as a control. The results showed that, under high-temperature stress, the growth of lettuce seedlings was weak, and the dry weight (DW) and fresh weight (FW) were reduced by 68.9% and 82%, respectively, compared with those of the normal-temperature controls. In addition, the degree of membrane lipid peroxidation increased, and the reactive oxygen species (ROS) level increased, both of which led to a significant increase in malondialdehyde (MDA) content and lipoxygenase (LOX) activity. Under high-temperature stress, the activity of superoxide dismutase (SOD) decreased, the activities of peroxidase (POD) and catalase (CAT) increased first but then decreased, and the activity of ascorbic acid peroxidase (APX) decreased first but then increased. Glutathione reductase (GR) activity, ascorbic acid (AsA) and glutathione (GSH) content showed an upward trend under high-temperature stress. The activities of glyoxalase (GloI and GloII) in the lettuce seedling leaves increased significantly under high-temperature stress. In contrast, the application of exogenous Spd alleviated the oxidative damage to the lettuce seedlings, which showed a decrease in MDA content and LOX activity and an increase in SOD, POD, CAT, APX, GR, GloI, and GloII activities. In addition, the antioxidant AsA and GSH contents also increased to varying degrees. It can be seen from the results that high temperature stress leads to an increase in the level of ROS and cause peroxidation in lettuce seedlings, and exogenous Spd can enhance the ability of lettuce seedlings to withstand high temperature by enhancing the antioxidant system, glyoxalase system and AsA-GSH cycle system.

Effect of soil amendments on antioxidant activity and photosynthetic pigments in pea crops grown in arsenic contaminated soil

The mechanism of arsenic (As) immobilization in soils is crucial for improving photosynthetic pigments and antioxidants in food crops. The effects of soil amendments with arbuscular mycorrhizal fungi (AMF), biochar (BC), selenium (Se), sulfur (S) and Si-gel on the concentrations of chlorophyll, carotenoid, proline, malondialdehyde (MDA), and the activity of ascorbate peroxidase (APX), guaiacol peroxidase (POD), and catalase (CAT) were studied in BARI pea (Pisum sativum) under As stress. Soil amendments with AMF, Se, Si-gel and S enhanced chlorophyll a and total chlorophyll contents by 31–35% and 60–75%, respectively. Likewise, CAT activity was increased by 24–46% in BC, AMF, Se, Si-gel and S-treated pea, respectively. APX and POD activity was also found to be enriched with the treatment of BC, AMF and Se. In contrast, the content of MDA and proline was found lower than that of control in peas. These findings indicate that oxidative damage, osmotic stress and cell injury were possibly reduced in As-stressed peas. Particularly, AMF and Se both were comparatively more potential in comparison to BC. Thus, soil amendments with AMF, BC and Se are significantly important for improving antioxidant enzyme activity of food crops grown in soil with elevated As levels.

Pseudophoenix ekmanii (Arecaceae) seeds at suboptimal temperature show reduced imbibition rates and enhanced expression of genes related to germination inhibition

Pseudophoenix ekmanii is a critically endangered palm species that can be found in the southeast of the Dominican Republic. The temperatures to which P. ekmanii seeds are exposed upon dispersal range from 32 to 23 °C (max and min) and can reach a low of approximately 20 °C in January. Our aim was to analyse the effect of suboptimal (20 °C) and optimal (30 °C) germination temperature on seed imbibition, moisture content, embryo growth and gene expression patterns in this tropical palm species. Seed imbibition was tracked using whole seeds, while moisture content was assessed for individual seed sections. Embryo and whole seed size were measured before and after full imbibition. For transcriptome sequencing, mRNA was extracted from embryo tissues only and the resulting reads were mapped against the Elaeis guineensis reference genome. Differentially expressed genes were identified after statistical analysis and subsequently probed for enrichment of Gene Ontology categories 'Biological process' and 'Cellular component'. Our results show that prolonged exposure to 20 °C slows whole seed and embryo imbibition and causes germination to be both delayed and inhibited. Embryonic transcriptome patterns associated with the negative regulation of germination by suboptimal temperature include up-regulation of ABA biosynthesis genes, ABA-responsive genes, as well as other genes previously related to physiological dormancy and inhibition of germination. Thus, our manuscript provides the first insights into the gene expression patterns involved in the response to suboptimal temperature during seed imbibition in a tropical palm species.

Functional characterization of the Glyoxalase-I (PdGLX1) gene family in date palm under abiotic stresses

Methylglyoxal (MG), a cytotoxic oxygenated short aldehyde, is a by-product of various metabolic reactions in plants, including glycolysis. The basal level of MG in plants is low, whereby it acts as an essential signaling molecule regulating multiple cellular processes. However, hyperaccumulation of MG under stress conditions is detrimental for plants as it inhibits multiple developmental processes, including seed germination, photosynthesis, and root growth. The evolutionarily conserved glyoxalase system is critical for MG detoxification, and it comprises of two-enzymes, the glyoxalase-I and glyoxalase-II. Here, we report the functional characterization of six putative glyoxalase-I genes from date palm (Phoenix dactylifera L.) (PdGLX1), by studying their gene expression under various environmental stress conditions and investigating their function in bacteria (Escherichia coli) and yeast (Saccharomyces cerevisiae) mutant cells. The putative PdGLX1 genes were initially identified using computational methods and cloned using molecular tools. The PdGLX1 gene expression analysis using quantitative PCR (qPCR) revealed differential expression under various stress conditions such as salinity, oxidative stress, and exogenous MG stress in a tissue-specific manner. Further, in vivo functional characterization indicated that overexpression of the putative PdGLX1 genes in E. coli enhanced their growth and MG detoxification ability. The putative PdGLX1 genes were also able to complement the loss-of-function MG hypersensitive GLO1 (YML004C) yeast mutants and promote growth by enhancing MG detoxification and reducing the accumulation of reactive oxygen species (ROS) under stress conditions as indicated by flow cytometry. These findings denote the potential importance of PdGLX1 genes in MG detoxification under stress conditions in the date palm.

Quantification of Methylglyoxal Levels in Cowpea Leaves in Response to Cowpea Aphid Infestation

Aphids are a serious pest of crops across the world. Aphids feed by inserting their flexible hypodermal needlelike mouthparts, or stylets, into their host plant tissues. They navigate their way to the phloem where they feed on its sap causing little mechanical damage to the plant. Additionally, while feeding, aphids secrete proteinaceous effectors in their saliva to alter plant metabolism and disrupt plant defenses to gain an advantage over the plant. Even with these arsenals to overcome plant responses, plants have evolved ways to detect and counter with defense responses to curtail aphid infestation. One of such response of cowpea to cowpea aphid infestation, is accumulation of the metabolite methylglyoxal. Methylglyoxal is an α,β-dicarbonyl ketoaldehyde that is toxic at high concentrations. Methylglyoxal levels increase modestly after exposure to a number of different abiotic and biotic stresses and has been shown to act as an emerging defense signaling molecule at low levels. Here we describe a protocol to measure methylglyoxal in cowpea leaves after cowpea aphid infestation, by utilizing a perchloric acid extraction process. The extracted supernatant was neutralized with potassium carbonate, and methylglyoxal was quantified through its reaction with N-acetyl-L-cysteine to form N-α-acetyl-S-(1-hydroxy-2-oxo-prop-1-yl)cysteine, a product that is quantified spectrophotometrically.

Silicon is dependent on hydrogen sulphide to improve boron toxicity tolerance in pepper plants by regulating the AsA-GSH cycle and glyoxalase system

The role of endogenous hydrogen sulphide (H₂S) in silicon-induced improvement in boron toxicity (BT) tolerance in pepper plants was studied. Two-week old seedlings were subjected to control (0.05 mM B) or 2.0 mM BT in a nutrient solution. These two treatments were combined with 2.0 mM Si. BT caused considerable reduction in biomass, chlorophyll a &b, photosystem II maximum quantum efficiency (Fv/Fm), glutathione and ascorbate in the pepper seedlings. However, it enhanced malondialdehyde (MDA) and hydrogen peroxide, electrolyte leakage, proline, H₂S, and activities of catalase, superoxide dismutase, peroxidase, and L-DES. Silicon stimulated growth, proline content and activities of various antioxidant biomolecules and enzymes, leaf Ca²⁺, K⁺ and N, endogenous H₂S and L-DES activity, but reduced H₂O₂ and MDA contents, membrane leakage and leaf B. Silicon-induced B tolerance was further enhanced by 0.2 mM NaHS, a H₂S donor. A scavenger of H₂S, hypotaurine (0.1 mM HT), was supplied together with Si and Si + NaHS to assess the involvement of H₂S in Si-induced BT tolerance of pepper plants. Hypotaurine inverted the positive role of Si on the antioxidant defence system by reducing endogenous H₂S, but NaHS supply along with Si + HT reversed the negative effects of HT, showing that H₂S participated in Si-induced BT tolerance of pepper plants.

Regulative role of calcium signaling on methylglyoxal-improved heat tolerance in maize (Zea mays L) seedlings

Nowadays, calcium (Ca2+) and methylglyoxal (MG) are all deemed to be second messengers in plants, which participate in various physiological processes, such as seed germination, seedling establishment, plant growth and development, as well as response to environmental stress. However, the Ca2+-MG interaction in the development of thermotolerance in maize seedlings remains unclear. Here, using maize seedlings as materials, the crosstalk between Ca2+ and MG signaling in the acquisition of thermotolerance was explored. The results showed that root-irrigation with Ca2+ and MG alone or in combination increased the survival rate of maize seedlings under heat stress, mitigated the decrease in the tissue vitality, and reduced the membrane lipid peroxidation (in term of the content of malondialdehyde), indicating that Ca2+ and MG could improve the thermotolerance in maize seedlings. In addition, MG-improved thermotolerance was impaired by ethylene glycol-bis(b-aminoethylether)-N,N,N΄,N΄-tetraacetic acid (a Ca2+ chelator), La3+ (plasma membrane Ca2+ channel blocker), ruthenium red (a mitochondrial Ca2+ channel blocker), neomycin (vacuole Ca2+ channel blocker), caffeine (an endoplasmic reticulum Ca2+ channel blocker), and calmodulin antagonists (chlorpromazine and trifluoperazine), respectively. Also, MG scavengers (N-acetyl-cysteine, aminoguanidine, and vitamin B6) had no significant effect on Ca2+-triggered thermotolerance (in terms of survival rate, malondialdehyde, and tissue vitality) of maize seedlings. The data illustrated that calcium signaling regulated MG-improved thermotolerance in maize seedlings by mobilizing intracellular and extracellular Ca2+ pools.

Exogenous application of hydrogen sulfide reduces chromium toxicity in maize seedlings by suppressing NADPH oxidase activities and methylglyoxal accumulation

Chromium (Cr) represents an important source of metallic stress in plants. Working with maize (Zea mays) seedlings, we characterize the suppressive effects of exogenously applied NaHS (a hydrogen sulfide; [H₂S] donor) on the toxic effects of Cr (VI). Heavy metal treatment reduced radicle and epicotyl lengths and fresh weights in seedlings at 6 and 9 days following germination. The negative Cr (200 μM) effect was countered by application with NaHS (500 μM) but this countering was reduced with the co-application of the H₂S generation inhibitor hydroxylamine (HA) or the H₂S scavenger hypotaurine (HT). The Cr-elicited H₂O₂ production was suppressed by NaHS and also by an inhibitor of the reactive oxygen species (ROS) generating NADPH oxidase (NOX). These effects were correlated with relative changes in carbomyl (-CO) and thiol (-SH) groups. Nitric oxide (NO) production increased by NaHS application with associated increase in S-nitrosoglutathione (GSNO) level, but low S-nitrosoglutathione reductase (GSNOR) activities indicating an elevated S-nitrosylation. Assessment of the role of the ascorbate-glutathione antioxidant cycle indicated that whilst ascorbate played at a best minor role, glutathione was more prominent. Methylglyoxal (MG) production was increased by Cr but reduced by NaHS through a mechanism which could be based on glutathione-S-transferase (GST) detoxification. Taken together data suggest that H₂S acts to counter Cr effect in maize by NOX suppression, mostly likely by the well-characterised S-nitrosylation mechanism, as well as a reduction of MG accumulation.

Metabolic Responses of Carotenoid and Cordycepin Biosynthetic Pathways in Cordyceps militaris under Light-Programming Exposure through Genome-Wide Transcriptional Analysis

Cordyceps militaris is currently exploited for commercial production of specialty products as its biomass constituents are enriched in bioactive compounds, such as cordycepin. The rational process development is important for economically feasible production of high quality bioproducts. Light is an abiotic factor affecting the cultivation process of this entomopathogenic fungus, particularly in its carotenoid formation. To uncover the cell response to light exposure, this study aimed to systematically investigate the metabolic responses of C. militaris strain TBRC6039 using integrative genome-wide transcriptome and genome-scale metabolic network (GSMN)-driven analysis. The genome-wide transcriptome analysis showed 8747 expressed genes in the glucose and sucrose cultures grown under light-programming and dark conditions. Of them, 689 differentially expressed genes were significant in response to the light-programming exposure. Through integration with the GSMN-driven analysis using the improved network (iRT1467), the reporter metabolites, e.g., adenosine-5'-monophosphate (AMP) and 2-oxoglutarate, were identified when cultivated under the carotenoid-producing condition controlled by light-programming exposure, linking to up-regulations of the metabolic genes involved in glyoxalase system, as well as cordycepin and carotenoid biosynthesis. These results indicated that C. militaris had a metabolic control in acclimatization to light exposure through transcriptional co-regulation, which supported the cell growth and cordycepin production in addition to the accumulation of carotenoid as a photo-protective bio-pigment. This study provides a perspective in manipulating the metabolic fluxes towards the target metabolites through either genetic or physiological approaches.

Involvement of L-Cysteine Desulfhydrase and Hydrogen Sulfide in Glutathione-Induced Tolerance to Salinity by Accelerating Ascorbate-Glutathione Cycle and Glyoxalase System in Capsicum

The aim of this study is to assess the role of l-cysteine desulfhydrase (l-DES) and endogenous hydrogen sulfide (H₂S) in glutathione (GSH)-induced tolerance to salinity stress (SS) in sweet pepper (Capsicum annuum L.). Two weeks after germination, before initiating SS, half of the pepper seedlings were retained for 12 h in a liquid solution containing H₂S scavenger, hypotaurine (HT), or the l-DES inhibitor dl-propargylglycine (PAG). The seedlings were then exposed for three weeks to control or SS (100 mmol L⁻¹ NaCl) and supplemented with or without GSH or GSH+NaHS (sodium hydrosulfide, H₂S donor). Salinity suppressed dry biomass, leaf water potential, chlorophyll contents, maximum quantum efficiency, ascorbate, and the activities of dehydroascorbate reductase, monodehydroascorbate reductase, and glyoxalase II in plants. Contrarily, it enhanced the accumulation of hydrogen peroxide, malondialdehyde, methylglyoxal, electrolyte leakage, proline, GSH, the activities of glutathione reductase, peroxidase, catalase, superoxide dismutase, ascorbate peroxidase, glyoxalase I, and l-DES, as well as endogenous H₂S content. Salinity enhanced leaf Na⁺ but reduced K⁺; however, the reverse was true with GSH application. Overall, the treatments, GSH and GSH+NaHS, effectively reversed the oxidative stress and upregulated salt tolerance in pepper plants by controlling the activities of the AsA-GSH and glyoxalase-system-related enzymes as well as the levels of osmolytes.

AcDCXR Is a Cowpea Aphid Effector With Putative Roles in Altering Host Immunity and Physiology

Cowpea, Vigna unguiculata, is a crop that is essential to semiarid areas of the world like Sub-Sahara Africa. Cowpea is highly susceptible to cowpea aphid, Aphis craccivora, infestation that can lead to major yield losses. Aphids feed on their host plant by inserting their hypodermal needlelike flexible stylets into the plant to reach the phloem sap. During feeding, aphids secrete saliva, containing effector proteins, into the plant to disrupt plant immune responses and alter the physiology of the plant to their own advantage. Liquid chromatography tandem mass spectrometry (LC-MS/MS) was used to identify the salivary proteome of the cowpea aphid. About 150 candidate proteins were identified including diacetyl/L-xylulose reductase (DCXR), a novel enzyme previously unidentified in aphid saliva. DCXR is a member of short-chain dehydrogenases/reductases with dual enzymatic functions in carbohydrate and dicarbonyl metabolism. To assess whether cowpea aphid DCXR (AcDCXR) has similar functions, recombinant AcDCXR was purified and assayed enzymatically. For carbohydrate metabolism, the oxidation of xylitol to xylulose was tested. The dicarbonyl reaction involved the reduction of methylglyoxal, an α-β-dicarbonyl ketoaldehyde, known as an abiotic and biotic stress response molecule causing cytotoxicity at high concentrations. To assess whether cowpea aphids induce methylglyoxal in plants, we measured methylglyoxal levels in both cowpea and pea (Pisum sativum) plants and found them elevated transiently after aphid infestation. Agrobacterium-mediated transient overexpression of AcDCXR in pea resulted in an increase of cowpea aphid fecundity. Taken together, our results indicate that AcDCXR is an effector with a putative ability to generate additional sources of energy to the aphid and to alter plant defense responses. In addition, this work identified methylglyoxal as a potential novel aphid defense metabolite adding to the known repertoire of plant defenses against aphid pests.

Deciphering the molecular mechanism behind stimulated co-uptake of arsenic and fluoride from soil, associated toxicity, defence and glyoxalase machineries in arsenic-tolerant rice

The current study elucidates the uncharacterized biohazard associated with rice growth in arsenic and fluoride co-contaminated sites. Analysis of the arsenic-tolerant rice cultivar, Muktashri (known to restrict arsenic uptake) revealed that fluoride largely stimulated arsenic bioaccumulation in the stressed tissues and vice versa. Gene expression studies revealed that high arsenic uptake was facilitated by the fluoride-dependent up regulation of phosphate transporter2 (PT2), PT8 and low silicon rice1 (Lsi1), and elevated fluoride accumulation was stimulated by the arsenic-mediated induction of chloride channels (CLCs). The endogenous accumulation of fluoride and arsenic increased reactive oxygen species (ROS), O₂^-, membrane peroxidation and arsenic localization within tissues. This inhibited plant growth by triggering chlorosis, electrolyte leakage, malondialdehyde production (due to high lipoxygenase activity), protein carbonylation, protease activity and methylglyoxal accumulation due to inhibited glyoxylase activity. Metabolic analysis showed inhibited proline biosynthesis along with increased channelization of glutathione towards phytochelatin synthase and glutathione-S-tranferase-dependent pathways. Inhibition of the antioxidant enzymes like catalase, ascorbate peroxidase and guaiacol peroxidase validated the inefficient scavenging of H₂O₂ during combined stress. In silico analyses predicted the ecotoxicological risks of arsenic-fluoride complex formed during joint stress. Overall, our investigation illustrated the underlying mechanism of arsenic-fluoride co-uptake which resulted in complete suppression of the 'tolerant'-phenotype in Muktashri seedlings.

Impact of inorganic salts on vase life and postharvest qualities of the cut flower of Perpetual Carnation

This study was carried out in the laboratory of Shangqiu Institute of Technology, Henan to investigate the effect of a different combination of inorganic salt on the quality and physiological characteristics of cut flowers (CFs) of Perpetual Carnation. Furthermore, to find out the best preservation solution of inorganic salt that can enhance the ornamental value of CFs of Carnation and prolong its vase life. Sucrose, 8-hydroxyquinoline, paclobutrazol, salicylic acid and different kinds of inorganic salts were added as a preservation solution. And the same amount of distilled water was used as control. The effects of these various inorganic salts on the morphological characteristics including vase life, changes in flower stems, fresh weight (FW) and water balance and the physiological characteristics including contents of malondialdehyde (MDA), cell membrane permeability and the contents of proline of carnation were investigated. The CFs placed in vase solution with inorganic salts showed significant changes in its morphology and physiological characteristics as compared to control. The changes in flower diameter (FD), FW, malondialdehyde and cell membrane permeability showed an increasing trend first and then decreasing. The value of water balance was observed with a downward trend. However, the vase life, FD, the contents of malondialdehyde, contents of proline and FW of CFs held in the preservative solution containing inorganic salts were increased than that of control. The fresh preservative solution contained sucrose 3% + 8-hydroxyquinoline (8-HQ) (200 mg·L‾1) + paclobutrazol (100 mg·L‾1) + salicylic acid (SA) (25 mg·L‾1) + CaCl2 (100 mg·L‾1) has the best effect on longevity (34 days), FW and FD of carnation CFs. This solution has improved the ornamental and physiological characteristics of fresh carnation CFs.

Al-induced proteomics changes in tomato plants over-expressing a glyoxalase I gene

Glyoxalase I (Gly I) is the first enzyme in the glutathionine-dependent glyoxalase pathway for detoxification of methylglyoxal (MG) under stress conditions. Transgenic tomato 'Money Maker' plants overexpressing tomato SlGlyI gene (tomato unigene accession SGN-U582631/Solyc09g082120.3.1) were generated and homozygous lines were obtained after four generations of self-pollination. In this study, SlGlyI-overepxressing line (GlyI), wild type (WT, negative control) and plants transformed with empty vector (ECtr, positive control), were subjected to Al-treatment by growing in Magnavaca's nutrient solution (pH 4.5) supplemented with 20 µM Al3+ ion activity. After 30 days of treatments, the fresh and dry weight of shoots and roots of plants from Al-treated conditions decreased significantly compared to the non-treated conditions for all the three lines. When compared across the three lines, root fresh and dry weight of GlyI was significant higher than WT and ECtr, whereas there was no difference in shoot tissues. The basal 5 mm root-tips of GlyI plants expressed a significantly higher level of glyoxalase activity under both non-Al-treated and Al-treated conditions compared to the two control lines. Under Al-treated condition, there was a significant increase in MG content in ECtr and WT lines, but not in GlyI line. Quantitative proteomics analysis using tandem mass tags mass spectrometry identified 4080 quantifiable proteins and 201 Al-induced differentially expressed proteins (DEPs) in root-tip tissues from GlyI, and 4273 proteins and 230 DEPs from ECtr. The Al-down-regulated DEPs were classified into molecular pathways of gene transcription, RNA splicing and protein biosynthesis in both GlyI and ECtr lines. The Al-induced DEPs in GlyI associated with tolerance to Al3+ and MG toxicity are involved in callose degradation, cell wall components (xylan acetylation and pectin degradation), oxidative stress (antioxidants) and turnover of Al-damaged epidermal cells, repair of damaged DNA, epigenetics, gene transcription, and protein translation. A protein-protein association network was constructed to aid the selection of proteins in the same pathway but differentially regulated in GlyI or ECtr lines. Proteomics data are available via ProteomeXchange with identifiers PXD009456 under project title '25Dec2017_Suping_XSexp2_ITAG3.2' for SlGlyI-overexpressing tomato plants and PXD009848 under project title '25Dec2017_Suping_XSexp3_ITAG3.2' for positive control ECtr line transformed with empty vector.

Exogenous methylglyoxal enhances the reactive aldehyde detoxification capability and frost-hardiness of wheat

Cold-acclimation is essential for the development of adequate frost-hardiness in cereals and therefore sudden freezes can cause considerable damage to the canopy. However, timely adding of an appropriate signal in the absence of cold acclimation may also harden wheat for the upcoming freeze. The feasibility of the promising signal molecule methylglyoxal was tested here for such applications and the signal mechanism was studied in bread wheat (Triticum aestivum L.) and durum wheat (Triticum turgidum L. ssp. durum). Spraying with 10 mM methylglyoxal did not decrease the fresh weight and photosynthetic parameters in most wheat varieties at growth temperature (21 °C). Photosynthetic parameters even improved and chlorophyll content increased in some cases. Increased transcript level of glutathione-S-transferases and omega-3 fatty acid desaturases was detected by qPCR 6 h after the last methylglyoxal spray. Aldo-keto reductase and glyoxalase enzyme activities, as well as sorbitol content of wheat plants increased 24 h after the last 10 mM methylglyoxal spray in most of the cultivars. These mechanisms may explain the increased freezing survival of methylglyoxal pretreated wheat plants from less than 10% to over 30%. Our results demonstrate that exogenous methylglyoxal treatment can be safely added to wheat plants as preparatory treatment without detrimental effects but inducing some of the stress-protective mechanisms, which contribute to frost-hardiness.

Stress responsive gene regulation in relation to hydrogen sulfide in plants under abiotic stress

Plants often face a variety of abiotic stresses, which affects them negatively and lead to yield loss. The antioxidant system efficiently removes excessive reactive oxygen species and maintains redox homeostasis in plants. With better understanding of these protective mechanisms, recently the concept of hydrogen sulfide (H₂ S) and its role in cell signaling has become the center of attention. H₂ S has been recognized as a third gasotransmitter and a potent regulator of growth and development processes such as germination, maturation, senescence and defense mechanism in plants. Because of its gaseous nature, H₂ S can diffuse to different part of the cells and balance the antioxidant pools by supplying sulfur to cells. H₂ S showed tolerance against a plethora of adverse environmental conditions like drought, salt, high temperature, cold, heavy metals and flood via changing in level of osmolytes, malonaldialdehyde, Na⁺ /K⁺ uptake, activities of H₂ S biosynthesis and antioxidative enzymes. It also promotes cross adaptation through persulfidation. H₂ S along with calcium, methylglyoxal and nitric oxide, and their cross talk induces the expression of mitogen activated protein kinases as well as other genes in response to stress. Therefore, it is sensible to evaluate and explore the stress responsive genes involved in H₂ S regulated homeostasis and stress tolerance. The current article is aimed to summarize the recent updates on H₂ S-mediated gene regulation in special reference to abiotic stress tolerance mechanism, and cross adaptation in plants. Moreover, new insights into the H₂ S-associated signal transduction pathway have also been explored.

Spermine ameliorates prolonged fluoride toxicity in soil-grown rice seedlings by activating the antioxidant machinery and glyoxalase system

The current manuscript presents the first report on the ameliorative roles of exogenous spermine (Spm) during prolonged fluoride-induced toxicity and oxidative damages in the susceptible rice cultivar, IR-64. The application of Spm increased the overall growth in the stressed seedlings by significantly restricting fluoride bioaccumulation within the shoots and roots. The Spm-treated stressed seedlings exhibited low chlorosis and induced activity of pyruvate dehydrogenase and nitrate reductase due to reduced accumulation and localization of reactive oxygen species (ROS) in the shoot and root. Spm-supplementation during stress reduced the levels of molecular damages by lowering malondialdehyde, electrolyte leakage and protein carbonylation, and lipoxygenase and protease activity due to effective detoxification of ROS by the antioxidants like proline, glycine-betaine, anthocyanin, flavonoids, phenolics and higher polyamines like Spm and spermidine. Excessive accumulation of the toxic methylglyoxal was reversed due to the activation of the glyoxalase system (comprising of glyoxalase I and II) and the ascorbate-glutathione cycle. Exogenous Spm also triggered the activity of superoxide dismutase, guaiacol peroxidase, glutathione peroxidase and phenylalanine ammonia lyase, which efficiently scavenged ROS in the stressed seedlings. Overall, Spm treatment mitigated the fluoride-induced injuries in IR-64 by reducing fluoride bioaccumulation and elaborately refining the various defence machineries.

Modulation of growth performance and coordinated induction of ascorbate-glutathione and methylglyoxal detoxification systems by salicylic acid mitigates salt toxicity in choysum (Brassica parachinensis L.)

Salinity represents a serious environmental threat to crop production and by extension, to world food supply, social and economic prosperity of the developing world. Salicylic acid (SA) is an endogenous plant signal molecule involved in regulating various plant responses to stress. In the present study, we characterized the regulatory role of exogenous SA for their ability to ameliorate deleterious effects of salt stress (0, 100, 150, 200 mM NaCl) in choysum plants through coordinated induction of antioxidants, ascorbate glutathione (AsA-GSH) cycle, and the glyoxalase enzymes. An increase in salt stress dramatically declined root and shoot growth, leaf chlorophyll and relative water content (RWC), subsequently increased electrolyte leakage (EL) and osmolytes accumulation in choysum plants. Salt stress disrupted the antioxidant and glyoxalase defense systems which persuaded oxidative damages and carbonyl toxicity, indicated by increased H₂O₂ generation, lipid peroxidation, and methylglyoxal (MG) content. However, application of SA had an additive effect on the growth of salt-affected choysum plants, which enhanced root length, plant biomass, chlorophyll contents, leaf area, and RWC. Moreover, SA application effectively eliminated the oxidative and carbonyl stress by improving AsA and GSH pool, upregulating the activities of antioxidant enzymes and the enzymes associated with AsA-GSH cycle and glyoxalase system. Overall, SA application completely counteracted the salinity-induced deleterious effects of 100 and 150 mM NaCl and partially mediated that of 200 mM NaCl stress. Therefore, we concluded that SA application induced tolerance to salinity stress in choysum plants due to the synchronized increase in activities of enzymatic and non-enzymatic antioxidants, enhanced efficiency of AsA-GSH cycle and the MG detoxification systems.

Methods for Screening Legume Crops for Abiotic Stress Tolerance through Physiological and Biochemical Approaches

Legume crops are subjected to a wide range of abiotic stresses, which stimulate an array of physiological, biochemical, and molecular responses. However, different genotypes may exhibit significant variations between individual responses, which can determine their tolerance or susceptibility to these stresses. The present chapter suggests a broad range of assays that can help in understanding stress perception by plants at cellular and molecular levels. The genotypes may be sorted depending on their tolerance potential, by broadly analysing morphological, physiological, biochemical, and enzyme kinetics parameters. These assays are very beneficial in revealing the mechanism of stress perception and response in varied plant types, and have helped in discriminating contrasting genotypes. Here, we have described detailed protocols of assays which may be carried out to assess tolerance or susceptibility to abiotic stresses. The analysis, as a whole, can help researchers understand the effect of abiotic stresses on plant biochemical pathways, be it photosynthesis, redox homeostasis, metabolite perturbation, signaling, transcription, and translation. These protocols may be beneficial in identification of suitable donors for breeding programs, as well as for identifying promising candidate genes or pathways for developing stress tolerant legume crops through genetic engineering.

Role of Exogenous and Endogenous Hydrogen Sulfide (H2S) on Functional Traits of Plants Under Heavy Metal Stresses: A Recent Perspective

Improving growth and productivity of plants that are vulnerable to environmental stresses, such as heavy metals, is of significant importance for meeting global food and energy demands. Because heavy metal toxicity not only causes impaired plant growth, it has also posed many concerns related to human well-being, so mitigation of heavy metal pollution is a necessary priority for a cleaner environment and healthier world. Hydrogen sulfide (H₂S), a gaseous signaling molecule, is involved in metal-related oxidative stress mitigation and increased stress tolerance in plants. It performs multifunctional roles in plant growth regulation while reducing the adverse effects of abiotic stress. Most effective function of H₂S in plants is to eliminate metal-related oxidative toxicity by regulating several key physiobiochemical processes. Soil pollution by heavy metals presents significant environmental challenge due to the absence of vegetation cover and the resulting depletion of key soil functions. However, the use of stress alleviators, such as H₂S, along with suitable crop plants, has considerable potential for an effective management of these contaminated soils. Overall, the present review examines the imperative role of exogenous application of different H₂S donors in reducing HMs toxicity, by promoting plant growth, stabilizing their physiobiochemical processes, and upregulating antioxidative metabolic activities. In addition, crosstalk of different growth regulators with endogenous H₂S and their contribution to the mitigation of metal phytotoxicity have also been explored.

Mechanisms of Sugar Beet Response to Biotic and Abiotic Stresses

Sugar beet is used not only in the sugar production, but also in a wide range of industries including the production of bioethanol as a source of renewable energy, extraction of pectin and production of molasses. The red beetroot has attracted much attention as health-promoting and disease-preventing functional food. The negative effects of environmental stresses, including abiotic and biotic ones, significantly decrease the cash crop sugar beet productivity. In this paper, we outline the mechanisms of sugar beet response to biotic and abiotic stresses at the levels of physiological change, the genes' functions, transcription and translation. Regarding the physiological changes, most research has been carried out on salt and drought stress. The functions of genes from sugar beet in response to salt, cold and heavy metal stresses were mainly investigated by transgenic technologies. At the transcriptional level, the transcriptome analysis of sugar beet in response to salt, cold and biotic stresses were conducted by RNA-Seq or SSH methods. At the translational level, more than 800 differentially expressed proteins in response to salt, K⁺/Na⁺ ratio, iron deficiency and resupply and heavy metal (zinc) stress were identified by quantitative proteomics techniques. Understanding how sugar beet respond and tolerate biotic and abiotic stresses is important for boosting sugar beet productivity under these challenging conditions. In order to minimize the negative impact of these stresses, studying how the sugar beet has evolved stress coping mechanisms will provide new insights and lead to novel strategies for improving the breeding of stress-resistant sugar beet and other crops.

Spermidine application reduces fluoride uptake and ameliorates physiological injuries in a susceptible rice cultivar by activating diverse regulators of the defense machinery

The manuscript illustrates the ameliorative effects of exogenously applied higher polyamine (PA), spermidine (Spd) in the susceptible indica rice cultivar IR-64 subjected to prolonged fluoride stress. The Spd treatment drastically reduced fluoride bioaccumulation by restricting entry of the anions through chloride channels and enabled better maintenance of the proton gradient via accumulation of P-H⁺/ATPase, thereby improving the root and shoot lengths, fresh and dry weights, RWC, chlorophyll content and activities of pyruvate dehydrogenase (PyrDH), α-amylase, and nitrate reductase (NR) in the Spd-treated, stressed plants. Expression of RuBisCo, PyrDH, α-amylase, and NR was stimulated. Spd supplementation reduced the molecular damage indices like malondialdehyde, lipoxygenase, protease activity, electrolyte leakage, protein carbonylation, H₂O₂, and methylglyoxal (detoxified by glyoxalase II). Mitigation of oxidative damage was facilitated by the accumulation and utilization of proline, glycine-betaine, total amino acids, higher PAs, anthocyanin, flavonoids, β-carotene, xanthophyll, and phenolics as verified from the expression of genes like P5CS, BADH1, SAMDC, SPDS, SPMS, DAO, PAO, and PAL. Spd treatment activated the ascorbate-glutathione cycle in the stressed seedlings. Expression and activities of enzymatic antioxidants showed that GPOX, APX, GPX, and GST were the chief ROS scavengers. Exogenous Spd promoted ABA accumulation by upregulating NCED3 and suppressing ABA8ox1 expression. ABA-dependent osmotic stress-responsive genes like Osem, WRKY71, and TRAB1 as well as ABA-independent transcription factor encoding gene DREB2A were induced by Spd. Thus, Spd treatment ameliorated fluoride-mediated injuries in IR-64 by restricting fluoride uptake, refining the defense machinery and activating the ABA-dependent as well as ABA-independent stress-responsive genes.

Is geographical variation driving the transcriptomic responses to multiple stressors in the kelp Saccharina latissima?

BACKGROUND

Kelps (Laminariales, Phaeophyceae) are brown macroalgae of utmost ecological, and increasingly economic, importance on temperate to polar rocky shores. Omics approaches in brown algae are still scarce and knowledge of their acclimation mechanisms to the changing conditions experienced in coastal environments can benefit from the application of RNA-sequencing. Despite evidence of ecotypic differentiation, transcriptomic responses from distinct geographical locations have, to our knowledge, never been studied in the sugar kelp Saccharina latissima so far.

RESULTS

In this study we investigated gene expression responses using RNA-sequencing of S. latissima from environments with contrasting temperature and salinity conditions - Roscoff, in temperate eastern Atlantic, and Spitsbergen in the Arctic. Juvenile sporophytes derived from uniparental stock cultures from both locations were pre-cultivated at 8 °C and SA 30. Sporophytes acclimated to 0 °C, 8 °C and 15 °C were exposed to a low salinity treatment (SA 20) for 24 h. Hyposalinity had a greater impact at the transcriptomic level than the temperature alone, and its effects were modulated by temperature. Namely, photosynthesis and pigment synthesis were extensively repressed by low salinity at low temperatures. Although some responses were shared among sporophytes from the different sites, marked differences were revealed by principal component analysis, differential expression and GO enrichment. The interaction between low temperature and low salinity drove the largest changes in gene expression in sporophytes from Roscoff while specimens from Spitsbergen required more metabolic adjustment at higher temperatures. Moreover, genes related to cell wall adjustment were differentially expressed between Spitsbergen and Roscoff control samples.

CONCLUSIONS

Our study reveals interactive effects of temperature and salinity on transcriptomic profiles in S. latissima. Moreover, our data suggest that under identical culture conditions sporophytes from different locations diverge in their transcriptomic responses. This is probably connected to variations in temperature and salinity in their respective environment of origin. The current transcriptomic results support the plastic response pattern in sugar kelp which is a species with several reported ecotypes. Our data provide the baseline for a better understanding of the underlying processes of physiological plasticity and may help in the future to identify strains adapted to specific environments and its genetic control.

PpAKR1A, a Novel Aldo-Keto Reductase from Physcomitrella Patens, Plays a Positive Role in Salt Stress

The moss Physcomitrella patens is tolerant of highly saline environments. In plants, salinity stress may induce the production of toxic reactive carbonyl species (RCS) and oxidative damage. Aldo-keto reductases (AKRs) are a large group of NADP-dependent oxidoreductases involved in RCS detoxification. However, many members in this superfamily remain uncharacterized. In this study, we cloned and characterised a putative AKR1 from P. patens, named PpAKR1A. Notably, the transcription level of PpAKR1A was induced by salt and methylglyoxal (MG) stress, and the recombinant PpAKR1A protein catalysed the reduction of toxic aldehydes. PpAKR1A knockout mutants of P. patens (ppakr1a) were sensitive to NaCl and MG treatment, as indicated by much lower concentrations of chlorophyll and much higher concentrations of MG and H₂O₂ than those in WT plants. Meanwhile, ppakr1a plants exhibited decreases in the MG-reducing activity and reactive oxygen species-scavenging ability in response to salt stress, possibly due to decreases in the activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). Our results indicate that PpAKR1A is an aldo-keto reductase that detoxifies MG and thus plays an important role in salt stress tolerance in P. patens.

24-Epibrassinolide (EBR) Confers Tolerance against NaCl Stress in Soybean Plants by Up-Regulating Antioxidant System, Ascorbate-Glutathione Cycle, and Glyoxalase System

: The present research was performed to assess the effect of 24-epibrassinolide (EBR) on salt-stressed soybean plants. Salt stress suppressed growth, biomass yield, gas exchange parameters, pigment content, and chlorophyll fluorescence, but all these parameters were up-regulated by EBR supply. Moreover, salt stress increased hydrogen peroxide, malondialdehyde, and electrolyte leakage. EBR supplementation reduced the accumulation of oxidative stress biomarkers. The activities of superoxide dismutase and catalase, and the accumulation of proline, glycinebetaine, total phenols, and total flavonoids increased with NaCl stress, but these attributes further increased with EBR supplementation. The activities of enzymes and the levels of non-enzymatic antioxidants involved in the Asc-Glu cycle also increased with NaCl stress, and further enhancement in these attributes was recorded by EBR supplementation. Salinity elevated the methylglyoxal content, but it was decreased by the EBR supplementation accompanying with up-regulation of the glyoxalase cycle (GlyI and GlyII). Salinity enhanced the Na+ uptake in root and shoot coupled with a decrease in uptake of Ca2+, K+, and P. However, EBR supplementation declined Na+ accumulation and promoted the uptake of the aforementioned nutrients. Overall, EBR supplementation regulated the salt tolerance mechanism in soybean plants by modulating osmolytes, activities of key enzymes, and the levels of non-enzymatic antioxidants.

GLYI4 Plays A Role in Methylglyoxal Detoxification and Jasmonate-Mediated Stress Responses in Arabidopsis thaliana

Plant hormones play a central role in various physiological functions and in mediating defense responses against (a)biotic stresses. In response to primary metabolism alteration, plants can produce also small molecules such as methylglyoxal (MG), a cytotoxic aldehyde. MG is mostly detoxified by the combined actions of the enzymes glyoxalase I (GLYI) and glyoxalase II (GLYII) that make up the glyoxalase system. Recently, by a genome-wide association study performed in Arabidopsis, we identified GLYI4 as a novel player in the crosstalk between jasmonate (JA) and salicylic acid (SA) hormone pathways. Here, we investigated the impact of GLYI4 knock-down on MG scavenging and on JA pathway. In glyI4 mutant plants, we observed a general stress phenotype, characterized by compromised MG scavenging, accumulation of reactive oxygen species (ROS), stomatal closure, and reduced fitness. Accumulation of MG in glyI4 plants led to lower efficiency of the JA pathway, as highlighted by the increased susceptibility of the plants to the pathogenic fungus Plectospherella cucumerina. Moreover, MG accumulation brought about a localization of GLYI4 to the plasma membrane, while MeJA stimulus induced a translocation of the protein into the cytoplasmic compartment. Collectively, the results are consistent with the hypothesis that GLYI4 is a hub in the MG and JA pathways.

Differential regulation of defence pathways in aromatic and non-aromatic indica rice cultivars towards fluoride toxicity

Excessive bioaccumulation of fluoride in IR-64 caused low abscisic acid level, inhibition of polyamine biosynthesis and ascorbate-glutathione cycle but not in Gobindobhog which had higher antioxidant activity. The current study presents regulation of diverse metabolic and molecular defence pathways during fluoride stress in non-aromatic rice variety, IR-64 and aromatic rice variety, Gobindobhog (GB). Increasing concentration of fluoride affected fresh weight, dry weight, vigour index and relative water content to a lesser extent in GB compared to IR-64. GB exhibited lower methylglyoxal accumulation and lipoxygenase activity compared to IR-64 during stress. The level of osmolytes (proline, amino acids and glycine-betaine) increased in both the stressed varieties. The biosynthesis of higher polyamines was stimulated in stressed GB. IR-64 accumulated higher amount of putrescine due to degradation of higher polyamines as supported by gene expression analysis. Unlike IR-64, GB efficiently maintained the ascorbate-glutathione cycle due to much lower fluoride bioaccumulation, compared to IR-64. GB adapted to fluoride stress by strongly inducing guaiacol peroxidase, phenylalanine ammonia lyase and a novel isozyme of superoxide dismutase. While GB accumulated higher abscisic acid (ABA) level during stress, IR-64 exhibited slow ABA degradation which enabled induction of associated osmotic stress-responsive genes. Unlike GB, ABA-independent DREB2A was downregulated in stressed IR-64. The research illustrates varietal differences in the defence machinery of the susceptible variety, IR-64, and the well adapted cultivar, GB, on prolonged exposure to increasing concentrations of fluoride.

Reactive Carbonyl Species: A Missing Link in ROS Signaling

As reactive oxygen species (ROS) play critical roles in plants to determine cell fate in various physiological situations, there is keen interest in the biochemical processes of ROS signal transmission. Reactive carbonyl species (RCS), the ,-unsaturated aldehydes and ketones produced from lipid peroxides, due to their chemical property to covalently modify protein, can mediate ROS signals to proteins. Comprehensive carbonyl analysis in plants has revealed that more than a dozen different RCS, e.g., acrolein, 4-hydroxy-(E)-2-nonenal and malondialdehyde, are produced from various membranes, and some of them increase and modify proteins in response to oxidative stimuli. At early stages of response, specific subsets of proteins are selectively modified with RCS. The involvement of RCS in ROS signaling can be judged on three criteria: (1) A stimulus to increase the ROS level in plants leads to the enhancement of RCS levels. (2) Suppression of the increase of RCS by scavenging enzymes or chemicals diminishes the ROS-induced response. (3) Addition of RCS to plants evokes responses similar to those induced by ROS. On these criteria, the RCS action as damaging/signaling agents has been demonstrated for root injury, programmed cell death, senescence of siliques, stomata response to abscisic acid, and root response to auxin. RCS thus act as damage/signal mediators downstream of ROS in a variety of physiological situations. A current picture and perspectives of RCS research are presented in this article.

Quercetin Mediated Salt Tolerance in Tomato through the Enhancement of Plant Antioxidant Defense and Glyoxalase Systems

Quercetin (Qu) is a strong antioxidant among the phenolic compounds having physiological and biochemical roles in plants. Hence, we have studied the Qu evolved protection against salinity in tomato (Solanum lycopersicum L.). Salinity caused ionic toxicity by increasing Na+ content in seedlings along with nutritional starvation of K+, Ca2+, and Mg2+. While osmotic stress was detected by higher free proline (Pro) content and lower leaf relative water content (LRWC) in salt-stressed seedlings. Salt toxicity also induced higher H2O2 generation, malondialdehyde (MDA) content and lipoxygenase (LOX) activity as a sign of oxidative stress. Tomato seedlings suffered from methylglyoxal (MG) toxicity, degradation of chlorophyll, along with lower biomass accumulation and growth due to salt exposure. However, Qu application under salinity resulted in lower Na+/K+ due to reduced Na+ content, higher LRWC, increased Pro, and reduction of H2O2 and MDA content, and LOX activity, which indicated alleviation of ionic, osmotic, and oxidative stress respectively. Quercetin caused oxidative stress, lessening through the strengthening of both enzymatic and non-enzymatic antioxidants. In addition, Qu increased glutathione S-transferase activity in salt-invaded seedlings, which might be stimulated reactive oxygen species (ROS) scavenging along with higher GSH content. As a result, toxic MG was detoxified in Qu supplemented salt-stressed seedlings by increasing both Gly I and Gly II activities. Moreover, Qu insisted on better plant growth and photosynthetic pigments synthesis in saline or without saline media. Therefore, exogenous applied Qu may become an important actor to minimize salt-induced toxicity in crops.

Explicating physiological and biochemical responses of wheat cultivars under acidity stress: insight into the antioxidant defense and glyoxalase systems

Soil acidity causes proton (H⁺) rhizotoxicity, inhibits plant growth and development, and is a major yield-limiting factor for wheat production worldwide. Therefore, we investigated the physiological and biochemical responses of wheat (Triticum aestivum L.) to acidity stress in vitro. Five popular wheat cultivars developed by Bangladesh Agricultural Research Institute (BARI), namely, BARI Gom-21, BARI Gom-24, BARI Gom-25, BARI Gom-26, and BARI Gom-30, were studied in growing media under four different pH levels (3.5, 4.5, 5.5, and 6.5). We evaluated the cultivars based on their relative water content, proline (Pro) content, growth, biomass accumulation, oxidative damage, membrane stability, and mineral composition, as well as the performance of the antioxidant defense and glyoxalase systems. Although decrements of pH significantly reduced the tested morphophysiological and biochemical attributes in all the cultivars, there was high variability among the cultivars in response to the varying pH of the growing media. Acidity stress reduced growth, biomass, water content, and chlorophyll content in all the cultivars. However, BARI Gom-26 showed the least damage, with the lowest H₂O₂ generation, lipid peroxidation (MDA), and greater membrane stability, which indicate better tolerance against oxidative damage. In addition, the antioxidant defense components, ascorbate (AsA) and glutathione (GSH), and their redox balance were higher in this cultivar. Maximum H₂O₂ scavenging due to upregulation of the antioxidant enzymes [AsA peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), GSH reductase (GR), GSH peroxidase (GPX), and GSH-S-transferase (GST)] was observed in BARI Gom-26, which also illustrated significant enhancement of methylglyoxal (MG) detoxification by upregulating glyoxalase I (Gly I) and glyoxalase II (Gly II). This study also showed that balanced essential nutrient content as well as lower toxic micronutrient content was found in BARI Gom-26. Therefore, considering the physiological and biochemical attributes and growth, we conclude that BARI Gom-26 can withstand acidity stress during the early seedling stage, by regulating the coordinated action of the antioxidant defense and glyoxalase systems as well as maintaining nutrient balance.

Coupling physiological analysis with proteomic profile to understand the photosynthetic responses of young Euterpe oleracea palms to drought

This study examined whether drought sensitivity in açaí (Euterpe oleracea Mart.) is associated with reductions in photosynthesis and increasing oxidative stress in response to down-regulation of proteins related to photosynthetic reactions, photorespiration, and antioxidant system. Well-watered (Control) and drought-stressed plants were compared when leaf water potential in stressed plants reached around - 1.5 and - 3.0 MPa, representing moderate and severe drought. Drought caused 84 and 96% decreases in net photosynthetic rate (P_n) and stomatal conductance. Stress-mediated changes in maximum quantum efficiency of photosystem II (PSII) photochemistry were unobserved, but drought decreased photochemical quenching, actual quantum yield of PSII electron transport, and apparent electron transport rate (ETR). Moderate and severe drought induced, respectively, decreases and increases in non-photochemical quenching (NPQ) and 74 and 273% increases in ETR/P_n. Moderate drought down-regulated PSII protein D2, chlorophyll a-b binding protein 8, photosystem I reaction center subunit N, sedoheptulose-1,7-bisphosphatase, and transketolase; while severe drought down-regulated LHC II proteins, ferredoxin-NADP reductase, ATP synthase subunits ε and ß, and carbonic anhydrase isoform X2. The glutamate-glyoxylate aminotransferase 2 and glycine dehydrogenase were down-regulated upon moderate drought, while catalase 2 and glycine cleavage system H protein 3 were up-regulated. Severe drought up-regulated glycolate oxidase, glycine cleavage system H protein 3, and aminomethyl transferase, but most of photorespiration-related proteins were only found in control plants. Down-regulation of chaperones and antioxidant enzymes and increased lipid peroxidation in stressed plants were observed upon both stress severities. Therefore, the decreases in P_n and failure in preventing oxidative damages through adjustments in NPQ and photorespiration- and antioxidant-related proteins accounted for drought sensitivity in açaí.

Methylglyoxal triggers the heat tolerance in maize seedlings by driving AsA-GSH cycle and reactive oxygen species-/methylglyoxal-scavenging system

Traditionally, methylglyoxal (MG) was looked upon as a toxic byproduct of cellular metabolism. Nowadays, MG has been found to be a novel signaling molecule. However, whether MG can trigger the heat tolerance in maize seedlings and the underlying mechanisms is still elusive. In this study, the maize seedlings irrigated with MG increased the survival percentage of seedlings under heat stress (HS), remitted a decrease in tissue vitality and an increase in electrolyte leakage, and reduced membrane lipid peroxidation, implying MG could trigger the heat tolerance of maize seedlings. The further experiments showed that MG drove the ascorbic acid (AsA)-glutathione (GSH) cycle by activating enzymes (glutathione reductase, monodehydroascorbate reductase, dehydroascorbate reductase, and ascorbate peroxidase) and increasing the contents of antioxidants (AsA and GSH) and the ratio of GSH/(GSH + oxidized glutathione) and AsA/(AsA + dehydroascorbate) under both non-HS and HS. Also, the reactive oxygen species (ROS)-scavenger system (catalase, guaiacol peroxidase, carotenoid, total phenols, and flavonoids) and MG-scavenger system (glyoxalase I and glyoxalas II) also were up-regulated in maize seedlings pretreated with MG under non-HS and HS. This work for the first time reported that MG could trigger the heat tolerance of maize seedlings by driving the AsA-GSH cycle and ROS-/MG-scavenging system.