Carbon monoxide enhances the chilling tolerance of recalcitrant Baccaurea ramiflora seeds via nitric oxide-mediated glutathione homeostasis

Exploring the Role of Carbon Monoxide in Seed Physiology: Implications for Stress Tolerance and Practical Uses

Carbon monoxide (CO) is recognized as a signaling molecule in plants, inducing various physiological responses. This article briefly examines the physiological functions of CO in seed biology and seedlings' responses to environmental stresses. The activity of heme oxygenase (HO), the main enzyme responsible for CO synthesis, is a key factor controlling CO levels in plant cells. CO can influence seed germination by regulating seed dormancy through interactions with genes and hormones. Additionally, CO positively affects seedling growth by enhancing the antioxidant system, thereby increasing resistance to oxidative damage caused by stress. CO has beneficial effects on root development, root length, stomatal closure, and regulation of the photosynthetic system. Its interaction with reactive oxygen species (ROS) mediates hormone- and light-dependent growth processes during the early stages of plant development under stress. Furthermore, CO interacts with other signaling molecules, such as nitric oxide (NO), molecular hydrogen (H2), and hydrogen sulfide (H2S). By gaining a better understanding of the molecular mechanisms underlying these processes, CO can be more effectively utilized to improve seed germination and seedling growth in agricultural practices.

Carbon monoxide is involved in melatonin-enhanced drought resistance in tomato seedlings by enhancing chlorophyll synthesis pathway

BACKGROUND

Drought is thought to be a major abiotic stress that dramatically limits tomato growth and production. As signal molecule, melatonin (MT) and carbon monoxide (CO) can enhance plant stress resistance. However, the effect and underlying mechanism of CO involving MT-mediated drought resistance in seedling growth remains unknown. In this study, tomato (Solanum lycopersicum L. 'Micro-Tom') seedlings were used to investigate the interaction and mechanism of MT and CO in response to drought stress.

RESULTS

The growth of tomato seedlings was inhibited significantly under drought stress. Exogenous MT or CO mitigated the drought-induced impairment in a dose-dependent manner, with the greatest efficiency provided by 100 and 500 µM, respectively. But application of hemoglobin (Hb, a CO scavenger) restrained the positive effects of MT on the growth of tomato seedlings under drought stress. MT and CO treatment promoted chlorophyll a (Chl a) and chlorophyll a (Chl b) accumulations. Under drought stress, the intermediate products of chlorophyll biosynthesis such as protoporphyrin IX (Proto IX), Mg-protoporphyrin IX (Mg-Proto IX), potochlorophyllide (Pchlide) and heme were increased by MT or CO, but uroporphyrinogen III (Uro III) content decreased in MT-treated or CO-treated tomato seedlings. Meanwhile, MT or CO up-regulated the expression of chlorophyll and heme synthetic-related genes SlUROD, SlPPOX, SlMGMT, SlFECH, SlPOR, SlChlS, and SlCAO. However, the effects of MT on chlorophyll biosynthesis were almost reversed by Hb.

CONCLUSION

The results suggested that MT and CO can alleviate drought stress and facilitate the synthesis of Chl and heme in tomato seedlings. CO played an essential role in MT-enhanced drought resistance via facilitating chlorophyll biosynthesis pathway.

Carbon monoxide/heme oxygenase system in plant: Roles in abiotic stress response and crosstalk with other signals molecules

Carbon monoxide (CO) has been recognized as a crucial gasotransmitter mainly produced by heme oxygenase (HO)-catalyzed heme degradation in plant. Recent studies have shown that CO plays an important role in regulating growth and development of plant, as well as and responding to a variety of abiotic stresses. Meanwhile, many studies have reported on CO working in combination with other signal molecules to mitigate abiotic stress. Here, we presented a comprehensive overview of recent developments in which CO reduces plant damage caused by abiotic stresses. The regulation of antioxidant system, photosynthetic system, ion balance and transport are the main mechanisms of CO-alleviated abiotic stress. We also proposed and discussed the relationship between CO and other signal molecules, including nitric oxide (NO), hydrogen sulfide (H2S), hydrogen gas (H2), abscisic acid (ABA), indole 3-acetic acid (IAA), gibberellin (GA), cytokine (CTK), salicylic acid (SA), jasmonic acid (JA), hydrogen peroxide (H2O2) and calcium ion (Ca2+). Furthermore, the important role of HO genes in alleviating abiotic stress was also discussed. We proposed promising and new research directions for the study of plant CO, which can provide further insights on the role of CO in plant growth and development under abiotic stress.

Signal Mediators in the Implementation of Jasmonic Acid's Protective Effect on Plants under Abiotic Stresses

Plant cells respond to stress by activating signaling and regulatory networks that include plant hormones and numerous mediators of non-hormonal nature. These include the universal intracellular messenger calcium, reactive oxygen species (ROS), gasotransmitters, small gaseous molecules synthesized by living organisms, and signal functions such as nitrogen monoxide (NO), hydrogen sulfide (H₂S), carbon monoxide (CO), and others. This review focuses on the role of functional linkages of jasmonic acid and jasmonate signaling components with gasotransmitters and other signaling mediators, as well as some stress metabolites, in the regulation of plant adaptive responses to abiotic stressors. Data on the involvement of NO, H₂S, and CO in the regulation of jasmonic acid formation in plant cells and its signal transduction were analyzed. The possible involvement of the protein components of jasmonate signaling in stress-protective gasotransmitter effects is discussed. Emphasis is placed on the significance of the functional interaction between jasmonic acid and signaling mediators in the regulation of the antioxidant system, stomatal apparatus, and other processes important for plant adaptation to abiotic stresses.

Ammonia borane positively regulates cold tolerance in Brassica napus via hydrogen sulfide signaling

BACKGROUND

Cold stress adversely influences rapeseeds (Brassica napus L.) growth and yield during winter and spring seasons. Hydrogen (H₂) is a potential gasotransmitter that is used to enhance tolerance against abiotic stress, including cold stress. However, convenience and stability are two crucial limiting factors upon the application of H₂ in field agriculture. To explore the application of H₂ in field, here we evaluated the role of ammonia borane (AB), a new candidate for a H₂ donor produced by industrial chemical production, in plant cold tolerance.

RESULTS

The application with AB could obviously alleviate the inhibition of rapeseed seedling growth and reduce the oxidative damage caused by cold stress. The above physiological process was closely related to the increased antioxidant enzyme system and reestablished redox homeostasis. Importantly, cold stress-triggered endogenous H₂S biosynthesis was further stimulated by AB addition. The removal or inhibition of H₂S synthesis significantly abolished plant tolerance against cold stress elicited by AB. Further field experiments demonstrated that the phenotypic and physiological performances of rapeseed plants after challenged with cold stress in the winter and early spring seasons were significantly improved by administration with AB. Particularly, the most studied cold-stress response pathway, the ICE1-CBF-COR transcriptional cascade, was significantly up-regulated either.

CONCLUSION

Overall, this study clearly observed the evidence that AB-increased tolerance against cold stress could be suitable for using in field agriculture by stimulation of H₂S signaling.

Nitric Oxide in Seed Biology

Nitric oxide (NO) has been recognized as a gasotransmitter in the mainstream of plant research since the beginning of the 21st century. It is produced in plant tissue and the environment. It influences plant physiology during every ontogenetic stage from seed germination to plant senescence. In this review, we demonstrate the increased interest in NO as a regulatory molecule in combination with other signalling molecules and phytohormones in the information network of plant cells. This work is a summary of the current knowledge on NO action in seeds, starting from seed pretreatment techniques applied to increase seed quality. We describe mode of action of NO in the regulation of seed dormancy, germination, and aging. During each stage of seed physiology, NO appears to act as a key agent with a predominantly beneficial effect.

De novo transcriptome assembly of the cotyledon of Camellia oleifera for discovery of genes regulating seed germination

BACKGROUND

Camellia oleifera (C.oleifera) is one of the most important wood oil species in the world. C.oleifera was propagated by nurse seedling grafting. Since the morphology of rootstocks has a significant impact on grafting efficiency and seedling quality, it is necessary to understand the molecular mechanism of morphogenesis for cultivating high-quality and controllable rootstocks. However, the genomic resource for this species is relatively limited, which hinders us from fully understanding the molecular mechanisms of seed germination in C.oleifera.

RESULTS

In this paper, using transcriptome sequencing, we measured the gene expression in the C.oleifera cotyledon in different stages of development and the global gene expression profiles. Approximately 45.4 gigabases (GB) of paired-end clean reads were assembled into 113,582 unigenes with an average length of 396 bp. Six public protein databases annotate 61.5% (68,217) of unigenes. We identified 11,391 differentially expressed genes (DEGs) throughout different stages of germination. Enrichment analysis revealed that DEGs were mainly involved in hormone signal transduction and starch sucrose metabolism pathways. The gravitropism regulator UNE10, the meristem regulators STM, KNAT1, PLT2, and root-specific transcription factor WOX11 all have higher gene expression levels in the CAM2 stage (seed soaking), which indicates that the cotyledon-regulated program for germination had initiated when the seeds were imbibition. Our data showed differentially reprogrammed to multiple hormone-related genes in cotyledons during C.oleifera seed germination.

CONCLUSION

Cotyledons play vital roles, both as the main nutrient provider and as one primary instructor for seed germination and seedling growth. Together, our study will significantly enrich the genomic resources of Camellia and help us understand the molecular mechanisms of the development in the seed germination and seedling growth of C.oleifera. It is helpful to culture standard and superior quality rootstock for C.oleifera breeding.

iTRAQ and RNA-seq analyses provide an insight into mechanisms of recalcitrance in a medicinal plant Panax notoginseng seeds during the after-ripening process

Panax notoginseng (Burk) F.H. Chen is an important economic and medicinal plant from the family of Araliaceae, and its seed is characterised by the recalcitrance and after-ripening process. However, the molecular mechanism on the dehydration sensitivity is not clear in recalcitrant seeds. In the present study, isobaric tag for relative and absolute quantification (iTRAQ) and RNA-seq were used to analyse the proteomic and transcriptomic changes in seeds of P. notoginseng in days after-ripening (DAR). A total of 454 differentially expressed proteins (DEPs) and 12000 differentially expressed genes (DEGs) were obtained. The activity of enzymes related to antioxidant system were significantly increased, and the late embryogenesis abundant (LEA) protein family and most members of glutathione metabolism enzymes have been downregulated during the after-ripening process. The lack or inadequate accumulation of LEA proteins in the embryo and the low activity of antioxidant defense in glutathione metabolism might be the key factors leading to the dehydration sensitivity in recalcitrant seeds of P. notoginseng. In addition, the increased activity of elycolysis (EMP), citric acid cycle (TCA) and pentose phosphate pathway (PPP) pathways might be one of important signals to complete the after-ripening process. Overall, our study might provide a new insight into the molecular mechanism on dehydration sensitivity of recalcitrant seeds.

Heme oxygenase-1/carbon monoxide signaling participates in the accumulation of triterpenoids of Ganoderma lucidum

Ganoderic triterpenoids (GTs) are the primary bioactive constituents of the Basidiomycotina fungus, Ganoderma lucidum. These compounds exhibit antitumor, anti-hyperlipidemic, and immune-modulatory pharmacological activities. This study focused on GT accumulation in mycelia of G. lucidum mediated by the heme oxygenase-1 (HO-1)/carbon monoxide (CO) signaling. Compared with the control, hemin (10 μmol/L) induced an increase of 60.1% in GT content and 57.1% in HO-1 activity. Moreover, carbon monoxide-releasing molecule-2 (CORM-2), CO donor, increased GT content by 56.0% and HO-1 activity by 18.1%. Zn protoporphyrin IX (ZnPPIX), a specific HO-1 inhibitor, significantly reduced GT content by 26.0% and HO-1 activity by 15.8%, while hemin supplementation reversed these effects. Transcriptome sequencing showed that HO-1/CO could function directly as a regulator involved in promoting GT accumulation by regulating gene expression in the mevalonate pathway, and modulating the reactive oxygen species (ROS) and Ca²⁺ pathways. The results of this study may help enhance large-scale GT production and support further exploration of GT metabolic networks and relevant signaling cross-talk.

Structural and functional insights into nitrosoglutathione reductase from Chlamydomonas reinhardtii

Protein S-nitrosylation plays a fundamental role in cell signaling and nitrosoglutathione (GSNO) is considered as the main nitrosylating signaling molecule. Enzymatic systems controlling GSNO homeostasis are thus crucial to indirectly control the formation of protein S-nitrosothiols. GSNO reductase (GSNOR) is the key enzyme controlling GSNO levels by catalyzing its degradation in the presence of NADH. Here, we found that protein extracts from the microalga Chlamydomonas reinhardtii catabolize GSNO via two enzymatic systems having specific reliance on NADPH or NADH and different biochemical features. Scoring the Chlamydomonas genome for orthologs of known plant GSNORs, we found two genes encoding for putative and almost identical GSNOR isoenzymes. One of the two, here named CrGSNOR1, was heterologously expressed and purified. Its kinetic properties were determined and the three-dimensional structures of the apo-, NAD⁺- and NAD⁺/GSNO-forms were solved. These analyses revealed that CrGSNOR1 has a strict specificity towards GSNO and NADH, and a conserved folding with respect to other plant GSNORs. The catalytic zinc ion, however, showed an unexpected variability of the coordination environment. Furthermore, we evaluated the catalytic response of CrGSNOR1 to thermal denaturation, thiol-modifying agents and oxidative modifications as well as the reactivity and position of accessible cysteines. Despite being a cysteine-rich protein, CrGSNOR1 contains only two solvent-exposed/reactive cysteines. Oxidizing and nitrosylating treatments have null or limited effects on CrGSNOR1 activity and folding, highlighting a certain resistance of the algal enzyme to redox modifications. The molecular mechanisms and structural features underlying the response to thiol-based modifications are discussed.

•

Chlamydomonas protein extracts catalyze NAD(P)H-dependent GSNO degradation.

•

Chlamydomonas GSNOR1 is a zinc-containing protein strictly relying on GSNO and NADH.

•

The 3D-structure of CrGSNOR1 revealed a conserved folding with other plant GSNORs.

•

CrGSNOR1 contains only two solvent-exposed/reactive cysteines.

•

Oxidizing and nitrosylating treatments have limited effects on CrGSNOR1 activity.

S-Nitrosoglutathione Reductase-The Master Regulator of Protein S-Nitrosation in Plant NO Signaling

S-nitrosation has been recognized as an important mechanism of protein posttranslational regulations, based on the attachment of a nitroso group to cysteine thiols. Reversible S-nitrosation, similarly to other redox-base modifications of protein thiols, has a profound effect on protein structure and activity and is considered as a convergence of signaling pathways of reactive nitrogen and oxygen species. In plant, S-nitrosation is involved in a wide array of cellular processes during normal development and stress responses. This review summarizes current knowledge on S-nitrosoglutathione reductase (GSNOR), a key enzyme which regulates intracellular levels of S-nitrosoglutathione (GSNO) and indirectly also of protein S-nitrosothiols. GSNOR functions are mediated by its enzymatic activity, which catalyzes irreversible GSNO conversion to oxidized glutathione within the cellular catabolism of nitric oxide. GSNOR is involved in the maintenance of balanced levels of reactive nitrogen species and in the control of cellular redox state. Multiple functions of GSNOR in plant development via NO-dependent and -independent signaling mechanisms and in plant defense responses to abiotic and biotic stress conditions have been uncovered. Extensive studies of plants with down- and upregulated GSNOR, together with application of transcriptomics and proteomics approaches, seem promising for new insights into plant S-nitrosothiol metabolism and its regulation.

S-Nitrosoglutathione Reductase-The Master Regulator of Protein S-Nitrosation in Plant NO Signaling

S-nitrosation has been recognized as an important mechanism of protein posttranslational regulations, based on the attachment of a nitroso group to cysteine thiols. Reversible S-nitrosation, similarly to other redox-base modifications of protein thiols, has a profound effect on protein structure and activity and is considered as a convergence of signaling pathways of reactive nitrogen and oxygen species. In plant, S-nitrosation is involved in a wide array of cellular processes during normal development and stress responses. This review summarizes current knowledge on S-nitrosoglutathione reductase (GSNOR), a key enzyme which regulates intracellular levels of S-nitrosoglutathione (GSNO) and indirectly also of protein S-nitrosothiols. GSNOR functions are mediated by its enzymatic activity, which catalyzes irreversible GSNO conversion to oxidized glutathione within the cellular catabolism of nitric oxide. GSNOR is involved in the maintenance of balanced levels of reactive nitrogen species and in the control of cellular redox state. Multiple functions of GSNOR in plant development via NO-dependent and -independent signaling mechanisms and in plant defense responses to abiotic and biotic stress conditions have been uncovered. Extensive studies of plants with down- and upregulated GSNOR, together with application of transcriptomics and proteomics approaches, seem promising for new insights into plant S-nitrosothiol metabolism and its regulation.

Crosstalk between reactive oxygen species and nitric oxide in plants: Key role of S-nitrosoglutathione reductase

Nitric oxide (.NO) acts as signaling molecule in plants being involved in diverse physiological processes such as germination, root growth, stomata closing and response to biotic and abiotic stress. S-Nitrosoglutathione (GSNO) is the storage and transport form of.NO and has a very important function in.NO signaling since it can transfer its.NO moiety to other proteins (trans-nitrosylation). The level of GSNO and thus the level of S-nitrosylated proteins are regulated by GSNO-reductase (GSNOR). In this way, this enzyme regulates the S-nitrosothiol levels and plays a balancing role in fine-tuning.NO signaling. Interestingly, oxidative post-translationally modification of GSNOR inhibited the activity of this enzyme suggesting a direct crosstalk between ROS- and RNS-signaling. In this review article the regulatory effects of ROS on GSNOR are highlighted and their physiological function in context of crosstalk between ROS and.NO and species in plants are discussed.

Carbon Monoxide Potentiates High Temperature-Induced Nicotine Biosynthesis in Tobacco

Carbon monoxide (CO) acts as an important signal in many physiological responses in plants, but its role in plant secondary metabolism is still unknown. Nicotine is the main alkaloid generated in tobacco and the plant hormone jasmonic acid (JA) has previously been reported to efficiently induce its biosynthesis. Whether and how CO interacts with JA to regulate nicotine biosynthesis in tobacco remains elusive. In this study, we demonstrate that high temperature (HT) induces quick accumulation of nicotine in tobacco roots, combined with an increase in CO and JA concentration. Suppressing CO generation reduced both JA and nicotine biosynthesis, whereas exogenous application of CO increased JA and nicotine content. CO causes an increased expression of NtPMT1 (a key nicotine biosynthesis enzyme), via promoting NtMYC2a binding to the G-box region of its promoter, leading to heightened nicotine levels under HT conditions. These data suggest a novel function for CO in stimulating nicotine biosynthesis in tobacco under HT stress, through a JA signal.

Overexpression of E3 Ubiquitin Ligase Gene AdBiL Contributes to Resistance against Chilling Stress and Leaf Mold Disease in Tomato

Ubiquitination is a common regulatory mechanism, playing a critical role in diverse cellular and developmental processes in eukaryotes. However, a few reports on the functional correlation between E3 ubiquitin ligases and reactive oxygen species (ROS) or reactive nitrogen species (RNS) metabolism in response to stress are currently available in plants. In the present study, the E3 ubiquitin ligase gene AdBiL (Adi3 Binding E3 Ligase) was introduced into tomato line Ailsa Craig via Agrobacterium-mediated method. Transgenic lines were confirmed for integration into the tomato genome using PCR. Transcription of AdBiL in various transgenic lines was determined using real-time PCR. Evaluation of stress tolerance showed that T₁ generation of transgenic tomato lines showed only mild symptoms of chilling injury as evident by higher biomass accumulation and chlorophyll content than those of non-transformed plants. Compared with wild-type plants, the contents of AsA, AsA/DHA, GSH and the activity of GaILDH, γ-GCS and GSNOR were increased, while H₂O₂, [Formula: see text], MDA, NO, SNOs, and GSNO accumulations were significantly decreased in AdBiL overexpressing plants in response to chilling stress. Furthermore, transgenic tomato plants overexpressing AdBiL showed higher activities of enzymes such as G6PDH, 6PGDH, NADP-ICDH, and NADP-ME involved in pentose phosphate pathway (PPP). The transgenic tomato plants also exhibited an enhanced tolerance against the necrotrophic fungus Cladosporium fulvum. Tyrosine nitration protein was activated in the plants infected with leaf mold disease, while the inhibition could be recovered in AdBiL gene overexpressing lines. Taken together, our results revealed a possible physiological role of AdBiL in the activation of the key enzymes of AsA-GSH cycle, PPP and down-regulation of GSNO reductase, thereby reducing oxidative and nitrosative stress in plants. This study demonstrates an optimized transgenic strategy using AdBiL gene for crop improvement against biotic and abiotic stress factors.

Nitric Oxide Overproduction in Tomato shr Mutant Shifts Metabolic Profiles and Suppresses Fruit Growth and Ripening

Nitric oxide (NO) plays a pivotal role in growth and disease resistance in plants. It also acts as a secondary messenger in signaling pathways for several plant hormones. Despite its clear role in regulating plant development, its role in fruit development is not known. In an earlier study, we described a short root (shr) mutant of tomato, whose phenotype results from hyperaccumulation of NO. The molecular mapping localized shr locus in 2.5 Mb region of chromosome 9. The shr mutant showed sluggish growth, with smaller leaves, flowers and was less fertile than wild type. The shr mutant also showed reduced fruit size and slower ripening of the fruits post-mature green stage to the red ripe stage. Comparison of the metabolite profiles of shr fruits with wild-type fruits during ripening revealed a significant shift in the patterns. In shr fruits intermediates of the tricarboxylic acid (TCA) cycle were differentially regulated than WT indicating NO affected the regulation of TCA cycle. The accumulation of several amino acids, particularly tyrosine, was higher, whereas most fatty acids were downregulated in shr fruits. Among the plant hormones at one or more stages of ripening, ethylene, Indole-3-acetic acid and Indole-3-butyric acid increased in shr, whereas abscisic acid declined. Our analyses indicate that the retardation of fruit growth and ripening in shr mutant likely results from the influence of NO on central carbon metabolism and endogenous phytohormones levels.

Asada-Halliwell pathway maintains redox status in Dioscorea alata tuber which helps in germination

Reactive Oxygen Species (ROS) are important regulatory molecules governing physiological processes. In the present study a biochemical and proteome level comparison of two contrasting growth stages of Dioscorea alata tuber namely germinating and mature tuber was performed in order to understand the tuber physiology and biochemistry. Existence of all the component enzymes [APx (ascorbate peroxidase), GR (glutathione reductase), DHAR (dehydroascorbate reductase), MDHAR (mono-dehydroascorbate reductase)] and major products [ascorbate (ASC) and glutathione (GSH)] of the cycle showed an operational Asada-Halliwell cycle in the tuber. A 2.65 fold increase in ASC content & a 3.8 fold increase in GR activity fortified the redox milieu during germination. In contrast a 5 fold higher H2O2 content (due to 3.08 fold lower APx activity) and accumulation of reactive nitrogen species (RNS) such as nitric oxide (NO, 2.4-fold) and S-nitrosothiol (SNO, 2.08 fold) contributed to overall oxidative conditions in the mature tuber. The carbonic anhydrase (CA, 7.5 fold), DHAR (5.31 fold) and MDHAR (7 fold) activities were higher in the germinating tuber in comparison with the mature tuber. GSNO negatively regulated the CA (3.6 & 3.95 fold), MDHAR (7.5 & 1.5 fold) and APx (2.3 & 1.81 fold) while another NO donor, CysNO negatively regulated the DHAR (2.24 & 1.32 fold) activity in the mature and germinating stages respectively indicating again that the lesser inhibition by NO (via nitrosylation) may be because of overall reducing environment in the germinating tuber. Increased SNO leading to S-nitrosylation of dioscorin was confirmed by Biotin switch assay. This is the first report showing dioscorin nitrosylation. The present analysis showed differential redox regulation and also suggests the physiological relevance of CA, DHAR, MDHAR, APx & GR in tuber germination for the first time. These enzymes may be used as potential markers of tuber germination in future.

Induction of Osmoregulation and Modulation of Salt Stress in Acacia gerrardii Benth. by Arbuscular Mycorrhizal Fungi and Bacillus subtilis (BERA 71)

The role of soil microbiota in plant stress management, though speculated a lot, is still far from being completely understood. We conducted a greenhouse experiment to examine synergistic impact of plant growth promoting rhizobacterium, Bacillus subtilis (BERA 71), and arbuscular mycorrhizal fungi (AMF) (Claroideoglomus etunicatum; Rhizophagus intraradices; and Funneliformis mosseae) to induce acquired systemic resistance in Talh tree (Acacia gerrardii Benth.) against adverse impact of salt stress. Compared to the control, the BERA 71 treatment significantly enhanced root colonization intensity by AMF, in both presence and absence of salt. We also found positive synergistic interaction between B. subtilis and AMF vis-a-vis improvement in the nutritional value in terms of increase in total lipids, phenols, and fiber content. The AMF and BERA 71 inoculated plants showed increased content of osmoprotectants such as glycine, betaine, and proline, though lipid peroxidation was reduced probably as a mechanism of salt tolerance. Furthermore, the application of bioinoculants to Talh tree turned out to be potentially beneficial in ameliorating the deleterious impact of salinity on plant metabolism, probably by modulating the osmoregulatory system (glycine betaine, proline, and phenols) and antioxidant enzymes system (SOD, CAT, POD, GR, APX, DHAR, MDAHR, and GSNOR).

Sensitivity to high temperature and water stress in recalcitrant Baccaurea ramiflora seeds

Southeast Asia experiences one of the highest rates of deforestation in the tropics due to agricultural expansion, logging, habitat fragmentation and urbanization. As tropical rainforests harbour abundant recalcitrant-seeded species, it is important to understand how recalcitrant seeds respond to deforestation and fragmentation. Baccaurea ramiflora is a recalcitrant-seeded species, widely distributed in Southeast Asian tropical rainforest. In this study, B. ramiflora seeds were sown in three plots, one in a nature reserve and two in disturbed holy hill forests, to investigate seed germination and seedling establishment in the field, while laboratory experiments were conducted to investigate the effects of high temperature and water stress on germination. It was found that seed germination and seedling establishment in B. ramiflora were clearly reduced in holy hills compared to the nature reserve, although the seeds were only moderately to minimally recalcitrant. This was potentially caused by increased temperature and decreased moisture in holy hills, for laboratory experiments showed that seed germination was greatly inhibited by temperatures ≥35 °C or water potentials ≤-0.5 MPa, and depressed by heat treatment at 40 °C when the continuous heating period lasted for 240 h or daily periodic heating exceeded 10 h. Unlike orthodox seeds, which can endure much higher temperatures in the air-dried state than in the imbibed state, both blotted and immersed B. ramiflora seeds lost viability within a narrow temperature range between 50 and 60 °C. As recalcitrant seeds can be neither air-dried nor heated, species producing recalcitrant seeds will suffer more than those producing orthodox seeds in germination and seedling establishment from increased temperature and decreased moisture in fragmented rainforests, which results in sensitivity of recalcitrant-seeded species to rainforest fragmentation.

Heme Oxygenase-1 Delays Gibberellin-Induced Programmed Cell Death of Rice Aleurone Layers Subjected to Drought Stress by Interacting with Nitric Oxide

Cereal aleurone layers undergo a gibberellin (GA)-regulated process of programmed cell death (PCD) following germination. Heme oxygenase-1 (HO-1) is known as a rate-liming enzyme in the degradation of heme to biliverdin IXα, carbon monoxide (CO), and free iron ions (Fe(2+)). It is a critical component in plant development and adaptation to environment stresses. Our previous studies confirmed that HO-1 inducer hematin (Ht) promotes the germination of rice seeds in drought (20% polyethylene glycol-6000, PEG) conditions, but the corresponding effects of HO-1 on the alleviation of germination-triggered PCD in GA-treated rice aleurone layers remain unknown. The present study has determined that GA co-treated with PEG results in lower HO-1 transcript levels and HO activity, which in turn results in the development of vacuoles in aleurone cells, followed by PCD. The pharmacology approach illustrated that up- or down-regulated HO-1 gene expression and HO activity delayed or accelerated GA-induced PCD. Furthermore, the application of the HO-1 inducer Ht and nitric oxide (NO) donor sodium nitroprusside (SNP) not only activated HO-1 gene expression, HO activity, and endogenous NO content, but also blocked GA-induced rapid vacuolation and accelerated aleurone layers PCD under drought stress. However, both HO-1 inhibitor zinc protoporphyrin IX (ZnPPIX) and NO scavenger 2-(4-carboxyphenyl0-4, 4,5,5-tetramethylimidazoline-l-oxyl-3-oxide potassium salt (cPTIO) reserved the effects of Ht and SNP on rice aleurone layer PCD under drought stress by down-regulating endogenous HO-1 and NO, respectively. The inducible effects of Ht and SNP on HO-1 gene expression, HO activity, and NO content were blocked by cPTIO. Together, these results clearly suggest that HO-1 is involved in the alleviation of GA-induced PCD of drought-triggered rice aleurone layers by associating with NO.

Mechanisms of nitric oxide crosstalk with reactive oxygen species scavenging enzymes during abiotic stress tolerance in plants

Nitric oxide (NO) acts in a concentration and redox-dependent manner to counteract oxidative stress either by directly acting as an antioxidant through scavenging reactive oxygen species (ROS), such as superoxide anions (O(2)(-)*), to form peroxynitrite (ONOO(-)) or by acting as a signaling molecule, thereby altering gene expression. NO can interact with different metal centres in proteins, such as heme-iron, zinc-sulfur clusters, iron-sulfur clusters, and copper, resulting in the formation of a stable metal-nitrosyl complex or production of varied biochemical signals, which ultimately leads to modification of protein structure/function. The thiols (ferrous iron-thiol complex and nitrosothiols) are also involved in the metabolism and mobilization of NO. Thiols bind to NO and transport it to the site of action whereas nitrosothiols release NO after intercellular diffusion and uptake into the target cells. S-nitrosoglutathione (GSNO) also has the ability to transnitrosylate proteins. It is an NO˙ reservoir and a long-distance signaling molecule. Tyrosine nitration of proteins has been suggested as a biomarker of nitrosative stress as it can lead to either activation or inhibition of target proteins. The exact molecular mechanism(s) by which exogenous and endogenously generated NO (or reactive nitrogen species) modulate the induction of various genes affecting redox homeostasis, are being extensively investigated currently by various research groups. Present review provides an in-depth analysis of the mechanisms by which NO interacts with and modulates the activity of various ROS scavenging enzymes, particularly accompanying ROS generation in plants in response to varied abiotic stress.

ROS-Mediated Inhibition of S-nitrosoglutathione Reductase Contributes to the Activation of Anti-oxidative Mechanisms

Nitric oxide (NO) has emerged as a signaling molecule in plants being involved in diverse physiological processes like germination, root growth, stomata closing and response to biotic and abiotic stress. S-nitrosoglutathione (GSNO) as a biological NO donor has a very important function in NO signaling since it can transfer its NO moiety to other proteins (trans-nitrosylation). Such trans-nitrosylation reactions are equilibrium reactions and depend on GSNO level. The breakdown of GSNO and thus the level of S-nitrosylated proteins are regulated by GSNO-reductase (GSNOR). In this way, this enzyme controls S-nitrosothiol levels and regulates NO signaling. Here we report that Arabidopsis thaliana GSNOR activity is reversibly inhibited by H₂O₂in vitro and by paraquat-induced oxidative stress in vivo. Light scattering analyses of reduced and oxidized recombinant GSNOR demonstrated that GSNOR proteins form dimers under both reducing and oxidizing conditions. Moreover, mass spectrometric analyses revealed that H₂O₂-treatment increased the amount of oxidative modifications on Zn²⁺-coordinating Cys47 and Cys177. Inhibition of GSNOR results in enhanced levels of S-nitrosothiols followed by accumulation of glutathione. Moreover, transcript levels of redox-regulated genes and activities of glutathione-dependent enzymes are increased in gsnor-ko plants, which may contribute to the enhanced resistance against oxidative stress. In sum, our results demonstrate that reactive oxygen species (ROS)-dependent inhibition of GSNOR is playing an important role in activation of anti-oxidative mechanisms to damping oxidative damage and imply a direct crosstalk between ROS- and NO-signaling.

Carbon Monoxide Interacts with Auxin and Nitric Oxide to Cope with Iron Deficiency in Arabidopsis

To clarify the roles of carbon monoxide (CO), nitric oxide (NO), and auxin in the plant response to iron deficiency (-Fe), and to establish how the signaling molecules interact to enhance Fe acquisition, we conducted physiological, genetic, and molecular analyses that compared the responses of various Arabidopsis mutants, including hy1 (CO deficient), noa1 (NO deficient), nia1/nia2 (NO deficient), yuc1 (auxin over-accumulation), and cue1 (NO over-accumulation) to -Fe stress. We also generated a HY1 over-expression line (named HY1-OX) in which CO is over-produced compared to wild-type. We found that the suppression of CO and NO generation using various inhibitors enhanced the sensitivity of wild-type plants to Fe depletion. Similarly, the hy1, noa1, and nia1/nia2 mutants were more sensitive to Fe deficiency. By contrast, the yuc1, cue1, and HY1-OX lines were less sensitive to Fe depletion. The hy1 mutant with low CO content exhibited no induced expression of the Fe uptake-related genes FIT1 and FRO2 as compared to wild-type plants. On the other hand, the treatments of exogenous CO and NO enhanced Fe uptake. Likewise, cue1 and HY1-OX lines with increased endogenous content of NO and CO, respectively, also exhibited enhanced Fe uptake and increased expression of bHLH transcriptional factor FIT1as compared to wild-type plants. Furthermore, we found that CO affected auxin accumulation and transport in the root tip by altering the PIN1 and PIN2 proteins distribution that control lateral root structure under -Fe stress. Our results demonstrated the integration of CO, NO, and auxin signaling to cope with Fe deficiency in Arabidopsis.

Quantitative proteomics analysis reveals that S-nitrosoglutathione reductase (GSNOR) and nitric oxide signaling enhance poplar defense against chilling stress

NO acts as the essential signal to enhance poplar tolerance to chilling stress via antioxidant enzyme activities and protein S -nitrosylation modification, NO signal is also strictly controlled by S -nitrosoglutathione reductase and nitrate reductase to avoid the over-accumulation of reactive nitrogen species. Poplar (Populus trichocarpa) are fast growing woody plants with both ecological and economic value; however, the mechanisms by which poplar adapts to environmental stress are poorly understood. In this study, we used isobaric tags for relative and absolute quantification proteomic approach to characterize the response of poplar exposed to cold stress. We identified 114 proteins that were differentially expressed in plants exposed to cold stress. In particular, some of the proteins are involved in reactive oxygen species (ROS) and reactive nitrogen species (RNS) metabolism. Further physiological analysis showed that nitric oxide (NO) signaling activated a series of downstream defense responses. We further demonstrated that NO activated antioxidant enzyme activities and S-nitrosoglutathione reductase (GSNOR) activities, which would reduce ROS and RNS toxicity and thereby enhance poplar tolerance to cold stress. Suppressing NO accumulation or GSNOR activity aggravated cold damage to poplar leaves. Moreover, our results showed that RNS can suppress the activities of GSNOR and NO nitrate reductase (NR) by S-nitrosylation to fine-tune the NO signal and modulate ROS levels by modulating the S-nitrosylation of ascorbate peroxidase protein. Hence, our data demonstrate that NO signaling activates multiple pathways that enhance poplar tolerances to cold stress, and that NO signaling is strictly controlled through protein post-translational modification by S-nitrosylation.

Nitric Oxide Mediates 5-Aminolevulinic Acid-Induced Antioxidant Defense in Leaves of Elymus nutans Griseb. Exposed to Chilling Stress

Nitric oxide (NO) and 5-aminolevulinic acid (ALA) are both extremely important signalling molecules employed by plants to control many aspects of physiology. In the present study, the role of NO in ALA-induced antioxidant defense in leaves of two sources of Elymus nutans Griseb. (Damxung, DX and Zhengdao, ZD) was investigated. Chilling stress enhanced electrolyte leakage, accumulation of malondialdehyde (MDA), hydrogen peroxide (H2O2) and superoxide radical in two E. nutans, which were substantially alleviated by exogenous ALA and NO application. Pretreatment with NO scavenger PTIO or NOS inhibitor L-NNA alone and in combination with ALA induced enhancements in electrolyte leakage and the accumulation of MDA, H2O2 and superoxide radical in leaves of DX and ZD exposed to chilling stress, indicating that the inhibition of NO biosynthesis reduced the chilling resistance of E. nutans and the ALA-enhanced chilling resistance. Further analyses showed that ALA and NO enhanced antioxidant defense and activated plasma membrane (PM) H+-ATPase and decreased the accumulation of ROS induced by chilling stress. A pronounced increase in nitric oxide synthase (NOS) activity and NO release by exogenous ALA treatment was found in chilling-resistant DX plants exposed to chilling stress, while only a little increase was observed in chilling-sensitive ZD. Furthermore, inhibition of NO accumulation by PTIO or L-NNA blocked the protective effect of exogenous ALA, while both exogenous NO treatment and inhibition of endogenous NO accumulation did not induce ALA production. These results suggested that NO might be a downstream signal mediating ALA-induced chilling resistance in E. nutans.

Comparative proteomic analysis reveals the role of hydrogen sulfide in the adaptation of the alpine plant Lamiophlomis rotata to altitude gradient in the Northern Tibetan Plateau

We found the novel role of hydrogen sulfide in the adaptation of the alpine plant to altitude gradient in the Northern Tibetan Plateau. Alpine plants have developed strategies to survive the extremely cold conditions prevailing at high altitudes; however, the mechanism underlying the evolution of these strategies remains unknown. Hydrogen sulfide (H2S) is an essential messenger that enhances plant tolerance to environmental stress; however, its role in alpine plant adaptation to environmental stress has not been reported until now. In this work, we conducted a comparative proteomics analysis to investigate the dynamic patterns of protein expression in Lamiophlomis rotata plants grown at three different altitudes. We identified and annotated 83 differentially expressed proteins. We found that the levels and enzyme activities of proteins involved in H2S biosynthesis markedly increased at higher altitudes, and that H2S accumulation increased. Exogenous H2S application increased antioxidant enzyme activity, which reduced ROS (reactive oxygen species) damage, and GSNOR (S-nitrosoglutathione reductase) activity, which reduced RNS (reactive nitrogen species) damage, and activated the downstream defense response, resulting in protein degradation and proline and sugar accumulation. However, such defense responses could be reversed by applying H2S biosynthesis inhibitors. Based on these findings, we conclude that L. rotata uses multiple strategies to adapt to the alpine stress environment and that H2S plays a central role during this process.

Heme-heme oxygenase 1 system is involved in ammonium tolerance by regulating antioxidant defence in Oryza sativa

Despite substantial evidence showing the ammonium-altered redox homeostasis in plants, the involvement and molecular mechanism of heme-heme oxygenase 1 (heme-HO1), a novel antioxidant system, in the regulation of ammonium tolerance remain elusive. To fill in these gaps, the biological function of rice HO1 (OsSE5) was investigated. Results showed that NH4 Cl up-regulated rice OsSE5 expression. Oxidative stress and subsequent growth inhibition induced by excess NH4 Cl was partly mitigated by pretreatment with carbon monoxide (CO, a by-product of HO1 activity) or intensified by zinc protoporphyrin (ZnPP, a potent inhibitor of HO1 activity). Pretreatment with HO1 inducer hemin, not only up-regulated OsSE5 expression and HO activity, but also rescued the down-regulation of antioxidant transcripts, total and related isozymatic activities, thus significantly counteracting the excess NH4 Cl-triggered reactive oxygen species overproduction, lipid peroxidation and growth inhibition. OsSE5 RNAi transgenic rice plants revealed NH4 Cl-hypersensitive phenotype with impaired antioxidant defence, both of which could be rescued by CO but not hemin. Transgenic Arabidopsis plants over-expressing OsSE5 also exhibited enhanced tolerance to NH4 Cl, which might be attributed to the up-regulation of several antioxidant transcripts. Altogether, these results illustrated the involvement of heme-HO1 system in ammonium tolerance by enhancing antioxidant defence, which may improve plant tolerance to excess ammonium fertilizer.

New clues for a cold case: nitric oxide response to low temperature

Low temperature is among the most frequent stresses met by plants during their lifespan, and a plant's ability to cold-acclimate is a determinant for further growth and development. Although intensive research has provided a good picture of the molecular and metabolic changes triggered by cold, the underlying regulatory mechanisms remain elusive and are thus being actively sought. Recent studies have shed light on the importance of nitric oxide (NO), a ubiquitous signalling molecule in eukaryotes, for plant tolerance to chilling and freezing. Indeed, NO formation following cold exposure has been reported in a range of plant species, and a series of proteins targeted by NO-based post-translational modifications have been identified. Moreover, key cold-regulated genes have been characterized as NO-dependent, suggesting the crucial importance of NO signalling for cold-responsive gene expression. This review provides a picture of our current understanding of the function of NO in the context of plant response to cold. Particular attention is dedicated to the open questions left by the fragmented data currently available concerning NO formation, transduction and biological significance for plant adaptation to low temperature.

Indole acetic acid is responsible for protection against oxidative stress caused by drought in soybean plants: the role of heme oxygenase induction

Objectives This study was focused on the role of indole acetic acid (IAA) in the defense against oxidative stress damage caused by drought in soybean plants and to elucidate whether heme oxygenase-1 (HO-1) and nitric oxide (NO) are involved in this mechanism. IAA is an auxin that participates in many plant processes including oxidative stress defense, but to the best of our knowledge no information is yet available about its possible action in drought stress. Methods To this end, soybean plants were treated with 8% polyethylene glycol (PEG) or 100 µM IAA. To evaluate the behavior of IAA, plants were pretreated with this compound previous to PEG addition. Lipid peroxidation levels (thiobarbituric acid reactive substances (TBARS)), glutathione (GSH) and ascorbate (AS) contents, catalase (CAT), superoxide dismutase (SOD), and guaiacol peroxidase (POD) activities were determined to evaluate oxidative damage. Results Drought treatment (8% PEG) caused a significant increase in TBARS levels as well as a marked decrease in the non-enzymatic (GSH and AS) and enzymatic (CAT, SOD, and POD) antioxidant defense systems. Pre-treatment with IAA prevented the alterations of stress parameters caused by drought, while treatment with IAA alone did not produce changes in TBARS levels, or GSH and AS contents. Moreover, the activities of the classical enzymes involved in the enzymatic defense system (SOD, CAT, and POD) remained similar to control values. Furthermore, this hormone could enhance HO-1 activity (75% with respect to controls), and this increase was positively correlated with protein content as well as gene expression. The direct participation of HO-1 as an antioxidant enzyme was established by performing experiments in the presence of Zn-protoporphyrin IX, a well-known irreversible inhibitor of this enzyme. It was also demonstrated that HO-1 is modulated by NO, as shown by experiments performed in the presence of an NO donor (sodium nitroprusside), an NO scavenger (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), or an NO synthesis inhibitor (N-nitro-l-arginine methyl ester, NAME). Discussion It is concluded that IAA is responsible, at least in part, for the protection against oxidative stress caused by drought in soybean plants through the modulation of NO levels which, in turn, enhances HO-1 synthesis and activity.

S-nitrosylation analysis in Brassica juncea apoplast highlights the importance of nitric oxide in cold-stress signaling

Reactive nitrogen species (RNS) including nitric oxide (NO) are important components of stress signaling. However, RNS-mediated signaling in the apoplast remains largely unknown. NO production measured in the shoot apoplast of Brassica juncea seedlings showed nonenzymatic nitrite reduction to NO. Thiol pool quantification showed cold-induced increase in the protein (including S-nitrosothiols) as well as non protein thiols. Proteins from the apoplast were resolved as 109 spots on the 2-D gel, while S-nitrosoglutathione-treated (a NO donor), neutravidin-agarose affinity chromatography-purified S-nitrosylated proteins were resolved as 52 spots. Functional categorization after MALDI-TOF/TOF identification showed 41 and 38% targets to be metabolic/cell-wall-modifying and stress-related, respectively, suggesting the potential role(s) of S-nitrosylation in regulating these responses. Additionally, identification of cold-stress-modulated putative S-nitrosylated proteins by nLC-MS/MS showed that only 38.4% targets with increased S-nitrosylation were secreted by classical pathway, while the majority (61.6%) of these were secreted by unknown/nonclassical pathways. Cold-stress-increased dehydroascorbate reductase and glutathione S-transferase activity via S-nitrosylation and promoted ROS detoxification by ascorbate regeneration and hydrogen peroxide detoxification. Taken together, cold-mediated NO production, thiol pool enrichment, and identification of the 48 putative S-nitrosylated proteins, including 25 novel targets, provided the preview of RNS-mediated cold-stress signaling in the apoplast.

Effects of carbon monoxide on quality, nutrients and antioxidant activity of post-harvest jujube

BACKGROUND

To effectively extend the shelf life of fresh jujube, carbon monoxide (CO), as a small molecular gas, was applied to fumigate fresh jujube. The quality and antioxidant activity of jujubes fumigated with carbon monoxide at concentrations of 0 (control), 5, 10, 20 and 40 µmol L⁻¹ for 1 h under ambient temperature were investigated.

RESULTS

The jujube fumigated with 10 µmol L⁻¹ CO showed the best preserving effect amongst all samples. At 30 days, the decay incidence of jujube fumigated with 10 µmol L⁻¹ CO is only two-thirds of that of control sample; its red index and weight loss rate were 22.8% and 19.4% lower, and its firmness, soluble solids content (SSC) and acidity were 18.7%, 5.4% and 12.2% higher than that of control samples, respectively. Its vitamin C and total flavonoid contents were also the highest. However, no significant difference in total polyphenol content was found. The jujubes treated with 10 µmol L⁻¹ CO exhibited the highest antioxidant activity in terms of reducing power and 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl radical scavenging activity. However, the jujubes fumigated with 40 µmol L⁻¹ CO showed inferior characteristics compared with the control sample.

CONCLUSION

Fumigating jujubes with proper concentration of CO probably is a potential novel method for post-harvest jujube preservation in the future.

Nitric oxide, antioxidants and prooxidants in plant defence responses

In plant cells the free radical nitric oxide (NO) interacts both with anti- as well as prooxidants. This review provides a short survey of the central roles of ascorbate and glutathione-the latter alone or in conjunction with S-nitrosoglutathione reductase-in controlling NO bioavailability. Other major topics include the regulation of antioxidant enzymes by NO and the interplay between NO and reactive oxygen species (ROS). Under stress conditions NO regulates antioxidant enzymes at the level of activity and gene expression, which can cause either enhancement or reduction of the cellular redox status. For instance chronic NO production during salt stress induced the antioxidant system thereby increasing salt tolerance in various plants. In contrast, rapid NO accumulation in response to strong stress stimuli was occasionally linked to inhibition of antioxidant enzymes and a subsequent rise in hydrogen peroxide levels. Moreover, during incompatible Arabidopsis thaliana-Pseudomonas syringae interactions ROS burst and cell death progression were shown to be terminated by S-nitrosylation-triggered inhibition of NADPH oxidases, further highlighting the multiple roles of NO during redox-signaling. In chemical reactions between NO and ROS reactive nitrogen species (RNS) arise with characteristics different from their precursors. Recently, peroxynitrite formed by the reaction of NO with superoxide has attracted much attention. We will describe putative functions of this molecule and other NO derivatives in plant cells. Non-symbiotic hemoglobins (nsHb) were proposed to act in NO degradation. Additionally, like other oxidases nsHb is also capable of catalyzing protein nitration through a nitrite- and hydrogen peroxide-dependent process. The physiological significance of the described findings under abiotic and biotic stress conditions will be discussed with a special emphasis on pathogen-induced programmed cell death (PCD).

Up-regulation of heme oxygenase-1 contributes to the amelioration of aluminum-induced oxidative stress in Medicago sativa

In this report, pharmacological, histochemical and molecular approaches were used to investigate the effect of heme oxygenase-1 (HO-1) up-regulation on the alleviation of aluminum (Al)-induced oxidative stress in Medicago sativa. Exposure of alfalfa to AlCl3 (0-100 μM) resulted in a dose-dependent inhibition of root elongation as well as the enhancement of thiobarbituric acid reactive substances (TBARS) content. 1 and 10 μM (in particular) Al(3+) increased alfalfa HO-1 transcript or its protein level, and HO activity in comparison with the decreased changes in 100 μM Al-treated samples. After recuperation, however, TBARS levels in 1 and 10 μM Al-treated alfalfa roots returned to control values, which were accompanied with the higher levels of HO activity. Subsequently, exogenous CO, a byproduct of HO-1, could substitute for the cytoprotective effects of the up-regulation of HO-1 in alfalfa plants upon Al stress, which was confirmed by the alleviation of TBARS and Al accumulation, as well as the histochemical analysis of lipid peroxidation and loss of plasma membrane integrity. Theses results indicated that endogenous CO generated via heme degradation by HO-1 could contribute in a critical manner to its protective effects. Additionally, the pretreatments of butylated hydroxytoluene (BHT) and hemin, an inducer of HO-1, exhibited the similar cytoprotective roles in the alleviation of oxidative stress, both of which were impaired by the potent inhibitor of HO-1, zinc protoporphyrin IX (ZnPP). However, the Al-induced inhibition of root elongation was not influenced by CO, BHT and hemin, respectively. Together, the present results showed up-regulation of HO-1 expression could act as a mechanism of cell protection against oxidative stress induced by Al treatment.

Redox control of plant growth and development

Redox changes determined by genetic and environmental factors display well-organized interactions in the control of plant growth and development. Diurnal and seasonal changes in the environmental conditions are important for the normal course of these physiological processes and, similarly to their mild irregular alterations, for stress adaptation. However, fast or large-scale environmental changes may lead to damage or death of sensitive plants. The spatial and temporal redox changes influence growth and development due to the reprogramming of metabolism. In this process reactive oxygen and nitrogen species and antioxidants are involved as components of signalling networks. The control of growth, development and flowering by reactive oxygen and nitrogen species and antioxidants in interaction with hormones at organ, tissue, cellular and subcellular level will be discussed in the present review. Unsolved problems of the field, among others the need for identification of new components and interactions in the redox regulatory network at various organization levels using systems biology approaches will be also indicated.

RuBisCO depletion improved proteome coverage of cold responsive S-nitrosylated targets in Brassica juncea

Although in the last few years good number of S-nitrosylated proteins are identified but information on endogenous targets is still limiting. Therefore, an attempt is made to decipher NO signaling in cold treated Brassica juncea seedlings. Treatment of seedlings with substrate, cofactor and inhibitor of Nitric-oxide synthase and nitrate reductase (NR), indicated NR mediated NO biosynthesis in cold. Analysis of the in vivo thiols showed depletion of low molecular weight thiols and enhancement of available protein thiols, suggesting redox changes. To have a detailed view, S-nitrosylation analysis was done using biotin switch technique (BST) and avidin-affinity chromatography. Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is S-nitrosylated and therefore, is identified as target repeatedly due to its abundance. It also competes out low abundant proteins which are important NO signaling components. Therefore, RuBisCO was removed (over 80%) using immunoaffinity purification. Purified S-nitrosylated RuBisCO depleted proteins were resolved on 2-D gel as 110 spots, including 13 new, which were absent in the crude S-nitrosoproteome. These were identified by nLC-MS/MS as thioredoxin, fructose biphosphate aldolase class I, myrosinase, salt responsive proteins, peptidyl-prolyl cis-trans isomerase and malate dehydrogenase. Cold showed differential S-nitrosylation of 15 spots, enhanced superoxide dismutase activity (via S-nitrosylation) and promoted the detoxification of superoxide radicals. Increased S-nitrosylation of glyceraldehyde-3-phosphate dehydrogenase sedoheptulose-biphosphatase, and fructose biphosphate aldolase, indicated regulation of Calvin cycle by S-nitrosylation. The results showed that RuBisCO depletion improved proteome coverage and provided clues for NO signaling in cold.

Jasmonate regulates the inducer of cbf expression-C-repeat binding factor/DRE binding factor1 cascade and freezing tolerance in Arabidopsis

The inducer of cbf expression (ICE)-C-repeat binding factor/DRE binding factor1 (CBF/DREB1) transcriptional pathway plays a critical role in modulating cold stress responses in Arabidopsis thaliana. Dissecting crucial upstream regulatory signals or components of the ICE-CBF/DREB1 cascade will enhance our understanding of plant cold-tolerance mechanisms. Here, we show that jasmonate positively regulates plant responses to freezing stress in Arabidopsis. Exogenous application of jasmonate significantly enhanced plant freezing tolerance with or without cold acclimation. By contrast, blocking endogenous jasmonate biosynthesis and signaling rendered plants hypersensitive to freezing stress. Consistent with the positive role of jasmonate in freezing stress, production of endogenous jasmonate was triggered by cold treatment. In addition, cold induction of genes acting in the CBF/DREB1 signaling pathway was upregulated by jasmonate. Further investigation revealed that several jasmonate ZIM-domain (JAZ) proteins, the repressors of jasmonate signaling, physically interact with ICE1 and ICE2 transcription factors. JAZ1 and JAZ4 repress the transcriptional function of ICE1, thereby attenuating the expression of its regulon. Consistent with this, overexpression of JAZ1 or JAZ4 represses freezing stress responses of Arabidopsis. Taken together, our study provides evidence that jasmonate functions as a critical upstream signal of the ICE-CBF/DREB1 pathway to positively regulate Arabidopsis freezing tolerance.

Nitric oxide-cold stress signalling cross-talk, evolution of a novel regulatory mechanism

Plants enhance their cold stress tolerance by cold acclimation, a process which results in vast reprogramming of transcriptome, proteome and metabolome. Evidence suggests nitric oxide (NO) production during cold stress which regulates genes (especially the C-repeat binding factor (CBF) cold stress signalling pathway), diverse proteins including transcription factors (TFs) and phosphosphingolipids. About 59% (redox), 50% (defence/stress) and 30% (signalling) cold responsive proteins are modulated by NO-based post translational modifications (PTMs) namely S-nitrosylation, tyrosine nitration and S-glutathionylation, suggesting a cross-talk between NO and cold. Analysis of cold stress responsive deep proteome in apoplast, mitochondria, chloroplast and nucleus suggested continuation of this cross-talk in sub-cellular systems. Modulation of cold responsive proteins by these PTMs right from cytoskeletal elements in plasma membrane to TFs in nucleus suggests a novel regulation of cold stress signalling. NO-mediated altered protein transport in nucleus seems an important stress regulatory mechanism. This review addresses the NO and cold stress signalling cross-talk to present the overview of this novel regulatory mechanism.

Hydrogen gas acts as a novel bioactive molecule in enhancing plant tolerance to paraquat-induced oxidative stress via the modulation of heme oxygenase-1 signalling system

Hydrogen gas (H2) was recently proposed as a novel antioxidant and signalling molecule in animals. However, the physiological roles of H2 in plants are less clear. Here, we showed that exposure of alfalfa seedlings to paraquat stress increased endogenous H2 production. When supplied with exogenous H2 or the heme oxygenase-1 (HO-1)-inducer hemin, alfalfa plants displayed enhanced tolerance to oxidative stress induced by paraquat. This was evidenced by alleviation of the inhibition of root growth, reduced lipid peroxidation and the decreased hydrogen peroxide and superoxide anion radical levels. The activities and transcripts of representative antioxidant enzymes were induced after exposure to either H2 or hemin. Further results showed that H2 pretreatment could dramatically increase levels of the MsHO-1 transcript, levels of the protein it encodes and HO-1 activity. The previously mentioned H2-mediated responses were specific for HO-1, given that the potent HO-1-inhibitor counteracted the effects of H2. The effects of H2 were reversed after the addition of an aqueous solution of 50% carbon monoxide (CO). We also discovered enhanced tolerance of multiple environmental stresses after plants were pretreated with H2 . Together, these results suggested that H2 might function as an important gaseous molecule that alleviates oxidative stress via HO-1 signalling.

Heme oxygenase-1 is involved in nitric oxide- and cGMP-induced α-Amy2/54 gene expression in GA-treated wheat aleurone layers

Here, α-Amy2/54 gene expression was used as a molecular probe to investigate the interrelationship among nitric oxide (NO), cyclic GMP (cGMP), and heme oxygenase-1 (HO-1) in GA-treated wheat aleurone layers. The inducible expressions of α-Amy2/54 and α-amylase activity were respectively amplified by two NO-releasing compounds, sodium nitroprusside (SNP) and spermine NONOate, in a GA-dependent fashion. Similar responses were observed when an inducer of HO-1, hemin-or one of its catalytic products, carbon monoxide (CO) in aqueous solution-was respectively added. The SNP-induced responses, mimicked by 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP), a cGMP derivative, were NO-dependent. This conclusion was supported by the fact that endogenous NO overproduction was rapidly induced by SNP, and thereafter induction of α-Amy2/54 gene expression and increased α-amylase activity were sensitive to the NO scavenger. We further observed that the above induction triggered by SNP and 8-Br-cGMP was partially prevented by zinc protoporphyrin IX (ZnPPIX), an inhibitor of HO-1. These blocking effects were clearly reversed by CO, confirming that the above response was HO-1-specific. Further analyses showed that both SNP and 8-Br-cGMP rapidly up-regulated HO-1 gene expression and increased HO activity, and SNP responses were sensitive to cPTIO and the guanylate cyclase inhibitor 6-anilino-5,8-quinolinedione (LY83583). Molecular evidence confirmed that GA-induced GAMYB and ABA-triggered PKABA1 transcripts were up-regulated or down-regulated by SNP, 8-Br-cGMP or CO cotreated with GA. Contrasting changes were observed when cPTIO, LY83583, or ZnPPIX was added. Together, our results suggested that HO-1 is involved in NO- and cGMP-induced α-Amy2/54 gene expression in GA-treated aleurone layers.