Exogenous Spd Research Articles

Effects of exogenous spermidine and spermine on antioxidant metabolism associated with cold-induced leaf senescence in Zoysiagrass (Zoysia japonica Steud.)

Zoysiagrass (Zoysia japonica Steud.) leaves lose their green colour as they undergo cold acclimation (CA) in late fall in many regions, and delaying leaf senescence can extend their green period. The objective of this study was to investigate whether exogenous spermidine (Spd) and spermine (Spm) can delay leaf senescence by enhancing reactive oxygen species (ROS)-scavenging antioxidant enzyme activity. Mature zoysiagrass (cv. Zenith) plants were treated with Spm (1 mM) or Spd (1 mM) or water (control). The treated plants were grown under normal conditions or subjected to cold acclimation CA for 35 days. CA treatment increased leaf electrolyte leakage (EL) and malondialdehyde (MDA) level, decreased chlorophyll (Chl) content, and induced leaf senescence. Foliar application of Spd and Spm reduced the decline in Chl content and reduced EL and MDA levels. CA treatment increased the ROS level and reduced antioxidant enzyme activity. Application of Spm and Spd reduced ROS accumulation and enhanced the activities of superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase under CA conditions. The results of this study indicated that exogenous Spd and Spm at 1 mM can delay CA-induced leaf senescence through enhancement of ROS-scavenging antioxidant activity in zoysiagrass.

Relationship between Polyamines and Anaerobic Respiration of Wheat Seedling Root under Water-Logging Stress

To elucidate the relationship between polyamines and anaerobic respiration of wheat (Triticum aestivum L.) seedling root under water-logging stress, the contents of polyamines (PAs), lactate and alcohol, and the activities of anaerobic respiration enzymes were investigated in seedling roots of two wheat cultivars, Yumai no. 18 and Yangmai no. 9. On the 5th day after water-logging treatment, spermidine (Spd) and spermine (Spm) contents increased significantly, pyruvate decarboxylase (PDC) activity increased and there was no difference between two cultivars. Alcohol dehydrogenase (ADH) activity and alcohol content in Yangmai no. 9 increased more markedly than Yumai no. 18, while lactate dehydrogenase (LDH) activity and the lactate content in the Yumai no. 18 increased more markedly than Yangmai no. 9. Treatments with exogenous Spd and Spm resulted in enhancing the increases in ADH activity, alcohol content, and the levels of Spd and Spm. This concomitantly inhibited the increases in LDH activity and lactate content in Yumai no. 18 under water-logging stress, alleviating stress-induced injury to the seedlings. Treatment with exogenous inhibitor methylglyoxyl-bis-guanylhydrazone (MGBG), resulted in reducing the increases in ADH activity, alcohol content, and Spd and Spm levels, promoting the increases in LDH activity and lactate content in Yangmai no. 9 under water-logging stress, and aggravating the stress-induced injury to the seedlings. The results suggested that under water-logging stress, increased Spd and Spm could facilitate the tolerance of wheat seedling to the stress by enhancing the increases in ADH activity and alcohol content, and inhibiting the increases in LDH activity and lactate content.

The hydrogen sulfide, a downstream signaling molecule of hydrogen peroxide and nitric oxide, involves spermidine-regulated transcription factors and antioxidant defense in white clover in response to dehydration

Hydrogen sulfide (H2S) nowadays is regarded as a novel gaseous signaling molecule in plants during environmental stress response. The spermidine (Spd), an important plant growth regulator, plays critical roles in regulating stress tolerance in plant species. Objectives of this study were to examine whether Spd could act as a H2S signaling activator to regulate stress-responsive transcription factors (TFs) and antioxidant defense and to further explore the possible crosstalk among Spd-induced hydrogen peroxide (H2O2), nitric oxide (NO), and H2S signaling in leaves of white clover. Results showed that dehydration or exogenous application of Spd could significantly increase L/D-cysteine desulfhydrate (L/DCD) activities and then cause a quick accumulation of H2S, followed by significant improvement of antioxidant enzyme (SOD, CAT, GPOX, APX, GR, DHAR, and MDHAR) activities and transcript levels of TFs (bZIP37, bZIP107, DREB2, DREB4, and WRKY108715) and genes encoding antioxidant enzymes. The inhibitors (AOA and NH2OH) of L/DCD activities could effectively attenuate dehydration- or Spd-induced these effects in leaves. Additionally, dehydration-induced increase in H2S accumulation, L/DCD and antioxidant enzyme activities, and genes expression were remarkably abolished by the application of Spd biosynthesis inhibitor (DCHA), whereas exogenous Spd significantly alleviate the inhibitory effect of DCHA on these parameters under dehydration condition. This indicated that H2S which was derived from L/DCD pathway might act as a downstream signaling of Spd, and Spd-activated H2S signaling was involved in dehydration-regulated TFs and antioxidant defense associated with dehydration tolerance. Further analyses found that Spd-induced H2O2 production could not be attenuated by scavengers of NO and H2S, but the scavenger of H2O2 effectively inhibited Spd-induced increases in NO and H2S. The Spd-induced H2S signaling was also substantially inhibited by the application of the NO scavenger. The result implied that Spd-induced H2O2 could be an upstream signal molecule of NO and H2S, and the Spd-induced H2S might act as the downstream signaling of NO in leaves. These obtained results provide the basic evidence to understand Spd-regulated signal transduction in white clover.

Exogenously applied spermidine alleviates photosynthetic inhibition under drought stress in maize (Zea mays L.) seedlings associated with changes in endogenous polyamines and phytohormones

Drought stress (DS) is a major environmental factor limiting plant growth and crop productivity worldwide. It has been established that exogenous spermidine (Spd) stimulates plant tolerance to DS. The effects of exogenous Spd on plant growth, photosynthetic performance, and chloroplast ultrastructure as well as changes in endogenous polyamines (PAs) and phytohormones were investigate in DS-resistant (Xianyu 335) and DS-sensitive (Fenghe 1) maize seedlings under well-watered and DS treatments. Exogenous Spd alleviated the stress-induced reduction in growth, photosynthetic pigment content, photosynthesis rate (Pn) and photochemical quenching (qP) parameters, including the maximum photochemistry efficiency of photosystem II (PSII) (Fv/Fm), PSII operating efficiency (ФPSII), and qP coefficient. Exogenous Spd further enhanced stress-induced elevation in non-photochemical quenching (NPQ) and the de-epoxidation state of the xanthophyll cycle (DEPS). Microscopic analysis revealed that seedlings displayed a more ordered arrangement of chloroplast ultrastructure upon Spd application during DS. Exogenous Spd increased the endogenous PA concentrations in the stressed plants. Additionally, exogenous Spd increased indoleacetic acid (IAA), zeatin riboside (ZR) and gibberellin A3 (GA3) and decreased salicylic acid (SA) and jasmonate (JA) concentrations under DS. These results indicate that exogenous Spd can alleviate the growth inhibition and damage to the structure and function of the photosynthetic apparatus caused by DS and that this alleviation may be associated with changes in endogenous PAs and phytohormones. This study contributes to advances in the knowledge of Spd-induced drought tolerance.

Spermidine-mediated hydrogen peroxide signaling enhances the antioxidant capacity of salt-stressed cucumber roots

Hydrogen peroxide (H2O2) is a key signaling molecule that mediates a variety of physiological processes and defense responses against abiotic stress in higher plants. In this study, our aims are to clarify the role of H2O2 accumulation induced by the exogenous application of spermidine (Spd) to cucumber (Cucumis sativus) seedlings in regulating the antioxidant capacity of roots under salt stress. The results showed that Spd caused a significant increase in endogenous polyamines and H2O2 levels, and peaked at 2 h after salt stress. Spd-induced H2O2 accumulation was blocked under salt stress by pretreatment with a H2O2 scavenger and respective inhibitors of cell wall peroxidase (CWPOD; EC: 1.11.1.7), polyamine oxidase (PAO; EC: 1.5.3.11) and NADPH oxidase (NOX; EC: 1.6.3.1); among these three inhibitors, the largest decrease was found in response to the addition of the inhibitor of polyamine oxidase. In addition, we observed that exogenous Spd could increase the activities of the enzymes superoxide dismutase (SOD; EC: 1.15.1.1), peroxidase (POD; EC: 1.11.1.7) and catalase (CAT; EC: 1.11.1.6) as well as the expression of their genes in salt-stressed roots, and the effects were inhibited by H2O2 scavengers and polyamine oxidase inhibitors. These results suggested that, by regulating endogenous PAs-mediated H2O2 signaling in roots, Spd could enhance antioxidant enzyme activities and reduce oxidative damage; the main source of H2O2 was polyamine oxidation, which was associated with improved tolerance and root growth recovery of cucumber under salt stress.

Identification of microRNAs associated with the exogenous spermidine-mediated improvement of high-temperature tolerance in cucumber seedlings (Cucumis sativus L.)

BackgroundHigh-temperature stress inhibited the growth of cucumber seedlings. Foliar spraying of 1.0 mmol·L− 1 exogenous spermidine (Spd) to the sensitive cucumber cultivar ‘Jinchun No. 2’ grown at high-temperature (42 °C/32 °C) in an artificial climate box improved the high-temperature tolerance. Although there have been many reports on the response of microRNAs (miRNAs) to high-temperature stress, the mechanism by which exogenous Spd may mitigate the damage of high-temperature stress through miRNA-mediated regulation has not been studied.ResultsTo elucidate the regulation of miRNAs in response to exogenous Spd-mediated improvement of high-temperature tolerance, four small RNA libraries were constructed from cucumber leaves and sequenced: untreated-control (CW), Spd-treated (CS), high-temperature stress (HW), and Spd-treated and high-temperature stress (HS). As a result, 107 known miRNAs and 79 novel miRNAs were identified. Eight common differentially expressed miRNAs (miR156d-3p, miR170-5p, miR2275-5p, miR394a, miR479b, miR5077, miR5222 and miR6475) were observed in CS/CW, HW/CW, HS/CW and HS/HW comparison pairs, which were the first set of miRNAs that responded to not only high-temperature stress but also exogenous Spd in cucumber seedlings. Five of the eight miRNAs were predicted to target 107 potential genes. Gene function and pathway analyses highlighted the integral role that these miRNAs and target genes probably play in the improvement of the high-temperature tolerance of cucumber seedlings through exogenous Spd application.ConclusionsOur study identified the first set of miRNAs associated with the exogenous Spd-mediated improvement of high-temperature tolerance in cucumber seedlings. The results could help to promote further studies on the complex molecular mechanisms underlying high-temperature tolerance in cucumber and provide a theoretical basis for the high-quality and efficient cultivation of cucumber with high-temperature resistance.

The Aspergillus flavus Spermidine Synthase (spds) Gene, Is Required for Normal Development, Aflatoxin Production, and Pathogenesis During Infection of Maize Kernels.

Aspergillus flavus is a soil-borne saprophyte and an opportunistic pathogen of both humans and plants. This fungus not only causes disease in important food and feed crops such as maize, peanut, cottonseed, and tree nuts but also produces the toxic and carcinogenic secondary metabolites (SMs) known as aflatoxins. Polyamines (PAs) are ubiquitous polycations that influence normal growth, development, and stress responses in living organisms and have been shown to play a significant role in fungal pathogenesis. Biosynthesis of spermidine (Spd) is critical for cell growth as it is required for hypusination-mediated activation of eukaryotic translation initiation factor 5A (eIF5A), and other biochemical functions. The tri-amine Spd is synthesized from the diamine putrescine (Put) by the enzyme spermidine synthase (Spds). Inactivation of spds resulted in a total loss of growth and sporulation in vitro which could be partially restored by addition of exogenous Spd. Complementation of the Δspds mutant with a wild type (WT) A. flavus spds gene restored the WT phenotype. In WT A. flavus, exogenous supply of Spd (in vitro) significantly increased the production of sclerotia and SMs. Infection of maize kernels with the Δspds mutant resulted in a significant reduction in fungal growth, sporulation, and aflatoxin production compared to controls. Quantitative PCR of Δspds mutant infected seeds showed down-regulation of aflatoxin biosynthetic genes in the mutant compared to WT A. flavus infected seeds. Expression analyses of PA metabolism/transport genes during A. flavus-maize interaction showed significant increase in the expression of arginine decarboxylase (Adc) and S-adenosylmethionine decarboxylase (Samdc) genes in the maize host and PA uptake transporters in the fungus. The results presented here demonstrate that Spd biosynthesis is critical for normal development and pathogenesis of A. flavus and pre-treatment of a Δspds mutant with Spd or Spd uptake from the host plant, are insufficient to restore WT levels of pathogenesis and aflatoxin production during seed infection. The data presented here suggest that future studies targeting spermidine biosynthesis in A. flavus, using RNA interference-based host-induced gene silencing approaches, may be an effective strategy to reduce aflatoxin contamination in maize and possibly in other susceptible crops.

Polyamines Regulate Strawberry Fruit Ripening by Abscisic Acid, Auxin, and Ethylene.

Polyamines (PAs) participate in many plant growth and developmental processes, including fruit ripening. However, it is not clear whether PAs play a role in the ripening of strawberry (Fragaria ananassa), a model nonclimacteric plant. Here, we found that the content of the PA spermine (Spm) increased more sharply after the onset of fruit coloration than did that of the PAs putrescine (Put) or spermidine (Spd). Spm dominance in ripe fruit resulted from abundant transcripts of a strawberry S-adenosyl-l-Met decarboxylase gene (FaSAMDC), which encodes an enzyme that generates a residue needed for PA biosynthesis. Exogenous Spm and Spd promoted fruit coloration, while exogenous Put and a SAMDC inhibitor inhibited coloration. Based on transcriptome data, up- and down-regulation of FaSAMDC expression promoted and inhibited ripening, respectively, which coincided with changes in several physiological parameters and their corresponding gene transcripts, including firmness, anthocyanin content, sugar content, polyamine content, auxin (indole-3-acetic acid [IAA]) content, abscisic acid (ABA) content, and ethylene emission. Using isothermal titration calorimetry, we found that FaSAMDC also had a high enzymatic activity with a Kd of 1.7 × 10-3 m In conclusion, PAs, especially Spm, regulate strawberry fruit ripening in an ABA-dominated, IAA-participating, and ethylene-coordinated manner, and FaSAMDC plays an important role in ripening.

Alleviation of Deleterious Effects due to 2-Benzoxazolinone by Exogenous Application of Spermidine in Solanum lycopersicum

ABSTRACTChemicals in root exudates can have deleterious effects on tomato (Solanum lycopersicum L.) growth and yield. Spermidine (Spd) acts as a plant growth regulator that plays a role in the regulation of physiological processes during stress. The present study reports the effect of exogenous Spd to mitigate the allelopathic stress of 2-benzoxazolinone (BOA) on tomato. The BOA treatment reduced fresh weight (FW) and dry weight (DW), relative water content (RWC), and decreased chlorophyll a, b, and carotenoid contents. Total soluble sugar (TSS) and protein contents were decreased due to treatment with BOA. Proline content, lipid peroxidation (LP), and antioxidant enzyme activities increased in BOA-treated plants. Electrolyte leakage (EL) from plant leaves increased due to treatment with BOA. Exogenous application to foliage with Spd increased RWC, FW and DW, photosynthetic pigments, and antioxidant enzyme activity in the BOA-treated seedlings. Protein and sugar contents, LP, and EL were reduced in seedlings exposed only to BOA. Exogenous foliar application of Spd appeared to induce protection against allelochemical stress by strengthening the protective system and helped maintain physiological functions in plants.

Exogenous spermidine maintains the chloroplast structure of cucumber seedlings and inhibits the degradation of photosynthetic protein complexes under high-temperature stress

Cucumbers (Cucumis sativus L.) are thermophilic horticulture crop but do not tolerate high temperature. The photosynthesis of cucumber under high temperature is highly susceptible to damage. To study the physiological mechanism of exogenous spermidine (Spd) on cucumber photosynthesis under heat stress, the sensitive cucumber cultivar ‘Jinchun no. 2’ was grown in substrate culture at a high temperature in an artificial climate box and treated with 1.0 mmol L−1 Spd under high-temperature stress (42/32 °C). The results showed that exogenous Spd alleviated the photosynthetic damage caused by heat shock, added the chlorophyll content and maintained the chloroplast structures relatively intact. Western blotting analysis showed that exogenous Spd inhibited the degradation of photosynthetic proteins, slowed the dissociation of the protein complexes, and maintained the stability of light-harvesting complexes (LHCs) in cucumber leaves under high-temperature stress. Twenty-two differentially expressed thylakoid membrane proteins involved in different photosynthetic processes were successfully authenticated by sodium dodecyl sulphate (SDS)-urea-PAGE and Blue native-polyacrylamide gel electrophoresis (BN-PAGE). The results showed that exogenous Spd regulated the expression of photosynthetic and bursal somatic membrane proteins, which resulted in adaptive changes under high-temperature stress at the transcriptional and translational levels, inhibited the degradation of thylakoid membrane proteins in cucumber leaves, and maintained the stable structure of the thylakoid membrane. Collectively, these results suggested that exogenous Spd alleviated high temperature-induced photosynthesis damage by improving the expression and synthesis of thylakoid membrane proteins, mitigating the dissociation of LHCII–Chl and thylakoid membrane protein complexes and maintaining the integrity and functional stability of the photosynthetic organ structure.

Polyamines regulating phytic acid degradation in mung bean sprouts.

Polyamines are essentially involved in cell division and differentiation. Transport of polyamines is adenosine triphosphate (ATP)-dependent, while phytic acid is the major reserve of phosphate essential to the energy-producing machinery of cells. Thus polyamines might enhance phytic acid degradation during mung bean germination. In this study, different polyamines (putrescine (Put), spermidine (Spd) and spermine (Spm)) and dicyclohexylamine (DCHA, an inhibitor of Spd synthesis) were applied to investigate the function of polyamines on phytic acid degradation. Spd exhibited the best effect at the same concentration. Simultaneously, exogenous Spd improved sprout growth and enhanced the accumulation of gibberellin acid 3 (GA3 ), indole-3-acetic acid (IAA), abscisic acid (ABA) and cytokinin (CTK). This must be due to the increased endogenous polyamine contents. Apart from dramatically reducing phytic acid content, Spd resulted in the up-regulation of PA, PAP, MIPP and ALP transcript levels and the enhancement of phytase and acid phosphatase activities. However, DCHA application caused the opposite results, because it decreased endogenous polyamine contents. Furthermore, Spd alleviated the DCHA-induced inhibitory effect to some extent. Overall, polyamines, especially Spd, could accelerate phytic acid degradation in mung bean sprouts by inducing the synthesis of endogenous polyamines and phytohormones and enhancing the growth of sprouts. © 2017 Society of Chemical Industry.

Physiological and biochemical mechanism of spermidine improving drought resistance in maize seedlings under drought stress.

To explore the role of exogenous spermidine (Spd) in enhancing the resistance of maize to drought stress, 15% polyethylene glycol (PEG-6000) was used to simulate drought stress and with 'Xianyu 335' (drought-insensitive) and 'Fenghe 1' (drought sensitive) as the experiment materials, the effects of Spd (0.1 mmol·L-1) on the growth, photosynthetic characteristics, chlorophyll content, osmotic adjustment substance, membrane lipid peroxidation and root activity of maize seedlings were investigated. The results showed that the application of Spd significantly promoted the growth of maize seedlings under drought stress, increased chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr) and water use efficiency (WUE), and decreased the enhancement of intercellular carbon dioxide concentration (Ci) in 'Fenghe 1'. Moreover, the stomatal and non-stomatal limitations of photosynthetic ability caused by drought stress in 'Fenghe 1' were effectively reduced by exogenous Spd. The application of Spd increased the content of proline and soluble sugar, decreased theO2-· generation rate, contents of H2O2 and MDA and cell membrane permeability, enhanced the root activity. The changes of drought-sensitive 'Fenghe 1' were greater than drought-tolerant 'Xianyu 335'. These results indicated that exogenous Spd had positive effects on the seedlings to capture and converse solar energy, thus promoting photosynthesis and the growth of maize seedlings. It would also enhance the adaptability of seedlings to drought stress by reducing the production of reactive oxygen species (ROS), increasing the accumulation of osmotic adjustment substances to stabilize the cell membrane system and improving the root vigor. The positive effects of Spd was more obvious for drought-sensitive variety 'Fenghe 1'.

Enhancing antioxidant systems by exogenous spermine and spermidine in wheat (Triticum aestivum) seedlings exposed to salt stress.

Plants have evolved complex mechanisms to mitigate osmotic and ionic stress caused by high salinity. The effect of exogenous spermine (Spm) and spermidine (Spd) on defence responses of wheat seedlings under NaCl stress was investigated by measuring antioxidant enzyme activities and the transcript expression of corresponding genes. Exogenous Spm and Spd decreased the level of malondialdehyde, increased chlorophyll and proline contents, and modulated PSII activity in wheat seedlings under salt stress. Spermidine alleviated negative effects on CO2 assimilation induced by salt stress in addition to significantly increasing the activity and content of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco). It appears Spd conferred salinity tolerance in wheat seedlings by enhancing photosynthetic capacity through regulation of gene expression and the activity of key CO2 assimilation enzymes. Exogenous Spm regulated activities of different antioxidant enzymes (catalase, glutathione reductase, dehydroascorbate reductase, ascorbate peroxidase, and superoxide dismutase) and efficiently modulate their transcription levels in wheat seedlings under salt stress. It is likely that Spm plays a key role in alleviating oxidative damage of salt stress by adjusting antioxidant enzyme activities in plants. In addition, exogenous Spd increased transcript level of spermine synthase under salt stress. Salinity stress also caused an increase in transcript levels of diamine oxidase (DAO) and polyamine oxidase (PAO). Exogenous Spd application resulted in a marked increase in free Spd and Spm contents under saline conditions. These results show that exogenous Spd and Spm effectively upregulated transcriptional levels of antioxidant enzyme genes and improved the defence response of plants under salt stress.

Exogenous spermidine enhances the photosynthetic and antioxidant capacity of rice under heat stress during early grain-filling period.

High temperature has adverse effects on rice growth by inhibiting the flag leaf photosynthetic and antioxidant capacity, which can be alleviated by various exogenous chemicals such as spermidine (Spd). However, the role of Spd in conferring heat tolerance in rice is not well documented. Conventional japonica rice varieties Wuyunjing 24 and Ningjing 3 were treated with high temperatures at 37.5/27.0°C (day/night) and foliar sprayed with 1mmolL-1 Spd after flowering. Results showed activities of superoxide dismutase (SOD) and peroxidase (POD) activities were deceased during high temperature treatment and eventually lead to the malondialdehyde (MDA) accumulation. Exogenous Spd significantly increased both SOD and POD activities at the later stage of high-temperature treatment, and reduced MDA accumulation were identified in both rice varieties. Application of Spd further increased the amount of soluble sugars during high temperature stress and that maintained the osmotic equilibrium of rice leaves. Spd significantly increased photosystem II (ΦPSII), photosynthetic electron transport rate (ETR), variable fluorescence/maximum fluorescence ratio (Fv'/Fm'), stomatal conductance and the photochemical reaction of light energy ratio (Pr), and ultimately improved the photosynthetic and transpiration rate during high temperature stress. In conclusion, exogenous Spd can effectively alleviate the adverse consequences of high temperature and could be further applied to provide strategies in mitigating the challenges of global warming-induced yield loss and other possible relevant issues.

Exogenous spermidine improves drought tolerance in maize by enhancing the antioxidant defence system and regulating endogenous polyamine metabolism

Drought stress is a primary abiotic constraint affecting crop production worldwide. In this study, the role of exogenous spermidine (Spd) in conferring drought-stress-tolerance in maize (Zea mays L.) seedlings was studied by analysing polyamine metabolism and the antioxidant defence system. Two maize cultivars, Xianyu 335 (drought resistant) and Fenghe 1 (drought susceptible), were subjected to drought stress (–0.8 MPa) induced by 15% polyethylene glycol 6000 with or without Spd (0.1 mm) application. Spd significantly reduced the inhibition of plant growth and decreased malondialdehyde and hydrogen peroxide contents and the generation rate of oxidised glutathione caused by drought stress, particularly in Fenghe 1. The activities of superoxide dismutase, ascorbate peroxidase and glutathione reductase further increased with the application of Spd to the stressed plants. Application of Spd significantly moderated the drought-induced reduction in activities of monodehydroascorbate reductase and dehydroascorbate and the ratio ascorbate : dehydroascorbate and reduced the ratio glutathione : oxidised glutathione. With the application of Spd, the contents of Spd and spermine and the activities of arginine decarboxylase, S-adenosyl methionine decarboxylase and diamine oxidase increased significantly in the stressed plants, and the increases were greater in Xianyu 335 than in Fenghe 1. Thus, exogenous Spd successfully reduced oxidative damage by enhancing the antioxidant components, raising the redox state of ascorbate and glutathione, and altering the polyamine pool, which play important roles in improving physiological characteristics and drought stress in maize.

The Alleviation of Heat Damage to Photosystem II and Enzymatic Antioxidants by Exogenous Spermidine in Tall Fescue.

Tall fescue (Festuca arundinacea Schreb) is a typical cool-season grass that is widely used in turf and pasture. However, high temperature as an abiotic stress seriously affects its utilization. The objective of this study was to explore the effect of spermidine (Spd) on heat stress response of tall fescue. The samples were exposed to 22°C (normal condition) or 44°C (heat stress) for 4 h. The results showed that exogenous Spd partially improved the quality of tall fescue leaves under normal temperature conditions. Nevertheless, after heat stress treatment, exogenous Spd significantly decreased the electrolyte leakage of tall fescue leaves. Spd also profoundly reduced the H2O2 and O2⋅- content and increased antioxidant enzymes activities. In addition, PAs can also regulate antioxidant enzymes activities including SOD, POD, and APX which could help to scavenge ROS. Moreover, application of Spd could also remarkably increase the chlorophyll content and had a positive effect on the chlorophyll α fluorescence transients under high temperature. The Spd reagent enhanced the performance of photosystem II (PSII) as observed by the JIP-test. Under heat stress, the Spd profoundly improved the partial potentials at the steps of energy bifurcations (PIABS and PItotal) and the quantum yields and efficiencies (φP0, δR0, φR0, and γRC). Exogenous Spd could also reduce the specific energy fluxes per QA- reducing PSII reaction center (RC) (TP0/RC and ET0/RC). Additionally, exogenous Spd improved the expression level of psbA and psbB, which encoded the proteins of PSII core reaction center complex. We infer that PAs can stabilize the structure of nucleic acids and protect RNA from the degradation of ribonuclease. In brief, our study indicates that exogenous Spd enhances the heat tolerance of tall fescue by maintaining cell membrane stability, increasing antioxidant enzymes activities, improving PSII, and relevant gene expression.

Relationship between seed quality and changes in conjugated polyamine in plasma membrane purified from wheat embryos during grain ripening

In order to explore the relationship between seed quality and changes in conjugated polyamine in plasma membrane purified from wheat embryos during grain ripening. Plasma membrane (PM) vesicles were isolated from the embryos of ripening wheat (Triticum aestivum L.) grains by the gradient centrifugation method. The contents of polyamines conjugated (covalently and non-covalently) to the PM vesicles were investigated. Results showed that after pollination, from the 22nd to the 32nd day, the embryos of wheat grains underwent dehydration, as judged by the decrease of embryo relative water content (ERWC). During embryo ripening, non-covalently conjugated (NCC)-Spd and NCC-Spm, covalently conjugated (CC)-Put and CC-Spd contents increased markedly, while relative embryo cell vigor (RECV) decreased slightly. The treatment with methylglyoxyl-bis (guanylhydrazone) (MGBG), an inhibitor of S-adenosylmethionine decarboxylase (SAMDC), inhibited the increases of the NCC-Spd and NCC-Spm contents, enhanced the decrease of RECV simultaneously, and decreased mature seed relative germination potential (RGP). The effects of MGBG were reversed by exogenous Spd and Spm. Phenanthrolin (o–Phen), an inhibitor of transglutaminase (TGase), inhibited the increases of CC-Put and CC-Spd contents, enhanced the decrease of RECV simultaneously, and decreased mature seed RGP. These results suggest that during embryo ripening, the levels of NCC-Spd, NCC-Spm, CC-Put, and CC-Spd increase, and these increases might affect embryo cell vigor and seed germination potential.

Polyamines contribute to salinity tolerance in the symbiosis Medicago truncatula-Sinorhizobium meliloti by preventing oxidative damage

Polyamines (PAs) such as spermidine (Spd) and spermine (Spm) are small ubiquitous polycationic compounds that contribute to plant adaptation to salt stress. The positive effect of PAs has been associated to a cross-talk with other anti-stress hormones such as brassinosteroids (BRs). In this work we have studied the effects of exogenous Spd and Spm pre-treatments in the response to salt stress of the symbiotic interaction between Medicago truncatula and Sinorhizobium meliloti by analyzing parameters related to nitrogen fixation, oxidative damage and cross-talk with BRs in the response to salinity.Exogenous PAs treatments incremented the foliar and nodular Spd and Spm content which correlated with an increment of the nodule biomass and nitrogenase activity. Exogenous Spm treatment partially prevented proline accumulation which suggests that this polyamine could replace the role of this amino acid in the salt stress response. Additionally, Spd and Spm pre-treatments reduced the levels of H2O2 and lipid peroxidation under salt stress. PAs induced the expression of genes involved in BRs biosynthesis which support a cross-talk between PAs and BRs in the salt stress response of M. truncatula-S. meliloti symbiosis.In conclusion, exogenous PAs improved the response to salinity of the M. truncatula-S. meliloti symbiosis by reducing the oxidative damage induced under salt stress conditions. In addition, in this work we provide evidences of the cross-talk between PAs and BRs in the adaptive responses to salinity.

The Variation Tendency of Polyamines Forms and Components of Polyamine Metabolism in Zoysiagrass (Zoysia japonica Steud.) to Salt Stress with Exogenous Spermidine Application.

To understand dynamic changes in polyamines (PAs) forms and components of polyamine metabolism in zoysiagrass (Zoysia japonica Steud.) response to salt stress with exogenous spermidine (Spd) application, two Chinese zoysia cultivars, z081 and z057, were exposed to sodium chloride stress for 2, 4, 6, and 8 days. The z057 cultivar possesses higher salinity tolerance than the z081 cultivar. Salt stress decreased the zoysiagrass fresh weight (FW) and increased free Spd and spermine (Spm) levels and soluble and insoluble putrescine (Put), Spd and Spm levels in both cultivars. Moreover, salt stress enhanced the activities of arginine decarboxylase (ADC), ornithine decarboxylase (ODC), S-adenosylmethionine decarboxylase (SAMDC), and diamine oxidase (DAO). Exogenous Spd increased PA metabolism and ADC, SAMDC, and DAO activities and decreased free Put levels under salt stress conditions in both cultivars. In addition, structural equation modeling (SEM) showed that ODC, SAMDC, and DAO contributed to PA metabolism, and endogenous Spd levels also contributed to endogenous Spm levels. Free PAs may be the primary factor influencing the variation of other PA forms. SEM also indicated that ADC and polyamine oxidase (PAO) play a limited role in enhancing zoysia salt tolerance via PA metabolism under salt stress.

Exogenous spermidine alleviates fruit granulation in a Citrus cultivar (Huangguogan) through the antioxidant pathway

The role of exogenous spermidine (Spd) in alleviating fruit granulation in the grafted seedlings of a Citrus cultivar (Huangguogan) was investigated. Granulation resulted in increased electrical conductivity, cell membrane permeability, and total pectin, soluble pectin, cellulose, and lignin contents. However, it decreased the activities of superoxide dismutase, peroxidase, and catalase, as well as the (Spd + Spm):Put ratio. The application of exogenous Spd onto Huangguogan seedlings significantly increased proline and ascorbate contents, but decreased the H2O2 and O 2 −· levels, which suggested that exogenous Spd provided some protection from oxidative damage. In addition, exogenous Spd decreased cell membrane permeability and MDA content, and increased the (Spd + Spm):Put ratio. The activities of antioxidant enzymes, such as catalase, peroxidase, and superoxide dismutase, were increased in Spd-treated seedlings affected by fruit granulation, resulting in a decrease in oxidative stress levels. The protective effects of Spd were reflected by a decrease in superoxide levels through osmoregulation, increased proline and ascorbate contents, and increased antioxidant activities. Our observations reveal the importance of exogenous Spd in alleviating citrus fruit granulation.