Spd Treatment Research Articles

Effect of low dose of spermidine on physiological changes in salt-stressed cucumber plants

The present study was aimed to assess the ameliorative potentiality of exogenously applied low dose of spermidine (Spd) (4.0 mL of 0.1 mM) against salt stress in cucumber (Cucumis sativus L.) plants. Salt stress inhibited plant growth, while Spd increased the shoot length and dry weight of leaves in salt-stressed plants. Chlorophyll, carotenoids, and sucrose contents were lower, and the accumulation of superoxide radical was higher in salt-affected plants than in controls, and these detrimental effects were mitigated by Spd treatment. Moreover, salinity diminished the reduced glutathione and total polyphenols and inhibited the activities of catalase, peroxidase, and polyphenol oxidase as compared with controls, and Spd treatment increased all antioxidant activities in salt-injured plants. NaCl-induced oxidative stress caused a significant decrease in GA4 and GA5 contents. Spd treatment ameliorated these salt stress effects by increasing the quantities of GA4. In addition, sodium content was higher and calcium content was lower in salt-treated plants, while Spd treatment reduced the sodium accumulation and increased the calcium level in plants exposed to NaCl. The results suggest that exogenous application of low Spd dose can ameliorate the salt stress effects on cucumber by modulating the components of photosynthetic pigments, antioxidants, gibberellins, and minerals.

Spermidine alleviates the growth of saline-stressed ginseng seedlings through antioxidative defense system

Protective effects of exogenous spermidine (Spd), activity of antioxygenic enzymes, and levels of free radicals in a well-known medicinal plant, Panax ginseng was examined. Seedlings grown in salinized nutrient solution (150mM NaCl) for 7d exhibited reduced relative water content, plant growth, increased free radicals, and showing elevated lipid peroxidation. Application of Spd (0.01, 0.1, and 1mM) to the salinized nutrient solution showed increased plant growth by preventing chlorophyll degradation and increasing PA levels, as well as antioxidant enzymes such as CAT, APX, and GPX activity in the seedlings of ginseng. During salinity stress, Spd was effective for lowering the accumulation of putrescine (Put), with a significant increase in the spermidine (Spd) and spermine (Spm) levels in the ginseng seedlings. A decline in the Put level ran parallel to the higher accumulation of proline (Pro), and exogenous Spd also resulted in the alleviation of Pro content under salinity. Hydrogen peroxide (H2O2) and superoxide (O2−) production rates were also reduced in stressed plants after Spd treatment. Furthermore, the combined effect of Spd and salt led to a significant increase in diamine oxidase (DAO), and subsequent decline in polyamine oxidase (PAO). These positive effects were observed in 0.1 and 1mM Spd concentrations, but a lower concentration (0.01mM) had a very limited effect. In summary, application of exogenous Spd could enhance salt tolerance of P. ginseng by enhancing the activities of enzyme scavenging system, which influence the intensity of oxidative stress.

Regulation of salicylic acid, jasmonic acid and fatty acids in cucumber (Cucumis sativus L.) by spermidine promotes plant growth against salt stress

Phytohormones and fatty acids play a significant role in developmental stages of plant growth and defense against biotic and abiotic stresses. The purpose of this study was to determine the spermidine (Spd)-induced phytohormones and fatty acids changes involve the acclimation of cucumber plants against salt stress. Plants exposed to salt stress had significant reduction in their growth. Exogenously applied Spd increased the shoot length and protein content in salt-stressed plants. The accumulation of total phenol and malondialdehyde was higher in salt-affected plants than in their controls and these detrimental effects were mitigated by Spd treatment. Moreover, salt stress caused a significant increase in salicylic acid (SA) and jasmonic acid (JA); while Spd treatment ameliorated these salt stress effects by reducing SA and JA content. The marked accumulation of total free fatty acid was observed in salt-stressed plants, while the application of Spd to salt-stressed plants reduced the total free fatty acid content. In addition, Spd inhibited the stearic acid, linoleic acid and linolenic acid in salt-stressed plants. The results of current study suggest that exogenous application of Spd-induced phytohormones and fatty acids changes would be a reason for increasing the acclimation of cucumber plants under salt stress condition.

Proteomics reveal cucumber Spd-responses under normal condition and salt stress

To investigate the effects of exogenous Spd on proteomic changes under normal condition and NaCl stress of 3 days in cucumber seedling leaves, a 2-DE gel electrophoresis and MALDI-TOF/TOF MS was performed. A total of 63 differentially expressed proteins responded to salt stress or exogenous Spd treatments, and they were all successfully identified by MALDI-TOF/TOF MS. Many changes were observed in the levels of proteins involved in energy and metabolic pathways, protein metabolic, stress defense, and other functional proteins. Increased salt tolerance by exogenous Spd would contribute to higher expressions of proteins involved in the SAMs metabolism, protein biosynthesis, and defense mechanisms on antioxidant and detoxification. Meanwhile, the regulation of Calvin cycle, protein folding assembly and the inhibition of protein proteolysis by Spd might play important roles in salt tolerance. This study provides insight that may facilitate a better understanding of the salt resistance by Spd in cucumber seedlings.

Exogenous Spermidine Inhibits Ethylene Production in Leaves of Cucumber Seedlings under NaCl Stress

To examine whether 1 mm of spermidine (Spd) modifies plant ethylene production in response to short-term salt stress, cucumber (Cucumis sativus) seedlings were grown in nutrient solution with or without 75 mm NaCl stress for 3 days, and the leaves were sprayed with 1 mm Spd or water (control). We investigate the effects of the treatments on ethylene production, 1-aminocyclopropane-1-carboxylate (ACC) content, 1-(malonylamino) cycolpvopane-1-carboxylic acid (MACC) content, activities of 1-aminocyclopropane-1-carboxylate synthase (ACS), and 1-aminocyclopropane-1-carboxylate oxidase (ACO) and gene expression of acs2, aco1, and aco2 in the cucumber leaves. The results indicate that ethylene production was increased significantly under salt stress as did ACC and MACC content, the activities of ACS and ACO, and the transcriptional level of acs2, whereas the gene expression of aco1 and aco2 was somewhat decreased. However, exogenous Spd treatment depressed the content of ACC and MACC, ACS activity, and the level of acs2 transcripts in the leaves of salt-stressed cucumber. Although the activity of ACO and gene expressions of aco1 and aco2 increased by Spd, ethylene emission was inhibited. Our results suggest that application of exogenous Spd could reverse salinity-induced ethylene production by inhibiting the transcription and activity of ACS under salt stress. We conclude that exogenous Spd could modify the biosynthesis of ethylene to enhance the tolerance of cucumber seedlings to salt stress.

Beneficial Role of Exogenous Spermidine on Nitrogen Metabolism in Tomato Seedlings Exposed to Saline-alkaline Stress

We studied the effects of exogenous spermidine (Spd) on plant growth and nitrogen metabolism in two cultivars of tomato (Solanum lycopersicum) that have differential sensitivity to mixed salinity-alkalinity stress: ‘Jinpeng Chaoguan’ (salt-tolerant) and ‘Zhongza No. 9’ (salt-sensitive). Seedling growth of both tomato cultivars was inhibited by salinity-alkalinity stress, but Spd treatment alleviated the growth reduction to some extent, especially in ‘Zhongza No. 9’. Exogenous Spd may help reduce stress-induced increases in free amino acids, ammonium (NH4+) contents, and NADH-dependent glutamate dehydrogenase (NADH-GDH) activities; depress stress-induced decreases in soluble protein and nitrate content; and depress nitrate reductase, nitrite reductase, glutamine synthetase (GS), NADH-dependent glutamate synthase (NADH-GOGAT), glutamate oxaloacetate transaminase (GOT), and glutamate pyruvate transaminase (GPT) activities, especially for ‘Zhongza No. 9’. Based on our results, we suggest that exogenous Spd promotes the assimilation of excess toxic NH4+ by coordinating and strengthening the synergistic action of NADH-GDH, GS/NADH-GOGAT, and transamination pathways, all during saline-alkaline stress. Subsequently, NH4+ and its related enzymes (GDH, GS, GOGAT, GOT, and GPT), in vivo, are maintained in a proper and balanced state to enable mitigation of stress-resulted damages. These results suggest that exogenous Spd treatment can relieve nitrogen metabolic disturbances caused by salinity-alkalinity stress and eventually promote plant growth.

Spermidine promotes stress resistance in Drosophila melanogaster through autophagy-dependent and -independent pathways.

The naturally occurring polyamine spermidine (Spd) has recently been shown to promote longevity across species in an autophagy-dependent manner. Here, we demonstrate that Spd improves both survival and locomotor activity of the fruit fly Drosophila melanogaster upon exposure to the superoxide generator and neurotoxic agent paraquat. Although survival to a high paraquat concentration (20 mM) was specifically increased in female flies only, locomotor activity and survival could be rescued in both male and female animals when exposed to lower paraquat levels (5 mM). These effects are dependent on the autophagic machinery, as Spd failed to confer resistance to paraquat-induced toxicity and locomotor impairment in flies deleted for the essential autophagic regulator ATG7 (autophagy-related gene 7). Spd treatment did also protect against mild doses of another oxidative stressor, hydrogen peroxide, but in this case in an autophagy-independent manner. Altogether, this study establishes that the protective effects of Spd can be exerted through different pathways that depending on the oxidative stress scenario do or do not involve autophagy.

Postharvest Polyamine Application Alleviates Chilling Injury and Affects Apricot Storage Ability

Fruit of two apricot cultivars 'Bagheri' and 'Asgarabadi' were treated with putrescine (Put) or spermidine (Spd) at 1 mM and then were stored at 1 °C for 21 days. Fruit were sampled weekly and stored 2 days at 20 °C for shelf-life study. The treatments reduced ethylene production and maintained the firmness and color of the fruit. Peroxidase (POX), catalase (CAT), superoxide dismutase (SOD), and polyphenol oxidase (PPO) activities and total phenol (TP) concentrations were measured during storage. Both cultivars showed chilling injury (CI) incidence, and the severity in control fruit was higher than either Put or Spd treatments. CI incidence in Spd-treated fruit was lower than that of Put-treated fruit. Polyamine (PA) treatment generally increased antioxidant enzyme activity of fruit during storage. PA treatments may help maintain the quality of apricot fruit during storage by inhibiting ripening and decreasing CI incidence.

Effect of exogenous spermidine on polyamine content and metabolism in tomato exposed to salinity–alkalinity mixed stress

We investigated the effects of seeds pretreatment with exogenous spermidine (Spd) on the polyamine content and metabolism in the roots of two cultivars of tomato (Solanum lycopersicum), Jinpengchaoguan and Zhongza No. 9 grown under conditions of mixed salinity-alkalinity stress. These cultivars differ in their tolerance to salinity stress, with the former more tolerant than the latter. PA content, whether in its free forms, soluble conjugated forms, or insoluble bound forms, increased significantly during salinity-alkalinity stress. The activities of S-adenosylmethionine decarboxylase (SAMDC) and diamine oxidase (DAO), concentrations of free Spd, soluble conjugated forms of Spd and spermine (Spm), and insoluble bound form of Spd in the roots were enhanced to a greater extent in cv. Jinpengchaoguan roots than in cv. Zhongza No.9 in response to salinity-alkalinity stress. Interestingly, Spd application to seeds markedly suppressed the accumulation of free Put, but promoted an increase in free Spd and Spm concentrations, as well as soluble conjugated forms of Spd and insoluble bound forms of Put in both cultivars. From these data, we deduced that exogenous Spd promotes the conversion of free Put into free Spd and Spm, and soluble conjugated forms and insoluble bound forms of PAs under salinity-alkalinity stress. Furthermore, under salinity-alkalinity stress conditions, exogenous Spd enhanced the activities of ODC, SAMDC and DAO, and reduced the activities of ADC and polyamine oxidase (PAO) in cv. Zhongza No.9 roots. In addition, exogenous Spd reduced the activities of ADC and ODC, and increased the activities of DAO and SAMDC in cv. Jinpengchaoguan roots under salinity-alkalinity stress conditions. These results suggest that exogenous Spd treatment can regulate the metabolic status of polyamines caused by salinity-alkalinity stress, and eventually enhance tolerance of tomato plants to salinity-alkalinity stress. Additionally, Spd treatments have varying effects on different tolerant tomato cultivars.

Effects of exogenous spermidine on photosynthesis, xanthophyll cycle and endogenous polyamines in cucumber seedlings exposed to salinity

The effects of exogenous spermidine (Spd, 1 mmol·L-1) on photosynthetic characteristics, xanthophylls cycle components and endogenous polyamines levels were investigated in cucumber seedlings subjected to salt stress (75 mmol·L-1 NaCl). Chlorophyll contents and net photosynthetic rate (PN) of cucumber seedlings showed a significant decrease under salinity but an increase with exogenous Spd application. Salt stress caused a remarkable decline in the maximum quantum efficiency (Fv/Fm) and the actual efficiency of photosystem II (ФPSⅡ), where an increase was observed in the constitutive loss processes (ΦNO). Application of exogenous Spd significantly decreased ФNO and enhanced regulated non-photochemical energy loss (ФNPQ) in the salt-stressed plants. Spd treatment caused an increase in the size of xanthophyll cycle pool (VAZ) and further enhanced de-epoxidation of the xanthophyll cycle (DEPS) under salt stress. These results suggest that exogenous Spd alleviated salt-mediated decline in photosynthetic efficiency through the enhanced involvement of the energy dissipation that is dependent on the xanthophyll cycle. In addition, foliar spray Spd significantly increased the free, bound and conjugated polyamines in the leaves of the salt stressed plants. Spd also increased the free putrescine (Put)/(Spd+Spm) ratio and decreased bound and conjugated Put/(Spd+Spm) under salinity. Thus, we conclude that Spd can alleviate salt-induced damage on cucumber seedlings by regulating the levels of endogenous polyamines, which was associated with an improvement in the photochemical efficiency of PSII of the salt stressed plants. Key words: Cucumber, endogenous polyamines, photosynthetic characteristics, salt stress, spermidine.

“NEPP” Peritoneal Dialysis Regimen has Beneficial Effects on Plasma Cel and 3-DG, but not Pentosidine, CML, and MGO

Standard peritoneal dialysis (PD) solutions contain high levels of glucose and glucose degradation products (GDPs), both contributing to the formation of advanced glycation end products (AGEs). We studied the contribution to plasma GDP and AGE levels of 2 PD regimens that differ in glucose and GDP loads: high load [standard PD (sPD) using 4 glucose-lactate exchanges] and low load [1 amino acid exchange, 1 icodextrin exchange, and 2 glucose-bicarbonate/lactate exchanges ("NEPP")]. In a prospective crossover study (2 periods of 24 weeks), new continuous ambulatory PD patients were randomized to NEPP-sPD (n = 23) or to sPD-NEPP (n = 27). After the start of PD, absolute increases were observed in plasma levels of 3-deoxyglucosone (3-DG, 220.4 nmol/L, p < 0.0001) and in N(ε)-(carboxymethyl) lysine (CML) in plasma proteins (0.02 μmol/L CML per 1 mol/L lysine, p < 0.0001). During the first 6 weeks, 3-DG tended to increase more with sPD treatment (p = 0.08), and CML, with NEPP treatment (p = 0.002). In both groups, N(ε)-(carboxyethyl)lysine (CEL) in plasma proteins declined significantly with the start of PD. Treatment with NEPP resulted in higher levels of methylglyoxal (MGO) and lower levels of 3-DG and CEL. Pentosidine in the albumin fraction tended to increase less during NEPP treatment. A low glucose and GDP PD regimen (NEPP) resulted in plasma levels of 3-DG and CEL that were lower than those with a glucose-based sPD regimen. Starting PD with NEPP was associated with a steeper increase in CML, and continuing treatment with NEPP resulted in higher MGO levels.

Perturbation of Polyamine Catabolism Can Strongly Affect Root Development and Xylem Differentiation

Spermidine (Spd) treatment inhibited root cell elongation, promoted deposition of phenolics in cell walls of rhizodermis, xylem elements, and vascular parenchyma, and resulted in a higher number of cells resting in G(1) and G(2) phases in the maize (Zea mays) primary root apex. Furthermore, Spd treatment induced nuclear condensation and DNA fragmentation as well as precocious differentiation and cell death in both early metaxylem and late metaxylem precursors. Treatment with either N-prenylagmatine, a selective inhibitor of polyamine oxidase (PAO) enzyme activity, or N,N(1)-dimethylthiourea, a hydrogen peroxide (H(2)O(2)) scavenger, reverted Spd-induced autofluorescence intensification, DNA fragmentation, inhibition of root cell elongation, as well as reduction of percentage of nuclei in S phase. Transmission electron microscopy showed that N-prenylagmatine inhibited the differentiation of the secondary wall of early and late metaxylem elements, and xylem parenchymal cells. Moreover, although root growth and xylem differentiation in antisense PAO tobacco (Nicotiana tabacum) plants were unaltered, overexpression of maize PAO (S-ZmPAO) as well as down-regulation of the gene encoding S-adenosyl-l-methionine decarboxylase via RNAi in tobacco plants promoted vascular cell differentiation and induced programmed cell death in root cap cells. Furthermore, following Spd treatment in maize and ZmPAO overexpression in tobacco, the in vivo H(2)O(2) production was enhanced in xylem tissues. Overall, our results suggest that, after Spd supply or PAO overexpression, H(2)O(2) derived from polyamine catabolism behaves as a signal for secondary wall deposition and for induction of developmental programmed cell death.

POLYAMINE ACCLIMATION ALLEVIATES HYPERSALINITY-INDUCED OXIDATIVE STRESS IN A MARINE GREEN MACROALGA, ULVA FASCIATA, BY MODULATION OF ANTIOXIDATIVE ENZYME GENE EXPRESSION1.

Transcripts and enzyme activities of antioxidative enzymes were increased by hypersalinity (90‰) in a marine macroalga, Ulva fasciata Delile (Lu etal. 2006, Sung etal. 2009). This study examined the effects of polyamines (PAs) on the induction of hypersalinity tolerance through the modulation of expression of antioxidative defense enzymes. Incubation of U. fasciata grown under 30‰ in the presence of putrescine (Put), spermidine (Spd), or spermine (Spm) (1 mM) for 12 h increased internal PA contents prior to 90‰ treatment. Spd or Spm pretreatments reduced H2 O2 accumulation and lipid peroxidation during 90‰ treatment and improved the recovery growth rate after transfer from 90‰ to 30‰. Increases in iron superoxide dismutase (FeSOD; EC 1.15.1.1) activity and transcript levels observed under 90‰ were further increased by Spd and Spm pretreatments, while Put pretreatment had no effect. Increases in MnSOD activity and transcript levels observed under 90‰ were enhanced by Spd and Put pretreatment. An observed increase in catalase (CAT; EC 1.11.1.6) activity and transcript levels under 90‰ was not affected by Spd and Spm pretreatments but was inhibited by Put pretreatment. Observed increases in ascorbate peroxidase (APX; EC 1.11.1.11) activity and transcript levels under 90‰ were inhibited by Put, Spd, and Spm pretreatments. In conclusion, Spd and Spm treatment affords U. fasciata protection against hypersalinity through the up-regulation of FeSOD gene expression, thereby alleviating oxidative damage.

Effect of exogenously applied spermidine on growth and physiology of citrus rootstock Troyer citrange under saline conditions

The aim of this study was to assess the effects of spermidine (Spd) on ameliorating adverse effects of salinity in Troyer citrange seedlings. For this purpose, 6-month-old, uniform-sized seedlings of Troyer citrange were transplanted to plastic containers containing Hoagland nutrient solution. Addition of 75 mM NaCl into the nutrient solution reduced the plant growth, leaf chlorophyll content, chlorophyll fluorescence yield (Fv/Fm), net photosynthetic rate, respiration rate, and total Spd, N, and Ca^{2+} + Mg^{2+} contents of the leaves. It increased the leaf proline, total putrescine (Put), total spermine (Spm), Na^+, and Cl^- contents of the leaves. Addition of Spd (0.1 or 0.5 mM) to the saline nutrient solution and its weekly sprays (1 or 5 mM) on NaCl-stressed plants improved leaf number, chlorophyll content, Fv/Fm, net photosynthetic rate, and N content; increased total Spd and Spm contents; and reduced Na+ contents of the plants. Leaf Ca^{2+} + Mg^{2+} contents were slightly improved only when Spd (0.5 mM) was added to the saline nutrient solution. Leaf P and K^+ contents were not significantly affected by the salinity or Spd treatments. Among the polyamines, Put content was least affected, while there was a sharp increase in Spm content due to the salinity and Spd treatments. These results suggest involvement of Spm in the salinity tolerance of citrus rootstock Troyer citrange.

Chilling-induced oxidative stress and polyamines regulatory role in two wheat varieties

Fifteen-day-old seedlings of two wheat varieties (Side 1 & Gimmiza 7) were randomly separated into three equal groups to investigate the effect of chilling stress on their antioxidant defense system. Moreover, the possible role of polyamines (PAs) pretreatment during alleviating chilling injuries. The first group was kept in a green house at 21/15°C (day/night) and 10: 14h light/dark (−ve control). Second seedlings group were chilled at 5°C for 6 or 9 hours (+ve control). The Seedlings of the third group were divided into three sub-groups and sprayed with 0.5, 1.0 and 2.0mM spermidine (Spd). After 12 hours of polyamine pre-treatments, the seedlings were incubated at 5°C for 6 or 9 hours. At the end of the chilling period, the treated plants were transferred to the pre-experimental conditions in the greenhouse where they recovered for 10 days. Chilling stress induced a significant increase of lipid peroxidation, membrane leakage and hydrogen peroxide level, while Spd treatments resulted in a significant decrease. In addition, endogenous PA level increased in response to chilling stress. Activities of catalase, peroxidase and ascorbate peroxidase declined after the exposure to chilling whereas glutathione and free ascorbate increased. Spd treatments alleviated the injury caused by chilling stress by preventing the decrease in the activity of the antioxidant enzymes. It can be concluded that the stress protection caused by spermidine treatment probably contributes to the enhancement of the activity of the free-radical scavenging systems. Moreover, it was clear that the Sids-1 cultivar was more tolerant to chilling stress than Gemmieza-7cultivar.

Effects of Exogenous Spermidine on Reactive Oxygen Levels and Antioxidative System of Tomato Seedling under Polyethlene Glycol Stress*

Two different drought-tolerant tomato cultivars were investigated under drought stress induced by 7.5% polyethylene glycol (PEG6000) in a nutrient solution culture system. The results showed that exogenous spermidine (Spd) (0.1 mmol L-1 ) treatment decreased O2-· production rate, and MDA and H2O2 contents, raised SOD, POD, CAT, APX and GR activities in the seedlings, and had no effect on MDHAR and DHAR activities. Spd treatment of ‘Huangguan’ seedlings with lower drought-resistance was more effective than that of ‘Maofen No. 802’ seedlings with stronger drought-resistance. It indicated that exogenous Spd treatment could to enhance the activities of some antioxidant enzymes and the contents of antioxidant substances, restrain embrane lipid peroxidation, reduce ROS levels and finally enhance the tolerance of tomato seedlings to drought environments. Fig 4, Ref 32

Exogenous polyamines affect mycorrhizal development of Glomus mosseae-colonized citrus (Citrus tangerine) seedlings.

To increase mycorrhizal colonization of citrus, exogenous polyamines (PAs) including putrescine (Put), spermidine (Spd), and spermine (Spm) were applied to three-month-old Glomus mosseae-colonized Citrus tangerine seedlings. Three months after the application of PAs, all the seedlings increased mycorrhizal colonization and entry points, Put and Spm treatments significantly increased the number of arbuscules, and Spd and Put treatments notably increased the number of vesicles. Applications of exogenous Put and Spd, but not Spm, markedly increased shoot and root dry weights of the mycorrhizal seedlings. PAs significantly increased leaf glucose content of mycorrhizal seedlings, and Put and Spd treatments markedly increased leaf sucrose content of mycorrhizal seedlings. Spm treatment significantly reduced root sucrose content of mycorrhizal seedlings, and only Put treatment significantly increased root glucose content of mycorrhizal seedlings. Compared to the sole mycorrhizal inoculation, exogenous PAs significantly reduced allocation of sucrose to root, and additional Spd significantly decreased allocation of glucose to root. The results demonstrated that exogenous PAs applications could improve mycorrhizal development of citrus seedlings, possibly due to changes of leaf and root sugar content.

Nanostructure Formation and Properties in Some Al Alloys after SPD and Heat Treatment

Influence of SPD process realized by ECAP on structural formation and mechanical properties was searched. Samples after ECAP were heat treated at various temperature and time conditions. Investigation material bases were high purity aluminium and aluminium alloys EN AW 6082, EN AW 2014. The best material properties are describing in dependence on experimental conditions.

Effect of Polyamines on Chilling Tolerance in Seed Imbibition and Seed Germination in Maize

Chilling injury caused by low temperature happens frequently during seed imbibition in maize (Zea mays L.). Polyamines (PAs) such as putrescine (Put), spermindine (Spd), and spermine (Spm) are accumulated in plants, maintaining the stability and integrality of membrane under low temperature stress and eliminating free radicals in cells. They have been used by presoaking and leaf spray in barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) respectively to improve the tolerance to abiotic stresses. In the present study, Spd and Spm were used as an inducer to investigate chilling tolerance during seed imbibition and seed germination in maize. Seeds of maize inbred lines ‘Hung C' (chilling-tolerant) and ‘Mo17' (chilling-sensitive) were soaked with 0.25 mmol L1 of Spd and Spm, respectively for 72 h under dark at 15℃, and the control was not treated with PAs.Part of the seeds were germinated for 7 d under 25℃ after imbibition for 48 h under 5℃ in dark. The germination rates were tested every day with 4 replicates (25 seeds per replicate) each. Other part of seeds were imbibed for 0, 12, 24, 36, and 48 h, respectively at 5℃ in dark. The embryos were separated from the seeds for testing the activities of peroxidase (POD), catalase (CAT), superoxide dismutase (SOD) and ascorbate peroxidese (APX) as well as the contents of proline (Pro), soluble protein, and nucleic acid in embryo leakage. All measurements repeated 3 times with 15 seeds each time. Under chilling stress, both Spd and Spm treatments increased the activities of POD, CAT, SOD, and APX, raised soluble protein and Pro contents, and reduced nucleic acid content in embryo leakage. The treatments also increased seed germination percentage and shortened the mean germination time (MGT) which increased by 18.5% and 14.0%, and decreased by 1.21 d and 1.14 d for Spd and Spm treatments, respectively as compared with those of control. During the imbibition under chilling stress, the activities of POD, CAT, SOD and APX, Pro and soluble protein contents in embryos and germination percentage were higher, whereas the content of nucleic acid and MGT were lower in untreated Huang C seeds than in untreated Mo17 seeds. The results suggested that Spd and Spm treatments can improve the chilling tolerance during seed imbibition, and enhance the germination of maize seeds.

Exogenous spermidine differentially alters activities of some scavenging system enzymes, H 2O 2 and superoxide radical levels in water-stressed cucumber leaves

In order to examine whether polyamines (PAs) modify the functioning of the scavenging system and oxidative stress levels in water-stressed plants, cucumber (Cucumis sativus L.) seedlings were treated with spermidine (Spd) prior to dehydration, and stress-evoked changes in superoxide dismutase (SOD) (EC 1.15.1.1), catalase (EC 1.11.1.6), guaiacol peroxidase (EC 1.11.1.7) activities, H(2)O(2) and superoxide radical levels were determined. Free PA content during Spd treatment and during the stress period were also determined. Exogenous application of Spd differentially influenced enzymes of the antioxidative system under stress conditions; we observed an increase of guaiacol peroxidase activity, and, to a lesser degree, a reduction of SOD and catalase activities in Spd-treated plants in comparison to untreated stressed plants. Hydrogen peroxide and superoxide radical contents were also reduced in stressed plants after Spd pretreatment. These positive effects were observed in the case of 1mM Spd concentration. A higher concentration (3mM) influenced negative, more significant stress-induced changes, but a lower concentration (0.1mM) had a very limited effect. In summary, PAs are able to moderate the activities of scavenging system enzymes and to influence oxidative stress intensity.