Endogenous Polyamines Research Articles

Protective effect of spermine against pentylenetetrazole kindling epilepsy induced comorbidities in mice

Nitric oxide (NO), an important intracellular signaling molecule is involved in modulation of neuronal transmission. The NO level increases during epileptic activity in animal models of epilepsy. However, its role in epileptic activity remains controversial. Spermine is an endogenous polyamine; possesses anti-oxidant property and has ability to modulate ion channels and NO synthase activity. Therefore, the present study was designed to investigate the role of NO pathway in the neuroprotective effect of spermine, in Pentylenetetrazol (PTZ) induced kindling epilepsy in mice. PTZ (35mg/kg; intraperitoneal, i.p.) was administered on every alternate day up to 29days and challenge test was performed on 33rd day. From 15th day, spermine (5 and 10mg/kg; i.p.), L-NAME (10mg/kg; i.p), l-Arginine (50mg/kg; i.p) and sodium valproate (400mg/kg; i.p.) were administered up to 33rd day. Animals were sacrificed on 34th day for estimation of biochemical and neurotransmitters. Pretreatment with spermine, considerably, reversed the PTZ induced alterations. Further, pretreatment of L-NAME and l-Arginine with 5 and 10mg/kg; i.p. spermine, respectively, leads to an increase and decrease in its protective effects. The present study suggests the involvement of NO pathway in the protective effect of spermine against PTZ-induced kindling epilepsy in mice.

Molecular phylogenomic study and the role of exogenous spermidine in the metabolic adjustment of endogenous polyamine in two rice cultivars under salt stress

Compelling evidences anticipated the well acclamation of involvement of exogenous and endogenous polyamines (PAs) in conferring salt tolerance in plants. Intracellular PA's anabolism and catabolism should have contributed to maintain endogenous PAs homeostasis to induce stress signal networks. In this report, the evolutionary study has been conducted to reveal the phylogenetic relationship of genes encoding enzymes of the anabolic and catabolic pathway of PAs among the five plant lineages including green algae, moss, lycophyte, dicot and monocot along with their respective exon–intron structural patterns. Our results indicated that natural selection pressure had considerable influence on the ancestral PA metabolic pathway coding genes of land plants. PA metabolic genes have undergone gradual evolution by duplication and diversification process leading to subsequent structural modification through exon–intron gain and loss events to acquire specific function under environmental stress conditions. We have illuminated on the potential regulation of both the pathways by investigating the real-time expression analyses of PA metabolic pathway related enzyme coding genes at the transcriptional level in root and shoot tissues of two indica rice varieties, namely IR 36 (salt sensitive) and Nonabokra (salt-tolerant) in response to salinity in presence or absence of exogenous spermidine (Spd) treatment. Additionally, we have performed tissue specific quantification of the intracellular PAs and tried to draw probable connection between the PA metabolic pathway activation and endogenous PAs accumulation. Our results successfully enlighten the fact that how exogenous Spd in presence or absence of salt stress adjust the intracellular PA pathways to equilibrate the cellular PAs that would have been attributed to plant salt tolerance.

Relationship of Sink Activity with Endogenous Hormones and Polyamine Contents in Inferior Kernels of Maize

Relationship of Sink Activity with Endogenous Hormones and Polyamine Contents in Inferior Kernels of Maize

Exogenously applied polyamines ameliorate osmotic stress-induced damages and delay leaf rolling by improving the antioxidant system in maize genotypes

Leaf rolling (LR), particularly in crops, is a dehydration avoidance mechanism that results from water loss in plants under drought conditions. Two maize cultivars (Zea mays L.) differing in their tolerance to drought (cultivar Side was selected as stress-tolerant and cultivar Karacay was selected as stress-sensitive) under PEG-induced drought stress were used in this study to understand the effects of polyamines (PAs) on LR response and the role of the antioxidant system in the delayed LR process. Aerial parts of the seedlings were excised prior to the experiment and then submerged in a Hoagland nutrient solution with or without 0.1 mM Putrescine and 0.1 mM Spermine for 17 h, after which they were submitted to osmotic stress treatments (5% PEG) for 24 h. LR was physically prevented in order to clarify the relationship between PAs and antioxidant systems in LR response. Plants were evaluated by measuring the accumulation of hydrogen peroxide (H2O2), lipid peroxidation, antioxidant enzyme activities, and nonenzymatic antioxidant levels. Exogenous applications of PAs prevented water loss and delayed LR in comparison with the control (seedlings treated only with PEG). PAs almost totally prevented increases in lipid peroxidation. Antioxidant enzyme activities in rolled leaves were induced in response to osmotic stress in both maize seedlings via PA application. Ascorbate, glutathione, and endogenous PA levels increased as a result of PA applications. H2O2 content was lower in PA-pretreated plants than in the control in both cultivars. The activity/effectiveness of antioxidant system components of the physical prevention of leaf rolling (PLR) group of plants were lower than those of the group of plants with rolled leaves, especially in sensitive Karacay, whereas more induced H2O2 content and lipid peroxidation were determined in the PLR group. In addition, exogenous applications of PAs further increased the components of Side's antioxidant system in comparison with Karacay. When considered together, the data suggest that exogenous PAs may have a H2O2-mediated regulatory role in the LR process through the induction of antioxidant machinery. A stimulated antioxidant system decreases oxidative stress damage from excess accumulation of H2O2, thus delaying LR. In summary, exogenous PAs could help plants invert the adverse effects of osmotic stress and might play a key role in providing tolerance in plants through modulating the antioxidant system and decreasing H2O2 levels and water loss in plants via LR, as an alternative drought-protection mechanism. In addition, maize cultivars with late LR by PA applications may be provided as an opportunity for improving yield potential in drought-prone areas.

Potassium-induced freezing tolerance is associated with endogenous abscisic acid, polyamines and soluble sugars changes in grapevine

Crop nutrition is a practical method against freezing injury which may improves grapevine freezing tolerance (FT) potential by increasing bud nitrogenous and carbohydrates storages. In this study the effect of foliar application of potassium sulfate (PS; K2SO4; 0, 1, 2 and 3%) on some physico-chemical properties of fruit and leaf mineral contents of ‘Sultana’ grapevine (Vitis vinifera L.) were studied. Moreover, to further elucidate the efficiency of foliar PS on FT and some relevant morpho-physiological changes were evaluated at four sampling dates: Nov., Jan., Mar., and Apr. following exposure to artificial freezing using electrolyte leakage and bud browning bioassay. In summer 2013 and 2014, PS was sprayed at fruit set, pea-sized berry, verison and maturity on 16 years old grapevines located in Malayer Grape Research Station (Iran) under a randomized complete block design. Based on results, foliar PS significantly affected yield, cluster weights, and berry weight and some fruit quality indices including soluble solids, titratable acidity, pH and phenolic compounds. Foliar PS significantly changed the leaf N, K, P, Mg, Zn and Fe concentrations. The effect of nutrition treatments was also significant on FT of grapevines at four sampling stages. In Jan., the highest FT (LT50=−25.97°C) and the lowest FT (LT50=−20.16°C) was found in 3% PS- treated and control untreated vines, in respectively. Moreover, PS especially at 3% resulted in higher increments in abscisic acid, total phenol, soluble sugars, and polyamines concentrations. Potassium spray increased membrane stability and decreased electrolyte leakage. The ability of Potassium in FT improvement (lower electrolyte leakage) was found to be related to change in endogenous abscisic acid concentration as a stress hormone in preliminary and subsequent changes in other metabolites such as accumulation of soluble sugars, polyamines, and phenolic acids.

Changes in polyamine levels in relationship to the growth and development of parthenocarpic fruits (shotberries) of olive (Olea europaea L.)

The effects of applied polyamines (PAs), putrescine (Put) and spermidine (Spd) on parthenocarpic fruits (shotberries) and fruit set of olive were assessed. Factorial experiments were conducted in a randomized complete block design with three replications. Putrescine at 2.5 and 5mM.l−1 and spermidine at 1.25 and 2.5mM.l−1 were sprayed on branch units on olive trees (Olea europaea L. cv. Fishomi) at full bloom (FB) and two weeks after full bloom (2WAFB). The number of normal fruits and shotberries were evaluated. Endogenous PAs in the mesocarp and seeds were determined at both times of PAs application until fruit maturity. The results showed that Put was very effective in decreasing the percentage of the shotberries and increasing the percentage of normal fruits when PAs applied at FB. Mesocarp had the highest Put content in Put at 5mM.l−1 and Spd at 2.5mM.l−1 treatments respectively. In seed, the highest PAs content was found in Put treatment at 5mM.l−1 and the highest Spm and Spd content was observed in Spd treatment at 2.5mM.l−1.

Effect of polyamine on seed germination of wheat under drought stress is related to changes in hormones and carbohydrates

Drought is a multifaceted stress condition that inhibits crop growth. Seed germination is one of the critical and sensitive stages of plants, and its process is inhibited or even entirely prevented by drought. Polyamines (PAs) are closely associated with plant resistance to drought stress and seed germination. However, little is known about the effect of PA on the seed germination of wheat under drought stress. This study investigated the involvement of PAs in regulating wheat seed germination under drought stress. Six wheat genotypes differing in drought resistance were used, and endogenous PA levels were measured during seed germination under different water treatments. In addition, external PA was used for seed soaking and the variation of hormones, total soluble sugar and starch were measured during the seed germination under different water treatments. These results indicated that the free spermidine (Spd) accumulation in seeds during the seed germination period favored wheat seed germination under drought stress; however, the free putrescine (Put) accumulation in seeds during the seed germination period may work against wheat seed germination under drought stress. In addition, seed soaking in Spd and spermine (Spm) significantly relieved the inhibition of seed germination by drought stress; however, soaking seeds in Put had no significant effect on seed germination under drought. External Spd and Spm significantly increased the endogenous indole-3-acetic acid (IAA), zeatin (Z)+zeatin riboside (ZR), abscisic acid (ABA), and gibberellins (GA) contents in seeds and accelerated the seed starch degradation and increased the concentration of soluble sugars in seeds during seed germination. This may promote wheat seed germination under drought stress. In conclusion, free Spd and Put are key factors for regulating wheat seed germination under drought stress and the effects of Spd and Put on seed germination under drought notably related to hormones and starch metabolism.

Agmatine, a potential novel therapeutic strategy for depression

Major depressive disorder is the most common psychiatric disorder with lifetime prevalence of up to 20% worldwide. It is responsible for more years lost to disability than any other disorder. Despite the fact that current available antidepressant drugs are safe and effective, they are far from ideal. In addition to the need to administer the drugs for weeks or months to obtain clinical benefit, side effects are still a serious problem. Agmatine is an endogenous polyamine synthesized by the enzyme arginine decarboxylase. It modulates several receptors and is considered as a neuromodulator in the brain. In this review, studies demonstrating the antidepressant effects of agmatine are presented and discussed, as well as, the mechanisms of action related to these effects. Also, the potential beneficial effects of agmatine for the treatment of other neurological disorders are presented. In particular, we provide evidence to encourage future clinical studies investigating agmatine as a novel antidepressant drug.

Effects of exogenous spermidine on antioxidant system of tomato seedlings exposed to high temperature stress

The effects of foliar spraying with spermidine (Spd) on antioxidant system in tomato (Lycopersicon esculentum Mill.) seedlings were investigated under high temperature stress. The high temperature stress significantly inhibited plant growth and reduced chlorophyll (Chl) content. Application of exogenous 1 mM Spd alleviated the inhibition of growth induced by the high temperature stress. Malondialdehyde (MDA), hydrogen peroxide (H2O2) content and superoxide anion (O2) generation rate were significantly increased by the high temperature stress, but Spd significantly reduced the accumulation of reactive oxygen species (ROS) and MDA content under the stress. The high temperature stress significantly decreased glutathione (GSH) content and activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR), but increased contents of dehydroascorbic acid (DHA), ascorbic acid (AsA), and oxidized glutathione (GSSG) in tomato leaves. However, Spd significantly increased the activities of antioxidant enzymes, levels of antioxidants and endogenous polyamines in tomato leaves under the high temperature stress. In addition, to varying degrees, Spd regulated expression of MnSOD, POD, APX2, APX6, GR, MDHAR, DHAR1, and DHAR2 genes in tomato leaves exposed to the high temperature stress. These results suggest that Spd could change endogenous polyamine levels and alleviate the damage by oxidative stress enhancing the non-enzymatic and enzymatic antioxidant system and the related gene expression.

Physiological and biochemical mechanisms of spermine-induced cadmium stress tolerance in mung bean (Vigna radiata L.) seedlings.

The role of exogenous spermine (0.25 mM Spm, a type of polyamine (PA) in reducing Cd uptake and alleviating Cd toxicity (containing 1 and 1.5mM CdCl2 in the growing media) effects was studied in the mung bean (Vigna radiata L. cv. BARI Mung-2) plant. Exogenously applied Spm reduced Cd content, accumulation, and translocation in different plant parts. Increasing phytochelatin content, exogenous Spm reduced Cd accumulation and translocation. Spm application reduced the Cd-induced oxidative damage which was reflected from the reduction of H2O2 content, O2•- generation rate, lipoxygenase (LOX) activity, and lipid peroxidation level and also reflected from the reduction of spots of H2O2 and O2•- from mung bean leaves (compared to control treatment). Spm pretreatment increased non-enzymatic antioxidant contents (ascorbate, AsA, and glutathione, GSH) and activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) which reduced oxidative stress. The cytotoxicity of methylglyoxal (MG) is also reduced by exogenous Spm because it enhanced glyoxalase system enzymes and components. Through osmoregulation, Spm maintained a better water status of Cd-affected mung bean seedlings. Spm prevented the chl damage and increased its content. Exogenous Spm also modulated the endogenous free PAs level which might have the roles in improving physiological processes including antioxidant capacity, osmoregulation, and Cd and MG detoxification capacity. The overall Spm-induced tolerance of mung bean seedlings to Cd toxicity was reflected through improved growth of mung bean seedlings.

Spermidine reduces lipid accumulation and necrotic core formation in atherosclerotic plaques via induction of autophagy

Background and aimsSpermidine is an endogenous biological polyamine that exhibits broad longevity-extending activities via the induction of autophagy. Because basal autophagy is atheroprotective during early atherosclerosis but dysfunctional in advanced plaques, the aim of the present study was to assess the potential beneficial effects of autophagy induction by spermidine on atherosclerotic plaque progression and composition. MethodsApolipoprotein E-deficient (ApoE−/−) mice were fed a Western-type diet for 20 weeks with or without 5 mM spermidine in the drinking water. Results(Immuno-)histochemical analysis of plaques in the aortic root, proximal ascending aorta and brachiocephalic artery showed that spermidine changed neither the size of the plaque nor its cellular composition. However, spermidine treatment significantly reduced necrotic core formation (6.6 ± 0.5% vs. 3.7 ± 0.5% in aortic root, p = 0.0008) and lipid accumulation inside the plaque (27 ± 3% vs. 17 ± 1% oil red O positivity in thoracic aorta, p = 0.017). In vitro experiments showed that macrophages, unlike vascular smooth muscle cells (VSMCs), were relatively insensitive to autophagy induction by spermidine. Along these lines, spermidine triggered cholesterol efflux in autophagy-competent VSMCs (5.7 ± 1.2% vs. 8.7 ± 0.2%, p = 0.0118), but not in autophagy-deficient Atg7F/FSM22α-Cre+ VSMCs or macrophages. Analogous to the experiments in vitro, spermidine affected neither necrosis nor lipid load in plaques of Atg7F/FSM22α-Cre+ApoE−/− mice. ConclusionsSpermidine inhibits lipid accumulation and necrotic core formation through stimulation of cholesterol efflux, albeit without changing plaque size or cellular composition. These effects, which are driven by autophagy in VSMCs, support the general idea that autophagy induction is potentially useful to prevent vascular disease.

Proteomic and Physiological Analyses Reveal Putrescine Responses in Roots of Cucumber Stressed by NaCl.

Soil salinity is a major environmental constraint that threatens agricultural productivity. Different strategies have been developed to improve crop salt tolerance, among which the effects of polyamines have been well-reported. To gain a better understanding of the cucumber (Cucumis sativus L.) responses to NaCl and unravel the underlying mechanism of exogenous putrescine (Put) alleviating salt-induced damage, comparative proteomic analysis was conducted on cucumber roots treated with NaCl, and/or Put for 7 days. The results showed that exogenous Put restored the root growth inhibited by NaCl. Sixty-two differentially expressed proteins implicated in various biological processes were successfully identified by MALDI-TOF/TOF MS. The four largest categories included proteins involved in defense response (24.2%), protein metabolism (24.2%), carbohydrate metabolism (19.4%), and amino acid metabolism (14.5%). Exogenous Put up-regulated most identified proteins involved in carbohydrate metabolism, implying an enhancement in energy generation. Proteins involved in defense response and protein metabolism were differently regulated by Put, which indicated the roles of Put in stress resistance and proteome rearrangement. Put also increased the abundance of proteins involved in amino acid metabolism. Meanwhile, physiological analysis showed that Put could further up-regulated the levels of free amino acids in salt stressed-roots. In addition, Put also improved endogenous polyamines contents by regulating the transcription levels of key enzymes in polyamine metabolism. Taken together, these results suggest that Put may alleviate NaCl-induced growth inhibition through degradation of misfolded/damaged proteins, activation of stress defense, and the promotion of carbohydrate metabolism to generate more energy.

Effects of Exogenous Spermidine on Carbon and Nitrogen Metabolism in Tomato Seedlings under High Temperature

We investigated the effects of exogenous spermidine (Spd) on the carbohydrate, nitrogen (N), and endogenous polyamine status of tomato (Solanum lycopersicum) seedlings exposed to high-temperature stress [38/28 °C (day/night)]. High-temperature stress reduced the contents of pyruvate and succinate and inhibited plant growth. The application of exogenous Spd alleviated the inhibition of plant growth induced by high temperature, and also led to an increase in pyruvate, citrate, and succinate levels. High temperature markedly increased the NH4+-N content and reduced the activities of nitrate reductase (NR), glutamine synthetase (GS), and glutamate dehydrogenase (GDH). Spd significantly alleviated the negative effects on NH4+-N assimilation induced by high-temperature stress. Moreover, Spd significantly increased the activities of NR and GDH in the high-temperature-stressed tomato leaves. In contrast, Spd application to high-temperature-stressed plant leaves counteracted high-temperature-induced mRNA expression changes in N metabolism. Spd significantly upregulated the transcriptional levels of NR, nitrite reductase, GS, GDH, and glutamate synthase (GOGAT). In addition, exogenous Spd significantly increased endogenous polyamines. These results suggest that Spd could improve carbohydrate and N status through regulating the gene expression and activity of key enzymes for N metabolism, thus confers the tolerance to high temperature on tomato seedlings.

Salicylic acid differently impacts ethylene and polyamine synthesis in the glycophyte Solanum lycopersicum and the wild-related halophyte Solanum chilense exposed to mild salt stress.

This study aimed to determine the effects of exogenous application of salicylic acid (SA) on the toxic effects of salt in relation to ethylene and polyamine synthesis, and to correlate these traits with the expression of genes involved in ethylene and polyamine metabolism in two tomato species differing in their sensitivity to salt stress, Solanum lycopersicum cv Ailsa Craig and its wild salt-resistant relative Solanum chilense. In S. chilense, treatment with 125 mM NaCl improved plant growth, increased production of ethylene, endogenous salicylic acid and spermine. The production was related to a modification of expression of genes involved in ethylene and polyamine metabolism. In contrast, salinity decreased plant growth in S. lycopersicum without affecting endogenous ethylene, salicylic or polyamine concentrations. Exogenous application of salicylic acid at 0.01 mM enhanced shoot growth in both species and affected ethylene and polyamine production in S. chilense. Concomitant application of NaCl and salicylic acid improved osmotic adjustment, thus suggesting that salt and SA may act in synergy on osmolyte synthesis. However, the beneficial impact of exogenous application of salicylic acid was mitigated by salt stress since NaCl impaired endogenous SA accumulation in the shoot and salicylic acid did not improve plant growth in salt-treated plants. Our results thus revealed that both species respond differently to salinity and that salicylic acid, ethylene and polyamine metabolisms are involved in salt resistance in S. chilense.

Prohexadione-Ca and coper effect on growth and acumulation of endogenous polyamines in pea plants

Abstract The effect of retardant Prohexadione-Ca (BAS 125 10W, BASF Corp., Germany) and heavy metal copper on growth and endogenous concentrations of free and conjugated putrescine, spermidine and spermine in roots and leaves of pea plants were investigated. It was found that the polyamine concentrations increased seven days after the treatments. Most considerable increase of polyamines was detected in plants treated with copper and Prohexadione-Ca. The variations in polyamine concentrations in leaves and roots of pea plants suggest that Prohexadione-Ca had a protective effect against Cu stress of pea plants, which was expressed by additional accumulation of polyamines.

Agmatine Reverses Sub-chronic Stress induced Nod-like Receptor Protein 3 (NLRP3) Activation and Cytokine Response in Rats.

The activation of Nod-like receptor protein 3 (NLRP3) has lately been implicated in stress and depression as an initiator mechanism required for the production of interleukin (IL)-1β and IL-18. Agmatine, an endogenous polyamine widely distributed in mammalian brain, is a novel neurotransmitter/neuromodulator, with antistress, anxiolytic and antidepressant-like effects. In this study, we examined the effect of exogenously administered agmatine on NLRP3 inflammasome pathway/cytokine responses in rats exposed to restraint stress for 7 days. The rats were divided into three groups: stress, stress+agmatine (40 mg/kg; i.p.) and control groups. Agmatine significantly down-regulated the gene expressions of all stress-induced NLRP3 inflammasome components (NLRP3, NF-κB, PYCARD, caspase-1, IL-1β and IL-18) in the hippocampus and prefrontal cortex (PFC) and reduced pro-inflammatory cytokine levels not only in both brain regions, but also in serum. Stress-reduced levels of IL-4 and IL-10, two major anti-inflammatory cytokines, were restored back to normal by agmatine treatment in the PFC. The findings of the present study suggest that stress-activated NLRP3 inflammasome and cytokine responses are reversed by an acute administration of agmatine. Whether antidepressant-like effect of agmatine can somehow, at least partially, be mediated by the inhibition of NLRP3 inflammasome cascade and relevant inflammatory responses requires further studies in animal models of depression.

Glia and glial polyamines. Role in brain function in health and disease

The roles of glia and polyamines (PA) in brain function and dysfunction are highlighted in this review. We emphasize that PA accumulation preferentially in glia, but not in neurons, is clearly evolutionarily determined; it is found throughout the brain, retina, peripheral nervous system, and in glial-neuronal co-cultures of multiple species, including man. This phenomenon raises key questions: (i) What are the mechanisms that underlie such uneven distribution, accumulation and release from glia? (ii) What are the consequences of PA fluxes within the brain on neuronal function? (iii) What are the roles of PAs in brain disorders and diseases? This review includes suggestions on the roles of PAs, such as putrescine (PT), spermidine (SPD), spermine (SPM) and their derivatives as novel glio-transmitters in brain since PA affect many neuronal and glial receptors, channels and transporters. Polyamines hitherto have been neglected, although it is evident that these molecules are key elements for normal brain function and their metabolic disorders, apparently, cause the development of many pathological syndromes and diseases. The study of endogenous PA allows one to put forward the basic principles of scientific research on glio-neuronal interactions and clinical therapies, which are based on the exclusivity of glial cells in terms of accumulation of PA and PA-dependent functions.

Insights into spermine-induced combined high temperature and drought tolerance in mung bean: osmoregulation and roles of antioxidant and glyoxalase system.

High temperature and drought stress often occur simultaneously, and due to global climate change, this kind of phenomenon occurs more frequently and severely, which exerts devastating effects on plants. Polyamines (PAs) play crucial roles in conferring abiotic stress tolerance in plants. Present study investigated how exogenous pretreatment of spermine (Spm, 0.2mM) enhances mung bean (Vigna radiata L. cv. BARI Mung-2) seedlings tolerance to high temperature (HT, 40°C) and drought [induced by 5% polyethyleneglycol (PEG)] stress individually and in combination. Spm pretreatment reduced reactive oxygen species (ROS) production including H2O2 and O2•-, lipoxygenase (LOX) activity, and membrane lipid peroxidation (indicated by malondialdehyde, MDA) under HT and/or drought stress. Histochemical staining of leaves with diaminobenzidine and nitro blue tetrazolium chloride also confirmed that Spm-pretreated seedlings accumulated less H2O2 and O2•- under HT and/or drought stress. Spermine pretreatment maintained the ascorbate (AsA) and glutathione (GSH) levels high, and upregulated the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) which were vital for imparting ROS-induced oxidative stress tolerance under HT and/or drought stress. The cytotoxic compound methylglyoxal (MG) was overproduced due to HT and/or drought, but exogenous Spm pretreatment reduced MG toxicity enhancing the glyoxalase system. Spermine pretreatment modulated endogenous PA levels. Osmoregulation and restoration of plant water status were other major contributions of Spm under HT and/or drought stress. Preventing photosynthetic pigments and improving seedling growth parameters, Spm further confirmed its influential roles in HT and/or drought tolerance.

Polyamines in Pollen: From Microsporogenesis to Fertilization.

The entire pollen life span is driven by polyamine (PA) homeostasis, achieved through fine regulation of their biosynthesis, oxidation, conjugation, compartmentalization, uptake, and release. The critical role of PAs, from microsporogenesis to pollen–pistil interaction during fertilization, is suggested by high and dynamic transcript levels of PA biosynthetic genes, as well as by the activities of the corresponding enzymes. Moreover, exogenous supply of PAs strongly affects pollen maturation and pollen tube elongation. A reduction of endogenous free PAs impacts pollen viability both in the early stages of pollen development and during fertilization. A number of studies have demonstrated that PAs largely function by modulating transcription, by structuring pollen cell wall, by modulating protein (mainly cytoskeletal) assembly as well as by modulating the level of reactive oxygen species. Both free low-molecular weight aliphatic PAs, and PAs conjugated to proteins and hydroxyl-cinnamic acids take part in these complex processes. Here, we review both historical and recent evidence regarding molecular events underlying the role of PAs during pollen development. In the concluding remarks, the outstanding issues and directions for future research that will further clarify our understanding of PA involvement during pollen life are outlined.

Effect of polyamines on the grain filling of wheat under drought stress

Drought inhibits wheat grain filling. Polyamines (PAs) are closely associated with plant resistance due to drought and grain filling of cereals. However, little is known about the effect of PAs on the grain filling of wheat under drought stress. This study investigated whether and how PAs are involved in regulating wheat grain filling under drought stress. Two wheat genotypes differing in drought resistance were used, and endogenous PA levels were measured during grain filling under different water treatments. Additionally, external PAs were used, and the variation of hormone levels in grains was measured during grain filling under drought stress. The results indicated that spermidine (Spd) and spermine (Spm) relieve the inhibition caused by drought stress, and putrescine (Put) has the opposite effect. The higher activities of S-adenosylmethionine decarboxylase and Spd synthase in grains promotes the synthetic route from Put to Spd and Spm and notably increases the free Spd and Spm concentrations in grains, which promotes grain filling and drought resistance in wheat. The effect of PA on the grain filling of wheat under drought stress was closely related to the endogenous ethylene (ETH), zeatin (Z) + zeatin riboside (ZR) and abscisic acid (ABA). Spd and Spm significantly increased the Z + ZR and ABA concentrations and decreased the ETH evolution rate in grains, which promoted wheat grain filling under drought. Put significantly increased the ETH evolution rate, which led to excessive ABA accumulation in grains, subsequently aggravating the inhibition of drought on wheat grain filling. This means that the interaction of hormones, rather than the action of a single hormone, was involved in the regulation of wheat grain filling under drought.