Comparative study on the effects of putrescine and spermidine pre-treatment on cadmium stress in wheat

Selenium treatment alters the accumulation of osmolytes in arsenic-stressed rice (Oryza sativa L.)

Arsenic (As), one of the major pollutants in the soil, is an important environmental concern as its consumption can cause adverse health symptoms in living organisms. Its contamination of rice grown over As-contaminated areas is a serious concern in South Asian countries. Selenium (Se) has been reported to influence various osmolytes under metal stress in plants. The present study reports the role of Se in mitigating As stress in rice by modulating osmolyte metabolism. Rice plants grown in As-amended soil (2.5-10 mg kg-1) in pots were treated with sodium selenate (0.5-1.0 mg Se kg-1 soil) in glass house conditions and leaf samples were collected at 60 and 90 days after sowing (DAS). As-treated rice leaves displayed a reduction in relative water content (RWC) and dry weight than control with a maximum reduction of 1.68- and 2.47-fold in RWC and 1.95- and 1.69-fold in dry weight in As10 treatment at 60 and 90 DAS, respectively. Free amino acids (1.38-2.26-fold), proline (3.88-3.93-fold), glycine betaine (GB) (1.27-1.72-fold), choline (1.67-3.1-fold), total soluble sugars (1.29-1.61-fold), and reducing sugars (1.67-2.19-fold) increased in As-treated rice leaves as compared to control at both stages. As stress increased the γ-aminobutyric acid (GABA), putrescine content, and glutamate decarboxylase activity whereas diamine oxidase and polyamine oxidase activities declined by 1.69-1.88-fold and 1.52-1.86-fold, respectively. Se alone or in combination with As improved plant growth, RWC, GB, choline, putrescine, and sugars; lowered proline and GABA; and showed a reverse trend of enzyme activities related to their metabolism than respective As treatments. As stress resulted in a higher accumulation of osmolytes to combat its stress which was further modulated by the Se application. Hence, the current investigation suggested the role of osmoprotectants in Se-induced amelioration of As toxicity in rice plants.

Polyamine, 1,3-diaminopropane, regulates defence responses on growth, gas exchange, PSII photochemistry and antioxidant system in wheat under arsenic toxicity

The metalloid arsenic (As) is extremely hazardous to all living organisms, including plants. Pollution with As is very detrimental to the photosynthetic machinery, cell division, energy generation, and redox status. In order to cope with stress, the use of growth regulators such as polyamines (PA), which strengthen the antioxidant system of plants, has become widespread in recent years. PAs can modulate the plant growth through basic mechanisms common to all living organisms, such as membrane stabilization, free radical scavenging, deoxyribonucleic acid (DNA), ribonucleic acid (RNA) and protein synthesis, enzyme activities and second messengers. However, the effect of 1,3- diaminopropane (Dap), which is a product of PA catabolism, is not clear enough in plants exposed to As toxicity. In the current study, the different concentrations of 1,3-diaminopropane (0.1, 0.5 and 1 mM Dap) were hydroponically treated to wheat (Triticum aestivum) under arsenic stress (100 μM As) and then relative growth rate (RGR), relative water content (RWC), proline content (Pro), gas exchange parameters, PSII photochemistry, chlorophyll fluorescence kinetics, antioxidant activity and lipid peroxidation were assessed. RGR, RWC, osmotic potential and Pro content decreased in As-applied plants. The inhibition of these parameters could be reversed by Dap treatments. Besides, Dap applications mitigated the As toxicity-induced suppression on chlorophyll fluorescence (Fv/Fm, Fv/Fo and Fo/Fm) and the performance of PSII photochemistry. As impaired the balance on antioxidant capacity by decreased activities of catalase (CAT), peroxidase (POX), glutathione peroxidase (GPX), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and the contents of ascorbate (AsA) and glutathione (GSH) and then lipid peroxidation (TBARS content) increased. In the presence of Dap under As stress, the plants exhibited an increase in superoxide dismutase (SOD), POX, and GPX. Dap treatments contributed to the maintenance of cellular redox state (AsA/DHA and GSH/GSSG) by regulating the activities/contents of enzyme/non-enzyme involved in the AsA-GSH cycle. After Dap applications against stress, ROS accumulation (H2O2 content) and lipid peroxidation (TBARS) were effectively reduced. The findings showed that by eliminating As-induced oxidative damage and protecting the biochemical processes of photosynthesis, Dap treatments have a substantial potential to give resistance to wheat.

Exogenous plant growth regulator and foliar fertilizers for phytoextraction of cadmium with Boehmeria nivea [L.] Gaudich from contaminated field soil

As a enrichment plant, ramie can be used for the phytoremediation of cadmium (Cd)-contaminated soil. However, it is worth exploring the role of plant growth regulators and foliar fertilizers in the process of plant growth and development and Cd adsorption. By measuring the agronomic traits, Cd content of aboveground and underground ramie, calculating the Cd transfer coefficient (TF) and Cd bioconcentration factors (BCF), and the correlation between various indicators. This study examined the effects of plant growth regulators and foliar fertilizers on ramie's capacity for Cd accumulation and transportation. Plant growth regulators and foliar fertilizers increased the Cd content of the aboveground ramie, reduced the Cd content of the underground ramie, and increased the TF. Among them, GA-1 increased the Cd content of the aboveground ramie to 3 times more than that of the control and reduced the Cd content of the underground ramie by 54.76%. Salicylic acid (SA) increased the Cd content of the aboveground ramie to three times more than that of the control. The combination of GA and foliar fertilizer reduced the Cd content of the aboveground and underground ramie and the TF and BCF of the underground ramie. After the hormones were sprayed, the TF of ramie had a significant positive correlation with the Cd content of the aboveground ramie; the BCF of the aboveground ramie had a significant positive correlation with the Cd content and TF of the aboveground ramie. The results indicate that Brassinolide (BR), gibberellin (GA), ethephon (ETH), polyamines (PAs), and salicylic acid (SA) have different effects on the enrichment and transport of Cd in ramie. This study provided an effective method to improve the capacity for ramie to adsorb heavy metals during cultivation.

Changes in polyamine contents during Fusarium graminearum and Fusarium verticillioides inoculation in maize seedlings with or without seed-priming

Maize (Zea mays L.) is the most produced field crop all over the world. One of its most critical diseases that results in economic loss is ear rot caused by various Fusarium species. Previous researches have shown that polyamines, found in all living cells, play crucial role in biotic stress responses. At the same time, biosynthesis of polyamines is of paramount importance not only for plants but also for their pathogens to promote stress tolerance and pathogenicity. In our study, we investigated the polyamine content changes induced in the seedlings of two maize genotypes of different susceptibility by isolates of Fusarium verticillioides and Fusarium graminearum, two Fusarium species of different lifestyles. Apart from that, it was examined how infection efficiency and changes in polyamine contents were modified by salicylic acid or putrescine seed soaking pre-treatments. Our observations confirmed that initial and stress-induced changes in the polyamine contents are not directly related to tolerance in either coleoptile or radicle. However, the two pathogens with different lifestyles induced remarkably distinct changes in the polyamine contents. The effect of the seed soaking pre-treatments depended on the pathogens and plant resistance as well: both salicylic acid and putrescine seed soaking had positive results against F. verticillioides, while in the case of infection with F. graminearum, seed soaking with distilled water alone affected biomass parameters positively in the tolerant genotype.

Neutral-to-positive cadmium effects on germination and seedling vigor, with and without seed priming

This review gathered and analyzed data about (i) the Cd-induced impacts on seed germination and seedling vigor, and (ii) the use of different priming agents to mitigate Cd-induced impacts on the early plant development. Critical evaluation of the obtained data revealed intriguing results. First, seeds of diverse species can endure exposures to Cd. Such endurance is exhibited as maintenance of or even improvement in the seed germination and vigor (up to 15% and 70%, respectively). Second, the main factors influencing seed tolerance to Cd toxicity are related to temporal variations in anatomical, physiological, and/or biochemical features. Third, Cd can trigger diverse transgenerational effects on plants by shaping seed endophytes, by modulating seed provisioning with resources and regulatory elements, and/or by altering seed (epi)genomics. Fourth, different chemical, biological and physical priming agents can mitigate Cd-induced impacts on seeds, sometimes enhancing their performance over the control (reference) values. Overall, this review shows that the impacts of Cd on seed germination and vigor encompass not only negative outcomes but also neutral and positive ones, depending upon the Cd dose, media properties, plant species and genotypes, plant developmental stage and organ, and management approaches. Increasing our understanding of plant tolerance mechanisms against the growing background Cd pollution is relevant to support breeding programs, agricultural practices, and health-environmental policies.

Putrescine-functionalized carbon quantum dot (put-CQD) nanoparticle: A promising stress-protecting agent against cadmium stress in grapevine (Vitis vinifera cv. Sultana)

Due to their sessile nature, plant cannot escape from stress factors in their growing environment, in either biotic or abiotic nature. Amid the abiotic stress factors; high levels of soil cadmium (Cd) impose heavy metal stress on plants, resulting in critical injuries and reduced agronomic performance. In order to buffer the adverse effects of Cd stress, novel nanoparticles (NP) have been applied and notable improvements have been reported. According to the literature, the protective roles of polyamines (e.g., Putrescine; Put) and carbon quantum dots (CQD) have been reported with respect to the plant productivity under either stress or non-stress conditions. Those reports led us to hypothesize that the conjugation of Put and CQD (Put-CQD NPs) might lead to further augmented performance of plants under stress and non-stress conditions. In this regard, we successfully synthesized a novel nanomaterial Put-CQD NPs. In this respect, Put (50 mg L^-1), CQD (50 mg L^-1) and Put-CQD NPs (25 and 50 mg L^-1) were sprayed in 'Sultana' grapevines under Cd stress (10 mg kg^-1). As expected, upon stress, Cd content in leaf and root tissues increased by 103.40% and 65.15%, respectively (p < 0.05). The high uptake and accumulation of Cd in plant tissues were manifested in significant alterations of physiological and biochemical attributes of the plant. Concerning stress markers, Cd stress caused increases in content of induced MDA, H₂O₂, and proline as well as electrolyte leakage rate. As expected, Cd stress caused critical reductions in fresh and dry leaf weight by 21.31% and 42.34%, respectively (p < 0.05). On the other hand, both Put-CQD NPs increased fresh and dry leaf weigh up to approximately 30%. The Cd-mediated disturbances in photosynthetic pigments and chlorophyll fluorescence were buffered with Put-CQD NPs. Of the defence system, enzymatic (SOD, APX, GP) as well as anthocyanin and phenolics were induced by both Cd stress and Put-CQD NPs (p < 0.05). On the other hand, Cd stress reduced content of polyamines (putrescine (Put), spermine (Spm) and spermidine (Spd) by 39.28%, 53.36%, and 39.26%, respectively (p < 0.05). However, the reduction levels were buffered by the treatments. Considering the effectiveness of both NP concentrations, the lower dose (25 mg L^-1) could be considered as an optimal concentration. To our knowledge, this is the first report of its kind as a potential agent to reduce the adverse effects of Cd stress in grapevines.

Melatonin improves the removal and the reduction of Cr(VI) and alleviates the chromium toxicity by antioxidative machinery in Rhodobacter sphaeroides

Bioremediation with photosynthetic bacteria (PSB) is thought to be a promising removal method for hexavalent chromium [Cr(VI)]-containing wastewater. In the present study, Rhodobacter sphaeroides (R. sphaeroides) SC01 was used for the investigation of Cr(VI) removal in Cr(VI)-contaminated solution in the presence of melatonin. It was found that exogenous melatonin alleviated oxidative damage to R. sphaeroides SC01, increased Cr (VI) absorption capacity of cell membrane, and improved the reduction efficiency of Cr(VI) via the activation of chromate reductants. The results showed that melatonin could further promote the increase in Cr(VI) removal efficiency, reaching up to 97.8%. Furthermore, melatonin application resulted in 296.9%, 44.4%, and 69.7% upregulation of ascorbic acid (AsA), glutathione (GSH), and cysteine (Cys) relative to non-melatioin treated R. sphaeroides SC01 at 48 h. In addition, the resting cells, cell-free supernatants (CFS), and cell-free extracts (CFE) with melatonin had a higher Cr(VI) removal rate of 18.6%, 82.0%, and 15.2% compared with non-melatonin treated R. sphaeroides SC01. Fourier transform infrared spectroscopy (FTIR) revealed that melatonin increased the binding of Cr(III) with PO4^3- and CO groups on cell membrane of R. sphaeroides SC01. X-ray diffractometer (XRD) analysis demonstrated that melatonin remarkably bioprecipitated the production of CrPO₄·6H₂O in R. sphaeroides SC01. Hence, these results indicated that melatonin plays the important role in the reduction and uptake of Cr(VI), demonstrating it is a great promising strategy for the management of Cr(VI) contaminated wastewater in photosynthetic bacteria.

A novel phytoremediation technology for polluted cadmium soil: Salix integra treated with spermidine and activated carbon

A variety of plants have been used as phytoremediation materials to remove Cd from polluted soil. However, the disadvantages of using plants for decontamination include low biomass, low uptake, and inefficiency. We conducted experiments to determine the effects of spermidine and activated carbon treatments of Salix integra on Cd removal. The results showed that exogenous spermidine and activated carbon increased plant growth and root development compared with the CK. The increased dry mass (39.65-92.95%) with the combined spermidine and activated carbon treatments was higher than that with either single treatment (14.79-62.80%). The root length, surface area, root volume, and root diameter with the combined spermidine and activated carbon treatments (53.51-189.35%, 113.08-207.62%, 111.71-499.27%, and 32.51-106.62%, respectively) were higher than those of the lone application treatments (19.35-132.23%, 52.33-111.57%, 35.08-297.07%, and 24.22-81.38%, respectively). In addition, spermidine and activated carbon application reduced the toxicity of Cd to S. integra by improving the antioxidant capacity, thereby increasing the accumulation of Cd. The application of spermidine and activated carbon also changed the distribution of Cd in each part of S. integra. There was increased accumulation of Cd in the shoots and better absorption by the S. integra shoots, thereby improving their Cd remediation efficiency. The combined 0.8 mM spermidine and 0.5 g kg^-1 activated carbon were most effective on removing Cd from the soil. The Cd removal efficiency was 78.11-120.86% higher than that of the CK. Our results may provide foundational information for understanding the mechanisms for the sustainable remediation of Cd-contaminated soil using a combination of spermidine and activated carbon.

Physiological and biochemical bases of spermidine-induced alleviation of cadmium and lead combined stress in rice

Cadmium (Cd) and lead (Pb) pollution is a major environmental issue affecting plant production. Spermidine (Spd) is involved in plant response to abiotic stress. However, the role and associated mechanism of Spd under Cd + Pb combined stress are poorly understood. The potential protective role of Spd at different concentration on rice (Oryza sativa L.) seedlings exposed to Cd + Pb treatment was investigated by a hydroponic experiment in this study. The results showed that exogenous Spd enhanced the tolerance of rice seedlings to Cd + Pb stress, resulted in an increase in plant height, root length, fresh weight and dry weight of roots and shoots. Further, application of Spd decreased the contents of hydrogen peroxide, superoxide anion, malondialdehyde, and the accumulation of Cd and Pb, and increased the contents of mineral nutrient, carotenoids, chlorophyll, proline, soluble sugar, soluble protein, total phenol, flavonoid, anthocyanin, and antioxidant enzymes activities in roots and shoots of rice seedlings under Cd + Pb stress. Particularly, 0.5 mmol L^-1 Spd was the most effective to alleviate the adverse impacts on growth and physiological metabolism of rice seedlings under Cd + Pb stress. Principal component analysis and heat map clustering established correlations between physio-biochemical parameters and further revealed Spd alleviated Cd + Pb damage in rice seedling was associated with inhibition of accumulation and translocation of Cd and Pb, increasing the contents of photosynthetic pigments and mineral nutrient and stimulation of antioxidative response and osmotic adjustment. Overall, our findings provide an important prospect for use of Spd in modulating Cd + Pb tolerance in rice plants. Spd could help to alleviate Cd + Pb damage through inhibition of accumulation and translocation of Cd and Pb and stimulation of oxidant-defense system and osmotic adjustment.

Versatile roles of polyamines in improving abiotic stress tolerance of plants

In recent years, extreme environmental cues such as abiotic stresses, including frequent droughts with irregular precipitation, salinity, metal contamination, and temperature fluctuations, have been escalating the damage to plants' optimal productivity worldwide. Therefore, yield maintenance under extreme events needs improvement in multiple mechanisms that can minimize the influence of abiotic stresses. Polyamines (PAs) are pivotally necessary for a defensive purpose under adverse abiotic conditions, but their molecular interplay in this remains speculative. The PAs' accretion is one of the most notable metabolic responses of plants under stress challenges. Recent studies reported the beneficial roles of PAs in plant development, including metabolic and physiological processes, unveiling their potential for inducing tolerance against adverse conditions. This review presents an overview of research about the most illustrious and remarkable achievements in strengthening plant tolerance to drought, salt, and temperature stresses by the exogenous application of PAs. The knowledge of underlying processes associated with stress tolerance and PA signaling pathways was also summarized, focusing on up-to-date evidence regarding the metabolic and physiological role of PAs with exogenous applications that protect plants under unfavorable climatic conditions. Conclusively, the literature proposes that PAs impart an imperative role in abiotic stress tolerance in plants. This implies potentially important feedback on PAs and plants' stress tolerance under unfavorable cues.

Spermine-mediated metabolic homeostasis improves growth and stress tolerance in creeping bentgrass (Agrostis stolonifera) under water or high-temperature stress

Plants have developed diverse defense strategies to reduce the detrimental effects of a wide range of environmental stresses. The objectives of this study were to explore the function of spermine (Spm) on mediating growth and physiological changes in water homeostasis, photosynthetic performance, and oxidative damage and to further examine the regulatory mechanism of Spm on global metabolites reprogramming and associated metabolic pathways in horticultural creeping bentgrass (Agrostis stolonifera) under water and heat stresses. The 21-days-old plants were pretreated with or without 100 μM Spm for 3 days and then subjected to water stress (17% polyethylene glycol 6000), high-temperature stress (40/35°C, day/night), or normal condition (control without water stress and heat stress) for 18 days. Results demonstrated that exogenous application of Spm could significantly increase endogenous polyamine (PAs), putrescine (Put), spermidine (Spd), and Spm contents, followed by effective alleviation of growth retardant, water imbalance, photoinhibition, and oxidative damage induced by water and heat stress. Metabolites' profiling showed that a total of 61 metabolites were differentially or commonly regulated by Spm in leaves. Spm upregulated the accumulation of mannose, maltose, galactose, and urea in relation to enhanced osmotic adjustment (OA), antioxidant capacity, and nitrogen metabolism for growth maintenance under water and heat stress. Under water stress, Spm mainly induced the accumulation of sugars (glucose-1-phosphate, sucrose-6-phosphate, fructose, kestose, maltotriose, and xylose), amino acids (glutamic acid, methionine, serine, and threonine), and organic acids (pyruvic acid, aconitic acid, and ketoglutaric acid) involved in the respiratory pathway and myo-inositol associated with energy production, the ROS-scavenging system, and signal transduction. In response to heat stress, the accumulation of alanine, glycine, gallic acid, malic acid, or nicotinic acid was specifically enhanced by Spm contributing to improvements in antioxidant potency and metabolic homeostasis. This study provides novel evidence of Spm-induced,tolerance to water and heat stresses associated with global metabolites reprogramming in favor of growth maintenance and physiological responses in horticultural plants.

Light Spectral Composition Modifies Polyamine Metabolism in Young Wheat Plants

Although light-emitting diode (LED) technology has extended the research on targeted photomorphogenic, physiological, and biochemical responses in plants, there is not enough direct information about how light affects polyamine metabolism. In this study, the effect of three spectral compositions (referred to by their most typical characteristic: blue, red, and the combination of blue and red [pink] lights) on polyamine metabolism was compared to those obtained under white light conditions at the same light intensity. Although light quality induced pronounced differences in plant morphology, pigment contents, and the expression of polyamine metabolism-related genes, endogenous polyamine levels did not differ substantially. When exogenous polyamines were applied, their roborative effect were detected under all light conditions, but these beneficial changes were correlated with an increase in polyamine content and polyamine metabolism-related gene expression only under blue light. The effect of the polyamines on leaf gene expression under red light was the opposite, with a decreasing tendency. Results suggest that light quality may optimize plant growth through the adjustment of polyamine metabolism at the gene expression level. Polyamine treatments induced different strategies in fine-tuning of polyamine metabolism, which were induced for optimal plant growth and development under different spectral compositions.

PAs Regulate Early Somatic Embryo Development by Changing the Gene Expression Level and the Hormonal Balance in Dimocarpus longan Lour

Polyamines (PAs) play an important regulatory role in many basic cellular processes and physiological and biochemical processes. However, there are few studies on the identification of PA biosynthesis and metabolism family members and the role of PAs in the transition of plant embryogenic calli (EC) into globular embryos (GE), especially in perennial woody plants. We identified 20 genes involved in PA biosynthesis and metabolism from the third-generation genome of longan (Dimocarpus longan Lour.). There were no significant differences between longan and other species regarding the number of members, and they had high similarity with Citrus sinensis. Light, plant hormones and a variety of stress cis-acting elements were found in these family members. The biosynthesis and metabolism of PAs in longan were mainly completed by DlADC2, DlSAMDC2, DlSAMDC3, DlSPDS1A, DlSPMS, DlCuAOB, DlCuAO3A, DlPAO2 and DlPAO4B. In addition, 0.01 mmol∙L⁻¹ 1-aminocyclopropane-1-carboxylic acid (ACC), putrescine (Put) and spermine (Spm), could promote the transformation of EC into GE, and Spm treatment had the best effect, while 0.01 mmol∙L⁻¹ D-arginine (D-arg) treatment inhibited the process. The period between the 9th and 11th days was key for the transformation of EC into GE in longan. There were higher levels of gibberellin (GA), salicylic acid (SA) and abscisic acid (ABA) and lower levels of indole-3-acetic acid (IAA), ethylene and hydrogen peroxide (H₂O₂) in this key period. The expression levels in this period of DlADC2, DlODC, DlSPDS1A, DlCuAOB and DlPAO4B were upregulated, while those of DlSAMDC2 and DlSPMS were downregulated. These results showed that the exogenous ACC, D-arg and PAs could regulate the transformation of EC into GE in longan by changing the content of endogenous hormones and the expression levels of PA biosynthesis and metabolism genes. This study provided a foundation for further determining the physicochemical properties and molecular evolution characteristics of the PA biosynthesis and metabolism gene families, and explored the mechanism of PAs and ethylene for regulating the transformation of plant EC into GE.

Phytochemical and physiological changes in Salvia officinalis L. under different irrigation regimes by exogenous applications of putrescine

Water stress is the major factor limiting plant productivity and quality in most regions of the world. In the present study, a two-year field experiment was conducted to determine the influence of putrescine (Put) on phytochemical, physiological, and growth parameters of Salvia officinalis L. under different irrigation regimes. The highest stem dry weight (56.05 and 65.21 g m⁻²) plus leaf dry weight (124.51 g m⁻²) were predicted in irrigation regimes of (20 and 40%) plus 20% available soil water was depleted (ASWD), respectively. Total phenolic content (TPC) was increased significantly under the irrigation regime of 80% with the application of distilled water in spring. TPC showed an increasing trend with increases in Put concentration under all irrigation regimes in both spring and summer. The highest total flavonoids content (TFC) in wavelengths of 415 and 367 nm were predicted in 2.25 mM Put. The highest ascorbate peroxidase (APX) activity (0.13 μmol mg⁻¹ protein) was predicted in the irrigation regime of 20% with the application of distilled water in spring and summer. There was a significantly negative correlation coefficient between APX, TPC, and TFC. Indeed, there was a decreasing trend in APX and an increasing trend in TPC and TFC with increases in Put concentration under the irrigation regime of 20% ASWD. The highest hydroxyl radical scavenging activity (HRSA) values were obtained under irrigation regimes of 49.27% and 20% ASWD in spring and summer, respectively. There was an increasing trend in endogenous Put with increases in the Put concentration. The responses of compatible osmolytes to irrigation regime can be expressed by quadratic model, suggesting maximum proline (0.52 mg g⁻¹), total reducing sugars (TRS) (0.37 mg g⁻¹), xylose (0.68 mg g⁻¹), and mannose (0.37 mg g⁻¹) values would be obtained in irrigation regimes of 68.33%, 48.33%, 53.75%, and 56.25% ASWD, respectively.

Improving water deficit tolerance of Salvia officinalis L. using putrescine

To study the effects of foliar application of putrescine (distilled water (0), 0.75, 1.5, and 2.25 mM) and water deficit stress (20%, 40%, 60%, and 80% available soil water depletion (ASWD)) on the physiological, biochemical, and molecular attributes of Salvia officinalis L., a factorial experiment was performed in a completely randomized design with three replications in the growth chamber. The results of Real-Time quantitative polymerase chain reaction (qRT-PCR) analysis showed that putrescine concentration, irrigation regime, and the two-way interaction between irrigation regime and putrescine concentration significantly influenced cineole synthase (CS), sabinene synthase (SS), and bornyl diphosphate synthase (BPPS) relative expression. The highest concentration of 1,8-cineole, camphor, α-thujone, β-thujone, CS, SS, and BPPS were obtained in the irrigation regime of 80% ASWD with the application of 0.75 mM putrescine. There was high correlation between expression levels of the main monoterpenes synthase and the concentration of main monoterpenes. The observed correlation between the two enzyme activities of ascorbate peroxidase (APX) and catalase (CAT) strongly suggests they have coordinated action. On the other hand, the highest peroxidase (PO) and superoxide dismutase (SOD) concentrations were obtained with the application of 0.75 mM putrescine under the irrigation regime of 40% ASWD. Putrescine showed a significant increase in LAI and RWC under water deficit stress. There was an increasing trend in endogenous putrescine when putrescine concentration was increased in all irrigation regimes. Overall, the results suggest that putrescine may act directly as a stress-protecting compound and reduced H₂O₂ to moderate the capacity of the antioxidative system, maintain the membrane stability, and increase secondary metabolites under water deficit stress.

Polyamine Metabolism under Different Light Regimes in Wheat

Although the relationship between polyamines and photosynthesis has been investigated at several levels, the main aim of this experiment was to test light-intensity-dependent influence of polyamine metabolism with or without exogenous polyamines. First, the effect of the duration of the daily illumination, then the effects of different light intensities (50, 250, and 500 μmol m^–2 s^–1) on the polyamine metabolism at metabolite and gene expression levels were investigated. In the second experiment, polyamine treatments, namely putrescine, spermidine and spermine, were also applied. The different light quantities induced different changes in the polyamine metabolism. In the leaves, light distinctly induced the putrescine level and reduced the 1,3-diaminopropane content. Leaves and roots responded differently to the polyamine treatments. Polyamines improved photosynthesis under lower light conditions. Exogenous polyamine treatments influenced the polyamine metabolism differently under individual light regimes. The fine-tuning of the synthesis, back-conversion and terminal catabolism could be responsible for the observed different polyamine metabolism-modulating strategies, leading to successful adaptation to different light conditions.

Phytohormones: Key players in the modulation of heavy metal stress tolerance in plants

Heavy metal (HM) stress in plants has received considerable global attention as it threatens sustainable growth in agriculture worldwide. Hence, desperate efforts have been undertaken for combating the effects of this stress in plants. Interestingly, the use of phytohormones in reducing the impact of HM toxicity has gained much momentum in the recent past. Phytohormones act as chemical messengers that improve the HM stress resistance in plants, thus allowing them to retain their growth and developmental plasticity. Their exogenous application as well as manipulation of endogenous levels through precise targeting of their biosynthesis/signaling components is a promising approach for providing a protective shield against HM stress in plants. However, for the successful use of phytohormones for field plants exposed to HM toxicity, in-depth knowledge of the key pathways regulated by them is of prime importance. Hence, the present review mainly summarizes the key conceptual developments on the involvement of phytohormones in the mitigation of HM stress in plants. The role of various genes, proteins, and signaling components involved in phytohormones associated HM stress tolerance and their modulation has also been discussed. Thus, this update will pave the way for improving HM stress tolerance in plants with the advent of phytohormones for sustainable agriculture growth in the future.

Protective Effects of Lactobacillus plantarum CCFM8610 against Acute Toxicity Caused by Different Food-Derived Forms of Cadmium in Mice

Cadmium (Cd) is an environmental pollutant that is toxic to almost every human organ. Oral supplementation with lactic acid bacteria (LAB) has been reported to alleviate cadmium toxicity. However, research on the mitigation of cadmium toxicity by LAB is still limited to inorganic cadmium, which is not representative of the varied forms of cadmium ingested daily. In this study, different foodborne forms of cadmium were adopted to establish an in vivo toxicity model, including cadmium–glutathione, cadmium–citrate, and cadmium–metallothionein. The ability of Lactobacillus plantarum CCFM8610 to reduce the toxic effects of these forms of cadmium was further investigated. The 16S rRNA gene sequencing and metabolomics technologies based on liquid chromatography with tandem mass spectrometry (LC–MS/MS) were adopted for the exploration of relevant protective mechanisms. The results demonstrated that the consumption of CCFM8610 can reduce the content of cadmium in mice and relieve the oxidative stress caused by different food–derived forms of cadmium, indicating that CCFM8610 has a promising effect on the remediation of the toxic effects of cadmium food poisoning. Meanwhile, protective effects on gut microflora and serum metabolites might be an important mechanism for probiotics to alleviate cadmium toxicity. This study provides a theoretical basis for the application of L. plantarum CCFM8610 to alleviate human cadmium poisoning.

Unfinished story of polyamines: Role of conjugation, transport and light-related regulation in the polyamine metabolism in plants

Polyamines play a fundamental role in the functioning of all cells. Their regulatory role in plant development, their function under stress conditions, and their metabolism have been well documented as regards both synthesis and catabolism in an increasing number of plant species. However, the majority of these studies concentrate on the levels of the most abundant polyamines, sometimes providing data on the enzyme activity or gene expression levels during polyamine synthesis, but generally making no mention of the fact that changes in the polyamine pool are very dynamic, and that other processes are also involved in the regulation of actual polyamine levels. Differences in the distribution of individual polyamines and their conjugation with other compounds were described some time ago, but these have been given little attention. In addition, the role of polyamine transporters in plants is only now being recognised. The present review highlights the importance of conjugated polyamines and also points out that investigations should not only deal with the polyamine metabolism itself, but should also cover other important questions, such as the relationship between light perception and the polyamine metabolism, or the involvement of polyamines in the circadian rhythm.

Validation of Reference Genes for Studying Different Abiotic Stresses in Oat (Avena sativa L.) by RT-qPCR

Oat (Avena sativa L.) is a widely cultivated cereal with high nutritional value and it is grown mainly in temperate regions. The number of studies dealing with gene expression changes in oat continues to increase, and to obtain reliable RT-qPCR results it is essential to establish and use reference genes with the least possible influence caused by experimental conditions. However, no detailed study has been conducted on reference genes in different tissues of oat under diverse abiotic stress conditions. In our work, nine candidate reference genes (ACT, TUB, CYP, GAPD, UBC, EF1, TBP, ADPR, PGD) were chosen and analysed by four statistical methods (GeNorm, Normfinder, BestKeeper, RefFinder). Samples were taken from two tissues (leaves and roots) of 13-day-old oat plants exposed to five abiotic stresses (drought, salt, heavy metal, low and high temperatures). ADPR was the top-rated reference gene for all samples, while different genes proved to be the most stable depending on tissue type and treatment combinations. TUB and EF1 were most affected by the treatments in general. Validation of reference genes was carried out by PAL expression analysis, which further confirmed their reliability. These results can contribute to reliable gene expression studies for future research in cultivated oat.

Arbuscular Mycorrhiza-Mediated Regulation of Polyamines and Aquaporins During Abiotic Stress: Deep Insights on the Recondite Players

Environmental stresses of (a)biotic origin induce the production of multitudinous compounds (metabolites and proteins) as protective defense mechanisms in plants. On account of the regulation of some of these compounds, arbuscular mycorrhizal fungi (AMF) reinforce the inherent tolerance of plants toward the stress of different origins and kind. This article reviews two specific fundamental mechanisms that are categorically associated with mycorrhiza in alleviating major abiotic stresses, salt, drought, and heavy metal (HM) toxicity. It puts emphasis on aquaporins (AQPs), the conduits of water and stress signals; and polyamines (PAs), the primordial stress molecules, which are regulated by AMF to assure water, nutrient, ion, and redox homeostasis. Under stressful conditions, AMF-mediated host AQP responses register distinct patterns: an upregulation to encourage water and nutrient uptake; a downregulation to restrict water loss and HM uptake; or no alterations. The patterns thereof are apparently an integrative outcome of the duration, intensity, and type of stress, AMF species, the interaction of fungal AQPs with that of plants, and the host type. However, the cellular and molecular bases of mycorrhizal influence on host AQPs are largely unexplored. The roles of PAs in augmenting the antioxidant defense system and improving the tolerance against oxidative stress are well-evident. However, the precise mechanism by which mycorrhiza accords stress tolerance by influencing the PA metabolism per se is abstruse and broadly variable under different stresses and plant species. This review comprehensively analyzes the current state-of-art of the involvement of AMF in "PA and AQP modulation" under abiotic stress and identifies the lesser-explored landscapes, gaps in understanding, and the accompanying challenges. Finally, this review outlines the prospects of AMF in realizing sustainable agriculture and provides insights into potential thrust areas of research on AMF and abiotic stress.

Effects of exogenous spermidine on poplar resistance to leaf and root herbivory as affected by soil cadmium stress

Elemental defense hypothesis (EDH) proposed that metal accumulation in plants could increase plant resistance to herbivores. However, the over-accumulation of metals in low-accumulators such as woody plants will cause adverse effects on plant health. Thus, the application of EDH on low-accumulators in metal contaminated areas is strongly limited. Since the supplement of exogenous spermidine (Spd) was reported to alleviate metal-induced toxicity in plants while stimulating metal accumulation in plant tissues, we hypothesized that such application will further improve plant resistance to herbivores. In this study, we employed a woody plant species, Populus yunnanensis, to test this hypothesis. We first tested a Spd concentration series applied on plants subjected to soil cadmium (Cd) stress and found that the 1 mM Spd strongly promoted plant growth while stimulated Cd accumulation in plant leaves and roots. We further conducted herbivore bioassays to test the growth performance and feeding preference of two leaf herbivore species and a root herbivore species that fed on plants from different treatments. The results showed that the inhibition effect of Cd stressed-plants on herbivore growth was significantly magnified by the addition of Spd. The growth weight of all the three tested herbivores were negatively correlated with increased Cd concentrations in plant tissues. In addition, the feeding preferences of the two leaf herbivore species were strongly repelled by leaf discs from Cd-treated plants with Spd supplement. The results suggested that the application of exogenous Spd at a certain dose could enhance elemental defense of plants against herbivory.

The effects of putrescine pre-treatment on osmotic stress responses in drought-tolerant and drought-sensitive wheat seedlings

Recent studies have demonstrated that exogenous polyamines have protective effects under various stress condition. A broader understanding of the role of the polyamine pool fine regulation and the alterations of polyamine-related physiological processes could be obtained by comparing the stress effects in different genotypes. In this study, the impact of pre-treatment with putrescine in response to osmotic stress was investigated in the drought-tolerant Katya and drought-sensitive Zora wheat (Triticum aestivum) cultivars. Photosynthetic performance, in vivo thermoluminescence emission from leaves, leaf temperature, polyamine and salicylic acid levels, contents of osmoprotectants, and activities of antioxidant enzymes in the leaves were investigated not only to reveal differences in the physiological processes associated to drought tolerance, but to highlight the modulating strategies of polyamine metabolism between a drought-tolerant and a drought-sensitive wheat genotype. Results showed that the tolerance of Katya under osmotic stress conditions was characterized by higher photosynthetic ability, stable charge separation across the thylakoid membrane in photosystem II, higher proline accumulation and antioxidant activity. Thermoluminescence also revealed differences between the two varieties - a downshift of the B band and an increase of the afterglow band under osmotic stress in Zora, providing original complementary information to leaf photosynthesis. Katya variety exhibited higher constitutive levels of the signaling molecules putrescine and salicylic acid compared to the sensitive Zora. However, responses to exogenous putrescine were more advantageous for the sensitive variety under PEG treatment, which may be in relation with the decreased catabolism of polyamines, suggesting the increased need for polyamine under stress conditions.

Integration of silicon and secondary metabolites in plants: a significant association in stress tolerance

As sessile organisms, plants are unable to avoid being subjected to environmental stresses that negatively affect their growth and productivity. Instead, they utilize various mechanisms at the morphological, physiological, and biochemical levels to alleviate the deleterious effects of such stresses. Amongst these, secondary metabolites produced by plants represent an important component of the defense system. Secondary metabolites, namely phenolics, terpenes, and nitrogen-containing compounds, have been extensively demonstrated to protect plants against multiple stresses, both biotic (herbivores and pathogenic microorganisms) and abiotic (e.g. drought, salinity, and heavy metals). The regulation of secondary metabolism by beneficial elements such as silicon (Si) is an important topic. Silicon-mediated alleviation of both biotic and abiotic stresses has been well documented in numerous plant species. Recently, many studies have demonstrated the involvement of Si in strengthening stress tolerance through the modulation of secondary metabolism. In this review, we discuss Si-mediated regulation of the synthesis, metabolism, and modification of secondary metabolites that lead to enhanced stress tolerance, with a focus on physiological, biochemical, and molecular aspects. Whilst mechanisms involved in Si-mediated regulation of pathogen resistance via secondary metabolism have been established in plants, they are largely unknown in the case of abiotic stresses, thus leaving an important gap in our current knowledge.

The protective effects of polyamines on salinity stress tolerance in foxtail millet (Setaria italica L.), an important C4 model crop

ABSTRACT

Soil salinity is a major abiotic stress that adversely affects crop growth, development and productivity worldwide. In this study, the individual and synergistic roles of putrescine (Put) and spermidine (Spd) in salinity stress tolerance of foxtail millet (Setaria italica L.) was assessed. In the present study, plants treated with combined biogenic amines Put + Spd possess very efficient antioxidant enzyme systems which help to control the uninhibited oxidation and protect the plants from oxidative damage by ROS scavenging. Additionally, lower concentration of Put + Spd under NaCl stress showed reduced hydrogen peroxide, electrolyte leakage and caspase-like activity than control. FTIR analysis underlying the ability of PAs induced tolerance and the chemical bonds of Put + Spd treated plants were reminiscent of control plants. Moreover, histochemical analysis with 2',7'-dichlorofluorescein diacetate (DCF-DA), 3,3'-Diaminobenzidine (DAB) and nitrotetrazolium blue chloride (NBT) revealed that ROS accumulation was inhibited by combined PAs under salt stress condition. These results showed that Put + Spd significantly improve the endogenous PAs, which enhance high-salinity stress tolerance by detoxifying ROS. For the first time, the synergistic ROS scavenging ability of Put along with Spd was investigated upon salinity tolerance in C4 model foxtail millet crop. Overall, our findings illustrated the implication for improving salinity tolerance of agronomically important crop species.

GRAPHIC ABSTRACT

Enhanced performance of Bacillus megaterium OSR-3 in combination with putrescine ammeliorated hydrocarbon stress in Nicotiana tabacum

Hydrocarbon stress (HS) has been causing decreased plant growth and productivity. Putrescine (Put) and growth promoting microbes are vital for plant growth and development under hydrocarbon stress. Current research work was carried out to evaluate the potential of Bacillus megaterium OSR-3 alone and in combination with Put to alleviate HS in Nicotiana tabacum (L.). The crude petroleum contaminated soil significantly reduced growth attributes of N. tabacum. B. megaterium OSR-3 inoculated plants subjected to HS exhibited improved photosynthetic rate, gas exchange characteristics, poline contents and protein level. Furthermore, bacterial inoculation enhanced the antioxidative activity of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) in tobacco plants subjected to HS. The HS alleviation in B. megaterium OSR-3 inoculated N. tabacum can be credited to the heightened activity of antioxidative enzymes, reduction in hydrogen peroxide (H2O2) and abridged synthesis of malondialdehyde (MDA). The increased synthesis of indole acetic acid (IAA) in HS stressed N. tabacum plants treated with co-application of B. megaterium OSR-3 and Put attenuated toxicity and amplified growth of plants. Additionally, the co-application of B. megaterium OSR-3 and Put also upregulated the activity of antioxidative enzymes and induced augmented level of proline and IAA in plants under HS regimes. Current research provides novel insight into the potential and mechanism of B. megaterium OSR-3 and Put in mitigation of HS in N. tabacum plants.

Molecular background of cadmium tolerance in Rht dwarf wheat mutant is related to a metabolic shift from proline and polyamine to phytochelatin synthesis

Plant height is among the most important agronomic traits influencing crop yield. Wheat lines carrying Rht genes are important in plant breeding due to their both higher yield capacity and better tolerance to certain environmental stresses. However, the effects of dwarf-inducing genes on stress acclimation mechanisms are still poorly understood. Under the present conditions, cadmium stress induced different stress responses and defence mechanisms in the wild-type and dwarf mutant, and the mutant with the Rht-B1c allele exhibited higher tolerance. In the wild type after cadmium treatment, the abscisic acid synthesis increased in the leaves, which in turn might have induced the polyamine and proline metabolisms in the roots. However, in the mutant line, the slight increment in the leaf abscisic acid content accompanied by relatively high salicylic acid accumulation was not sufficient to induce such a great accumulation of proline and putrescine. Although changes in proline and polyamines, especially putrescine, showed similar patterns, the accumulation of these compounds was antagonistically related to the phytochelatin synthesis in the roots of the wild type after cadmium stress. In the dwarf genotype, a favourable metabolic shift from the synthesis of polyamine and proline to that of phytochelatin was responsible for the higher cadmium tolerance observed.

Synergistic ameliorative effect of iron oxide nanoparticles and Bacillus subtilis S4 against arsenic toxicity in Cucurbita moschata: polyamines, antioxidants, and physiochemical studies

The present study was intended to assess the potential of iron oxide nanoparticles (IONPs) and Bacillus subtilis S4 in mitigation of arsenic (As) stress in Cucurbita moschata. Cucurbita moschata seedlings were subjected to As stress for 60 days. Reduced level of growth parameters including photosynthetic pigments, rate of photosynthesis and gas exchange characteristics was observed in seedlings subjected to As stress. However, IONPs and B. subtilis S4 improved growth attributes and proline contents in supplemented C. moschata seedlings. Bacillus subtilis S4 inoculated seedlings showed higher activity of peroxidase (POD) and superoxide dismutase (SOD) under As toxicity. Similarly, the co-application of IONPs and B. subtilis S4 further increased the activity of these antioxidative enzymes. The As stress alleviation in inoculated C. moschata seedlings is credited to reduced levels of hydrogen peroxide (H₂O₂), malondialdehyde (MDA) and electrolyte leakage (EL) in IONPs and B. subtilis S4-treated plants. Furthermore, synergism between plant growth promoting bacteria (PGPB) and IONPs enhanced the biosynthesis of stress mitigating polyamines including spermidine and putrescine in As-stressed seedlings. Current research reveals that synergistic application of IONPs and B. subtilis S4 is an effective sustainable and ecofriendly approach for alleviation of As stress in C. moschata seedlings.

The unknown soldier in citrus plants: polyamines-based defensive mechanisms against biotic and abiotic stresses and their relationship with other stress-associated metabolites

Citrus plants are challenged by a broad diversity of abiotic and biotic stresses, which definitely alter their growth, development, and productivity. In order to survive the various stressful conditions, citrus plants relay on multi-layered adaptive strategies, among which is the accumulation of stress-associated metabolites that play vital and complex roles in citrus defensive responses. These metabolites included amino acids, organic acids, fatty acids, phytohormones, polyamines (PAs), and other secondary metabolites. However, the contribution of PAs pathways in citrus defense responses is poorly understood. In this review article, we will discuss the recent metabolic, genetic, and molecular evidence illustrating the potential roles of PAs in citrus defensive responses against biotic and abiotic stressors. We believe that PAs-based defensive role, against biotic and abiotic stress in citrus, is involving the interaction with other stress-associated metabolites, particularly phytohormones. The knowledge gained so far about PAs-based defensive responses in citrus underpins our need for further genetic manipulation of PAs biosynthetic genes to produce transgenic citrus plants with modulated PAs content that may enhance the tolerance of citrus plants against stressful conditions. In addition, it provides valuable information for the potential use of PAs or their synthetic analogs and their emergence as a promising approach to practical applications in citriculture to enhance stress tolerance in citrus plants.

2-Hydroxymelatonin mitigates cadmium stress in cucumis sativus seedlings: Modulation of antioxidant enzymes and polyamines

Cadmium level is continuously increasing in agricultural soils mainly due to anthropogenic activities. Cadmium is one of the most phytotoxic metals in the soils. The present study investigates the possible role of 2-hydroxymelatonin (2-OHMT) in assuagement of Cd-toxicity in cucumber (Cucumis sativus L.) plants. 2-OHMT is an important metabolite produced through interaction of melatonin with oxygenated compounds. Cadmium stress decreased the activity of antioxidant enzymes and polyamines. However, exogenously applied 2-OHMT enhanced plant growth attributes including photosynthetic rate, intercellular CO₂ concentration, stomatal conductance and transpiration rate in treated plants. In addition, 2-OHMT induced enhancement of the activity of PAs biosynthesizing enzymes (putrescine, spermidine and spermine) in conjunction with reduction in activity of polyamine oxidase (PAO). 2-OHMT mitigated Cd stress through up-regulation in expression of stress related CS-ERS gene along with the amplified activity of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) in treated seedlings. The improved activity of antioxidant scavengers played central role in reduction of hydrogen peroxide (H₂O₂), electrolyte leakage (EL) and malondialdehyde (MDA) in plants under Cd stress. Recent findings also advocate the positive correlation between PAs and ethylene, as both possess common precursor. The current study reveals that priming seeds with 2-OHMT reduces Cd-toxicity and makes it possible to cultivate cucumber in Cd-contaminated areas. Future experiments will perhaps help in elucidation of 2-OHMT intervened stress mitigation procedure in C. sativus crop. Furthermore, research with reference to potential of 2-OHMT for stress alleviation in other horticultural and agronomic crops will assist in enhancement of crop productivity.

The Role of Salicylic Acid in Plants Exposed to Heavy Metals

Salicylic acid (SA) is a very simple phenolic compound (a C₇H₆O₃ compound composed of an aromatic ring, one carboxylic and a hydroxyl group) and this simplicity contrasts with its high versatility and the involvement of SA in several plant processes either in optimal conditions or in plants facing environmental cues, including heavy metal (HM) stress. Nowadays, a huge body of evidence has unveiled that SA plays a pivotal role as plant growth regulator and influences intra- and inter-plant communication attributable to its methyl ester form, methyl salicylate, which is highly volatile. Under stress, including HM stress, SA interacts with other plant hormones (e.g., auxins, abscisic acid, gibberellin) and promotes the stimulation of antioxidant compounds and enzymes thereby alerting HM-treated plants and helping in counteracting HM stress. The present literature survey reviews recent literature concerning the roles of SA in plants suffering from HM stress with the aim of providing a comprehensive picture about SA and HM, in order to orientate the direction of future research on this topic.

The Role of Salicylic Acid in Plants Exposed to Heavy Metals

Salicylic acid (SA) is a very simple phenolic compound (a C7H6O3 compound composed of an aromatic ring, one carboxylic and a hydroxyl group) and this simplicity contrasts with its high versatility and the involvement of SA in several plant processes either in optimal conditions or in plants facing environmental cues, including heavy metal (HM) stress. Nowadays, a huge body of evidence has unveiled that SA plays a pivotal role as plant growth regulator and influences intra- and inter-plant communication attributable to its methyl ester form, methyl salicylate, which is highly volatile. Under stress, including HM stress, SA interacts with other plant hormones (e.g., auxins, abscisic acid, gibberellin) and promotes the stimulation of antioxidant compounds and enzymes thereby alerting HM-treated plants and helping in counteracting HM stress. The present literature survey reviews recent literature concerning the roles of SA in plants suffering from HM stress with the aim of providing a comprehensive picture about SA and HM, in order to orientate the direction of future research on this topic.

Polyamine-Induced Hormonal Changes in eds5 and sid2 Mutant Arabidopsis Plants

Polyamines are multifaceted compounds which play a role in regulating plant growth and stress tolerance in interactions with plant hormones. The aim of the present study was to reveal how exogenous polyamines influence the synthesis of salicylic acid, with a special emphasis on the effect of salicylic acid deficiency on the polyamine metabolism and polyamine-induced changes in other plant hormone contents. Our hypothesis was that the individual polyamines induced different changes in the polyamine and salicylic acid metabolism of the wild type and salicylic acid-deficient Arabidopsis mutants, which in turn influenced other hormones. To our knowledge, such a side-by-side comparison of the influence of eds5-1 and sid2-2 mutations on polyamines has not been reported yet. To achieve our goals, wild and mutant genotypes were tested after putrescine, spermidine or spermine treatments. Polyamine and plant hormone metabolism was investigated at metabolite and gene expression levels. Individual polyamines induced different changes in the Arabidopsis plants, and the responses were also genotype-dependent. Polyamines upregulated the polyamine synthesis and catabolism, and remarkable changes in hormone synthesis were found especially after spermidine or spermine treatments. The sid2-2 mutant showed pronounced differences compared to Col-0. Interactions between plant hormones may also be responsible for the observed differences.

Pattern of changes in salicylic acid-induced protein kinase (SIPK) gene expression and salicylic acid accumulation in wheat under cadmium exposure

Salicylic acid-induced protein kinase (SIPK) is known as a 'master switch' for stress responses in plants. It can be induced by salicylic acid (SA) and several stress factors. The main aim of the present study was to reveal the relationship between SA accumulation and the gene expression level of SIPK during 50 and 250 µm Cd stress in wheat plants. Quantitative real-time PCR was used for determination of the gene expression level of SIPK. Salicylic acid content measurement was performed with an HPLC system equipped with a fluorescence detector. Cadmium treatment increased the endogenous SA level and expression level of SIPK in a concentration-dependent manner. Induction of SIPK expression preceded the accumulation of endogenous SA. Although SA treatment induced dramatic endogenous SA accumulation, its SIPK-inducing effect was moderate. In roots, higher induction of SIPK was observed than in leaves. The same tendency of SIPK expression was observed in both Cd- and SA-treated plants, as decisively the highest transcript level was detected after 30 min of treatment, but thereafter the expression decreased rapidly to control level or even below. The induction of SIPK was transient in all cases, and even a very high SA level in either the leaves or roots was not able to maintain the elevated expression level of this gene. The results suggest that SIPK has a role in initiating Cd stress response and the exogenous SA-induced signalling process.

Alleviation of cadmium-induced genotoxicity and cytotoxicity by calcium chloride in faba bean (Vicia faba L. var. minor) roots

Alleviation of cadmium-induced root genotoxicity and cytotoxicity by calcium chloride (CaCl₂) in faba bean (Vicia faba L. var. minor) seedlings were studied. Faba bean seeds were treated with H₂O or 2% CaCl₂ for 6 h before germination. Seeds were then exposed to 0 and 50 µM CdCl₂ concentrations for 7 days. Genotoxic damaging effects of Cd was examined through the determination of the mitotic index (MI), chromosomal aberrations (CA) and micronucleus (MN) in the meristem cells of faba bean roots. Similarly, effects of Cd stress on metal accumulation, total membrane lipid contents, total fatty acid composition (TFA), lipid peroxidation as indicated by malondialdehyde production, soluble protein and non-protein thiols (NP-SH) contents, hydrogen peroxide production and the activities of superoxide dismutase (SOD), catalase (CAT) and guaiacol peroxidase (GPX) were evaluated after 7 days of Cd stress in the seedling roots. Cd stress resulted in the reduction of MI, in addition to MN formation and CA induction in the roots of non-primed seeds (treated with H₂O). Moreover, Cd induced lipid peroxidation, H₂O₂ overproduction and loss of membrane lipid amount and soluble protein content, and changes in the TFA composition in roots of faba bean seedlings. SOD activity declined, but CAT and GPX activities increased. However, seed pre-treatment with CaCl₂ attenuated the genotoxic and cytotoxic effects of Cd on Vicia faba roots. The results showed that CaCl₂ induced reduction of Cd accumulation, improved cell membrane stability and increased the antioxidant defence systems, thus reducing and alleviating Cd genotoxicity and oxidative damage.

Polyamine Action under Metal/Metalloid Stress: Regulation of Biosynthesis, Metabolism, and Molecular Interactions

Polyamines (PAs) are found in all living organisms and serve many vital physiological processes. In plants, PAs are ubiquitous in plant growth, physiology, reproduction, and yield. In the last decades, PAs have been studied widely for exploring their function in conferring abiotic stresses (salt, drought, and metal/metalloid toxicity) tolerance. The role of PAs in enhancing antioxidant defense mechanism and subsequent oxidative stress tolerance in plants is well-evident. However, the enzymatic regulation in PAs biosynthesis and metabolism is still under research and widely variable under various stresses and plant types. Recently, exogenous use of PAs, such as putrescine, spermidine, and spermine, was found to play a vital role in enhancing stress tolerance traits in plants. Polyamines also interact with other molecules like phytohormones, nitric oxides, trace elements, and other signaling molecules to providing coordinating actions towards stress tolerance. Due to the rapid industrialization metal/metalloid(s) contamination in the soil and subsequent uptake and toxicity in plants causes the most significant yield loss in cultivated plants, which also hamper food security. Finding the ways in enhancing tolerance and remediation mechanism is one of the critical tasks for plant biologists. In this review, we will focus the recent update on the roles of PAs in conferring metal/metalloid(s) tolerance in plants.

Exogenous spermidine elevating cadmium tolerance in Salix matsudana involves cadmium detoxification and antioxidant defense

In this study, exogenous spermidine role on Salix matsudana tolerance to cadmium was evaluated. Spermidine and cadmium presented antagonistic effects on the biomass, copper and zinc concentrations in S. matsudana. cadmium mainly distributed in the cell wall of subcellular fraction; 46.97%-60.43% of cadmium existed in a sodium chloride-extracted form. Cadmium contents in roots, leaves, and twigs ranged from 2002.67 to 3961.00, 111.59 to 229.72, and 102.56 to 221.27 mg/kg, respectively. Spermidine application elevated cadmium concentrations in the roots, cuttings, and cell wall and the ratio of deionized water-extracted cadmium, but decreased cadmium levels in the twigs and leaves and the fractions of cadmium extracted by ethanol and sodium chloride, respectively. Putrescine and malondialdehyde were important indicators of cadmium-induced oxidative damage. Exogenous spermidine alleviated the accumulation of superoxide anion, hydrogen peroxide, malondialdehyde via promoting the levels of spermidine, soluble protein, superoxide dismutase, reductive ascorbate, glutathione reductase, and glutathione peroxidase in S. matsudana leaves under the corresponding cadmium stress. The results indicated that S. matsudana was a candidate for cadmium rhizoremediation and extraction in leaves; the spermidine application enhanced the cadmium tolerance of S. matsudana through promoting cadmium accumulation in roots, cell wall, and less bioactive chemical forms and the antioxidative ability.

Polyamine Function in Plants: Metabolism, Regulation on Development, and Roles in Abiotic Stress Responses

Polyamines (PAs) are low molecular weight aliphatic nitrogenous bases containing two or more amino groups. They are produced by organisms during metabolism and are present in almost all cells. Because they play important roles in diverse plant growth and developmental processes and in environmental stress responses, they are considered as a new kind of plant biostimulant. With the development of molecular biotechnology techniques, there is increasing evidence that PAs, whether applied exogenously or produced endogenously via genetic engineering, can positively affect plant growth, productivity, and stress tolerance. However, it is still not fully understood how PAs regulate plant growth and stress responses. In this review, we attempt to cover these information gaps and provide a comprehensive and critical assessment of the published literature on the relationships between PAs and plant flowering, embryo development, senescence, and responses to several (mainly abiotic) stresses. The aim of this review is to summarize how PAs improve plants' productivity, and to provide a basis for future research on the mechanism of action of PAs in plant growth and development. Future perspectives for PA research are also suggested.

Genome-wide identification of genes involved in polyamine biosynthesis and the role of exogenous polyamines in Malus hupehensis Rehd. under alkaline stress

Polyamines (PAs) in plants are growth substrates with functions similar to phytohormones. Although they contribute to diverse processes, little is known about their role in stress responses, especially for perennial woody plants. We conducted a genome-wide investigation of 18 sequences involved in PA biosynthesis in the genome of apple (Malus domestica). Further analysis was performed to construct a phylogenetic tree, analyze their protein motifs and gene structures. In addition, we developed their expression profiles in response to stressed conditions. Both MDP0000171041 (MdSAMDC1) and MDP0000198590 (MdSPDS1) were induced by alkaline, salt, ABA, cold, and dehydration stress treatments, suggesting that these genes are the main contributors to activities of S-adenosylmethionine decarboxylase (EC 4.1.1.50) and spermidine synthase (EC 2.5.1.16) in apple. Changes in PA biosynthesis under stress conditions indicated that spermidine and spermine are more essential than putrescine for apple, especially when responding to alkaline or salt stress. When seedlings of M. hupehensis Rehd. were supplied with exogenous PAs, their leaves showed less chlorosis under alkaline stress when compared with untreated plants. This application also inhibited the decline in SPAD levels and reduced relative electrolyte leakage in those stressed seedlings, while increasing their concentration of active iron. These results suggest that the alteration in PA biosynthesis confers enhanced tolerance to alkaline stress in M. hupehensis Rehd.