Effect of exogenous spermidine on polyamine metabolism in water hyacinth leaves under mercury stress

The influence of exogenous spermidine (Spd) on arginine decarboxylase (ADC), ornithine decarboxylase (ODC), polyamine oxidase (PAO) activities and polyamines (PAs), proline contents in water hyacinth leaves under Mercury (Hg) stress was investigated after 6 days treatment. The results showed that free putrescine (Put) content increased, the contents of free spermidine (Spd) and spermine (Spm) and the (Spd + Spm)/Put ratio in water hyacinth leaves decreased significantly with the increase of the Hg concentrations. Hg stress also disturbed the activities of ADC, ODC and PAO and caused changes on proline content. Compared to the Hg-treatment only, exogenous Spd (0.1 mM) significantly reduced the accumulation of free Put, increased the contents of free Spd and Spm and the ratio of (Spd + Spm)/Put in water hyacinth leaves. Furthermore, exogenous Spd enhanced the activities of ADC, ODC and PAO and significantly increased proline content. The PS-conjugated PAs and PIS-bound PAs changed in the same trend as free PAs. These results suggest that exogenous Spd can alleviate the metabolic disturbance of polyamines caused by Hg in water hyacinth leaves.     

Exogenously applied polyamines increase drought tolerance of rice by improving leaf water status,photosynthesis and membrane properties

Drought stress hampers rice performance principally by disrupting the plant–water relations and structure of biological membranes. This study appraised the role of polyamines (PAs) in improving drought tolerance in fine grain aromatic rice (Oryza sativa L.). Three PAs [putrescine (Put), spermidine (Spd) and spermine (Spm)] were used each at 10 μM as seed priming (by soaking seeds in solution) and foliar spray. Primed and non-primed seeds were sown in plastic pots with normal irrigation in a phytotron. At four-leaf stage, plants were subjected to drought stress by bringing the soil moisture down to 50% of field capacity by halting water supply. For foliar application, 10 μM solutions each of Put, Spd and Spm were sprayed at five-leaf stage. Results revealed that drought stress severely reduced the rice fresh and dry weights, while PAs application improved net photosynthesis, water use efficiency, leaf water status, production of free proline, anthocyanins and soluble phenolics and improved membrane properties. PAs improved drought tolerance in terms of dry matter yield and net photosynthesis was associated with the maintenance of leaf water status and improved water use efficiency. Among the antioxidants, catalase activity was negatively related to H₂O₂ and membrane permeability, which indicated alleviation of oxidative damage on cellular membranes by PAs application. Foliar application was more effective than the seed priming, and among the PAs, Spm was the most effective in improving drought tolerance.     

Proline controls the level of polyamines in common sage plants under normal conditions and at UV-B irradiation

Common sage (Salvia officinalis L.) plants grown in water culture to the stage of 4–5 true leaves were treated for 12, 24, 36, or 48 h with proline added to nutrient medium to a final concentration of 5 mM, or irradiated with UV-B light (12.3 kJ/m² for 10 min), or subjected to combined action of these factors. In these plants, activity of proline dehydrogenase (PDH), the content of proline, and the contents of free and conjugated polyamines were determined in the leaves and roots. It was shown that, in control plants, the content of endogenous proline was close to zero. In the presence of proline in medium, its total content in the roots was 9 μmol/g fr wt in 12 h of exposure, whereas in the leaves the content of proline increased only in 24 h and achieved only 1 μmol/g fr wt. The content of free putrescine increased in the leaves and especially in the roots after 10-min irradiation with UV-B light. The biosynthesis of putrescine was induced in the presence of proline in medium and was observed earlier than after UV-B irradiation. UV-B irradiation affected not only the synthesis of putrescine but also that of spermidine and spermine; it also induced accumulation of their soluble conjugates. Exogenous proline enhanced putrescine synthesis but inhibited the formation of polyamine soluble conjugates. At combined treatment of the two factors, the content of free putrescine in the leaves displayed a tendency to the rise and in the roots, to the decrease. At the same time, the content of polyamine free conjugates increased in both leaves and roots. All these facts could be considered as an indirect indication of relationship between proline and polyamine biosyntheses. We can also state that an artificially created high proline concentration in common sage tissues characterized of its low constitutive level resulted in disturbances in the homeostasis of low-molecular cell metabolites and induced a requirement in its restoration by diverse ways. This agrees with activation of PDH, a key enzyme of proline degradation. Induction of polyamine biosynthesis and changes in the content of their soluble conjugates might be one of the ways for such restoration. Under stress conditions, the high proline concentration is not toxic for plants because polyamines and proline are the components of the plant defense system, thus weakening damaging effects of abiotic stressors.     

Role of polyamines on de novo shoot morphogenesis from cotyledons of Brassica campestris ssp. pekinensis (Lour) Olsson in vitro

Summary The promotive effect of ethylene inhibitors (Els), i.e. AgNO₃ and aminoethoxyvinylglycine (AVG) on de novo shoot regeneration from cultured cotyledonary explants of Brassica campestris ssp. pekinensis cv. Shantung in relation to polyamines (PAs) was investigated. The endogenous levels of free putrescine and spermidine in the explant decreased sharply after 1–3 days of culture, whereas endogenous spermine increased, irrespective of the absence or presence of Els. AgNO₃ at 30 M did not affect endogenous PAs during two weeks of culture. In contrast, explants grown on medium containing 5 M AVG produced higher levels of free putrescine and spermine which increased rapidly after three days and reached a peak at 10 days. An exogenous application of 5 mM putrescine also resulted in a similar surge of endogenous free spermine of the explant. More strikingly, shoot regeneration from explants grown in the presence of 1–20 mM putrescine, 0.1–2.5 mM spermidine, or 0.1–1 mM spermine was enhanced after three weeks of culture. However, exogenous PAs generally did not affect ethylene production, and endogenous levels of 1-aminocyclopropane-1-carboxylate (ACC) synthase activity and ACC of the explant. This study shows the PA requirement for shoot regeneration from cotyledons of B. campestris ssp. pekinensis in vitro, and also indicates that the promotive effect of PAs on regeneration may not be due to an inhibition of ethylene biosynthesis.Abbreviations PAs polyamines - AVG aminoethoxyvinylglycine - SAM S-adenosylmethionine - ACC 1-aminocyclopropane-1-carboxylate - Els ethylene inhibitors     

Polyamines content and physiological and biochemical responses to ladder concentration of nickel stress in Hydrocharis dubia (Bl.) Backer leaves

Influence of ladder concentration of nickel (Ni) on the leaves of Hydrocharis dubia were studied after 3 days treatment. The accumulation of Ni, the content of polyamines, proline, malondialdehyde (MDA) and soluble protein, as well as the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in the leaves were investigated. The result indicated that the toxicity of Ni manifested in respective aspect of physiological and biochemical characters. Significant increase of Ni concentration in the leaf tissue was observed, which was concentration dependent. Visible symptoms of Ni toxicity: chlorosis and necrosis occurred following the 3rd day. Meantime, treatment with Ni resulted in the increase in the generation rate of O₂^•− in the leaves. SOD and CAT activities decreased significantly in response to Ni treatment, it was possibly the reason of accumulation of O₂^•−. However, a several-fold decrease in POD activities was found. Our results indicated that because of prolonged increases in O₂^•− level, oxidative damage, measured as the level of lipid peroxidation, occured in the leaves of Ni treated fronds. The changes of the content of polyamines (PAs) were also investigated in the leaves of Hydrocharis dubia. Ni treatment significantly increased the putrescine (Put) level and lowered spermidine (Spd) and spermine (Spm) levels, thereby significantly reducing the ratio of free (Spd + Spm)/Put in leaves, which has been considered as the signal under stress. Although the trend that PS-conjugated PAs and PIS-bound PAs changed the same as free PAs, they changed in more less extent.     

Exogenous polyamines enhance copper tolerance of Nymphoides peltatum

The protective effects of polyamines (PAs) against copper (Cu) toxicity were investigated in the leaves of Nymphoides peltatum. Cu treatment increased the putrescine (Put) level and lowered spermidine (Spd) and spermine (Spm) levels, thereby reducing the (Spd+Spm)/Put ratio in leaves. Exogenous application of Spd or Spm markedly reversed these Cu-induced effects for all three PAs and partially restored the (Spd+Spm)/Put ratio in leaves. It also significantly enhanced the level of proline, retarded the loss of soluble protein, decreased the rate of O2*- generation and H2O2 content, and prevented Cu-induced lipid peroxidation. Furthermore, exogenous Spd and Spm reduced the accumulation of Cu and effectively maintained the balance of nutrient elements in plant leaves under Cu stress. These results suggest that exogenous application of Spd or Spm can enhance the tolerance of N. peltatum to Cu by increasing the levels of endogenous Spd and Spm as well as the (Spd+Spm)/Put ratio.     

Evaluation of Polyamine and Proline Levels during Low Temperature Acclimation of Citrus

The polyamines (PA) putrescine (Put), spermidine (Spd), and spermine (Spm) were measured during 3 weeks exposure to cold hardening (15.6°C day and 4.4°C night) and nonhardening (32.2°C day and 21.1°C night) temperature regimes in three citrus cultivars: sour orange (SO) (Citrus aurantium L.), `valencia' (VAL) (Citrus sinensis L. Osbeck), and rough lemon (RL) (Citrus jambhiri Lush). The changes in PA were compared to the amount of free proline, percent wood kill and percent leaf kill. A 2- to 3-fold increase in Spd concentrations were observed in hardened RL, SO, and VAL leaves compared to nonhardened leaves. Spermidine reached its highest level of approximately 200 nanomoles per gram fresh weight after 1 week of acclimation in both SO and VAL leaves, while RL spermidine content continued to increase up to the third week of acclimation. Spm levels in acclimated VAL and RL leaves increased 1- to 4-fold. However, SO leaves Spm content decreased with acclimation. Putrescine levels in SO and VAL increased 20 to 60% during the first 2 weeks of acclimation then declined after 3 weeks. RL putrescine content was not affected by cold acclimation. The data presented here provided direct relationship between increased Spd concentration and citrus cold hardiness. Free proline was 3- to 6-fold higher in acclimated than in nonacclimated trees. Results also demonstrate that in acclimated versus nonacclimated citrus trees the absolute amount rather than the ratio of increase in free proline is more important in predicting their ability to survive freezing stress.     

Polyamines increase carpospore output and growth during in vitro cultivation of Hydropuntia cornea

Carpospore output and development in the marine red alga Hydropuntia cornea J. Agardh. were increased by adding polyamines (PAs) (putrescine, spermidine and spermine) singly or in combinations at 10⁻⁹, 10⁻⁶ and 10⁻³ M. Cell divisions after spore release and development of apical axis between 17 and 21 days characterized carpospore development. PAs increased carpospore development by promoting cell divisions to form cell masses between day 2 and 3. Morphogenesis to develop apical axes occurred at day 7. Spermine at 10⁻⁶ M and a combination of putrescine 10⁻⁹ M + spermidine 10⁻⁹ M + spermine 10⁻⁹ M gave a higher number of carpospores and enhanced their further development to sporelings.     

Leucine and spermidine enhance shoot differentiation in cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis> L.)

Enhanced numbers of multiple shoots were induced from shoot tip explants of cucumber. The effects of amino acids (leucine, isoleucine, methionine, threonine, and tryptophan) and polyamines (spermidine, spermine, and putrescine) along with benzyladenine (BA) on multiple shoot induction were investigated. A Murashige and Skoog (MS) medium containing a combination of BA (4.44 μM), leucine (88 μM), and spermidine (68 μM) induced the maximum number of shoots (36.6 shoots per explant) compared to BA (4.44 μM) alone or BA (4.44 μM) with leucine (88 μM). The regenerated shoots were elongated on the same medium. Elongated shoots were transferred to the MS medium fortified with BA (4.44 μM), leucine (88 μM), and putrescine (62 μM) for root induction. Rooted plants were hardened and successfully established in soil with a 90% survival rate.     

Proline protects <Emphasis Type="Italic">Atropa belladonna</Emphasis> plants against nickel salt toxicity

Atropa belladonna L. plants were grown in water culture for 8 weeks before the nutrient medium was supplemented with NiCl₂ to final concentrations of 0 (control treatment), 50, 100, 150, 200, 250, and 300 μM. After 4 days of plant growing in the presence of nickel chloride, the content of water, proline, Ni, Fe, free polyamines, as well as lipid peroxidation rates were measured. The addition of 100–150 μM Ni to the medium significantly reduced the fresh weight increments and water content in comparison with these parameters for untreated plants; 200 μM Ni caused serious, although nonlethal damage to the plants, whereas 250 and 300 μM Ni proved to be lethal. In the aboveground organs, the major part of Ni was accumulated in the apical leaves. When the plants were treated with 200 μM Ni, the Ni content in apical leaves was 220 μg/g dry wt, while Ni content in roots reached 1500 μg/g dry wt. The treatment of plants with proline in the presence of 200 μM Ni inhibited Ni accumulation in tissues. The proline-treated plants exhibited elevated iron content in leaves and especially in roots and were characterized by comparatively low rates of lipid peroxidation and by sustained leaf water status. When 200 μM Ni was applied, the content of free putrescine decreased, while the contents of spermine and spermidine in leaves increased appreciably with respect to the control values. The toxic effect of nickel was accompanied not only by an enhanced accumulation of high- molecular-weight polyamines but also by their oxidative degradation, which was evident from the 14-fold increase in the content of 1,3-diaminopropane. The protective effect of exogenous proline in the presence of high nickel concentrations was manifested in lowered lipid peroxidation rates, alleviation of iron deficiency, and in retarded oxidative degradation of polyamines.     

Transport and subcellular localization of polyamines in carrot protoplasts and vacuoles

Putrescine and spermidine uptake in carrot (Daucus carota L., cv “Tip top”) protoplasts and isolated vacuoles was studied. Protoplasts and vacuoles accumulated polyamines very quickly, with maximum absorption within 1 to 2 minutes. The insertion of a washing layer containing 100 millimolar unlabeled putrescine or spermidine did not change this pattern, but strongly reduced the uptake of putrescine and spermidine in protoplasts and in vacuoles. The dependence of spermidine uptake on the external concentration was linear up to the highest concentrations tested in protoplasts, while that in vacuoles showed saturation kinetics below 1 millimolar (K_m = 61.8 micromolar) and a linear component from 1 to 50 millimolar. Spermidine uptake in protoplasts increased linearly between pH 5.5 and 7.0, while there was a distinct optimum at pH 7.0 for vacuoles. Preincubation of protoplasts with 1 millimolar Ca²⁺ affected only surface binding but not transport into the cells. Nonpermeant polycations such as La³⁺ and polylysine inhibited spermidine uptake into protoplasts. Compartmentation studies showed that putrescine and spermidine were partly vacuolar in location and that exogenously applied spermidine could be recovered inside the cells. The characteristics of the protoplast and vacuolar uptake system induce us to put forward the hypothesis of a passive influx of polyamines through the plasmalemma and of the presence of a carrier-mediated transport system localized in the tonoplast.     

Response to copper and cadmium stress in wild-type and copper tolerant strains of the lichen alga <Emphasis Type="Italic">Trebouxia erici</Emphasis>: metal accumulation,toxicity and non-protein thiols

Cysteine, glutathione (GSH) and phytochelatins were determined in the cells of both wild and copper tolerant strains of the lichen alga Trebouxia erici following short-term (24 h) exposure to copper and cadmium and long-term (4 weeks) exposure to copper. Both metals caused concentration dependent synthesis of phytochelatins (PC₂–PC₅), but cadmium was a more potent activator of phytochelatin synthesis, even inducing synthesis of PC₅. The copper-tolerant strain did not reveal a higher degree of phytochelatin synthesis than the wild strain, and at 5 μM Cu production of phytochelatins was in fact significantly lower. Lower levels of phytochelatin correlated with significantly decreased intracellular copper content in the copper-tolerant strain. Both strains maintained high GSH levels even at a high copper concentration of 5 μM, and only the highest copper concentration (10 μM) was toxic for both strains, causing a decrease of GSH and PC content in algal cells. Cadmium had less effect on GSH in the cells of both tested strains. In the long term experiments, only relatively small amounts of PC₂ were detected in both strains, but the copper-tolerant strain retained significantly higher levels of reduced glutathione, probably due to the lesser degree of oxidative stress caused by Cu. The significant increase of cysteine synthesis in the copper-tolerant strain found in the present study may be related to copper tolerance in T. erici, while decreased intracellular Cu uptake, detoxification by PCs and increased free proline levels for protection of chloroplast membranes may also be implicated.     

Exogenous Spermidine Modulates Osmoregulatory Substances and Leaf Stomata to Alleviate the Damage to Lettuce Seedlings Caused by High Temperature Stress

Lettuce (Lactuca sativa L.) prefers cool environments, and high temperatures affect its yield and quality. Polyamines (PAs) have a mitigating effect on plant abiotic stresses. The effect of exogenous spermidine (Spd) on the osmoregulatory substances and stomata of seedlings of the non-heat-tolerant lettuce variety ‘Bei San 3’ under high temperature stress was investigated at 35 °C/30 °C (day/night) under spray treatment with Spd. The results showed that exogenous Spd increased the total fresh weight, root-to-shoot ratio, leaf length, leaf width, root volume, and root surface area of lettuce under high temperature stress and reduced levels of malondialdehyde. The endogenous polyamine content was changed, and endogenous spermidine (Spd) and putrescine (Put) were increased. The accumulation of six organic osmoregulatory substances was promoted, resulting in enhanced betaine aldehyde dehydrogenase (BADH), choline monooxygenase (CMO), proline catalase pyrroline-5-carboxylate synthase (P5CS), ornithine aminotransferase (OAT), and pyrroline-5-carboxylate reductase (P5CR) activity. The production and activity of the degrading enzymes proline dehydrogenase (PDH) and proline oxidase (POX) were inhibited, and the activity of glutamic acid decarboxylase (GAD), the key enzyme of γ-aminobutyric (GABA), was suppressed. In addition, exogenous Spd increased the contents of Ca, K, Fe, Mn, Zn, and NO₃^? ions in lettuce leaves under high temperature stress, promoted K⁺ efflux and Ca²⁺ influx, and reduced the relative stomatal aperture. In summary, exogenous Spd mitigates lettuce injury caused by high temperature stress by increasing the content of osmoregulatory substances and altering stomatal morphology.

     

On the mechanism of dormancy release in grapevine buds: a comparative study between hydrogen cyanamide and sodium azide

The effect of low doses (LD)—0.1 kJ m⁻² d⁻¹ and high doses (HD)—0.3 kJ m⁻² d⁻¹ of UV-C irradiation on free, conjugated and bound spermine, spermidine and putrescine in leaves of young pea plants after 7 and 14 days of consecutive treatment was studied. Free polyamine (PA) fractions increased mainly in LD treated plants, while conjugated fractions decreased. Bound fractions accumulated mainly at the end of the experiment (after 14 days of UV-C irradiation). The results are interpreted in relation to the possible role of endogenous bound PAs in the prevention of membrane damage induced by UV-C irradiation. Stress markers (malondialdehyde and electrolyte leakage) increased after 7 days of UV-C treatment, and reached control values by the end of the experiment (mainly after HD treatment). Malondialdehyde concentration correlated negatively with UV-C—induced bound fraction and total PAs. The results support the conclusion that endogenous PAs lessen membrane damage in young pea plants provoked by UV-C irradiation.     

Changes of free, soluble conjugated and bound polyamine titers of jojoba explants under sodium chloride salinity in vitro

Jojoba (Simmondsia chinensis L.) single node explants were cultured in a basal medium supplemented with 17.8 microM 6-benzyladenine and four levels of sodium chloride concentration (0, 56.41, 112.82 and 169.23 mM). The free, the soluble conjugated and the insoluble bound forms of polyamines (PAs) (putrescine (Put), spermidine (Spd) and spermine (Spm)) were determined monthly during a 3-month proliferation stage. Free Put and Spd were found in higher levels in the control treatment, while Spm content was higher in the salt treatments. All soluble conjugated PAs were found to be in lower concentrations in explants growing on medium supplemented with salt, while the opposite was true for the insoluble bound PAs. It appeared that certain PAs and PAs forms could play a significant role in the adaptation mechanism of jojoba under saline conditions.     

Effect of 24-epibrassinolide on biomass, growth and free proline concentration in Spirulina platensis (Cyanophyta) under NaCl stress

In this study, biomass, growth and free proline concentration were investigated in Spirulina platensis treated with different concentrations of NaCl (50, 100, 150, and 200 mM) and 24-epibrassinolide (24-epiBL) hormone (0.5, 1.0, and 3.0 μM) over 5 days. As a result of analysing the cultures under salinity stress, it was determined that biomass and growth rate decreased significantly, while proline concentration increased considerably under salinity stress. The increase in the concentration of proline suggests a role in response to NaCl stress. Among the cultures treated with different concentrations of 24-epiBL, maximum growth was determined at the cultures at 1.0 μM 24-epiBL. Algal growth was also greater at the 0.5 and 3.0 μM concentrations of 24-epiBL with respect to control cultures. With respect to control, 24-epiBL affected growth rate and biomass positively, but proline concentration did not change. Among the cultures supplied with different combinations of NaCl and 24-epiBL, growth rate increased in 150/0.5 and 150/3.0 mM/μM concentrations, but was maximal for the culture containing 150/1.0 mM/μM combination. The increase in algal growth suggests a role for 24-epiBL in partially alleviated to NaCl stress. These results suggest that 24-epiBL may have a protective role for S. platensis reducing the inhibitor effects of salinity stress.     

Relationships between polyamines, ethylene, osmoprotectants and antioxidant enzymes activities in wheat seedlings after short-term PEG- and NaCl-induced stresses

Contents of ethylene, osmoprotectants, levels and forms of polyamines (PAs) and activities of antioxidant enzymes in the leaves and roots were investigated for five wheat cultivar seedlings (differing in drought tolerance) exposed to osmotic stress (?1.5 MPa). Stress was induced by 2-day-long treatment of plants with polyethylene glycol 6000 (PEG) or NaCl added to hydroponic cultures. Nawra, Parabola and Manu cv. (drought tolerant) showed a marked increase in osmoprotectors (proline and soluble carbohydrates, mainly glucose, saccharose and maltose), free PAs (putrescine Put, spermidine Spd and spermine Spm) and Spd-conjugated levels, in both leaves and roots, after PEG-treatments. Radunia and Raweta (drought sensitive) exhibited smaller changes in the content of these substances. The analysis of enzymes involved in proline metabolism revealed the glutamate as a precursor of proline synthesis in PEG-induced stress conditions. The increase in the activity of antioxidative enzymes, especially catalase and peroxidases, was characteristic for tolerant wheat plants, but for sensitive ones, a decrease in superoxide dismutase and an increase in mainly glutathione reductase activities were observed. After NaCl-treatment smaller changes of all biochemical parameters were registered in comparison with PEG-induced stress. Exceptions were the higher values of ethylene content and a significant increase in saccharose, raffinose and maltose levels (only in stress sensitive plants). The proline synthesis pathway was stimulated from both glutamate and ornithine precursors. These results suggest that the accumulation of inorganic ions in NaCl-stressed plants may be involved in protective mechanisms as an additional osmoregultor. Thus, a weaker stressogenic effect as determined as water deficit by leaf relative water content and relative dry weight increase rate and differences in metabolite synthesis in comparison with PEG stress was observed. Proline seems to be the most important osmo-protector in osmotic stress initiated by both PEG and NaCl. The synthesis of sugars and PAs may be stimulated in a stronger stress conditions (PEG).     

Changes in Polyamine Contents Development of the Frog, Microhyla ornata

Putrescine, spermidine and spermine levels were measured during development, metamorphosis and adult life of the frog, Microhyla ornata . Development of Microhyla was accompanied by high fluctuating levels of putrescine and spermidine with low and steady levels of spermine. Putrescine was the major polyamine during development from egg to mature tadpole. During metamorphosis both putrescine and spermidine decreased significantly; but the decrease in putrescine content was more rapid than that of spermidine. Thus, in the freshly metamorphosed frog, the concentration of spermidine exceeded that of putrescine. In most of the adult tissues also spermidine concentration was higher than putrescine and spermine. While the free form of putrescine and spermidine increased during early development of the fertilized egg to tadpole, the levels of protein conjugated polyamines decreased. In the free form, putrescine was the major polyamine while in the protein conjugated form spermidine concentration was higher than putrescine and spermine. Thus polyamine pattern is different in early development, during metamorphosis and in differentiated adult tissues of this frog. ∞-Difluoromethylornithine treatment at early blastula stage did not interfere with the normal development of Microhyla embryos.     

Polyamines are involved in the gynogenesis process in onion

Haploidization in onion ( Allium cepa L.) using immature flower buds simulates zygotic embryogenesis with no fecundation. In order to know the involvement of polyamines (PAs) in this process, we determined the concentration of endogenous PAs in flower buds and experimented the addition of various combinations of PA molecules in the medium. At the inoculation stage, high levels of free and conjugated spermidine and low putrescine + hydroxyputrescine/spermidine + spermine ratio characterized the highest responsive varieties. During in vitro culture, high levels of putrescine and its derivatives characterized the lowest responsive varieties, whereas high levels of spermidine and spermine characterized responsive varieties. The putrescine + hydroxyputrescine + homospermidine/spermidine + spermine ratio remained low in responsive varieties. The addition of spermidine or spermine (2 × 10⁻³  M ) to the culture medium improved significantly the embryo production. Our results suggest that the arginine decarboxylase pathway is involved in PA biosynthesis during the in vitro culture of flower buds. Our study showed that specific ratios of PAs are required for successful gynogenesis in onion.