Free Polyamine Levels Research Articles

PtrABF of Poncirus trifoliata functions in dehydration tolerance by reducing stomatal density and maintaining reactive oxygen species homeostasis.

Abscisic acid-responsive element (ABRE)-binding factors (ABFs) play important roles in abiotic stress responses; however, the underlying mechanisms are poorly understood. In this study, it is reported that overexpression of Poncirus trifoliata PtrABF significantly enhanced dehydration tolerance. The transgenic lines displayed smaller stomatal apertures, reduced stomatal density/index, and lower expression levels of genes associated with stomatal development. PtrABF was found to interact with PtrICE1, a homologue of ICE1 (Inducer of CBF Expression 1) that has been shown to be critical for stomatal development. Microarray analysis revealed that a total of 70 genes were differentially expressed in the transgenic line, 42 induced and 28 repressed. At least two units of ABREs and coupling elements were present in the promoters of most of the induced genes, among which peroxidase and arginine decarboxylase were verified as bona fide targets of PtrABF. Transgenic plants exhibited higher antioxidant enzyme activities and free polyamine levels, but lower levels of reactive oxygen species (ROS) and malondialdehyde. Polyamines were revealed to be associated with ROS scavenging in the transgenic plants due to a modulation of antioxidant enzymes triggered by signalling mediated by H2O2 derived from polyamine oxidase (PAO)-mediated catabolism. Taken together, the results indicate that PtrABF functions positively in dehydration tolerance by limiting water loss through its influence on stomatal movement or formation and maintaining ROS homeostasis via modulation of antioxidant enzymes and polyamines through transcriptional regulation of relevant target genes.

Involvement of polyamines in creasing of sweet orange [Citrus sinensis (L.) Osbeck] fruit

Creasing is a physiological disorder in the rind of sweet orange [Citrus sinensis (L.) Osbeck] fruit and causes serious economic losses in the world. The involvement of polyamines in creasing and rind thickness of sweet orange fruit was investigated employing exogenous applications of putrescine (PUT) and a reversible inhibitor of polyamine biosynthesis (guanylhydrazone; MGBG) at different fruit developmental stages through regulating endogenous levels of free PUT, spermidine (SPD), spermine (SPM) and total polyamines in albedo and flavedo tissues of the fruit. A spray application of PUT depending upon its concentration and time of application reduced creasing index percent (CI) and increased rind thickness in Washington Navel and Lane Late fruit during 2011 and 2012. Single spray of PUT (500–1000μM) applied at fruit set or golf ball stage was more effective in reducing CI as compared to all other treatments, in both the cultivars. PUT applied at fruit set, golf ball or mature fruit stage resulted in increased levels of endogenous free polyamines (PUT, SPD, SPM and total free polyamines) in the flavedo and albedo tissues of fruit in both cultivars. Single spray application of MGBG (1000μM) at the golf ball stage significantly increased CI in Washington Navel and Lane Late orange fruit. In conclusion, these results suggest the involvement of polyamines in creasing of sweet orange fruit.

Polyamines in conventional and organic vegetables exposed to exogenous ethylene

Relationships between endogenous levels of polyamines by thin layer chromatography (TLC) and gas chromatography (GC), nitrate and response to the application of ethylene were established between organic and conventional vegetables (broccoli, collard greens, carrots and beets), both raw and cooked. Responses to ethylene showed that organic plants were less responsive to the growth regulator. The levels of free polyamines obtained by TLC were higher in organic vegetables. Organic broccoli showed higher levels of putrescine (Put), and cooking resulted in lowering the overall content of these amines. Conventional collard green showed the highest level of putrescine in the leaves compared with organic. Tubers of carrots and beets contain the highest levels of Put. These plants also contain high levels of spermine. GC analysis showed the highest polyamines contents compared with those obtained by TLC. Cooking process decreased putrescine and cadaverine content, both in conventionally and organically grown vegetables. Organic beets contain lower NO3− compared with its conventional counterpart.

ICE1 of Poncirus trifoliata functions in cold tolerance by modulating polyamine levels through interacting with arginine decarboxylase.

ICE1 (Inducer of CBF Expression 1) encodes a MYC-like basic helix-loop-helix transcription factor that acts as a central regulator of cold response. In this study, we elucidated the function and underlying mechanisms of PtrICE1 from trifoliate orange [Poncirus trifoliata (L.) Raf.]. PtrICE1 was upregulated by cold, dehydration, and salt, with the greatest induction under cold conditions. PtrICE1 was localized in the nucleus and could bind to a MYC-recognizing sequence. Ectopic expression of PtrICE1 in tobacco and lemon conferred enhanced tolerance to cold stresses at either chilling or freezing temperatures. Yeast two-hybrid screening revealed that 21 proteins belonged to the PtrICE1 interactome, in which PtADC (arginine decarboxylase) was confirmed as a bona fide protein interacting with PtrICE1. Transcript levels of ADC genes in the transgenic lines were slightly elevated under normal growth condition but substantially increased under cold conditions, consistent with changes in free polyamine levels. By contrast, accumulation of the reactive oxygen species, H2O2 and O2 (-), was appreciably alleviated in the transgenic lines under cold stress. Higher activities of antioxidant enzymes, such as superoxide dismutase and catalase, were detected in the transgenic lines under cold conditions. Taken together, these results demonstrated that PtrICE1 plays a positive role in cold tolerance, which may be due to modulation of polyamine levels through interacting with the ADC gene.

Relationship between Endogenous Polyamines and Floral Bud Differentiation in Chrysanthemum morifolium under Short-day Conditions

This study was carried out to investigate the relationship between endogenous polyamines (PAs) and floral bud differentiation in chrysanthemum (Chrysanthemum morifolium). In this study, PA content (free, bound, and conjugated) in apical buds, leaves, and roots changed appreciably during floral bud differentiation. PAs accumulated during series of processes such as floral induction, differentiation of floret primordia, and crown formation in apical buds; changes in PAs in apical buds may have a relationship with those in leaves and roots. The levels of free PAs and conjugated PAs [putrescine (Put) and spermine (Spm)] in apical buds rapidly increased during the initiation stage of floral bud differentiation, while free and conjugated spermidine (Spd) reached their highest levels at the stage of floret primordium differentiation. In the free, conjugated, and bound PA fractions, the changes in Spm content were negligible compared to those of Put and Spd throughout the experiment. These findings indicate that PAs participate in regulating the process of flower bud differentiation in chrysanthemum.

Endogenous Levels of Polyamines under Water-Deficit Stress during Cotton’s Reproductive Development

Polyamines, putrescine (PUT), spermidine (SPD) and spermine (SPM) are implicated in plants’ responses under conditions of abiotic stress. Previous research in other crops has indicated that polyamines and changes in their concentrations are associated with drought tolerance under conditions of water-deficit stress; however, no information exists on cotton (Gossypium hirsutum L.). Growth chamber experiments were conducted with two cotton cultivars differing in drought tolerance, ST5288B2F (drought-sensitive) and Siokra L23 (drought-tolerant) in order to investigate the distribution of free polyamines, the effect of water-deficit stress on the polyamine metabolism of cotton reproductive units and their subtending leaves as well as the possible relationship between polyamines and drought tolerance in cotton. Our results showed that cotton ovaries contained significantly higher levels of total free polyamines compared to their subtending leaves under both control and water stress conditions. Water-deficit stress significantly increased PUT concentrations in ST5288B2F, while SPM levels significantly decreased in Siokra L23. The results indicated that water-deficit stress significantly affected cotton polyamine metabolism in reproductive structures and their subtending leaves; however, no clear relationship between drought-tolerance and changes in polyamine accumulation was established. Further research is needed to elucidate the mechanism according to which water-deficit stress affects polyamine metabolism.

Occurrence of polyamines in root nodules of Phaseolus vulgaris in symbiosis with Rhizobium tropici in response to salt stress

Polyamines (PAs) are low molecular weight aliphatic compounds that have been shown to be an important part of plant responses to salt stress. For that reason in this work we have investigated the involvement of PAs in the response to salt stress in root nodules of Phaseolus vulgaris in symbiosis with Rhizobium tropici. The level and variety of PAs was higher in nodules, compared to leaves and roots, and in addition to the common PAs (putrescine, spermidine and spermine) we found homospermidine (Homspd) as the most abundant polyamine in nodules. UPLC-mass spectrometry analysis revealed the presence of 4-aminobutylcadaverine (4-ABcad), only described in nodules of Vigna angularis before. Indeed, the analysis of different nodular fractions revealed higher level of 4-ABcad, as well as Homspd, in bacteroids which indicate the production of these PAs by the bacteria in symbiosis. The genes involved in PAs biosynthesis in nodules displayed an induction under salt stress conditions which was not consistent with the decline of free PAs levels, probably due to the nitrogen limitations provoked by the nitrogenase activity depletion and/or the conversion of free PAs to theirs soluble conjugated forms, that seems to be one of the mechanisms involved in the regulation of PAs levels. On the contrary, cadaverine (Cad) and 4-ABcad concentrations augmented by the salinity, which might be due to their involvement in the response of bacteroids to hyper-osmotic conditions. In conclusion, the results shown in this work suggest the alteration of the bacteroidal metabolism towards the production of uncommon PAs such as 4-ABcad in the response to salt stress in legume root nodules.

The transition of proembryogenic masses to somatic embryos in Araucaria angustifolia (Bertol.) Kuntze is related to the endogenous contents of IAA, ABA and polyamines

In somatic embryogenesis (SE) of conifers, the inability of many embryogenic cell lines to form well-developed somatic embryos may results from failure and constraints during the transition of proembryogenic masses (PEMs) to early somatic embryos. In the present work, we propose the inclusion of a preculture and prematuration steps looking at enhancing PEM III-to-early somatic embryos transition. It was further hypothesized that these results would correlate with the contents of endogenous indole-3-acetic acid (IAA), abscisic acid (ABA) and polyamines (PA). To test these hypotheses, the embryogenic culture was subjected to preculture with fluridone (FLD) and prematuration treatments with different combinations of carbon source and polyethylene glycol (PEG). The frequency of PEM III was increased after FLD preculture and the contents of IAA and ABA decreased, while the contents of PA increased. Putrescine (Put) was the most abundant PA present at this stage, followed by spermidine (Spd) and spermine (Spm). In early embryogenesis, prematuration treatments supplemented with maltose or lactose plus PEG enhanced the PEM III-to-early somatic embryos transition. IAA and ABA contents increased at this stage, while a decrease of the total free PA levels was observed. Put was the most abundant PA, followed by Spd and Spm, mainly in the treatment supplemented with PEG. This resulted in a decrease of PA ratio (Put/Spd + Spm) and, hence, PEM III-to-early somatic embryos transition. It was concluded that the preculture with FLD and prematuration treatments promote the PEM III-to-early somatic embryos transition throughout the whole early developmental process in Araucaria angustifolia.

Changes in free polyamine levels, expression of polyamine biosynthesis genes, and performance of rice cultivars under salt stress: a comparison with responses to drought.

Soil salinity affects a large proportion of rural area and limits agricultural productivity. To investigate differential adaptation to soil salinity, we studied salt tolerance of 18 varieties of Oryza sativa using a hydroponic culture system. Based on visual inspection and photosynthetic parameters, cultivars were classified according to their tolerance level. Additionally, biomass parameters were correlated with salt tolerance. Polyamines have frequently been demonstrated to be involved in plant stress responses and therefore soluble leaf polyamines were measured. Under salinity, putrescine (Put) content was unchanged or increased in tolerant, while dropped in sensitive cultivars. Spermidine (Spd) content was unchanged at lower NaCl concentrations in all, while reduced at 100 mM NaCl in sensitive cultivars. Spermine (Spm) content was increased in all cultivars. A comparison with data from 21 cultivars under long-term, moderate drought stress revealed an increase of Spm under both stress conditions. While Spm became the most prominent polyamine under drought, levels of all three polyamines were relatively similar under salt stress. Put levels were reduced under both, drought and salt stress, while changes in Spd were different under drought (decrease) or salt (unchanged) conditions. Regulation of polyamine metabolism at the transcript level during exposure to salinity was studied for genes encoding enzymes involved in the biosynthesis of polyamines and compared to expression under drought stress. Based on expression profiles, investigated genes were divided into generally stress-induced genes (ADC2, SPD/SPM2, SPD/SPM3), one generally stress-repressed gene (ADC1), constitutively expressed genes (CPA1, CPA2, CPA4, SAMDC1, SPD/SPM1), specifically drought-induced genes (SAMDC2, AIH), one specifically drought-repressed gene (CPA3) and one specifically salt-stress repressed gene (SAMDC4), revealing both overlapping and specific stress responses under these conditions.

Changes in polyamine profile in host and non-host oat–powdery mildew interactions

Oat (Avena sativa L.) crop constitutes a rich source of biologically active secondary metabolites. Most of these compounds act as chemical signals and defense metabolites and constitute a potential source for the development of control methods for specific diseases. Polyamines are low molecular organic cations involved in various physiological events, particularly those related to abiotic stress responses, albeit recently their potential in disease resistance has been investigated. In this work we monitored the polyamine content in leaves of both resistant and susceptible oat cultivars in response to Blumeria graminis f.sp. avenae (Bga, host interaction) and with Blumeria graminis f.sp. hordei (non-host interaction). Our results show significant differences between the resistant and susceptible cultivars for specific free polyamine levels, and also with respect to the non-host interaction at crucial stages of the infection process. In addition, polyamine degradation products, such as 1.3-diamino propane increased following pathogen challenge, suggesting a role for reactive oxygen species derived from this pathway in resistance. Exogenous application of polyamines to leaf surface increased penetration resistance of oat against Bga. Overall, data support both, a direct and indirect role for polyamines in resistance in host and non-host interactions, in responses of oat against appropriate and inappropriate powdery mildew formae speciales.

Ionizing radiation induced changes in phenotype, photosynthetic pigments and free polyamine levels in Vigna radiata (L.) Wilczek

Effects of gamma rays on the free polyamine (PA) levels were studied in Vigna radiata (L.) Wilczek. Seeds exposed to different doses of gamma rays were checked for damage on phenotype, germination frequency and alteration in photosynthetic pigments. Free polyamine levels were estimated from seeds irradiated in dry and water imbibed conditions. Polyamine levels of seedlings grown from irradiated seeds, and irradiated seedlings from unexposed seeds were also measured. Damage caused by gamma irradiation resulted in decrease in final germination percentage and seedling height. Photosynthetic pigments decreased in a dose dependent manner as marker of stress. Polyamines decreased in irradiated dry seeds and in seedlings grown from irradiated seeds. Radiation stress induced increase in free polyamines was seen in irradiated imbibed seeds and irradiated seedlings. Response of polyamines towards gamma rays is dependent on the stage of the life cycle of the plant.

Influence of differing nitrogen nutrition on polyamines and non-structural carbohydrates during different developmental stages of grapevines (c.v. White Riesling).

Polyamines (PA) are triggered by external inducers (hormones, fertilization, nutrients etc.). In triggered systems, the level of free PAs increase before the onset of cell division. PAs are high dur- onset of development as compared with other stages of development. During a fertilisa- tion experiment with amounts of N and timing, non-structural carbohydrates and PAs were determined in leaves, and developing Leaves: PAs were lowest in the unfertilized plots; fertilization showed no differentiated effects. PA-concentrations peaked after full bloom and fell to 50% of the starting value at the stage pea-sized berries. Shoots: belonging to the leaves with the same plastochron-index showed a similar behaviour like PA in leaves. Stems: Putrescine (Put) and Spermidine (Spd) show a clear time course. Put decreases until fully developed and after- wards a slight increase until pea sized berries. Spd behaves nearly inverse: peak at increasing of the flowers and a minimum at fruit set. Berries: all four tested PAs show a clear pattern of their time course. Agmatine (Agm) is highest at 27 May (five to six leaves unfolded), lowest at 5 June and peaking again at fully developed (24 June). At fruit set concentrations are as low as at 5 June (flowers are growing). Put is high at five to six leaves unfolded, decreases continuously until fully developed and a maximum at fruit set. Spd shows a maximum at are grow- ing and reaches a minimum at fruit set. Spd has nearly constant concentrations through five to six leaves unfolded until are fully developed in all fertilizer variants. At fruit set is a maxi- mum. peaks at fully developed, decreases to fruit set and increases again at pea sized berries. Treatments show a differentiation; highest values are found with the plot 90/60. A direct connection to the carbohydrate metabolism could not detected during this experiment.

Changes in the levels of jasmonates and free polyamines induced by Na2SO4 and NaCl in roots and leaves of the halophyte Prosopis strombulifera

Prosopis strombulifera, a common legume in high-salinity soils of Argentina, is a useful model for elucidation of salt tolerance mechanisms and specific biochemical pathways in halophytes, since its NaCl tolerance exceeds the limit described for most halophytic plants. We analyzed the effects of the increasing concentration of two main soil salts, Na2SO4 and NaCl, on growth parameters of P. strombulifera, chlorophyll levels, and content of jasmonates (JAs) and polyamines (PAs), which are key molecules involved in stress responses. P. strombulifera showed a halophytic response (growth promo- tion) to NaCl, but strong growth inhibition by iso-osmotic solutions of Na2SO4. Chlorophyll levels, number of leaves and leaf area were also differentially affected. An important finding was the partial alleviation of SO 2− 4 toxicity by treatment with two-salt mixture. JAs are not directly involved in salt tolerance in this species since its levels decrease under all salt treatments. Beneficial effects of Putrescine (Put) accumulation in NaCl treated plants maybe inferred probably associated with the antioxidative defense system. Another novel finding is the accumulation of the uncommon PA cadaverine in roots under high Na2SO4, which may be related to SO 2− 4 toxicity.

Protective effect of ascorbic acid after single and repetitive administration of cadmium in Swiss mice

The aim of the study was to delineate the protective effect of ascorbic acid with plausible mechanism after single and repetitive cadmium administration to Swiss mice. The effects of single high dose administration of CdCl2 (6 mg/kg) or ascorbic acid (AsA) (50 mg/kg) and chronic (three times) administration of Cd at low dose (2 mg/kg) or AsA at same dose (50 mg/kg) were compared in Swiss albino mice. Changes of lipid peroxidation [determined by the malonyldialdehyde (MDA) concentration] were taken as a measure of the oxidative stress intensity. Lipid fatty acid’s unsaturation related to the permeability of cell membranes was also examined. Mobilization of the immune system was determined by analyzing changes in antioxidant concentrations of AsA and glutathione (GSH), and by measuring the activation of antioxidant enzymes SOD, GPx and CAT. In addition, the level of free polyamines and variation in their proportions were examined. In conclusion, exposure to higher levels of cadmium will have more deleterious effects on the body rather than chronic exposure at lower levels with this toxic metal, while this study clearly demonstrated the protective effects of AsA in a mouse model.

Bound Putrescine, a Distinctive Player under Salt Stress in the Natrophilic Sugar Beet in Contrast to Glycophyte Tobacco

The influence of salinity on the different polyamine fractions (free, conjugated, and bound) was compared in a natrophilic halophyte (Beta vulgaris L. cv. IC) and a salt sensitive glycophyte (Nicotiana rustica L. cv. Basmas). Low-level salinity (25 mM NaCl) and high salinity (150 and 50 mM NaCl for sugar beet and tobacco, respectively) were supplied in hydroponics. Under low salinity shoot dry weight increased in sugar beet, but decreased in tobacco. Under high salinity growth reduction in sugar beet and tobacco were similar. However, sugar beet accumulated higher Na and Cl in roots and shoots than tobacco. Low salinity caused an increase (22%) in the rate of net CO2 assimilation in sugar beet. This parameter was depressed in both species under high salinity. Sugar beet had constitutively higher free spermine levels in roots and shoots than tobacco. Spermidine levels were constitutively higher in shoots of sugar beet and in roots of tobacco. Under salt stress tobacco plants tended to increase free polyamine levels. The most important salt–induced rise in polyamine titer, however, was found in roots and shoots of sugar beet. In sugar beet roots the bound putrescine fraction increased 9.3-fold under growth- stimulating salt supply (25mM) and 20fold under salt stress (150 mM). In tobacco roots this fraction only increased 2.3 and 3.8-fold under mild (25 mM) and high salt stress (50 mM), respectively. Our results provide support to the view that bound putrescine contributes to the protection against salt stress in the natrophilic sugar beet.

THE INTERACTION BETWEEN ETHYLENE AND POLYAMINES DURING RIPENING OF OLIVE FRUIT

Ripening is a complex and highly regulated phenomenon involving many endogenous and environmental factors, all of which must be correctly balanced in order to achieve the best fruit quality. Ripening control in olive is an important issue because, owing to early harvest and long storage times, fruit quality (oil/canning) can deteriorate before reaching the consumer. Ethylene and polyamines are known to have opposite effects in relation to fruit ripening and senescence. In fact, polyamine and ethylene physiologies may be linked during fruit development. This work describes the changes in endogenous free polyamines levels and ethylene production during fruit development from two cultivars of Olea europaea L. (‘Arbequina’ and ‘Picual’). Ethylene production (the 1-aminocyclopropane-1-carboxylic acid (ACC) level) has been determined by gas chromatography and polyamine content (putrescine, spermidine and spermine) by dansylation and separation of dansyl derivatives by HPLC. To investigate the relationships between ethylene and free polyamines in olive fruit, the effect of exogenous polyamines (putrescine and spermidine) and aminooxy-acetic acid (AOA, inhibitor of ethylene biosynthesis) on polyamines and ACC levels was also examined in ripening olive fruit. Fruit treatments were performed in planta.

Polyamine Homeostasis in Wild Type and Phenolamide Deficient Arabidopsis thaliana Stamens

Polyamines (PAs) like putrescine, spermidine, and spermine are ubiquitous polycationic molecules that occur in all living cells and have a role in a wide variety of biological processes. High amounts of spermidine conjugated to hydroxycinnamic acids are detected in the tryphine of Arabidopsis thaliana pollen grains. Tapetum localized spermidine hydroxycinnamic acid transferase (SHT) is essential for the biosynthesis of these anther specific tris-conjugated spermidine derivatives. Sht knockout lines show a strong reduction of hydroxycinnamic acid amides (HCAAs). The effect of HCAA-deficient anthers on the level of free PAs was measured by a new sensitive and reproducible method using 9-fluorenylmethyl chloroformate (FMOC) and fluorescence detection by HPLC. PA concentrations can be accurately determined even when very limited amounts of plant material, as in the case of A. thaliana stamens, are available. Analysis of free PAs in wild type stamens compared to sht deficient mutants and transcript levels of key PA biosynthetic genes revealed a highly controlled regulation of PA homeostasis in A. thaliana anthers.

Effect of ozone exposure on polyamines in Scots pine trees

Effects of ozone exposure on polyamines in Pinus sylvestris L. were studied in a long-term experiment. Ten- to 15-year-old Scots pines were exposed to target ozone levels which began at ambient + 40 ppb in May, decreasing to ambient air only by September for 3 growing seasons. The amount of ozone applied followed the natural pattern of variation in ozone concentrations in Northern Finland. The free, soluble conjugated and insoluble conjugated polyamines were analyzed during the experiment and shortly after termination of exposure as well as at the beginning of the following growing season. A carry-over effect was observed as ozone-induced reduction of free spermidine in the oldest needle year class, which developed during the first exposure season of the experiment. This reduction was observed both after the second and the third ozone exposure season. Conversely, after termination of the experiment, levels of free polyamines increased in the following growing season, and soluble conjugated polyamines decreased in the developing needles. The post-treatment changes in polyamine concentrations are hypothesized to be caused by stress-induced injuries or delayed recovery of metabolic processes rather than protective responses. It is noteworthy that some responses in polyamines were found in the developing needles nine months after terminating the ozone exposure. This suggests that stress-induced injuries to older needles affected metabolism of new developing needles.

Effect of putrescine on the conversion of protocorm-like bodies of Dendrobium officinale to shoots

The addition of 1.5 mM putrescine to the culture medium facilitated the conversion of protocorm-like bodies (PLBs) of Dendrobium officinale to shoots. The administration of 1.0 mM of the polyamine inhibitor, α-DL-difluoromethylarginine, decreased the conversion of PLBs to shoots. Compared to the control, the PLBs treated with 1.5 mM putrescine had higher levels of total intracellular free polyamines. The enhanced conversion of PLBs to shoots following the addition of putrescine was accompanied by an increase in the ratio of total cytokinins (CTKs) to indole-3-acetic acid (IAA). Analysis of enzyme activities indicated that the increased endogenous level of total CTKs driven by putrescine was associated with the inhibition of CTK decomposition by CTK oxidase, while the decreased endogenous level of IAA was associated with the promotion of IAA decomposition by IAA oxidase. In addition, putrescine increased the ratio of reduced glutathione to oxidized glutathione in the conversion process of PLBs to shoots.

Helianthus tuberosus and polyamine research: Past and recent applications of a classical growth model

The earliest studies concerning polyamines (PAs) in plants were performed by using in vitro cultured explants of Helianthus tuberosus dormant tuber. This parenchyma tissue was particularly useful due to its susceptibility to several growth substances, including PAs. During tuber dormancy, PA levels are too low to sustain cell division; thus Helianthus represents a natural PA-deficient model. When cultivated in vitro in the presence of auxins, Helianthus tuber dormant parenchyma cells at the G(0) stage start to divide synchronously acquiring meristematic characteristics. The requirement for auxins to induce cell division can be substituted by aliphatic PAs such as putrescine, spermidine or spermine. Cylinders or slices of explanted homogeneous tuber parenchyma were cultured in liquid medium for short-term studies on the cell cycle, or on solid agar medium for long-term experiments. Morphological and physiological modifications of synchronously dividing cells were studied during the different phases of the cell cycle in relation to PAs biosynthesis and oxidation. Long-term experiments led to the identification of the PAs as plant growth regulators, as the sole nitrogen source, as tuber storage substances and as essential factors for morphogenetic processes and cell homeostasis. More recently this system was used to study the effects on plant cell proliferation of platinum- or palladium-derived drugs (cisplatin and platinum or palladium bi-substituted spermine) that are used in human cancer cell lines as antiproliferative and cytotoxic agents. Cisplatin was the most active both in cell proliferation inhibition and on PA metabolism. Similar experiments were performed using three agmatine analogous. Different effects of these compounds were observed on cell proliferation, free PA levels and enzyme activities, leading to a hypothesis of a correlation between their chemical structure and the agmatine metabolism in plants.