Stabilization of Oat Leaf Protoplasts through Polyamine-mediated Inhibition of Senescence

Protoplasts isolated from Avena sativa L. leaves undergo progressive senescence when incubated aseptically in 0.6 m mannitol with or without added nutrients. This senescence is manifested by morphological deterioration and ultimate lysis of protoplasts, by a decrease in incorporation of [(3)H]uridine and [(3)H]leucine into macromolecules, and by a sharp increase in ribonuclease activity.The presence in the incubation medium of l-arginine, l-lysine, certain polyamines related to these amino acids (cadaverine, putrescine, spermidine), Ca(2+), or streptomycin stabilizes the protoplasts. Protoplasts incubated with 10 mml-arginine or l-lysine show an initial inhibition of [(3)H]uridine incorporation, but with time, incorporation is restored to levels greater than in control protoplasts. The rise in ribonuclease activity of protoplasts is completely inhibited if the protoplasts are incubated with 10 mml-arginine. Greater incorporation of [(3)H]uridine into RNA of aging protoplasts is also maintained by appropriate concentration of cadaverine, putrescine, spermidine, Ca(2+), or streptomycin in the incubation medium; the same concentrations of these substances stabilize the protoplasts against additional lysis.     

Reversal by aminoguanidine of the inhibition of proliferation of human fibroblasts by spermidine and spermine.

The inhibitory effect of the polyamines, spermidine and spermine, on the proliferation of human fibroblasts in culture was found to be reversed by the addition of aminoguanidine (AM), a specific and highly effective inhibitor of diamine oxidase (DAO) present in fetal calf serum (FCS). Aminoguanidine itself in concentration as high as 10(-3) M exhibited no effect upon cell proliferation nor did putrescine at similar concentrations. However, at higher concentrations of putrescine, cell proliferation was inhibited and this inhibition was unaffected by the addition of mM concentrations of AM. These studies support earlier hypotheses on the mechanisms of the toxic effects of polyamines on cell proliferation and establish further that the diamine oxidase-catalyzed metabolism of spermine and spermidine is necessary for their toxic effects in cell culture.     

Studies on the interaction of homologues of spermine with deoxyribonucleic acid and with bacterial protoplasts

Four homologues of the naturally occurring polyamine spermine, of the type H(2)N.[CH(2)](3).NH.[CH(2)] (n).NH.[CH(2)](3).NH(2) where n=2, 3, 5 and 6, have been synthesized. Their ability to stabilize Escherichia coli protoplasts against osmotic lysis was compared with that of spermine. All homologues were approximately as effective as spermine. The effect of low concentrations of the homologues on the T(m) of calf thymus DNA and of Aerobacter aerogenes DNA in 0.03m-sodium chloride-1mm-potassium dimethylglutarate buffer, pH6.2, was tested. The increase in T(m) for a given concentration of amine was found to be n=5>n=4 and n=6> n=3>n=2. When calf thymus DNA in 0.15m-sodium chloride-15mm-sodium citrate was used spermine gave the highest increase in T(m). It is concluded that the stabilization of E. coli protoplasts by tetra-amines is a non-specific effect independent of chain length, whereas the elevation of T(m) of DNA is a more specific effect which depends on chain length.     

Steroid Lysis of Protoplasts and Effects of Stabilizers and Steroid Antagonists

Six synthetic antimicrobial steroids were examined for indications of their mechanism of action. Dequadin acetate, cetyl pyridinium chloride (CPC), and sodium deoxycholate were studied for comparison. Aerated cells of Sarcina lutea were washed, suspended in 1.06 M sucrose, and converted to protoplasts with 20 mug/ml of lysozyme. Lysis was measured optically at 650 mmu as a decrease in optical density. Screening tests with 50 mug/ml of each compound showed five steroids and CPC to be lytic. Protoplasts were strongly protected from lysis by pretreatment with 0.001 to 0.004 M spermine tetrahydrochloride. Other polyamines, such as spermidine phosphate, were less protective, and putrescine was ineffective. Uranyl nitrate (5 x 10(-4) M) rapidly agglutinated protoplasts and protected them from rupture by the lytic agents. Similar studies with 0.001 to 0.004 M Mg(++) showed varying degrees of protection, which, in most cases, was only temporary. Steroidal lysis did not appear to be related to chelation, since ethylenediaminetetraacetate did not cause lysis alone and antagonized some lytic compounds. Lecithin, Tween 80, Tween 20, and Span 20 at 0.05% exhibited certain effects on protoplast stability. Span 20 strongly prevented lysis by steroids. Tween 20 alone quickly caused protoplast rupture. Lecithin and Tween 80, which also caused lysis alone, interfered with lytic steroids and CPC. The test compounds were both inhibitory and lethal to cells of Sarcina lutea. The results suggest that direct action on cell membranes may be chiefly responsible for the antimicrobial properties of the steroids.     

Differential effects of polyamines on rat thyroid protein kinase activities

Ornithine decarboxylase, the rate-limiting enzyme in polyamine biosynthesis, has been shown to be regulated in thyroid by thyrotropin both in vivo and in vitro. Little, however, is known of the role of polyamines in thyroid cell function. Since studies in other tissues suggest that polyamines may influence protein phosphorylation, we studied the effect of the polyamines on various protein kinase activities in rat thyroid. Putrescine, spermidine, and spermine inhibit cyclic-AMP-dependent histone H1 kinase activity when measured in the cytosol fraction of rat thyroid; this effect is largely reproduced by NaCl concentrations of equivalent ionic strength. Both spermidine and spermine effect a 1.6-2.4-fold increase in cytosolic cyclic-AMP-independent (messenger-independent) casein kinase activity; stimulation by both polyamines is maximal at 5mM. A similar profile of stimulation is observed for messenger-independent casein kinase activity in crude nuclear preparations. Sodium chloride fails to stimulate both cytosolic and nuclear messenger-independent casein kinase activities at ionic strength equivalent to the spermine concentrations used. Spermine, but not putrescine, spermidine, or sodium chloride, inhibits calcium/phospholipid-dependent protein kinase C activity in cytosol extracts partially purified by DEAE chromatography. These findings suggest that regulation of protein kinase(s) by polyamines may represent a proximal locus (i) of action of thyrotropin-regulated ornithine decarboxylase activity in thyroid.     

Polyamines inhibit biosynthesis of ethylene in higher plant tissue and fruit protoplasts

Ethylene production in apple fruit and protoplasts and in leaf tissue was inhibited by spermidine or spermine. These polyamines, as well as putrescine, inhibited auxin-induced ethylene production and the conversion of methionine and 1-aminocyclopropane-1-carboxylic acid to ethylene. Polyamines were more effective as inhibitors of ethylene synthesis at the early, rather than at the late, stages of fruit ripening. Ca²⁺ in the incubation medium reduced the inhibitory effect caused by the amines. A possible mode of action by which polyamines inhibit ethylene production is discussed.     

Effect of polyamines on actomyosine-ATP-ase activity in smooth muscles of the uterus

The ability of the aliphatic polyamines to inhibit [figure: see text] the ATPase activity of smooth muscle actomyosine satisfies the succession: spermine > spermidine > putrescine that is correlated with magnitude of positive charge at physiological value of pH. The most effective inhibitor of the ATP hydrolysis process is the spermine, which highest inhibitory action is manifested at 10(-3) M concentration, in lesser concentration (10(-5) M) activates the actomyosine ATPase. While defining the kinetic parameters of the ATP hydrolysis reaction catalyzed by uterus myometrium the correlation between inhibiting the ATPase activity of myometrium contractile complex under introduction into the incubation medium of 10(-3) M spermine and decreasing the affinity of actomyosine for ATP was made; the activating effect of spermine on ATPase activity of actomyosine complex in the presence of 10(-5) M spermine correlated with the increase of actomyosine affinity for Mg2+.     

Influence of polyamines on the activity of DNA polymerase I from Escherichia coli.

The influence of polyamines on the various activities of DNA polymerase I from Escherichia coli (EC 2.7.7.7) has been investigated. For all high molecular weight DNAs spermine and spermidine caused up to 80% inhibition when present in high concentrations, i.e. above 1 mM for spermine and 2 mM for spermidine. In the presence of low concentrations of polyamines a small activation was seen for some DNAs. The diamines cadaverine and putrescine had little influence on the rate of synthesis with natural occurring DNAs. In the case of d(A--T)n the activation/inhibition was found to be markedly dependent on the molecular weight of the samples used. With a low molecular weight DNA, 5.6 S, addition of spermidine resulted in up to 3-fold stimulation of activity. The activation was dependent on the concentration of MgCl2 and ionic strength; increasing concentration of these gave a decrease in the degree of activation. Polyamines also had a dramatic effect on the rate of synthesis using the homopolymers (dA)n . (dT)10 and (rA)n . (dT)10 . (20:1) as primers. Putrescine, in particular, increased the activity up to 10-fold with (rA)n . (dT)10 and somewhat less for (dA)n . (dT)10. The apparent Km for the primer (rA)n . (dT)10 decreased approx. 35-fold in the presence of 6.6 mM putrescine. There was no influence on the apparent Km for dTTP. The influence of polyamines on both the 5' leads to 3' and 3' leads to 5' nuclease activity was also investigated. Inhibition of nuclease activity was observed in the presence of polyamines, particularly with spermine. Thus with d(A--T)n and T7 DNA as substrates addition of 0.7 mM spermine resulted in almost complete inhibition of the activity. The dramatic inhibition observed with high concentrations of spermine (spermidine) both in the case of polymerizing and nuclease activity is thought to be due to polyamine-induced aggregation of DNA molecules.     

Characterization of antilipolytic action of polyamines in isolated rat adipocytes.

The interactions of polyamines with the lipolytic system were studied in isolated rat adipocytes. Spermine, spermidine and putrescine significantly inhibited adenosine deaminase-stimulated lipolysis. An antilipolytic effect of spermine was detectable at a concentration of 0.25 mM (P less than 0.05). At a concentration of 10 mM all three polyamines inhibited the stimulated lipolysis by 50-60% (P less than 0.001). In addition, spermine enhanced the antilipolytic sensitivity of insulin. Spermine (1 mM) decreased the half-maximal inhibitory concentration of insulin from 320 +/- 70 pM to 56 +/- 20 pM (P less than 0.01). The antilipolytic effects and the cyclic-AMP-lowering effects of the polyamines were almost completely prevented in the presence of different phosphodiesterase (PDE) inhibitors (3-isobutyl-1-methylxanthine and RO 20-1724) and, in addition, polyamines had no effect on lipolysis stimulated by dibutyryl cyclic AMP, indicating that polyamines may inhibit lipolysis by activating the PDE enzyme. This latter suggestion was confirmed by demonstrating that spermine (5 mM) significantly enhanced the low-Km PDE enzyme activity (P less than 0.01). Finally, the amounts of polyamines present in isolated adipocytes were measured, and the estimated cytoplasmic concentrations were 0.02 mM (putrescine), 0.86 mM (spermidine), and 1.0 mM (spermine). It is concluded that polyamines may possibly be involved in the physiological regulation of triacylglycerol mobilization in adipocytes.     

CLEARANCE OF THE POLYAMINES FROM THE PERFUSED CEREBROVENTRICULAR SYSTEM OF THE RABBIT

Abstract— The clearance of the polyamines spermidine and spermine from cerebrospinal fluid was investigated in the rabbit by ventriculocisternal perfusion. Clearance involved both saturable and nonsaturable uptake processes. The saturable component was a high affinity system with an affinity constant of 21 μ m for spermidine and 24 μ m for spermine. The clearance of spermidine was reduced by the presence of spermine and vice-versa. Other polyamine congeners also reduced spermidine and spermine clearance and it is suggested that the two polyamines share the same carrier. Evidence for concentrative uptake of polyamines into choroid plexus is presented and it is suggested that an active system may also transport polyamines into brain tissue. At high perfusion concentrations simple diffusion may also take place.     

Dicyclohexylamine-induced shift of biosynthesis from spermidine to spermine in plant protoplasts

An improved analytical method, based on high pressure liquid chromatography, has been developed for the simultaneous determination of the polyamines and S-adenosyl-containing compounds in extracts of plant protoplasts. The method involves simple procedures for sample preparation and permits quantification of 1 picomole or less for all the compounds. This method has been used to study the effects of dicyclohexylamine, an inhibitor of plant spermidine synthase (Sindhu, R. K., S. S. Cohen 1984 Plant Physiol 74: 645-649), on biosynthesis of polyamines and 1-aminocyclopropane-1-carboxylate in protoplasts derived from Chinese cabbage leaves. Dicyclohexylamine effectively inhibits spermidine synthase in vivo. Inhibition of the synthesis of spermidine by dicyclohexylamine resulted in a stimulation of spermine synthesis, without significant effect on the synthesis of 1-aminocyclopropane-1-carboxylate. Decarboxylated S-adenosylmethionine is present in control Chinese cabbage protoplasts at ~10⁻¹⁸ moles per cell, and dicyclohexylamine caused an increase of this metabolite of up to 10-fold in a 4-hour period. The increase in decarboxylated S-adenosylmethionine permitted an increased synthesis of spermine. These findings suggest that the availability of decarboxylated S-adenosylmethionine may be rate-limiting for the synthesis of spermine in plant protoplasts.     

The biochemistry, genetics, and regulation of polyamine biosynthesis in Saccharomyces cerevisiae

We have studied the enzymes and genes involved in the biosynthesis of putrescine, spermidine, and spermine in Saccharomyces cerevisiae. Mutants have been isolated with defects in the biosynthetic pathway as follows: spe10 mutants, deficient in ornithine decarboxylase, cannot make putrescine, spermidine, or spermine; spe2 mutants, lacking S-adenosylmethionine decarboxylase, cannot make spermidine or spermine; spe3 mutants, lacking putrescine aminopropyltransferase, cannot make spermidine or spermine; and spe4 and spe40 mutants, lacking spermidine aminopropyltransferase, contain no spermine and permit growth of spe10 mutants. Studies with these mutants have shown that in yeast: 1) polyamines are absolutely required for growth; 2) putrescine is formed only by decarboxylation or ornithine; 3) two separate aminopropyltransferases are required for spermidine and spermine synthesis; 4) spermine and spermidine are important in the regulation of ornithine decarboxylase and the amines exert this control by a posttranslational modification of the enzyme; and 5) spermidine or spermine is essential for sporulation of yeast and for the maintenance of the double-stranded RNA killer plasmid. Recent studies in amine-deficient mutants of Escherichia coli have shown an important role of the polyamines in protein synthesis in vivo.     

Polyamines and amino acid incorporation in vitro into microsomes of rat cerebral cortex

1. Polyamines were found to be associated with microsomes of rat cerebral cortex, the amount of spermine being about four times that of spermidine. Cell sap contained more spermidine than spermine. 2. Both polyamines were able to stimulate the incorporation of [(14)C]valine into microsomes in vitro with a maximum rate equal to 250% of the control. Polyamines stimulated at concentrations close to the amount of spermine and spermidine naturally present in the system. 3. Spermine (0.05mm) was used to study the mechanism of action of polyamines. The increasing of microsome and cell-sap concentration facilitated the action of spermine, but the same process was inhibited by increasing pH5-enzyme concentration. 4. Spermine did not affect the association of [(14)C]valine with tRNA in cell sap, but increased the rate of aminoacyl-tRNA formation in pH5 enzyme preparations. However, this process was not affected in any case when incorporating microsomes were present. 5. It is suggested that microsomes are the main site of action of polyamines.     

Cellular systems for the study of the biosynthesis of polyamines and ethylene,as well as of virus multiplication

Leaves of Chinese cabbage from healthy plants or from those infected with turnip yellow mosaic virus yield protoplasts which convert methionine to protein, S-adenosylmethionine, decarboxylated S-adenosylmethionine, spermidine, spermine and 1-aminocyclopropane-1-carboxylate. The enzyme spermidine synthase is entirely cytosolic and has been purified extensively. An inhibitor of this enzyme, dicyclohexylamine, blocks spermidine synthesis in intact protoplasts, and in so doing stimulates spermine synthesis. Aminoethoxyvinylglycine blocks the conversion of S-adenosylmethionine to 1-aminocyclopropane-1-carboxylate, the precursor to ethylene, in protoplasts. This inhibitor markedly stimulates the synthesis of both spermidine and spermine. Essentially all the protoplasts obtained from new leaves of plants infected 7 days earlier are infected. On incubation, such protoplasts convert exogenous methionine to viral protein and viral spermidine whose specific radioactivity is twice that of total cell spermidine. Exogeneous spermidine is also converted to cell putrescine and viral spermidine and spermine. Normal and virus-infected cells are being studied for their content of phenolic acid amides of the polyamines.     

Polyamines are essential for the synthesis of 2-ricinoleoyl phosphatidic acid in developing seeds of castor

The major fatty acid component of castor (Ricinus communis L.) oil is ricinoleic acid (12-hydroxy-cis-9-octadecenoic acid), and unsaturated hydroxy acid accounts for >85% of the total fatty acids in triacylglycerol (TAG). TAG had a higher ricinoleate content at position 2 than at positions 1 and 3. Although lysophosphatidic acid (LPA) acyltransferase (EC 2.3.1.51), which catalyzes acylation of LPA at position 2, was expected to utilize ricinoleoyl-CoA preferentially over other fatty acyl-CoAs, no activity was found for ricinoleoyl-CoA in vitro at concentrations at which other unsaturated acyl-CoAs were incorporated rapidly. However, activity for ricinoleoyl-CoA appeared with addition of polyamines (putrescine, spermidine, and spermine), while polyamines decreased the rates of incorporation of other acyl-CoAs into position 2. The order of effect of polyamines on LPA acyltransferase activity was spermine > spermidine >> putrescine. At concentrations of spermine and spermidine of >0.1 mM, ricinoleoyl-CoA served as an effective substrate for LPA acyltransferase reaction. The concentrations of spermine and spermidine in the developing seeds were estimated at ∼0.09 and ∼0.63 mM, respectively. These stimulatory effects for incorporation of ricinoleate were specific to polyamines, but basic amino acids were ineffective as cations. In contrast, in microsomes from safflower seeds that do not contain ricinoleic acid, spermine and spermidine stimulated the LPA acyltransferase reaction for all acyl-CoAs tested, including ricinoleoyl-CoA. Although the fatty acid composition of TAG depends on both acyl-CoA composition in the cell and substrate specificity of acyltransferases, castor bean polyamines are crucial for incorporation of ricinoleate into position 2 of LPA. Polyamines are essential for synthesis of 2-ricinoleoyl phosphatidic acid in developing castor seeds.     

Polyamines decrease Ca(2+) sensitivity of tension and increase rates of activation in skinned cardiac myocytes

Owing in part to their interactions with membrane proteins, polyamines (e.g., spermine, spermidine, and putrescine) have been identified as potential modulators of membrane excitability and Ca(2+) homeostasis in cardiac myocytes. To investigate whether polyamines also affect cardiac myofilament proteins, we assessed the effects of polyamines on contractility using rat myocytes and trabeculae that had been permeabilized with Triton X-100. Spermine, spermidine, and putrescine reversibly increased the [Ca(2+)] required for half-maximal tension (i.e., right-shifted tension pCa curves), with the following order of efficacy: spermine (+4) > spermidine (+3) > putrescine (+2). However, synthetic analogs that differed from spermine in charge distribution were not as effective as spermine in altering isometric tension. None of the polyamines had a significant effect on maximal tension, except at high concentrations. After flash photolysis of DM-Nitrophen (a caged Ca(2+) chelator), spermine accelerated the rate of tension development at low and intermediate but not high [Ca(2+)]. These results indicate that polyamines, especially spermine, interact with myofilament proteins to reduce apparent Ca(2+) binding affinity and speed cross-bridge cycling kinetics at submaximal [Ca(2+)].     

Effect of spermine on lysis and reproduction by bacteriophages phi-X174, lambda, and f2

Groman, Neal B. (University of Washington, Seattle), and Grace Suzuki. Effect of spermine on lysis and reproduction by bacteriophages phiX174, lambda, and f(2). J. Bacteriol. 92:1735-1740. 1966.-A test was made of the hypothesis that lysis by all bacteriophages shares as a common and critical step an alteration in the osmotic stability of the infected cell. This was done by examining the effect of spermine on lysis. Spermine is one of a number of compounds which can stabilize spheroplasts and protoplasts to lysis in distilled water. Spermine stabilized both phiX174- and f(2)-infected cells at concentrations ranging from 2 x 10(-3) to 4 x 10(-2)m, but failed to stabilize lambda-infected cells at concentrations up to 8 x 10(-2)m. Stabilization was reflected both in optical density measurements and in the retention of mature phage in structures sedimentable at low speeds. At optimal concentration, over 90% of the phage was retained in these structures. These data suggest that the mechanism of lysis by phiX174 and f(2) differs sharply from that caused by lambda, and other observations suggest that there are differences in the lytic process of phiX174 and f(2) as well. Spermine also displayed a differential effect on phage reproduction. The reproduction of lambda and f(2) was inhibited by spermine, though the data do indicate that maturation occurs in its presence. The reproduction of phiX174 was enhanced by spermine.     

Effect of spermine on association of protein kinase C with phospholipid vesicles

The in vitro mechanism by which polyamines affect protein kinase C (PK C) activation process was investigated in a reconstituted system consisting of purified enzyme and phospholipid vesicles of various phosphatidylserine content. It was found that the addition of spermine greatly interferes with the association of PK C to liposomes. This tetramine, at micromolar concentrations, was most potently effective while other polyamines such as spermidine and putrescine were almost ineffective; therefore the modulatory action appeared to be structure specific. The spermine effect is dramatically influenced by the density of the phosphatidylserine present on the liposome, suggesting the complex formation with the acidic component on phospholipid vesicles to be the mechanism by which this polyamine exerts its modulatory action.     

The role of polyamine depletion and accumulation of decarboxylated S-adenosylmethionine in the inhibition of growth of SV-3T3 cells treated with alpha-difluoromethylornithine.

The effects of alpha-difluoromethylornithine, a specific inhibitor of ornithine decarboxylase, on cell growth rate, polyamine content and the content of decarboxylated S-adenosylmethionine in SV-3T3 transformed mouse fibroblasts were studied. DL-alpha-Difluoromethylornithine at 1 mM or higher concentrations decreased the growth rate by over 90% after 2 or more days of exposure, but the cells remained viable, although quiescent for at least 9 days. Addition of 10 microM-spermidine or -spermine or 50 microM-putrescine at any time throughout this period completely reversed the inhibition of growth. Treatment with alpha-difluoromethylornithine decreased putrescine and spermidine contents by more than 98% and that of spermine by 60%, but cells exposed to exogenous polyamines did not require complete replenishment of the polyamine pools to resume growth. In fact, a virtually normal growth rate was obtained in cells lacking putrescine, having 2% of normal spermidine content and 156% of normal spermine. These results suggest that the well-known increase in putrescine and spermidine in cells stimulated for growth is not essential for this to occur and that mammalian cells can utilize spermine as their only polyamine. A substantial reversal of the growth-inhibitory effect of alpha-difluoromethylornithine was produced by a number of polyamines not normally found in mammalian cells, including the spermidine analogues aminopropylcadaverine and sym-homospermidine, which were partially converted into their respective spermine analogues by addition of an aminopropyl group within the cell. The spermine analogue sym-norspermine was also effective, but the maximal growth rate produced by these unphysiological polyamines was only 60-70% of that produced by the normal polyamines. These results indicate that spermidine and spermine have the optimal length for activation of the cellular processes critically dependent on polyamines and should help in identifying these processes. Exposure to alpha-difluoromethylornithine leads to an enormous rise in the concentration of decarboxylated S-adenosylmethionine, which reached a peak at 530-fold after 3 days of exposure and steadily declined to 140-fold after 11 days. This increase was abolished by addition of exogenous polyamines, which rapidly decreased the activity of S-adenosylmethionine decarboxylase. The increase in decarboxylated S-adenosylmethionine is unlikely to be solely responsible for the decrease to the same extent by spermine, sym-norspermidine and sym-homospermidine, which produce 97%, 16% and 60% of the control growth rate, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)     

Stimulating effect of spermine on bulblet formation in bulb-scale segments of Lilium longiflorum

When bulb-scale segments of Lilium longiflorum were cultured on a medium containing auxin and cytokinin, the proportion of the expiants with newly-formed bulblets was significantly increased by the application of different polyamines. The most effective polyamine was spermine, where more than 90% of segments formed an average of 5 bulblets as compared to controls where less than 50% explants formed an average of 1.5 bulblets. Application of arginine one of the precursors putrescine biosynthesis, slightly promoted bulblet formation. The putrescine-stimulated bulblet formation was strongly inhibited by simultaneous addition of an inhibitor of the spermidine synthase, cyclohexylamine. The spermidine-promoted bulblet formation, however, could not be suppressed by this inhibitor. The promotive effect of spermidine on bulblet formation was reversed by an inhibitor of the spermine synthase, N-(3-aminopropyl)cyclohexylamine, but application of this inhibitor with spermine did not show any apparent effect on the bulblet formation. Endogenous level of spermine increased in common during bulblet formation that were stimulated by exogenous polyamines. Thus, spermine seemed to be the main stimulating chemical on bulblet formation in lily bulb-scale segments.Abbreviations APCHA N-(3-aminopropyl)cyclohexylamine - Arg arginine - BA benzyladenine - CHA cyclohexylamine - MS Murashige and Skoog's - NAA naphthaleneacetic acid - Orn ornithine - Put putrescine - Spd spermidine - Spm spermine