Possible Involvement Of Polyamines Research Articles

Changes in primary metabolism and associated gene expression during host-pathogen interaction in clubroot resistance of Brassica napus.

The role of primary metabolism during Brassica napus-Plasmodiophora brassicae interaction leading to clubroot resistance has not yet been investigated thoroughly. In this study, we investigated some of the primary metabolites and their derivatives as well as expression of the genes involved in their biosynthesis to decipher this host-pathogen interaction. For this, two sets (clubroot resistant and susceptible) of canola lines were inoculated with P. brassicae pathotype 3A to investigate the endogenous levels of primary metabolites at 7-, 14-, and 21-days after inoculation (DAI). The associated pathways were curated, and expression of the selected genes was analyzed using qRT-PCR. Our results suggested the possible involvement of polyamines (spermidine and spermine) in clubroot susceptibility. Some of the amino acids were highly abundant at 7- or 14-DAI in both resistant and susceptible lines; however, glutamine and the amino acid derivative phenylethylamine showed higher endogenous levels in the resistant lines at later stages of infection. Organic acids such as malic, fumaric, succinic, lactic and citric acids were abundant in the susceptible lines. Conversely, the abundance of salicylic acid (SA) and the expression of benzoate/salicylate carboxyl methyltransferase (BSMT) were higher in the resistant lines at the secondary stage of infection. A reduced disease severity index and gall size were observed when exogenous SA (1.0 mM) was applied to susceptible B. napus; this further supported the role of SA in clubroot resistance. In addition, a higher accumulation of fatty acids and significant upregulation of the pathway genes, glycerol-3-phosphate dehydrogenase (GPD) and amino alcohol phosphotransferase (AAPT) were observed in the resistant lines at 14- and 21-DAI. In contrast, some of the fatty acid derivatives such as phosphatidylcholines represented a lower level in the resistant lines. In conclusion, our findings provided additional insights into the possible involvement of primary metabolites and their derivatives in clubroot resistance.

Osmotic Stress and ABA Affect Immune Response and Susceptibility of Grapevine Berries to Gray Mold by Priming Polyamine Accumulation.

Abiotic factors inducing osmotic stress can affect plant immunity and resistance against pathogen attack. Although a number of studies have characterized grapevine responses to various forms of biotic and abiotic stresses, the relationships between osmotic stress response and susceptibility of mature berries to Botrytis cinerea still remain unknown. In this study, we investigated the effects of osmotic stress and abscisic acid (ABA) on defense responses of mature grapevine berries before and after B. cinerea infection. We focused on the possible involvement of polyamines in the interaction between osmotic stress response and susceptibility to B. cinerea. We showed that osmotic stress induced by PEG or sucrose, and exogenous ABA induce transient but low defense responses, including weak expression of PR genes and phytoalexin synthesis in mature berries. This was accompanied by an upregulation of NCED2 involved in ABA biosynthesis and a large production of free polyamines. However, osmotic stress followed by B. cinerea infection primed berries for enhanced accumulation of polyamines, but slowed down the defense responses and increased susceptibility to the pathogen. A weak increase of diamine- and polyamine-oxidase activities was also recorded in stressed berries, but declined after pathogen infection. The pretreatment of stressed berries with appropriate inhibitors of diamine- and polyamine-oxidases further increased polyamine level and greatly lowered defense responses, leading to higher susceptibility to B. cinerea. These results suggest that increased polyamine titer through low activation of their oxidative degradation in grape berries may contribute at least in part to the weakening of defense responses and subsequent disease susceptibility.

Polyamine metabolism and biosynthetic genes expression in tomato (Lycopersicon esculentum Mill.) seedlings during cold acclimation

To elucidate the possible involvement of polyamines (PAs) in the chilling tolerance of tomato, we have investigated the metabolism of PAs, physiological features including levels of compatible solutes (soluble sugar, soluble protein, proline) and the malondialdehyde (MDA) content in the leaves of two tomato cultivar seedlings differing in chilling tolerance during cold acclimation. Putrescine (Put) has been shown to accumulate in leaves of both cultivars but to be higher in cv. Mawa (chilling-tolerant) than in cv. Moneymaker (chilling-sensitive) during cold acclimation. Arginine decarboxylase (ADC) activities increased in both cultivars in response to cold acclimation; however, almost no changes of ornithine decarboxylase (ODC) activities were observed in both cultivars. Furthermore, we found LeADC and LeODC expressions enhanced partly, but the LeADC1 expression did not improve in two cultivars under cold acclimation. Activity levels of diamine oxidase (DAO), polyamine oxidase (PAO), soluble sugar and soluble protein contents were higher in cv. Mawa than those in cv. Moneymaker under cold acclimation. PAs catabolism might influence proline accumulation in tomato leaves under cold acclimation. MDA content did not obviously increase in both cultivars except when the Put accumulation was reduced. Furthermore, we found that the chilling tolerances of tomato seedlings were reduced by exogenous d-arginine (D-Arg) application, but by adding back Put, the chilling tolerances were enhanced. Hence, the results suggest that Put plays an important role in tomato chilling tolerance.

Enhanced salt-induced antioxidative responses involve a contribution of polyamine biosynthesis in grapevine plants

The possible involvement of polyamines in the salt stress adaptation was investigated in grapevine (Vitis vinifera L.) plantlets focusing on photosynthesis and oxidative metabolism. Salt stress resulted in the deterioration of plant growth and photosynthesis, and treatment of plantlets with methylglyoxal-bis(guanylhydrazone) (MGBG), a S-adenosylmethionine decarboxylase (SAMDC) inhibitor, enhanced the salt stress effect. A decrease in PSII quantum yield (Fv/Fm), effective PSII quantum yield (Y(II)) and coefficient of photochemical quenching (qP) as well as increases in non-photochemical quenching (NPQ) and its coefficient (qN) was observed by these treatments. Salt and/or MGBG treatments also triggered an increase in lipid peroxidation and reactive oxygen species (ROS) accumulation as well as an increase of superoxide dismutase (SOD) and peroxidase (POX) activities, but not ascorbate peroxidase (APX) activity. Salt stress also resulted in an accumulation of oxidized ascorbate (DHA) and a decrease in reduced glutathione. MGBG alone or in combination with salt stress increased monodehydroascorbate reductase (MDHAR), SOD and POX activities and surprisingly no accumulation of DHA was noticed following treatment with MGBG. These salt-induced responses correlated with the maintaining of high level of free and conjugated spermidine and spermine, whereas a reduction of agmatine and putrescine levels was observed, which seemed to be amplified by the MGBG treatment. These results suggest that maintaining polyamine biosynthesis through the enhanced SAMDC activity in grapevine leaf tissues under salt stress conditions could contribute to the enhanced ROS scavenging activity and a protection of photosynthetic apparatus from oxidative damages.

Study on changes of polyamine levels in mice with the development of U14 cervical cancer

This study was performed to investigate the possible involvement of polyamines in the development of cervical cancer. The objective of the present study was therefore to find the specific polyamine indicators, which could be used as useful markers for the early determination of cervical cancer. A simple method for the simultaneous determination of plasma concentrations of five polyamines in normal and U14 model mice was developed by using HPLC-MS. The samples were derivatized by benzoyl chloride. The derived polyamines were separated on a C18 column by a gradient elution with methanol–water, and then detected with HPLC-MS. The results showed that all polyamine levels in the U14 model mice were higher than those in normal ones. The cadaverine, putrescine and 1, 3-diaminopropane levels were significantly higher in U14 model mice plasma than those in normal mice plasma, especially the putrescine and 1, 3-diaminopropane (P<0.01). The cadaverine, putrescine and 1, 3-diaminopropane levels were significantly higher in U14 mice model urine than those in normal mice urine, especially the cadaverine and 1, 3-diaminopropane (P<0.01). Putrescine, cadaverine and 1, 3-diaminopropane might be the indicators of the cervical cancer.

Possible involvement of polyphenols and polyamines in salt tolerance of almond rootstocks

Leaf physiological and biochemical adaptive strategies and more particularly the possible involvement of polyamines and polyphenols in salt stress tolerance were investigated. Three almond rootstocks (GN15, GF677 and bitter almond) were subjected to 0, 25, 50 and 75mM NaCl for 30 days. The dry mass of leaves, stems and roots decreased with increasing salt concentration in the irrigation solution regardless of genotype. Photosynthetic assimilation rate decreased in the three almond rootstocks, but more so in GF677 and bitter almond. The accumulation of toxic ions was greater in the leaves than in the roots in all genotypes. GN15 accumulated less Na(+) and Cl(-) than GF677 and bitter almond. GF677 accumulated polyphenols, but had less anthocyanin and antioxidant activity in its leaves compared to bitter almond. It seems that GN15 was more able to tolerate the excess of toxic ions using anthocyanins which are abundant in its red leaves and free polyamines for a more efficient response to stress. However, most of the antioxidant activity was found in the leaves and was lower in the roots. Given that the upper part of the tree will be of a different cultivar after grafting, this advantage may not be relevant for the tree's survival. GF677 showed a different antioxidant strategy; it maintained a stable carotenoids content and accumulated polyphenols in its leaves. The three rootstocks used different strategies to deal with the excess of salt in the growth medium.

Cissus quadrangularis L. extract attenuates chronic ulcer by possible involvement of polyamines and proliferating cell nuclear antigen.

The present study was designed to investigate whether Cissus quandrangularis extract (CQE) had healing effects on gastric ulcer, through modulation of polyamines and proliferating cell nuclear antigen (PCNA) in rats. Administration of acetic acid (AA) was accompanied by reduced PCNA which was determined by immunohistochemical staining, 3H-thymidine incorporation using liquid scintillation spectrometry, mitochondrial marker enzymes, polyamine contents and transforming growth factor-alpha (TGF-α) expression in gastric mucosa of rats. Administration of CQE after the application of AA to the stomach enhanced the reduction of ulcer area in a dose-dependent manner which was confirmed by histoarchitecture. Moreover, CQE significantly increased the 3H-thymidine incorporation and the levels of polyamines such as putrescine, spermine and spermidine in ulcerated rats. In addition, the extract offers gastroprotection in the ulcerated area by increased expression of TGF-α and also reversed the changes in the gastric mucosa of ulcerated rats with significant elevation in mitochondrial tricarboxylic acid (TCA) cycle enzymes and PCNA levels. Based on these results, the healing effect of CQE on AA induced gastric mucosal injury in rats may be attributed to its growth promoting and cytoprotective actions, possibly involving an increase in tissue polyamine contents and cell proliferation.

Involvement of polyamines, abscisic acid and anti-oxidative enzymes in adaptation of Blue Panicgrass ( Panicum antidotale Retz.) to saline environments

A hydroponic experiment was conducted to assess the possible involvement of polyamines (PAs), abscisic acid (ABA) and anti-oxidative enzymes such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in adaptation of six populations of Panicum antidotale Retz. to selection pressure (soil salinity) of a wide range of habitats. Plants of six populations were collected from six different habitats with ECe ranging from 3.39 to 19.23 dS m −1 and pH from 7.65 to 5.86. Young tillers from 6-month-old plants were transplanted in plastic containers each containing 10 l of half strength Hoagland's nutrient solution alone or with 150 mol m −3 NaCl. After 42 days growth, contents of polyamines (Put, Spd and Spm) and ABA, and the activities of anti-oxidative enzymes (SOD, POD and CAT) of all populations generally increased under salt stress. The populations collected from highly saline habitats showed a greater accumulation of polyamines and ABA and the activities of anti-oxidative enzymes as compared to those from mild or non-saline habitats. Moreover, Spm/Spd and Put/(Spd + Spm) ratios generally increased under salt stress. However, the populations from highly saline environments had significantly higher Spm/Spd and Put/(Spd + Spm) ratios as compared to those from mild or non-saline environments. Similarly, the populations adapted to high salinity accumulated less Na + and Cl − in culm and leaves, and showed less decrease in leaf K + and Ca 2+ under salinity stress. Higher activities of anti-oxidative enzymes and accumulation of polyamines and ABA, and increased Spm/Spd and Put/(Spm + Spd) ratios were found to be highly correlated with the degree of adaptability of Panicum to saline environment.

Polyamine Production in Lichens Under Metal Pollution Stress

In the present study, thalli of the lichen species Pseudevernia furfuracea Zopf. and Evernia prunastri (L.) Ach. transplanted around an oil-fired power station. Following an exposure of 4 months, trace element concentrations (Al, Cd, Cr, Cu, Fe, Ni, Pb, V and Zn) and polyamine (PA) content [putrescine (Put), spermidine (Spd) and spermine (Spm)] of thalli were measured to study the polyamines production in lichens under metal pollution stress. The polyamine production was not significantly different for the two species but two types of statistically significant relationships were revealed between polyamines production and metals concentration in lichen thalli: a positive linear relationship for the pairs total PAs–Cd (P. furfuracea), total PAs–Cu (E. prunastri), Put–Pb (E. prunastri), Spm–Pb (E. prunastri) and a second-order polynomial relationship for the pairs Put–Cd (P. furfuracea), Spm–Cr (E. prunastri) and total PAs–V (E. prunastri). A possible involvement of polyamines in metal pollution stress response of lichens is discussed.

Attenuation of cold-induced apoptosis by exogenous melatonin in carrot suspension cells: the possible involvement of polyamines.

Pretreatment with 43 nM (10 ng/mL) to 86 nM melatonin for 5 days significantly attenuated cold-induced apoptosis in carrot suspension cells (Daucus carota L.) as evidenced by the TUNEL procedure, DNA fragmentation and the morphological changes revealed by electronic microscopy observations. The antiapoptotic effect of melatonin was initially thought to be a result of its antioxidant actions. In our study, however, reactive oxygen species (ROS) generation remained unaffected by melatonin treatment, suggesting that melatonin plays its protective role not related to its direct ROS scavenger. At the same time, notable increases in putrescine and spermidine levels were observed in melatonin-treated cells, which may be responsible for the alleviation of the cold-induced apoptosis. The possible involvement of polyamines in the antiapoptotic effect of melatonin was further confirmed by the inhibitory effect of exogenous polyamines on apoptosis as displayed by the DNA laddering assay.

Polyamines are not Indispensable for the Cold-acclimatory Increase of Chilling Tolerance in Cucumber during Exposure to Moderately Low Temperature

Possible involvement of polyamines in the cold-acclimatory increase in chilling tolerance in cucumber (Cucumis sativus L.) was investigated. When the first leaf was fully expanded, chill-sensitive cultivar Suyo and chill-tolerant cultivar Jinchun No.3 plants were exposed to 10/8°C (day/night, a 12-hr photoperiod) under moderate light for 2 days to acclimate to cold. These plants together with control plants grown at 28/22°C were chilled at 3°C in darkness for 24 hr and returned to 28/22°C for another 24 hr. Chilling injury symptoms that developed in control leaves during rewarming were more severe in 'Suyo' than in 'Jinchun No.3'. In contrast, acclimation-treated leaves suffered little if any chilling injury in both cultivars. Cold-acclimated leaves of 'Jinchun No.3' showed a transient and marked increase in spermidine content during chilling and rewarming compared to that before chilling. In cold-acclimated leaves of 'Suyo', however, chillmediated changes in polyamine content were much smaller than those of 'Jinchun No.3'. Such absence of enhanced polyamine biosynthesis in cold-acclimated 'Suyo' leaves indicates that polyamines are not indispensable for the cold-acclimatization increase in chilling tolerance in cucumber.

Enhanced susceptibility of photosynthesis to low-temperature photoinhibition due to interruption of chill-induced increase of S-adenosylmethionine decarboxylase activity in leaves of spinach (Spinacia oleracea L.).

The possible involvement of polyamines in the chilling tolerance of spinach (Spinacia oleracea L.) was investigated focusing on photosynthesis. During chilling at 8/5C (day/night) for 6 d, S-adenosylmethionine decarboxylase (SAMDC) activity increased significantly in leaves in parallel with the increase in putrescine and spermidine (Spd) content in leaves and chloroplasts. Treatment of leaves with methylglyoxal-bis(guanylhydrazone) (MGBG), an SAMDC inhibitor, resulted in the deterioration of plant growth and photosynthesis under chilling conditions, which was reversed by the concomitant treatment with Spd through the roots. Plants treated with MGBG showed lower photochemical efficiency of PSII than either the control or plants treated with MGBG plus Spd during chilling and even after transfer to warm conditions, suggesting an increase of photoinhibition due to low Spd in chloroplasts. Indeed, MGBG-treated plants had much lower activities of thylakoid electron transport and enzymes in carbon metabolism as well as higher degrees of lipid peroxidation of thylakoid membranes compared to the control. These results indicate that the enhanced activity of SAMDC with a consequential rise of Spd in chloroplasts is crucial for the cold acclimation of the photosynthetic apparatus in spinach leaves.

Role of polyamines in the cytokinin-dependent physiological processes II. Modulation of polyamine levels during cytokinin-stimulated expansion of cucumber cotyledons

The cucumber cotyledon expansion test was used as a model system to study a possible relationship between cytokinin and polyamines. When kinetin was applied to excised cotyledons incubated in the dark it caused a marked increase in the activity of arginine decarboxylase. As a result of ADC action, putrescine content also rose markedly, whereas the level of spermidine and spermine decreased. However, inhibition of putrescine biosynthesis with D-arginine did not affect cytokinin promotion growth. Applied alone, putrescine had no significant effect on growth. These results indicate that the large increase in putrescine content that derives from cytokinin treatment cotyledons is not essential for cytokinin-induced expansion of cotyledons. Addition of K+ and Ca2+ ions to the cotyledons incubated with cytokinin caused a marked reduction in the putrescine level and ADC activity. The higher level of putrescine (35 %) and spermine (62 %) bound to chromatin and the large increase (174 %) in spermidine content bound to ribosomes which derive from cytokinintreated cotyledons in relation to literature data can indicate that these polyamines may play an important role in gene expression during cytokinin-stimulated expansion of cucumber cotyledons. The inhibition of cytokinin effect, viz. enlargement of the cotyledons by inhibitors of spermidine biosynthesis, additionally suggessted a possible involvement of polyamines in cytokinin action.

Involvement of polyamines in the chilling tolerance of cucumber cultivars.

The possible involvement of polyamines (PAs) in the chilling tolerance of cucumber (Cucumis sativus L. cv Jinchun No. 3 and cv Suyo) was investigated. Plants with the first expanded leaves were exposed to 3 degrees C or 15 degrees C in the dark for 24 h (chilling), and then transferred to 28 degrees C/22 degrees C under a 12-h photoperiod for another 24 h (rewarming). Chilling-tolerant cv Jinchun No. 3 showed a marked increase of free spermidine (Spd) in leaves, once during chilling and again during rewarming. Putrescine increased significantly during rewarming, but the increase of spermine was slight. Any of these PAs did not increase in chilling-sensitive cv Suyo during either period. PA-biosynthetic enzyme activities appear to mediate these differences between cultivars. Pretreatment of Spd to cv Suyo prevented chill-induced increases in the contents of hydrogen peroxide in leaves and activities of NADPH oxidases and NADPH-dependent superoxide generation in microsomes and alleviated chilling injury. Pretreatment of methylglyoxal-bis-(guanylhydrazone), a PA biosynthesis inhibitor, to chilled cv Jinchun No. 3 prevented Spd increase and enhanced microsomal NADPH oxidase activity and chilling injury. The results suggest that Spd plays important roles in chilling tolerance of cucumber, probably through prevention of chill-induced activation of NADPH oxidases in microsomes.

198 Possible Involvement of Polyamines in Floral Stimulus in Springbearing Strawberries

A prevailing hypothesis indicates that a decrease in vegetative growth and cessation in floral initiation in strawberry in response to changes in photoperiod and temperature may correlate with hormonally induced changes. We investigated changes in endogenous free polyamines in crowns, flowers, leaves, and fruit of springbearing strawberries (Fragaria xananassa cvs. Chandler and Earliglow) in response to varying temperatures to induce flowering. Spermidine was the prominent free amine in crowns. No marked changes of putrescine, spermidine, and spermine were observed in crowns during the transition from vegetative to reproductive growth in either cultivar. In contrast, high levels of free polyamines were noted in young developing tissues such as the most recently initiated leaves, flower buds, and green fruit. When the putrescine synthesis inhibitor difluoromethylonithine (DFMO, 1 mm) was exogenously applied, levels of putrescine, spermidine, and spermine were altered in crown tissues in greenhouse experiments. These findings indicate that free polyamines may potentially be associated with the stimulation of new growth in springbearing strawberries under the present experimental conditions evaluated.

Specific requirement of putrescine for the mitogenic action of juvenile hormone on adult insect neuroblasts.

Persistent neurogenesis in an adult insect brain was recently shown to be stimulated by juvenile hormone (JH). This morphogenetic hormone was also shown to act on polyamine biosynthesis. To analyze the possible involvement of polyamines in the neurogenic action of JH, two series of experiments were carried out with adult female crickets, Acheta domesticus: (i) inhibition of the first key enzyme in polyamine biosynthesis, ornithine decarboxylase, with alpha-difluoromethylornithine (alpha-DFMO), and examination of the effects of this treatment on the neuroblast proliferation response to JH; and (ii) examination of the effects of putrescine supplementation on the mitotic index of JH-deprived and alpha-DFMO-treated females. In control females, alpha-DFMO treatment, as well as JH deprivation, greatly reduced neuroblast proliferation. Putrescine supplementation in alpha-DFMO-treated insects overcame the effects of alpha-DFMO, and allowed for detection of putrescine in the neural tissue and stimulation of brain neurogenesis. In JH-deprived females, alpha-DFMO treatment completely prevented the stimulatory action of JH on neuroblast proliferation and on brain putrescine levels. By contrast, putrescine feeding of JH-deprived animals was able to mimic the stimulatory effect of JH: brain putrescine levels increased and neuroblast proliferation was restored. To our knowledge, this report demonstrates for the first time that in vivo administration of putrescine can mimic the effects of a morphogenetic hormone on adult neuroblast proliferation, and shows the importance of polyamines, especially putrescine, in the transduction of JH message in neural tissue.

Polyamine synthesis and accumulation in the hypersensitive response to TMV in Nicotiana tabacum

summaryThe possible involvement of polyamines in the tobacco mosaic virus (TMV)‐induced hypersensitive reaction (HR) in Nicotiana tabacum (L.) cv. Samsun NN, which bears the N resistance gene, was investigated. Concentrations of free and conjugated polyamines, as well as the activities of their biosynthetic enzymes ornithine decarboxylase (ODC) and arginine decarboxylase (ADC), were analysed in the necrotic area (I, internal zone) and in the two concentric zones surrounding it (M, middle zone; E, external zone) during the progression of the HR (1, 3 and 5 d from TMV inoculation). Results were compared with those obtained in control plants (mock‐inoculated) and with the pattern in susceptible TMV‐infected tobacco plants.In the HR, concentration increased towards zone I for free putrescine and spermidine. Highest concentrations in zones M and I occurred on day 3. Conjugated polyamines similarly showed an increasing concentration gradient towards zone I, with maximum accumulation on day 5. ODC and ADC activities also showed an increasing gradient towards zone I that could be related to the increase in free and conjugated polyamines. By contrast, in control plants concentrations of free and conjugated polyamines decreased from day 1 to day 5, ODC activity increased slightly, whereas ADC activity did not show significant changes. In the TMV‐infected susceptible tobacco plants, polyamines tended to remain in the free state instead of being conjugated as infection progressed. These results suggest that polyamines could play a role in mechanisms of resistance to biotic stress.

Inhibitory role of ecdysone on neurogenesis and polyamine metabolism in the adult cricket brain

Persistent neuroblasts that continue to produce interneurons were discovered in the mushroom bodies of the adult house cricket, Acheta domesticus (Cayre et al., 1994). In the present work, we examine the influence of ecdysone on this neurogenesis. In control females, the mitotic index decreased concomitantly to the rise of ecdysteroid titer, which accompanied oocyte maturation, whereas it remained unchanged in ovariectomized females. Furthermore, ecdysone injection into ovariectomized animals had a significant inhibitory action on neuroblast mitotic activity. Since cell proliferation and neuronal diferentiation have been shown to be affected by polyamines, we also studied the action of ecdysone on polyamine metabolism. Ovariectomy induced a decrease in polyamine levels of fat body and markedly increased brain spermidine levels. In neural tissue, ecdysone injection into ovariectomized females reduced spermidine levels to control values. Our results suggest that adult cricket brain is a target for ecdysone action. Moreover, the tight correlation we demonstrated between neurogenesis and polyamine titers underlines the possible involvement of polyamines in neuroblast proliferation. Arch. Insect Biochem. Physiol. 35:85–97, 1997. © 1997 Wiley-Liss, Inc.

Inhibitory role of ecdysone on neurogenesis and polyamine metabolism in the adult cricket brain

Persistent neuroblasts that continue to produce interneurons were discovered in the mushroom bodies of the adult house cricket, Acheta domesticus (Cayre et al., 1994). In the present work, we examine the influence of ecdysone on this neurogenesis. In control females, the mitotic index decreased concomitantly to the rise of ecdysteroid titer, which accompanied oocyte maturation, whereas it remained unchanged in ovariectomized females. Furthermore, ecdysone injection into ovariectomized animals had a significant inhibitory action on neuroblast mitotic activity. Since cell proliferation and neuronal diferentiation have been shown to be affected by polyamines, we also studied the action of ecdysone on polyamine metabolism. Ovariectomy induced a decrease in polyamine levels of fat body and markedly increased brain spermidine levels. In neural tissue, ecdysone injection into ovariectomized females reduced spermidine levels to control values. Our results suggest that adult cricket brain is a target for ecdysone action. Moreover, the tight correlation we demonstrated between neurogenesis and polyamine titers underlines the possible involvement of polyamines in neuroblast proliferation. Arch. Insect Biochem. Physiol. 35:85–97, 1997. © 1997 Wiley-Liss, Inc.

Polyamines in normal and auxin‐induced strawberry fruit development

The possible involvement of polyamines during strawberry (Fragaria×ananassa Duch.) fruit development was investigated. Putrescine, spermidine, and spermine were identified in strawberry receptacles and achenes at all stages of development. Total (free) polyamine levels decreased from a maximum of 485 nmol g−1 fresh weight at pollination to a minimum of 55 nmol g−1 fresh weight in ripe receptacles. Total polyamine concentrations during corresponding stages of development were consistently higher in achenes than in receptacles, and ranged from 891 to 203 nmol g−1 fresh weight. Removal of achenes from the surface of developing receptacles 10 days after pollination reduced receptacle growth, and re‐initiation of growth by application of 1 mMα‐naphtaleneacetic acid (α‐NAA) was accompanied by a rapid increase in polyamine concentrations 24 h after treatment. Polyamine content per receptacle increased &gt;3‐fold in normally developing receptacles and in de‐achened, auxin‐treated receptacles 10 days after removal of achenes, but did not increase during this period in de‐achened receptacles not treated with exogenous auxin. α‐NAA increased growth and polyamine levels to a greater extent than the structurally related, but less effective auxin, β‐NAA. Polyamine concentrations in receptacles with intact achenes remained similar to those of auxin depleted (de‐achened) receptacles, implying that the concentration of these compounds may not be limiting following achene removal.