Involvement of polyamines in the drought resistance of rice

This study investigated whether and how polyamines (PAs) in rice (Oryza sativa L.) plants are involved in drought resistance. Six rice cultivars differing in drought resistance were used and subjected to well-watered and water-stressed treatments during their reproductive period. The activities of arginine decarboxylase, S-adenosyl-L-methionine decarboxylase, and spermidine (Spd) synthase in the leaves were significantly enhanced by water stress, in good agreement with the increase in putrescine (Put), Spd, and spermine (Spm) contents there. The increased contents of free Spd, free Spm, and insoluble-conjugated Put under water stress were significantly correlated with the yield maintenance ratio (the ratio of grain yield under water-stressed conditions to grain yield under well-watered conditions) of the cultivars. Free Put at an early stage of water stress positively, whereas at a later stage negatively, correlated with the yield maintenance ratio. No significant differences were observed in soluble-conjugated PAs and insoluble-conjugated Spd and Spm among the cultivars. Free PAs showed significant accumulation when leaf water potentials reached -0.51 MPa to -0.62 MPa for the drought-resistant cultivars and -0.70 MPa to -0.84 MPa for the drought-susceptible ones. The results suggest that rice has a large capacity to enhance PA biosynthesis in leaves in response to water stress. The role of PAs in plant defence to water stress varies with PA forms and stress stages. In adapting to drought it would be good for rice to have the physiological traits of higher levels of free Spd/free Spm and insoluble-conjugated Put, as well as early accumulation of free PAs, under water stress.     

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.     

Stress-dependent accumulation of spermidine and spermine in the halophyte Mesembryanthemum crystallinum under salinity conditions

We studied the effects of chloride salinity (300 and 500 mM NaCl) on the content of free polyamines (PAs) from putrescine (Put) family in Mesembryanthemum crystallinum L. leaves and roots. The contents of Put and spermidine (Spd) in leaves increased temporarily, achieving the highest values on the third day of salinity treatment; thereafter (by days 7–14), they dropped sharply. The content of spermine (Spm) increased gradually, and its high level was maintained until the end of experiment. The dynamics of Spm accumulation in leaves under salinity conditions resembled that of phosphoenolpyruvate carboxylase (PEPC), a key enzyme of the water-saving CAM pathway of photosynthesis. This indicates indirectly the involvement of Spm in the common ice plant adaptation to salinity. A decrease in the molar ratios of Spd to Spm in the leaves under salinity conditions could point to the acceleration of Spm biosynthesis (accumulation) during plant adaptation, whereas the levels of Spm precursors, Put and Spd, did not increase. This phenomenon could be explained by an accelerated conversion of Spd into Spm, an active liberation of free Spm from its conjugates, or changes in the rates of studied PA biosynthesis and degradation under salinity. At the same time, the intracellular concentration of ethylene rose under these conditions. It was supposed and then demonstrated, that the pathway of ethylene biosynthesis and that of the synthesis of Put family PAs compete under severe salinity conditions. This competition might be based on the disturbances in sulfur metabolism and a decrease in the methionine content, an immediate precursor of S-adenosyl-L-methionine.     

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.     

The Possible Role of Polyamines to the Recalcitrance of “Kalamata” Olive Leafy Cuttings to Root

The objective of this study was to investigate the role of endogenous polyamines (PAs) (the sum of free plus soluble conjugate plus insoluble bound) on rooting potential of leafy cuttings of an easy, that is,“Arbequina” and a difficult-to-root olive cultivar, that is, “Kalamata”. Subsamples of cuttings were taken for PAs analysis before planting in the mist system and during the early phases of rhizogenesis (EPR). “Arbequina” exhibited higher initial free and total PA content than “Kalamata”. Spermidine (Spd) was the predominant PA observed in both cultivars. A low content of free putrescine (Put) and Spd was found in both cultivars, whereas spermine (Spm) was occasionally detected. “Arbequina” as well as “Kalamata” exhibited the highest free Put and free Spd in summer and Put was the predominant PA among the free PAs. “Arbequina” exhibited the highest individual and total PAs in spring, followed by those in summer and autumn. In contrast, “Kalamata” had the maximum PAs in summer and the lowest in autumn. Changes in the endogenous content of individual and total PAs during the EPR were also observed. Treatment of “Kalamata” cuttings in autumn with both indole-3-butyric acid (IBA) and Put increased rooting compared to IBA alone. Among the PAs administered, Put was the most effective, whereas Spd and Spm failed to promote rooting. PAs, especially in their free form, seem to be involved in the rooting process of olive cuttings; Put application enhanced the rooting response of the difficult-to-root “Kalamata” olive cultivar.     

The Relationship between Polyamines and Hormones in the Regulation of Wheat Grain Filling

The grain weight of wheat is strongly influenced by filling. Polyamines (PA) are involved in regulating plant growth. However, the effects of PA on wheat grain filling and its mechanism of action are unclear. The objective of the present study was to investigate the relationship between PAs and hormones in the regulation of wheat grain filling. Three PAs, spermidine (Spd), spermine (Spm), and putrescine (Put), were exogenously applied, and the grain filling characteristics and changes in endogenous PA and hormones, i.e., indole-3-acetic acid (IAA), zeatin (Z) + zeatin riboside (ZR), abscisic acid (ABA), ethylene (ETH) and gibberellin 1+4 (GAs), were quantified during wheat grain filling. Exogenous applications of Spd and Spm significantly increased the grain filling rate and weight, but exogenous Put had no significant effects on these measures. Exogenous Spd and Spm significantly increased the endogenous Spd, Spm, Z+ZR, ABA, and IAA contents and significantly decreased ETH evolution in grains. The endogenous Spd, Spm and Z+ZR contents were positively and significantly correlated with the grain filling rate and weight of wheat, and the endogenous ETH evolution was negatively and significantly correlated with the wheat grain filling rate and weight. Based upon these results, we concluded that PAs were involved in the balance of hormones that regulated the grain filling of wheat.     

Promoter strength influences polyamine metabolism and morphogenic capacity in transgenic rice tissues expressing the oat adc cDNA constitutively

We analyzed molecularly and biochemically a series of transgenic rice lines expressing the oat adc (arginine decarboxylase) cDNA under the control of the constitutive maize ubiquitin 1 promoter. We established baseline biochemical parameters to elucidate the role of polyamines (PAs) during morphogenesis. We measured mRNA levels, ADC enzyme activity and cellular PAs in dedifferentiated callus. Polyamine levels were also quantified in two subsequent developmental stages – regenerating tissue and differentiated shoots. We observed significant (P<0.05) differences in the levels of individual PAs at the three developmental stages. The amounts of putrescine (Put) and spermidine (Spd) in dedifferentiated transgenic callus were lower than those in the wild type or in hpt (hygromycin resistant)-controls, whereas the amount of spermine (Spm) was increased up to two-fold. In regenerating tissue, this trend was reversed, with significantly higher levels of Put and Spd (P<0.05), and lower levels of Spm (P<0.05) compared to non-transformed or hpt-control tissues at the same developmental stage. In differentiated shoots, there was a general increase in PA levels, with significant increases in Put, Spd, and Spm (P<0.05); on occasion reaching six times the level observed in wild type and hpt-control tissues. These results contrast those we reported previously using the weaker CaMV 35S promoter driving adc expression. mRNA measurements and ADC enzyme activity were consistently higher (P<0.01) in all tissues expressing pUbiadcs compared to equivalent tissues engineered with 35Sadc. Our findings are consistent with a threshold model which postulates that high adc expression leading to production of Put above a basal level is necessary to generate a big enough metabolic pool to trigger PA flux through the pathway leading to an increase in the concentration of Spd and Spm. This can be best accomplished by a strong constitutive promoter driving adc. We discuss our results in the context of flux through the PA pathway and its impact on morphogenesis.     

盐适应过程中香根草内源游离态、结合态、束缚态多胺含量的变化

研究了不同浓度NaCl胁迫下,香根草（Vetiteria zizanioides）根、叶中的游离态、结合态、束缚态多胺（PAs）[包括腐胺（Put）,尸胺（Cad）,亚精胺（Sod）和精胺（Spm）]含量的变化。在中度盐胁迫（100,200mmol L^-1NaCl）9天时,香根草基本能够正常生长,但在重度盐胁迫（300mmol L^-1NaCl）下,其生长受到严重抑制。在上述3个不同浓度的NaCl胁迫下,香根草根、叶中游离态Put,Cad,spd,Stma和总的游离态PAs含量明显下降,在高盐浓度下下降幅更大;结合态Put,Cad,Sod,Spm和总的结合态PAs含量显著上升,但在重度盐胁迫下升幅较小或与对照相当;束缚态Put,Cad和总的束缚态PAs含量均减少,而束缚态Spd和Spm含量在叶中是下降的,在根中则增加,且在中度盐胁迫下更明显。对根和叶片而言,除游离态（Spd＋Spm）,Put比值在重度盐胁迫下较对照显著下降外,其它游离态、结合态、束缚态和总的（Spd＋Spm）／Put比值在不同盐胁迫下均上升,在中度盐胁迫下更明显。这表明,维持多胺总量的稳态和较高的（Spd＋Spm）／Put比值是香根草适应中度盐胁迫的一个重要机制。     

Involvement of polyamines in gibberellin-induced development of seedless grape berries

The roles of polyamines (PAs) in the development of seedless grape berries induced by gibberellin (GA₃) was investigated. The development of seedless grape berries was stimulated by the application of putrescine (Put), but not by that of spermidine (Spd) and spermine (Spm), regardless of the presence of GA₃. At harvest, the fresh weight of seedless grape berries treated with 500 ppm Put + 25 ppm GA₃ and 500 ppm Put increased to 111 and 112%, respectively, of the control. Treatment with methylglyoxal-bis (guanyl hydrazone), a potent inhibitor of S-adenosylmethionine decarboxylase that plays a role in Spd and Spm synthesis, did not affect the development of seedless grape berries induced by 100 ppm GA₃. The application of 100 ppm GA₃ significantly increased endogenous free Put levels. Levels of free Spd and Spm were not affected by GA₃. Although the levels of endogenous perchloric acid insoluble bound PAs were higher than those of free PAs, obvious changes in the levels of bound PAs were not observed. These results indicate that free Put is implicated in the development of seedless grape berries induced by GA₃.     

Polyamine metabolism of potato seed-tubers during long-term storage and early sprout development

Growth potential of potato (Solanum tuberosum L.) plants is influenced by seed-tuber age. After 24 days of growth, single-eye seedcores from 7-month-old seed-tubers produced 64% more foliar dry matter than those from 19-month-old seed-tubers, reflecting a higher growth rate. This study was initiated to determine if differences in polyamine (PA) metabolism are associated with aging and age-reduced vigor of potato seed-tubers. As tubers aged in storage, putrescine (Put) increased 2.2-fold, while spermidine (Spd) and spermine (Spm) decreased 33% and 38%, respectively. Ethylene content of the tuber tissue also increased with advancing age, suggesting that during the aging process S-adenosylmethionine was directed toward ethylene biosynthesis at the expense of the PAs. Single-eye cores from 7- and 19-month-old tubers were sown and PA levels in core and shoot tissues were monitored during plant development. Put titer of younger cores increased 8.8-fold by 12 days. In contrast, the increase in Put over the initial titer in older cores was 2.9-fold. The reduced ability of older cores to synthesize Put during plant establishment is probably due to a 45% decline in ornithine decarboxylase activity between 12 and 16 days after planting. Lack of available Put substrate limited the biosynthesis of Spd and Spm, and thus their concentrations remained lower in older cores than in younger cores. Lower PA titer in older cores during plant establishment is thus coincident with reduced growth potential. Concentrations of Put and Spd were higher in shoots developing from older cores throughout the study, but there was no age-related difference in Spm content. In contrast, activities of arginine and S-adenosylmethionine decarboxylases were higher in shoots from younger cores during establishment. The results indicate that aging affects PA metabolism in both tuber and developing plant tissues, and this may relate to loss of growth potential with advancing seed-tuber age.     

Do exogenous polyamines have an impact on the response of a salt-sensitive rice cultivar to NaCl?

In order to analyze the putative impact of polyamines (PAs) on the plant response to salt, seedlings from the salt-sensitive rice cultivar I Kong Pao (IKP) were exposed for 5, 12 and 19 days to 0, 50 or 100 mM NaCl in the absence, or in the presence of exogenous PAs (putrescine (Put), spermidine (Spd) or spermine (Spm) 1mM) or inhibitors of PA synthesis (methylglyoxalbis-guanyl hydrazone (MGBG) 1mM, cyclohexylammonium (CHA) 5mM and D-arginine (D-Arg) 5mM). The addition of PAs in nutritive solution reduced plant growth in the absence of NaCl and did not afford protection in the presence of salt. PA-treated plants exhibited a higher K+/Na+ ratio in the shoots, suggesting an improved discrimination among monovalent cations at the root level, especially at the sites of xylem loading. The diamine Put induced a decrease in the shoot water content in the presence of NaCl, while Spd and Spm had no effects on the plant water status. In contrast to Spd, Spm was efficiently translocated to the shoots. Both PAs (Spd and Spm) induced a decrease in cell membrane stability as suggested by a strong increase in malondialdehyde content of PA-treated plants exposed to NaCl. These results are discussed in relation to the putative functions of PAs in stressed plant metabolism.     

Polyamine and nitric oxide levels relate with morphogenetic evolution in somatic embryogenesis of <Emphasis Type="Italic">Ocotea catharinensis</Emphasis>

In this study we examined the effect of polyamines (PAs) putrescine (Put), spermidine (Spd) and spermine (Spm) on growth, morphology evolution, endogenous PAs levels and nitric oxide (NO) release in Ocotea catharinensis somatic embryo cultures. We observed that Spd and Spm reduced culture growth, permitted embryo morphogenetic evolution from the earliest to last embryo development stages, increased endogenous PAs levels, and induced NO release in O. catharinensis somatic embryos. On the other hand, Put had little effect on these parameters. Spd and Spm could successfully be used to promote somatic embryo maturation in O. catharinensis. The results suggest that Spd and Spm have an important role during the growth, development and morphogenetic evolution of somatic embryos, through alterations in the endogenous nitric oxide and PAs metabolism in this species.     

Excretion of polyamines in alfalfa and tobacco suspension-cultured cells and its possible role in maintenance of intracellular polyamine contents

Changes in polyamines (PAs) in cells and cultivation media of alfalfa (Medicago sativa L.) and tobacco bright yellow 2 (BY-2) (Nicotiana tabacum L.) cell suspension cultures were studied over their growth cycles. The total content of PAs (both free and conjugated forms) was nearly 10 times higher in alfalfa, with high level of free putrescine (Put) (in exponential growth phase it represented about 65-73% of the intracellular Put pool). In contrast, the high content of soluble Put conjugates was found in tobacco cells (in exponential phase about 70% of the intracellular Put). Marked differences occurred in the amount of PAs excreted into the cultivation medium: alfalfa cells excreted at the first day after inoculation 2117.0, 230.5, 29.0 and 88.0 nmol g(-1) of cell fresh weight (FW) of Put, spermidine (Spd), spermine (Spm) and cadaverine (Cad), respectively, while at the same time tobacco cells excreted only small amount of Put and Spd (12.7 and 2.4 nmol g(-1) FW, respectively). On day 1 the amounts of Put, Spd, Spm and Cad excreted by alfalfa cells represented 21, 38, 12 and 15% of the total pool (intra- plus extra-cellular contents) of Put, Spd, Spm and Cad, respectively. In the course of lag-phase and the beginning of exponential phase the relative contents of extracellular PAs continually decreased (with the exception of Cad). On day 10, the extracellular Put, Spd, Spm and Cad still represented 11.3, 10.9, 2.1 and 27% of their total pools. The extracellular PAs in tobacco cells represented from day 3 only 0.1% from their total pools. The possible role of PA excretion into the cultivation medium in maintenance of intracellular PA contents in the cells of the two cell culture systems, differing markedly in growth rate and PA metabolism is discussed.     

NaCl胁迫对结荚期菜用大豆叶片游离态多胺水平的影响

采用蛭石栽培,在100mmol·L-1NaCl胁迫下,对耐盐性不同的2个菜用大豆[Glycinemax(L.)Merr.]品种结荚期干物质积累、单株产量及叶片游离态多胺(PAs)水平的变化进行了研究。结果表明:NaCl胁迫显著降低了菜用大豆植株干重及单株产量,但耐盐品种"绿领特早"的降幅低于盐敏感品种"理想高产95-1";与"理想高产95-1"相比,"绿领特早"叶片在整个NaCl胁迫期间均维持了相对较低的H2O2含量、游离态腐胺(Put)含量及较高的游离态亚精胺(Spd)含量,在胁迫6～15d期间维持了相对较高的游离态精胺(Spm)含量、(Spd+Spm)/Put值及较低的Put/PAs值。说明耐盐品种"绿领特早"叶片具有较强的由游离态Put向游离态Spd和Spm转化的能力,维持了较低的游离态Put含量和较高的游离态Spd及Spm含量,进而抑制了活性氧过量积累。     

多胺对宁夏枸杞愈伤组织器官发生和体细胞胚发生的影响

利用已建立的宁夏枸杞（Lycium barbarumL.)愈伤组织器官发生和体细胞胚发生体系,对多胺在其离体形态发生中的作用进行研究。通过检测内源多胺含量发现,在所研究的三种多胺中,Put是器官发生途径的主要多胺,而在体细胞胚发生途径Spd含量占优势。Put含量变化在两条途径中相似：在愈伤组织分化的早期迅速积累不仅又下降,随着芽原基和球形胚的形成含量又进一步上升。器官发生中Spd最高含量仅在培养的第一天后,Spd含量才开始上升,到第十天时达到最高值。三种外源多胺的添加均有有效地促进两种离体分化途径的形态建成：Spd(100 μmol/L）能显著增加不定芽数,而体细胞胚发生中Spd(100μmol/L）而Put（100μmol/L）的单独处理能最好地促进体细胞胚形成和进一步发育成苗;尽管Spm在离体形态发生中含量较低,但添加外源Spm也促进了不定芽形成和体细胞胚形成然后成苗。多胺生物合成抑制剂CHA处理阻碍不定芽形成和和体细胞胚的进一步发育;但是MGBG对器官发生途径中的形态建成没有影响,即降低体细胞胚的发生频率及再生苗数。添加Spd(50μmol/L)能部分逆转CHA、MGBG的抑制效应。以上结果表明,多胺对宁夏枸杞器官发生和体细胞胚发生途径的离体形态建成有一定影响。     

Effect of root-applied spermidine on growth and respiratory metabolism in roots of cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis>) seedlings under hypoxia

The effects of exogenous spermidine (Spd) application to hypoxic nutrient solution on the contents of endogenous polyamines (PAs) and respiratory metabolism in the roots of cucumber (Cucumis sativus L.) seedlings were investigated. Cucumber seedlings were grown hydroponically in control and hypoxic nutrient solutions with and without addition of Spd at a concentration of 0.05 mM. The activities of key enzymes involved in the tricarboxylic acid cycle (TCAC), such as succinate dehydrogenase (SDH) and isocitrate dehydrogenase (IDH), were significantly inhibited under root-zone hypoxia with dissolved oxygen (DO) at 1 mg/l. In contrast, the activities of enzymes involved in the process of fermentation, such as pyruvate decarboxylase (PDC), alcohol dehydrogenase (ADH), lactate dehydrogenase (LDH), and alanine aminotransferase (AlaAT), were significantly increased. Thus, aerobic respiration was inhibited and fermentation was enhanced in the roots of cucumber seedlings as a result of decreasing ATP content to inhibit the dry weight of seedlings under hypoxic stress. Moreover, the contents of free, soluble conjugated, and insoluble bound putrescine (Put), Spd, and spermine (Spm) in the roots of cucumber seedlings were significantly increased under hypoxia stress. Interestingly, application of Spd to hypoxic roots markedly suppressed the accumulation of free Put and, in contrast, promoted an increase in free Spd and Spm, as well as soluble conjugated and insoluble bound Put, Spd, and Spm contents. From these data, we deduced that exogenous Spd promotes the conversion of free Put into free Spd and Spm, and soluble conjugated and insoluble bound PAs under hypoxia stress. Furthermore, the activities of LDH, PDC, and ADH were suppressed and, in contrast, the activities of SDH and IDH were enhanced by application of exogenous Spd to hypoxic roots. As a result, aerobic respiration was enhanced but fermentation metabolism was inhibited in the roots of cucumber seedlings, leading to an increase in ATP content to alleviate the inhibited dry weight of seedlings due to hypoxia stress. These results suggest that application of Spd to hypoxic nutrient solution promoted conversion of free Put into free Spd and Spm as well as soluble conjugated and insoluble bound PAs, further enhanced IDH and SDH activities, and inhibited ethanol fermentation and lactate fermentation, resulting in increased ATP content and eventually enhanced tolerance of cucumber plants to root-zone hypoxia.     

低氧胁迫下24-表油菜素内酯对黄瓜幼苗叶片光合特性及多胺含量的影响

采用1/2 Hoagland营养液培养,研究了低氧胁迫下24-表油菜素内酯(EBR)对黄瓜幼苗叶片光合特性及多胺含量的影响.结果表明：低氧胁迫下黄瓜幼苗的净光合速率(P_n)、气孔导度(g_s)、蒸腾速率(T_r)、胞间CO₂浓度(C_i)显著下降,而叶绿素含量显著提高,幼苗生长受抑;低氧胁迫显著提高了黄瓜幼苗叶片的腐胺(Put)、亚精胺(Spd)、精胺(Spm)、多胺(PAs)含量和Put/PAs,但降低了(Spd+Spm) /Put.低氧胁迫下,外源EBR不仅显著提高了黄瓜幼苗的P_n、g_s、T_r及叶绿素含量,也显著提高了黄瓜幼苗叶片的游离态Spm、结合态Spd、Spm及束缚态Put、Spd、Spm含量,促进了PAs的进一步积累,且降低了Put/PAs,提高了(Spd+Spm)/Put．可见,外源EBR调节了黄瓜幼苗内源多胺含量及形态的变化,维持了较高的光合性能,促进了叶面积和干物质量的显著增加,缓解了低氧胁迫对黄瓜幼苗的伤害.     

Physiological and biochemical responses induced by lead stress in Spirodela polyrhiza

The effects of increasing lead concentration on the activities of superoxide dismutase (SOD), peroxides (POD) and catalase (CAT), levels of ascorbate (AsA), reduced glutathione (GSH), Pb accumulation and its influence on nutrient elements, polyamines (PAs) content, as well as activities of polyamine oxidase (PAO) and ornithine decarboxylase (ODC), were investigated in Spirodela polyrhiza. POD and CAT activities increased progressively followed by a decline, while SOD activity gradually fell. The effect of Pb application on AsA content was similar to that seen for POD and CAT activities. GSH content initially rose but then declined. A significant enhancement in Pb accumulation was observed, except in the 25?μM Pb treatments. Nutrient elements were also affected. Moreover, Pb stress induced a considerable decrease in total spermidine (Spd), while the levels of total putrescine (Put) and spermine (Spm) initially increased at 25?μM Pb but then declined. Free and perchloric acid soluble conjugated (PS-conjugated) PAs contents changed in a similar way to total PAs. In addition, Pb stress induced a continuous accumulation of perchloric acid insoluble bound (PIS-bound) Spm and an initial accumulation of PIS-bound Put and Spd. The ratio of free (Spd?+?Spm)/Put significantly declined whereas the ratio of total (Spd?+?Spm)/Put rose at low Pb concentrations (25 and 50?μM). PAO activity rose gradually with an increase in Pb concentration, reaching peak values at 100?μM, while ODC activity first increased at 25?μM Pb and then declined. The results indicated that the tolerance of S. polyrhiza to Pb stress was enhanced by activating the antioxidant system, preventing the entry of the Pb ion and altering the content of polyamines.     

氯化钠胁迫对嫁接黄瓜叶片多胺含量的影响

以日本耐盐品种‘帝王新土佐’南瓜为砧木,以’新泰密刺’黄瓜为接穗,在100 mmol·L^-1 NaCl胁迫下,对黄瓜嫁接和自根植株不同时期叶片中不同形态多胺含量的变化进行了研究.结果表明：NaCl胁迫下黄瓜嫁接植株游离态腐胺（Put）含量在胁迫2 d时与自根植株无显著差异,其余时间均显著高于自根植株;游离态亚精胺（Spd）和游离态精胺（Spm）含量在整个胁迫期间均显著高于自根植株;游离态多胺总量（PAs）在胁迫第4天出现峰值;嫁接植株游离态Put/PAs值在胁迫4 d时与自根植株无显著差异,其余胁迫时间均显著低于自根植株,而(Spd+Spm)/Put值在整个胁迫期间均显著高于自根植株;嫁接植株结合态和束缚态Put、Spd和Spm含量在整个胁迫期间均显著高于自根植株,结合态和束缚态PAs在胁迫第6天出现峰值;结合态多胺的Put/PAs值和(Spd+Spm)/Put值变化趋势与游离态多胺一致;嫁接植株束缚态Put/PAs值在胁迫6 d时与自根植株无显著差异,其余时间均显著低于自根植株,而(Spd+Spm)/Put值在整个胁迫期间均显著高于自根植株.表明黄瓜嫁接植株表现出较强的耐盐特征.     

Stress‐induced changes in polyamine and tyramine levels can regulate proline accumulation in tomato leaf discs treated with sodium chloride

The effect of salt stress on proline (Pro) accumulation and its relationship with the changes occurring at the level of polyamine (PA) metabolism and tyramine were investigated in leaf discs of tomato (Lycopersicon esculentum). The rate of accumulation of Pro, PA and tyramine was higher in the salt-sensitive than in the salt-tolerant cultivar. In the salt-sensitive cultivar, Pro started to accumulate 4 h after the onset of the NaCl treatment, its maximum level being reached 27 h later. The lag phase was associated with a rapid decrease in putrescine (Put) and spermidine (Spd) and some increase in 1,3-diaminopropane (Dap), a product of Spd and/or spermine (Spm) oxidation. This was followed by an increase in agmatine (Agm), cadaverine (Cad), Spm and tyramine. α-DL-difluoromethylarginine (DFMA), an inhibitor of arginine decarboxylase (ADC, EC 4.1.1.19), induced a decrease in the Put level in both control and stressed discs, while α-DL-difluoromethylomithine (DFMO), an inhibitor of ornithine decarboxylase (ODC, EC 4.1.1.17), caused a decrease in Spd and Spm levels only in salinized discs. These data suggest that ADC is operating under both control and stress conditions, whereas ODC activity is promoted only in response to salt stress. DFMA also depressed the salt-induced Pro accumulation while DFMO did not inhibit this response. In salt-stressed leaf discs, the decrease in Spd level in response to methylglyoxal-bis-(guanylhydrazone) (MGBG) or cyclohexylammonium (CHA) treatment suggests that salt stress did not block SAM decarboxylase or Spd synthase activities. However, the increased level of Dap reflected a salt stress-promoted oxidation of PA. CHA and MGBG had no effect on Pro accumulation. Putrescine, Dap and especially tyramine supplied at low concentrations stimulated the Pro response which was, however, suppressed by application of Spm. Treatment with aminoguanidine, an inhibitor of diamine oxidases, also strongly inhibited Pro accumulation. These data suggest that salt-induced Pro accumulation in tomato leaf discs is closely related to changes in their PA metabolism, either via substrate-product relationships or regulatory effects at target(s) which remain to be characterized.