Participation of ornithine decarboxylase in early stages of tomato fruit development

Achievements and perspectives of synthetic biology in botanical insecticides

Botanical insecticides are the origin of all insecticidal compounds. They have been widely used to control pests in crops for a long time. Currently, the commercial production of botanical insecticides extracted from plants is limited because of insufficient raw material supply. Synthetic biology is a promising and effective approach for addressing the current problems of the production of botanical insecticides. It is an emerging biological research hotspot in the field of botanical insecticides. However, the biosynthetic pathways of many botanical insecticides are not completely elucidated. On the other hand, the cytotoxicity of botanical pesticides and low efficiency of these biosynthetic enzymes in new hosts make it still challenging for their heterologous production. In the present review, we summarized the recent developments in the heterologous production of botanical insecticides, analyzed the current challenges, and discussed the feasible production strategies, focusing on elucidating biosynthetic pathways, enzyme engineering, host engineering, and cytotoxicity engineering. Looking to the future, synthetic biology promises to further advance heterologous production of more botanical pesticides.

Genome wide survey, and expression analysis of Ornithine decarboxylase gene associated with alkaloid biosynthesis in plants

Plant ODC (ornithine decarboxylase) plays a vital role in normalizing cell division in actively growing tissues. The ODC is a key precursor enzyme for nicotine and nornicotine biosynthesis in plants. ODCs are widely present in many plant families but have not been functionally validated and characterized at the molecular level. In the present study, 58 plant ODCs were identified and were found to contain two putative regulatory motifs, specifically PLP (Pyridoxal 5'-phosphate) and Orn/DAP/Arg decarboxylase family 2 pyridoxal-phosphate, that are highly conserved among diverse plant species. Further, the cis-regulatory elements and interacting partners of the gene revealed the importance of ODC in various metabolic pathways. The qRT-PCR revealed highest relative expression of ODC in floral meristem and roots. Our results suggest that ODC can be effectively used as an ideal candidate for engineering polyamine biosynthesis and would be crucial for developing ultra-low nicotine content tobacco lines via genome editing.

Update on the Roles of Polyamines in Fleshy Fruit Ripening, Senescence, and Quality

Ripening of fleshy fruits involves complex physiological, biochemical, and molecular processes that coincide with various changes of the fruit, including texture, color, flavor, and aroma. The processes of ripening are controlled by ethylene in climacteric fruits and abscisic acid (ABA) in non-climacteric fruits. Increasing evidence is also uncovering an essential role for polyamines (PAs) in fruit ripening, especially in climacteric fruits. However, until recently breakthroughs have been made in understanding PA roles in the ripening of non-climacteric fruits. In this review, we compare the mechanisms underlying PA biosynthesis, metabolism, and action during ripening in climacteric and non-climacteric fruits at the physiological and molecular levels. The PA putrescine (Put) has a role opposite to that of spermidine/spermine (Spd/Spm) in cellular metabolism. Arginine decarboxylase (ADC) is crucial to Put biosynthesis in both climacteric and non-climacteric fruits. S-adenosylmethionine decarboxylase (SAMDC) catalyzes the conversion of Put to Spd/Spm, which marks a metabolic transition that is concomitant with the onset of fruit ripening, induced by Spd in climacteric fruits and by Spm in non-climacteric fruits. Once PA catabolism is activated by polyamine oxidase (PAO), fruit ripening and senescence are facilitated by the coordination of mechanisms that involve PAs, hydrogen peroxide (H₂O₂), ABA, ethylene, nitric oxide (NO), and calcium ions (Ca²⁺). Notably, a signal derived from PAO5-mediated PA metabolism has recently been identified in strawberry, a model system for non-climacteric fruits, providing a deeper understanding of the regulatory roles played by PAs in fleshy fruit ripening.

FaPAO5 regulates Spm/Spd levels as a signaling during strawberry fruit ripening

Polyamines are important for non-climacteric fruit ripening according to an analysis of the model plant strawberry. However, the molecular mechanism underlying the polyamine accumulation during ripening has not been fully elucidated. In this study, an examination of our proteome data related to strawberry fruit ripening revealed a putative polyamine oxidase 5, FaPAO5, which was localized in the cytoplasm and nucleus. Additionally, FaPAO5 expression levels as well as the abundance of the encoded protein continually decreased during ripening. Inhibiting FaPAO5 expression by RNAi promoted Spd, Spm, and ABA accumulation while inhibited H2O2 production, which ultimately enhanced ripening as evidenced by the ripening-related events and corresponding gene expression changes. The opposite effects were observed in FaPAO5-overexpressing transgenic fruits. Analyses of the binding affinity and enzymatic activity of FaPAO5 with Spm, Spd, and Put uncovered a special role for FaPAO5 in the terminal catabolism of Spm and Spd, with a K d of 0.21 and 0.29 µM, respectively. Moreover, FaPAO5 expression was inhibited by ABA and promoted by Spd and Spm. Furthermore, the RNA-seq analysis of RNAi and control fruits via differentially expressed genes (DEGs) indicated the six most enriched pathways among the differentially expressed genes were related to sugar, abscisic acid, ethylene, auxin, gibberellin, and Ca2+. Among four putative PAO genes in the strawberry genome, only FaPAO5 was confirmed to influence fruit ripening. In conclusion, FaPAO5 is a negative regulator of strawberry fruit ripening and modulates Spm/Spd levels as a signaling event, in which ABA plays a central role.

Nicotine Biosynthesis inNicotiana: A Metabolic Overview

Alkaloids are important compounds found in Nicotiana plants, essential in plant defense against herbivores. The main alkaloid of Nicotiana tabacum, nicotine, is produced in roots and translocated to the leaves. Nicotine is formed by a pyrrolidine and a pyridine ring in a process involving several enzymes. The pyridine ring of nicotine is derived from nicotinic acid, whereas the pyrrolidine ring originates from polyamine putrescine metabolism. After synthesis in root cortical cells, a set of transporters is known to transport nicotine upward to the aerial part and store it in leaf vacuoles. Moreover, nicotine can be metabolized in leaves, giving rise to nornicotine through the N-demethylation process. Some Nicotiana wild species produce acyltransferase enzymes, which allow the plant to make N-acyl-nornicotine, an alkaloid with more potent insecticidal properties than nicotine. However, although we can find a wealth of information about the alkaloid production in Nicotiana spp., our understanding about nicotine biosynthesis, transport, and metabolism is still incomplete. This review will summarize these pathways on the basis on recent literature, as well as highlighting questions that need further investigation.

Salinity in Autumn-Winter Season and Fruit Quality of Tomato Landraces

Tomato landraces, originated by adaptive responses to local habitats, are considered a valuable resource for many traits of agronomic interest, including fruit nutritional quality. Primary and secondary metabolites are essential determinants of fruit organoleptic quality, and some of them, such as carotenoids and phenolics, have been associated with beneficial proprieties for human health. Landraces' fruit taste and flavour are often preferred by consumers compared to the commercial varieties' ones. In an autumn-winter greenhouse hydroponic experiment, the response of three Southern-Italy tomato landraces (Ciettaicale, Linosa and Corleone) and one commercial cultivar (UC-82B) to different concentrations of sodium chloride (0 mM, 60 mM or 120 mM NaCl) were evaluated. At harvest, no losses in marketable yield were noticed in any of the tested genotypes. However, under salt stress, fresh fruit yield as well as fruit calcium concentration were higher affected in the commercial cultivar than in the landraces. Furthermore, UC-82B showed a trend of decreasing lycopene and total antioxidant capacity with increasing salt concentration, whereas no changes in these parameters were observed in the landraces under 60 mM NaCl. Landraces under 120 mM NaCl accumulated more fructose and glucose in the fruits, while salt did not affect hexoses levels in UC-82B. Ultra-performance liquid chromatography-tandem mass spectrometry analysis revealed differential accumulation of glycoalkaloids, phenolic acids, flavonoids and their derivatives in the fruits of all genotypes under stress. Overall, the investigated Italian landraces showed a different behaviour compared to the commercial variety UC-82B under moderate salinity stress, showing a tolerable compromise between yield and quality attributes. Our results point to the feasible use of tomato landraces as a target to select interesting genetic traits to improve fruit quality under stress conditions.

Cucumber ovaries inhibited by dominant fruit express a dynamic developmental program, distinct from either senescence-determined or fruit-setting ovaries

Cucurbits represent an attractive model to explore the dynamics of fruit set, whose regulation is not fully understood, despite its importance for yield determination. A fertilized ovary must integrate signals from distant plant parts and 'decide' whether to set fruit, or remain inhibited and later senesce. Here, we set out to characterize first-fruit inhibition (FFI), that is, the inhibitory effect of the first fruit on subsequent development of younger ovaries during pollination-induced and parthenocarpic fruit set. After the first fertilized ovaries set fruit, younger fertilized ovaries remained in a temporary state of inhibition. Such ovaries preserved their size and green color, and if the older fruit were removed within a 1-week reversibility window, they set fruit. The FFI effect was documented in both fertilized and parthenocarpic ovaries. We compared the gene expression profiles of pollinated ovaries (committed to set fruit) with respect to those affected by FFI, and to non-pollinated ovaries (undergoing senescence). The three fates of the ovaries were characterized by wide changes in gene expression, with several specific transcripts being up- or down-regulated in response to pollination, and to the presence of inhibitory fruit. Metabolic profiling was undertaken and integrated with the transcriptomic data in order to characterize early physiological changes that occur in post-anthesis ovaries in parthenocarpic and non-parthenocarpic genotypes. The combined results are discussed with respect to current models of fruit set and specifically with regard to FFI. Moreover, these metabolome and transcriptome data provide a valuable resource for studying ovary development and fruit set.

Solanum lycopersicum AUXIN RESPONSE FACTOR 9 regulates cell division activity during early tomato fruit development

The transformation of the ovary into a fruit after successful completion of pollination and fertilization has been associated with many changes at transcriptomic level. These changes are part of a dynamic and complex regulatory network that is controlled by phytohormones, with a major role for auxin. One of the auxin-related genes differentially expressed upon fruit set and early fruit development in tomato is Solanum lycopersicum AUXIN RESPONSE FACTOR 9 (SlARF9). Here, the functional analysis of this ARF is described. SlARF9 expression was found to be auxin-responsive and SlARF9 mRNA levels were high in the ovules, placenta, and pericarp of pollinated ovaries, but also in other plant tissues with high cell division activity, such as the axillary meristems and root meristems. Transgenic plants with increased SlARF9 mRNA levels formed fruits that were smaller than wild-type fruits because of reduced cell division activity, whereas transgenic lines in which SlARF9 mRNA levels were reduced showed the opposite phenotype. The expression analysis, together with the phenotype of the transgenic lines, suggests that, in tomato, ARF9 negatively controls cell division during early fruit development.

Arginine decarboxylase and polyamines required for embryogenesis in the wild carrot

Embryogenic cultures of Daucus carota treated with 1 millimolar alpha-difluoromethylarginine, a specific inhibitor of arginine decarboxylase, exhibited nearly a 50 percent reduction in embryo formation compared with controls. Putrescine and spermidine concentrations in the treated cells were greatly reduced. Addition of putrescine, spermidine, or spermine to the culture medium restored embryogenesis in the treated cultures. Embryogenesis was not significantly affected by alpha-difluoromethylornithine, an inhibitor of ornithine decarboxylase. These results suggest that polyamines have a major function in plant embryo development and that the wild carrot synthesizes polyamines through the biosynthetic pathway involving arginine decarboxylase rather than ornithine decarboxylase.

Differential and functional interactions emphasize the multiple roles of polyamines in plants

Biogenic amines putrescine, spermidine and spermine are ubiquitous in nature and have interested researchers because they are essential for cell division and viability, and due to a large body of their pharmacological effects on growth and development in most living cells. The genes and enzymes involved in their biosynthetic pathways are now established and characterized. In recent years, molecular aspects of polyamine action have also begun to emerge. Our model is the ripening tomato fruit in which processes of cell division, cell expansion and cell growth have ceased, and yet the cells are responsive at biochemical and molecular levels to genetically manipulated concentrations of putrescine (Put), spermidine (Spd) and spermine (Spm). Thus, transcriptome, limited protein profiling, and metabolome studies of transgenic tomato fruit have yielded significant new information on cellular processes impacted by polyamine manipulation. We have used these datasets to determine the linear correlation coefficients between the endogenous levels of Put, Spd and Spm with several parameters. Results of our analysis presented here show that effects of the diamine Put generally contrast those with polyamines Spd and Spm, emphasizing that individual biogenic amines should be considered to have defined action in plant biology and that they differentially affect growth and development. A multiple function model of polyamine action is discussed to explain the role of polyamines in most organisms, in general, and ripening fruit, in particular.

Flower fertilization and fruit development prompt changes in free polyamines and ethylene in damson plum (Prunus insititia L.)

The flower opening of damson plum (Prunus insititia L.) was accompanied by an increase in the content of free-polyamines (PA) in the sepals, petals and sex organs, the ovary being most active in accumulating spermine (Spm). The fertilization process and senescence brought on a decline in ovarian Spm, but stimulated putrescine (Put) and spermidine (Spd) content in the sepals. The endocarp of this climacteric fruit produced only ethylene at the end of the S1 phase and throughout S2, in which there was a great richness in ACC and MACC. The greatest amounts of ACC and MACC were observed in the ripening mesocarp and epicarp. The contribution of the endocarp and epicarp to the total ACC in the developing fruit was very similar. During flowering and S1 and S2 phases, Spd was the most abundant PA; in contrast, during S3 and S4 Put was most abundant. The mesocarp contributed the most to the total content in PA throughout the fruit development. The control of SAM distribution towards ethylene and/or PA appears to differ during the development of the endocarp, as the only peak of free-Put (detected in S2) coincided with the highest ACC accumulation and ethylene production. On the contrary, in S3 it is probable that SAM was transformed preferentially into PA, given that free-Spd and Spm, hardly detectable in S1 and S2, peaked in this phase in which there was no gas production.

Endogenous free polyamines and their role in fruit set of low and high parthenocarpic ability citrus cultivars

Endogenous free polyamines (PAs), putrescine, spermidine and spermine, from developing fruitlets of Citrus species (Citrus unshiu Marc. and Citrus clementina Hort ex Tanaka) which differ in their parthenocarpic ability, and from uniflowered leafy and leafless inflorescences differing in their ability to set, have been determined by dansylation and separation of dansyl derivatives by HPLC. No significant differences in PAs content were observed between species or between leafy and leafless inflorescences which, nevertheless, significantly differed in fruit set. However, significant differences in their content were found in developing fruitlets, depending on the preceding flowering intensity of the tree and on the fruitlet load. These results suggest that, in Citrus, PAs may act as a nitrogen source rather than a regulator of fruit set.

Polyamine metabolism is altered in unpollinated parthenocarpic pat-2 tomato ovaries

Facultative parthenocarpy induced by the recessive mutation pat-2 in tomato (Lycopersicon esculentum Mill.) depends on gibberellins (GAs) and is associated with changes in GA content in unpollinated ovaries. Polyamines (PAs) have also been proposed to play a role in early tomato fruit development. We therefore investigated whether PAs are able to induce parthenocarpy and whether the pat-2 mutation alters the content and metabolism of PAs in unpollinated ovaries. Application of putrescine, spermidine, and spermine to wild-type unpollinated tomato ovaries (cv Madrigal [MA/wt]) induced partial parthenocarpy. Parthenocarpic growth of MA/pat-2 (a parthenocarpic near-isogenic line to MA/wt) ovaries was negated by paclobutrazol (GA biosynthesis inhibitor), and this inhibition was counteracted by spermidine. Application of alpha-difluoromethyl-ornithine (-Orn) and/or alpha-difluoromethyl-arginine (-Arg), irreversible inhibitors of the putrescine biosynthesis enzymes Orn decarboxylase (ODC) and Arg decarboxylase, respectively, prevented growth of unpollinated MA/pat-2 ovaries. Alpha-difluoromethyl-Arg inhibition was counteracted by putrescine and GA(3), whereas that of alpha-difluoromethyl-Orn was counteracted by GA(3) but not by putrescine or spermidine. In unpollinated MA/pat-2 ovaries, the content of free spermine was significantly higher than in MA/wt ovaries. ODC activity was higher in pat-2 ovaries than in MA/wt. Transcript levels of genes encoding ODC and spermidine synthase were also higher in MA/pat-2. All together, these results strongly suggest that the parthenocarpic ability of pat-2 mutants depends on elevated PAs levels in unpollinated mutant ovaries, which correlate with an activation of the ODC pathway, probably as a consequence of elevated GA content in unpollinated pat-2 tomato ovaries.

The polyamines of Xanthium strumarium and their response to photoperiod

Flowering plants of Xanthium strumarium L., grown in 8 h photoperiods, were analysed for polyamines. Putrescine, spermidine and spermine were found throughout the plant in three forms: (a) as free polyamines; (b) conjugates soluble in 5% trichloracetic acid (TCA); and (c) bound to the TCA-insoluble precipitate. On a fresh weight basis, total polyamines are most abundant in young leaves and buds, especially flower buds. Spermidine predominates in the free polyamine fractions, while spermine is dominant in the conjugated fraction. Transfer of vegetative plants from 16 h photoperiods to 1, 2, 3, or 4 inductive cycles (8 h light + 16 h uninterrupted dark) caused rapid and marked changes in the polyamine titer of the leaves and ultimately, floral initiation. The titer of free putrescine per mg protein declined progressively with induction in all leaf sizes, while the titers of free spermidine and spermine rose during days 2 and 3 in small and expanding leaves. Conjugated putrescine, spermidine and spermine rose sharply after only 1 inductive cycle, especially in small and expanding leaves, and maintained the higher level for at least several cycles. In plants given 4 inductive cycles, buds harvested after 4 additional days had sharply elevated levels of conjugated polyamines, especially spermine, on a protein basis.

The regulation of ornithine decarboxylase gene expression by sucrose and small upstream open reading frame in tomato (Lycopersicon esculentum Mill)

We identified a near-full-length cDNA clone encoding ornithine decarboxylase (ODC) from tomato (Lycopersicon esculentum Mill). It contained a small upstream open reading frame (uORF) within its 5' untranslated region. An in vitro translation assay demonstrated that the uORF repressed expression of downstream ORF. Neither nucleotide nor predicted peptide sequence of the uORF was responsible for the repression. The presence of upstream AUG codon was shown to be responsible. ODC expression appeared to be organ specific. The ODC gene was expressed in roots, hypocotyls and sink leaves but not in source leaves. ODC transcripts were observed in apical meristem of primary roots, and were distributed in cells of cortex layer preferentially. ODC expression responded immediately to sucrose availability via the sucrose-specific pathway independent of hexokinase. Sucrose induction of ODC gene was seen in roots, hypocotyls and flowers but not in mature leaves. Moreover, only the root apical meristem responded to sucrose availability. These observations indicate that the spatial pattern of ODC expression is closely associated with cell proliferation and that sucrose sensing plays a major role in the spatial pattern of ODC expression. Also, the differential regulation of ODC and arginine decarboxylase gene expression by factors modulating plant growth suggests that they would have different physiological roles in plant development.

Photoinduction of arginine decarboxylase activity in leaves of Pharbitis nil

The activity of arginine decarboxylase (ADC) in leaves of Pharbitis nil was induced by light. The ADC activity increased to a maximum 1 h after illumination, followed by a gradual decrease. This suggested light either induced synthesis of ADC protein de novo or was involved in its activation. Cycloheximide inhibited the photoinduction of ADC activity, and the half life of ADC in leaves was 30-40 min. The temperature and relative humidity in darkness before illumination had no effect on the photoinduction of ADC activity, contrary to the photoresponse of S-adenosylmethionine decarboxylase (SAMDC) activity where the conditions of darkness before lights-on have a marked effect. The light response of the polyamine (PA)-biosynthetic enzyme activity produced transient accumulation of PA. The level of spermidine increased in leaves in which activities of both SAMDC and ADC increased after illumination, while the level of putrescine increased in leaves in which the activity of ADC increased but that of SAMDC did not.

Expression of ornithine decarboxylase is transiently increased by pollination, 2,4-dichlorophenoxyacetic acid, and gibberellic acid in tomato ovaries

A cDNA encoding for a functional ornithine decarboxylase has been isolated from a cDNA library of carpels of tomato (Lycopersicon esculentum Mill.). Ornithine decarboxylase in tomato is represented by a single-copy gene that we show to be up-regulated during early fruit growth induced by 2,4-dichlorophenoxyacetic acid and gibberellic acid.

Arginase, Arginine Decarboxylase, Ornithine Decarboxylase, and Polyamines in Tomato Ovaries (Changes in Unpollinated Ovaries and Parthenocarpic Fruits Induced by Auxin or Gibberellin)

Arginase (EC 3.5.3.1) activity has been found in the ovaries and Young fruits of tomato (Lycopersicon esculentum Mill. cv Rutgers).Changes in arginase, arginine decarboxylase (EC 4.1.1.19), and ornithine decarboxylase activity (EC 4.1.1.17) and levels of free and conjugated putrescine, spermidine, and spermine were determined in unpollinated ovaries and in parthenocarpic fruits during the early stages of development induced by 2,4-dichlorophenoxyacetic acid (2,4-D) or gibberellic acid (GA3). Levels of arginase, free spermine, and conjugates of the three polyamines were constant in unpollinated ovaries and characteristic of a presenescent step. A marked decrease in arginase activity, free spermine, and polyamine conjugates was associated with the initiation of fruit growth due to cell division, and when cell expansion was initiated, the absence of arginase indicated a redirection of nitrogen metabolism to the synthesis of arginine. A transient increase in arginine decarboxylase and ornithine decarboxylase was also observed in 2,4-D-induced fruits. In general, 2,4-D treatments produced faster changes than GA3, and without treatment, unpollinated ovaries developed only slightly and senescence was hardly visible. Sensitivity to 2,4-D and GA3 treatment remained for at least 2 weeks postanthesis.

Expression of arginine decarboxylase is induced during early fruit development and in young tissues of Pisum sativum (L.)

A cDNA coding for arginine decarboxylase (ADC, EC 4.1.1.19) has been isolated from a cDNA library of parthenocarpic young fruits of Pisum sativum (L.). The deduced aminoacid sequence is 74%, 46% and 35% identical to ADCs from tomato, oat and Escherichia coli, respectively. When the pea ADC cDNA was put under the control of the galactose inducible yeast promoter CYC1-GAL10 and introduced into Saccharomyces cerevisiae, it conferred galactose-regulated expression of the ADC activity. The ADC activity expressed in S. cerevisiae was inhibited 99% by alpha-DL-difluoromethylarginine (DFMA), a specific inhibitor of ADC activity. No activity was detected in the untransformed S. cerevisiae, nor when it was transformed with an antisense ADC construct. This provides direct evidence that the ADC cDNA from pea encoded a functional, specific ADC activity and that S. cerevisiae is able to process correctly the protein. In the pea plant, gene expression of the ADC is high in young developing tissues like shoot tips, young leaflets and flower buds. Fully expanded leaflets and roots have much lower, but still detectable, levels of the ADC transcript. In the ovary and fruit, they are developmentally regulated, showing high levels of expression during the early stages of fruit growth, which in pea is mainly due to cell expansion. The observed changes in the steady-state levels of ADC mRNA alone, however, cannot account for the differences in ADC activity suggesting that other regulatory mechanisms must be acting.

Arginine Decarboxylase and Putrescine Oxidase in Ovaries of Pisum sativum L. (Changes during Ovary Senescence and Early Stages of Fruit Development)

Enzymatic activities involved in putrescine metabolism in ovaries of Pisum sativum L. during ovary senescence and fruit set were investigated. Accumulation of putrescine was observed during incubation of extracts from gibberellic acid-treated unpollinated ovaries (young developing fruits) but not in extracts from untreated ovaries (senescent ovaries). Extracts from pea ovaries showed arginine decarboxylase (ADC) activity, but ornithine decarboxylase and arginase activity were not detected. ADC activity decreased in presenescent ovaries and increased markedly after induction of fruit set with gibberellic acid. Increases in ADC activity were also observed with application of other plant growth substances (benzy-ladenine and 2,4-dichlorophenoxyacetic acid), after pollination, and in the slender (la crys) pea mutant. By contrast, putrescine oxidase activity increased in presenescent ovaries but did not increase during early fruit development. All of these results suggest that ADC and putrescine oxidase are involved in the control of putrescine metabolism. Ovary senescence is characterized by the absence of putrescine biosynthesis enzymes and increased levels of putrescine oxidase and fruit development by an increase in ADC and a constant level of putrescine oxidase.

Correlation between Ornithine Decarboxylase and Putrescine in Tomato Plants Infected by Citrus Exocortis Viroid or Treated with Ethephon

We have investigated the arginine decarboxylase (ADC, EC 4.1.1.19) and ornithine decarboxylase (ODC, EC 4.1.1.17) activities and the levels of conjugated polyamines to explain the decrease of free putrescine level caused by citrus exocortis viroid (CEVd) and ethephon treatment in tomato (Lycopersicon esculentum Mill. cv Rutgers) plants (J.M. Belles, J. Carbonell, V. Conejero [1991] Plant Physiol 96: 1053-1059). This decrease correlates with a decrease in ODC activity in CEVd-infected or ethephon-treated plants; ADC activity was not altered. CEVd infection had no effect on polyamine conjugates, and ethephon produced a decrease in putrescine conjugates. Interference with ethylene action by silver ions prevented the decrease in ODC activity and in free and conjugated putrescine. It is suggested that changes in putrescine level after CEVd infection and ethephon treatment are regulated via ODC activity and that conjugation is not involved.

Purification and characterization of two ribonucleases from developing tomato fruit

Two neutral ribonucleases have been purified from developing tomato fruit. Their activity is maximal 5 days after anthesis, declines during maturation, and then increases slightly in the mature green through breaker stages. The ribonucleases Tf1 and Tf2 have molecular weights of 59 and 29 K, respectively, based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and are glycoproteins. The reduced and denatured Tf1 is composed of two subunits, 30 and 29 K, of which only the 30-K subunit displays ribonuclease activity after renaturation. Reduced and denatured Tf2 is a single 29-K polypeptide that is renaturable to an active ribonuclease. Only the 30-K, active subunit of Tf1 is immunologically cross-reactive with Tf2. Both ribonucleases are cyclyzing endoribonucleases with a strong preference for cleavage at pyrimidine residues, thus generating oligonucleotide products ending with pyrimidine 2',3'-cyclic phosphate. These tomato fruit ribonucleases share a number of properties in common with the S-glycoprotein ribonucleases that are involved in self-incompatibility reactions in some solanaceous plants.

Polyamines and the Cell Cycle of Catharanthus roseus Cells in Culture

Investigation was made on the effect of partial depletion of polyamines (PAs), induced by treatment with inhibitors of the biosynthesis of PAs, on the distribution of cells at each phase of the cell cycle in Catharanthus roseus (L.) G. Don. cells in suspension cultures, using flow cytometry. More cells treated with inhibitors of arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) were accumulated in the G(1) phase than those in the control, while the treatment with an inhibitor of spermidine (SPD) synthase showed no effect on the distribution of cells. The endogenous levels of the PAs, putrescine (PUT), SPD, and spermine (SPM), were determined during the cell cycle in synchronous cultures of C. roseus. Two peaks of endogenous level of PAs, in particular, of PUT and SPD, were observed during the cell cycle. Levels of PAs increased markedly prior to synthesis of DNA in the S phase and prior to cytokinesis. Activities of ADC and ODC were also assayed during the cell cycle. Activities of ADC was much higher than that of ODC throughout the cell cycle, but both activities of ODC and ADC changed in concert with changes in levels of PAs. Therefore, it is suggested that these enzymes may regulate PA levels during the cell cycle. These results indicate that inhibitors of PUT biosynthesis caused the suppression of cell proliferation by prevention of the progression of the cell cycle, probably from the G(1) to the S phase, and PUT may play more important roles in the progression of the cell cycle than other PAs.

Polyamine Metabolism in Ripening Tomato Fruit : II. Polyamine Metabolism and Synthesis in Relation to Enhanced Putrescine Content and Storage Life of a/c Tomato Fruit

The fruit of the Alcobaca landrace of tomato (Lycopersicon esculentum Mill.) have prolonged keeping qualities (determined by the allele a/c) and contain three times as much putrescine as the standard Rutgers variety (A/c) at the ripe stage (ARG Dibble, PJ Davies, MA Mutschler [1988] Plant Physiol 86: 338-340). Polyamine metabolism and biosynthesis were compared in fruit from Rutgers and Rutgers-a/c-a near isogenic line possessing the allele a/c, at four different stages of ripening. The levels of soluble polyamine conjugates as well as wall bound polyamines in the pericarp tissue and jelly were very low or nondetectable in both genotypes. The increase in putrescine content in a/c pericarp is not related to normal ripening as it occurred with time and whether or not the fruit ripened. Pericarp discs of both normal and a/c fruit showed a decrease in the metabolism of [1,4-(14)C]putrescine and [terminal labeled-(3)H]spermidine with ripening, but there were no significant differences between the two genotypes. The activity of ornithine decarboxylase was similar in the fruit pericarp of the two lines. Arginine decarboxylase activity decreased during ripening in Rutgers but decreased and rose again in Rutgers-a/c fruit, and as a result it was significantly higher in a/c fruit than in the normal fruit at the ripe stage. The elevated putrescine levels in a/c fruit appear, therefore, to be due to an increase in the activity of arginine decarboxylase.

Analysis of a cDNA encoding arginine decarboxylase from oat reveals similarity to the Escherichia coli arginine decarboxylase and evidence of protein processing

Arginine decarboxylase is the first enzyme in one of the two pathways of putrescine synthesis in plants. We purified arginine decarboxylase from oat leaves, obtained N-terminal amino acid sequence, and then used this information to isolate a cDNA encoding oat arginine decarboxylase. Comparison of the derived amino acid sequence with that of the arginine decarboxylase gene from Escherichia coli reveals several regions of sequence similarity which may play a role in enzyme function. The open reading frame (ORF) in the oat cDNA encodes a 66 kDa protein, but the arginine decarboxylase polypeptide that we purified has an apparent molecular weight of 24 kDa and is encoded in the carboxyl-terminal region of the ORF. A portion of the cDNA encoding this region was expressed in E. coli, and a polyclonal antibody was developed against the expressed polypeptide. The antibody detects 34 kDa and 24 kDa polypeptides on Western blots of oat leaf samples. Maturation of arginine decarboxylase in oats appears to include processing of a precursor protein.

Polyamines in plant physiology

The diamine putrescine, the triamine spermidine, and the tetramine spermine are ubiquitous in plant cells, while other polyamines are of more limited occurrence. Their chemistry and pathways of biosynthesis and metabolism are well characterized. They occur in the free form as cations, but are often conjugated to small molecules like phenolic acids and also to various macromolecules. Their titer varies from approximately micromolar to more than millimolar, and depends greatly on environmental conditions, especially stress. In cereals, the activity of one of the major polyamine biosynthetic enzymes, arginine decarboxylase, is rapidly and dramatically increased by almost every studied external stress, leading to 50-fold or greater increases in putrescine titer within a few hours. The physiological significance of this increase is not yet clear, although most recent work suggests an adaptive, protective role. Polyamines produced through the action of ornithine decarboxylase, by contrast, seem essential for DNA replication and cell division. The application of exogenous polyamines produces effects on patterns of senescence and morphogenesis, suggesting but not proving a regulatory role for polyamines in these processes. The evidence for such a regulatory role is growing.

Polyamines and Flower Development in the Male Sterile Stamenless-2 Mutant of Tomato (Lycopersicon esculentum Mill.) : II. Effects of Polyamines and Their Biosynthetic Inhibitors on the Development of Normal and Mutant Floral Buds Cultured in Vitro

The floral organs of the male sterile stamenless-2 (sl-2/sl-2) mutant of tomato (Lycopersicon esculentum Mill.) contain significantly higher level of polyamines than those of the normal (R Rastogi, VK Sawhney [1990] Plant Physiol 93: 439-445). The effects of putrescine, spermidine and spermine, and three different inhibitors of polyamine biosynthesis on the in vitro development of floral buds of the normal and sl-2/sl-2 mutant were studied. The polyamines were inhibitory to the in vitro growth and development of both the normal and mutant floral buds and they induced abnormal stamen development in normal flowers. The inhibitors of polyamine biosynthesis also inhibited the growth and development of floral organs of the two genotypes, but the normal flowers showed greater sensitivity than the mutant. The inhibitors also promoted the formation of normal-looking pollen in stamens of some mutant flowers. The effect of the inhibitors on polyamine levels was not determined. The polyamine-induced abnormal stamen development in the normal, and the inhibitor-induced production of normal-looking pollen in mutant flowers support the suggestion that the elevated polyamine levels contribute to abnormal stamen development in the sl-2/sl-2 mutant of tomato.

Polyamines and Flower Development in the Male Sterile Stamenless-2 Mutant of Tomato (Lycopersicon esculentum Mill.) : I. Level of Polyamines and Their Biosynthesis in Normal and Mutant Flowers

The levels of free putrescine, spermidine, and spermine, and the activities of ornithine decarboxylase and s-adenosylmethionine decarboxylase were determined in the floral organs of the normal and a male sterile stamenless-2 (sl-2/sl-2) mutant of tomato (Lycopersicon esculentum Mill.). Under the intermediate temperature regime, all mutant floral organs possessed significantly higher levels of polyamines and enzyme activities than their normal counterparts. In the low temperature-reverted mutant stamens, the polyamine levels and the activity of PA biosynthetic enzymes were not significantly different from the normal. It is suggested that the abnormal stamen development in the sl-2/sl-2 mutant is, in part, related to elevated levels of endogenous PAs.

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.

Polyamine synthesis in maize cell lines

Uptake of [(14)C]putrescine, [(14)C]arginine, and [(14)C]ornithine was measured in five separate callus cell lines of Zea mays. Each precursor was rapidly taken into the intracellular pool in each culture where, on the average, 25 to 50% of the total putrescine was found in a conjugated form, detected after acid hydrolysis. Half-maximal labeling of each culture was achieved in less than 1 minute. Within this time frame of precursor incorporation, only putrescine derived from arginine was conjugated, indicating that putrescine pools derived from arginine may initially be sequestered from ornithine-derived putrescine. The decarboxylase activities were measured in each culture after addition of exogenous polyamine to the growth medium to assess differential regulation of the decarboxylases. Arginine and ornithine decarboxylase activities were augmented by added polyamine, the effect on arginine decarboxylase being eightfold greater than on ornithine decarboxylase. Levels of extractable ornithine decarboxylase were consistently 15- to 100-fold higher than arginine decarboxylase, depending on the titer of extracellular polyamine. Taken as whole the results support the idea that there are distinct populations of polyamine that are initially sequestered after the decarboxylase reactions and that give rise to separate end products and possibly have separate functions.

Phytochrome-Mediated Control of Diamine Oxidase Level in the Epicotyl of Etiolated Lentil (Lens culinaris Medicus) Seedlings

Diamine oxidase (DAO; EC 1.4.3.6) levels are strongly reduced in epicotyls of 3-day-old etiolated lentil (Lens culinaris Medicus) seedlings upon exposure to continuous red and blue light, as compared to etiolated controls. Far-red light inhibits DAO activity to a lesser extent. A less marked effect can also be obtained by short (5-10 min) daily exposures. Phytochrome involvement in this light-mediated response has been demonstrated by red/far-red reversibility experiments. These findings provide the first evidence that mechanisms underlying the photoregulation of DAO level in the Leguminosae are related to photomorphogenesis and are essentially unrelated to the photosynthetic capacity of the seedling.

Interrelationship of Polyamine and Ethylene Biosynthesis during Avocado Fruit Development and Ripening

Concentrations of polyamines (PA) and the activities of the PA-synthesizing enzymes ornithine decarboxylase (ODC) and arginine decarboxylase (ADC) extracted from the mesocarp tissue of avocado (Persea americana Mill, cv ;Simmonds') fruits at different stages of development were compared with DNA content and the activities of 5'-methylthioadenosine (MTA) nucleosidase and 5-methylthioribose (MTR) kinase. Putrescine, spermidine, and spermine were at their peak concentrations during the early stages of fruit development (362, 201, and 165 nanomoles per gram fresh weight, respectively, at 15 days from full bloom), then declined to 30% or less at full maturity. Agmatine showed only a slight change in concentration throughout the fruit development. The activity of ODC, which was low during flowering (8 nmoles per milligram protein per hour), increased more than threefold during the first 2 months then declined at the later stages of fruit development, while ADC activity showed only a slight increase. DNA content followed a similar pattern of change as that of PA and ODC. The decline in DNA and ODC activity suggest a lack of correlation between cell proliferation and PA at the later stages of the avocado fruit development. It is also possible that any cell division which may take place during the latter stages of the fruit development is not sufficient to alter the pattern of PA biosynthesis. MTA nucleosidase and MTR kinase activities increased during the first 15 days of fruit development followed by a slight decline at 60 and 90 days from full bloom. At 120 days (1 month before full maturity) both MTA nucleosidase and MTR kinase activities increased significantly. During maximum ethylene synthesis, MTA nucleosidase and MTR kinase activities were approximately fivefold and eightfold, respectively, higher than during maximum PA synthesis. The data indicate that the MTA molecules produced during PA and ethylene synthesis are actively metabolized to MTR and MTR-1-P, the two intermediates involved in the regeneration of S-adenosylmethionine from MTA. The data also suggest that the PA and ethylene biosynthetic pathways are not actively competing for the same substrates at any given stage of the avocado fruit development and ripening.

Polyamine content of long-keeping alcobaca tomato fruit

Fruit of tomato landrace Alcobaca, containing the recessive allele alc, ripen more slowly, with a reduced level of ethylene production, and have prolonged keeping qualities. The levels of polyamines in pericarp tissues of alc and ;wild type' Alc (cv Rutgers and Alcobaca-red) fruit were measured by HPLC in relation to ripening. Putrescine was the predominant polyamine with a lower content of spermidine, while spermine was just detectable. The level of putrescine was high at the immature green stage and declined in the mature green stage. In Alc fruit the decline persisted but in alc fruit the putrescine level increased during ripening to a level similar to that present at the immature green stage. There was no pronounced change or difference in spermidine levels. The enhanced polyamine level in alc fruit may account for their ripening and storage characteristics.

Effect of polyamine biosynthetic inhibitors on alkaloids and organogenesis in tobacco callus cultures

We studied the effects of inhibitors of ornithine decarboxylase (ODC), arginine decarboxylase (ADC) and spermidine synthase (Spd synthase) on organogenesis and the titers of polyamines (PA) and alkaloids in tobacco calli. DL-alpha-diffluromethylarginine (DFMA) and D-arginine (D-Arg), both inhibitors of ADC activity, were more effective than DL-alpha-difluromethylorinithine (DFMO), an inhibitor of ODC, in reducing titers of PA and the putrescine (Put)-derived alkaloids (nornicotine and nicotine). Dicyclohexylammonium sulfate (DCHA), an inhibitor of Spd synthase, was also more efficient than DFMO in reducing PA and alkaloid levels. Root organogenesis is inversely related to the titers of Put and alkaloids. Thus, DFMA and D-Arg, which strongly inhibit Put and alkaloid biosynthesis, markedly promote root organogenesis, while control callus with high Put and alkaloid content showed poor root organization. These results suggest that morphological differentiation is not required for activation of secondary metabolic pathways and support the view that ADC has a major role in the generation of Put going to the pyrrolidine ring of tobacco alkaloids.

Changes in Amines and Biosynthetic Enzyme Activities in p-Fluorophenylalanine Resistant and Wild Type Tobacco Cell Cultures

The levels of free amines and the activities of their biosynthetic enzymes were measured in a p-fluorophenylalanine resistant Nicotiana tabacum L. cv Xanthi cell line (TX4) which accumulates high levels of cinnamoylamides, and a wild type cell line (TX1). Putrescine in TX1 and spermidine in TX1 and TX4 increased 4-fold by day 4 but declined by day 8 of the culture period. Spermine levels were consistently low, while tyramine was not found in TX1 until day 9 when a gradual rise was noted. Ornithine decarboxylase activity in TX1 and TX4 increased slightly through day 2 but declined gradually thereafter. S-Adenosylmethionine decarboxylase activity remained low throughout the culture period, and tyrosine and arginine decarboxylases in TX1 were very low in activity. In contrast, the activities of tyrosine and arginine decarboxylases were elevated in TX4, but a 3-fold increase in tyramine after a subculture was not accompanied by a rise in tyrosine decarboxylase. However, tyrosine decarboxylase activity did increase during a second rise in tyramine levels in aging cells, late in the culture period. Although significant differences exist in amine levels, between TX4 and TX1, it is unclear how altered amine metabolism relates to p-fluorophenylalanine resistance.

Control by ethylene of arginine decarboxylase activity in pea seedlings and its implication for hormonal regulation of plant growth

Activity of arginine decarboxylase in etiolated pea seedlings appears 24 hours after seed imbibition, reaches its highest level on the 4th day, and levels off until the 7th day. This activity was found in the apical and subapical tissue of the roots and shoots where intensive DNA synthesis occurs. Exposure of the seedlings to ethylene greatly reduced the specific activity of this enzyme. The inhibition was observed within 30 min of the hormone application, and maximal effect-90% inhibition-after 18 hours. Ethylene at physiological concentrations affected the enzyme activity; 50% inhibitory rate was recorded at 0.12 microliters per liter ethylene and maximal response at 1.2 microliters per liter. Ethylene provoked a 5-fold increase in the K(m) (app) of arginine decarboxylase for its substrate and reduced the V(max) (app) by 10-fold. However, the enzyme recovered from the inhibition and regained control activity 7 hours after transferral of the seedlings to ethylene-free atmosphere. Reducing the endogenous level of ethylene in the tissue by hypobaric pressure, or by exposure to light, as well as interfering with ethylene action by treatment with silver thiosulfate or 2,5-norbornadiene, caused a gradual increase in the specific activity of arginine decarboxylase in the apical tissue of the etiolated seedlings. On the basis of these findings, the possible control of arginine decarboxylase activity by endogenous ethylene, and its implication for the hormone effect on plant growth, are discussed.

Prevention of a plant disease by specific inhibition of fungal polyamine biosynthesis

DL-alpha-Difluoromethylornithine (DFMO), an inhibitor of the polyamine biosynthetic enzyme ornithine decarboxylase (EC 4.1.1.17), strongly retards the growth of several species of phytopathogenic fungi in vitro. Such inhibition can be completely reversed by putrescine or spermidine, confirming the essentiality of polyamines for growth of fungal hyphae. We now show that DFMO can protect bean plants (Phaseolus vulgaris Linnaeus cv. Pinto) against infection by uredospores of the bean rust fungus, Uromyces phaseoli Linnaeus, race O. Unifoliolate leaves of 10-day-old greenhouse-grown seedlings were sprayed with 400 microliter per leaf of DFMO at various concentrations in 0.01% Tween 20 at pH 7.0 before or after inoculation with uredospores of Uromyces. After 16 hr in darkness in dew chambers to facilitate spore germination, plants were transferred to the greenhouse, arranged randomly, and examined for local lesions 7 days later. All concentrations of DFMO 0.50 mM or higher gave complete protection against the pathogen; at lower concentrations, postinoculation treatments with DFMO were generally more effective than preinoculation. The appearance of lesions on plants treated with lower concentrations of DFMO was retarded 2-6 days. DFMO also confers protection on unsprayed parts of treated plants, indicating the translocation of some protective effect from sprayed areas. DL-alpha-Difluoromethylarginine, an analogous inhibitor of arginine decarboxylase (EC 4.1.1.19), which is the rate-limiting enzyme in an alternative pathway for polyamine biosynthesis in higher plants, confers no protection even at 5 mM. This emphasizes ornithine decarboxylase as the biochemical locus of choice for the prevention of plant diseases by inhibiting polyamine metabolism.

Assaying ornithine and arginine decarboxylases in some plant species

A release of (14)CO(2) not related to ornithine decarboxylase activity was found in crude leaf extracts from Lycopersicon esculentum, Avena sativa, and especially from the pyrrolizidine alkaloid-bearing Heliotropium angiospermum when incubated with [1-(14)C]- or [U-(14)C]ornithine. The total (14)CO(2) produced was about 5- to 100-fold higher than that due to ornithine decarboxylase activities calculated from labeled putrescine (Put) found by thin-layer electrophoresis in the incubation mixtures. Partial purification with (NH(4))(2)SO(4) did not eliminate completely the interfering decarboxylation. When incubated with labeled arginine, a very significant (14)CO(2) release not related to arginine decarboxylase activity was observed only in extracts from H. angiospermum leaves, especially in Tris.HCl buffer. Under the assay conditions, these extracts exhibited oxidative degradation of added Put and agmatine (Agm) and also revealed a high arginase activity. Amino-guanidine at 0.1 to 0.2 millimolar prevented Put degradation and greatly decreased oxidative degradation of Agm; ornithine at 15 to 20 millimolar significantly inhibited arginase activity. A verification of the reliability of the standard (14)CO(2)-based method by assessing labeled Put and/or Agm-formed in the presence of added aminoguanidine and/or ornithine when needed-is recommended especially when crude or semicrude plant extracts are assayed.When based on Put and/or Agm formed at 1.0 to 2.5 millimolar of substrate, the activities of ornithine decarboxylase and arginine decarboxylase in the youngest leaves of the tested species ranged between 1.1 and 3.6 and 1 and 1600 nanomoles per hour per gram fresh weight, respectively. The enzyme activities are discussed in relation to the biosynthesis of pyrrolizidine alkaloids.

Activities of arginine and ornithine decarboxylases in various plant species

In extracts from the youngest leaves of Avena sativa, Hordeum vulgare, Zea Mays, Pisum sativum, Phaseolus vulgaris, Lactuca sativa, and four pyrrolizidine alkaloid-bearing species of Heliotropium, the activities of ornithine decarboxylase, close to V(max), ranged between traces and 1.5 nanomoles per hour per gram fresh weight when based on putrescine formed during incubation with labeled ornithine. The arginine decarboxylase activities in the same extracts ranged between 8 and 8000 nanomoles per hour per gram fresh weight being lowest in the borages and highest in oat and barley. alpha-Difluoromethylornithine and alpha-difluoromethylarginine inhibited ornithine and arginine decarboxylases, respectively, in all species. Agmatine, putrescine, spermidine, and spermine were found in all, diaminopropane in eight, and cadaverine in three species.No correlation was observed between arginine or ornithine decarboxylase level and the levels of total polyamines. The in vitro decarboxylase activities found in the borages cannot explain the high accumulation of putrescine-derived pyrrolizidines in their youngest leaves if the pyrrolizidines are produced in situ from arginine and/or ornithine as precursors; other possibilities are discussed.In assays of ornithine decarboxylase, an interference of decarboxylation not due to this enzyme was observed in extracts from all species. In arginine decarboxylase assays, the interfering decarboxylation as well as the interference of arginase were apparent in two species. Addition of aminoguanidine was needed to suppress oxidative degradation of putrescine and agmatine during incubation of extracts from pea, bean, lettuce, Heliotropium angiospermum, and Heliotropium indicum.

Polyamine levels as related to growth, differentiation and senescence in protoplast-derived cultures of Vigna aconitifolia and Avena sativa

We have previously reported that aseptically cultured mesophyll protoplasts of Vigna divide rapidly and regenerate into complete plants, while mesophyll protoplasts of Avena divide only sporadically and senesce rapidly after isolation. We measured polyamine titers in such cultures of Vigna and Avena, to study possible correlations between polyamines and cellular behavior. We also deliberately altered polyamine titer by the use of selective inhibitors of polyamine biosynthesis, noting the effects on internal polyamine titer, cell division activity and regenerative events. In Vigna cultures, levels of free and bound putrescine and spermidine increased dramatically as cell division and differentiation progressed. The increase in bound polyamines was largest in embryoid-forming callus tissue while free polyamine titer was highest in root-forming callus. In Avena cultures, the levels of total polyamines decreased as the protoplast senesced. The presence of the inhibitors alpha-difluoromethyl-arginine (specific inhibitor of arginine decarboxylase), alpha-difluoromethylornithine (specific inhibitor of ornithine decarboxylase) and dicyclohexylamine (inhibitor of spermidine synthase) reduced cell division and organogenesis in Vigna cultures. Addition of low concentration of polyamines to such cultures containing inhibitors or removal of inhibitors from the culture medium restored the progress of growth and differentiation with concomitant increase in polyamine levels.

Changes in polyamine biosynthesis associated with postfertilization growth and development in tobacco ovary tissues

Polyamine (PA) titers and the activities of arginine decarboxylase (ADC, EC 4.1.1.19) and ornithine decarboxylase (ODC, EC 4.1.1.17), enzymes which catalyze rate-limiting steps in PA biosynthesis, were monitored during tobacco ovary maturation. In the period between anthesis and fertilization, the protein content of ovary tissues rapidly increased by about 40% and was accompanied by approximately a 3-fold increase in ODC activity, while ADC activity remained nearly constant. PA titers also remained relatively unchanged until fertilization, at which time they increased dramatically and the DNA content of ovary tissues doubled. This increase in PA biosynthesis was correlated with a further 3-fold increase in ODC activity, reaching a maximum 3 to 4 days after fertilization. During this time, ADC activity increased only slightly and accounted for approximately 1% of the total decarboxylase activity when ODC activity peaked. The postfertilization burst of biosynthetic activities slightly preceded a period of rapid ovary enlargement, presumably due to new cell division. During later stages of ovary development, DNA levels fell precipitously, while PA titers and decarboxylase activities decreased to preanthesis levels more slowly. In this period, growth producing a 300% increase in ovary fresh weight appears to be the result of cell enlargement. Synchronous changes in PA titers and in the rates of PA biosynthesis, macromolecular synthesis, and growth in the tobacco ovary suggest that PAs may play a role in the regulation of postfertilization growth and development of this reproductive organ.