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

Purification and characterization of tomato arginine decarboxylase and its inhibition by the bacterial small molecule phevamine A

Polyamines play essential roles in plant growth and survival. Arginine decarboxylase (ADC), which converts arginine to agmatine, catalyzes the first step in polyamine biosynthesis from arginine. However, few biochemical studies with purified plant ADCs have been conducted to evaluate their catalytic efficiency. Tomato genome encodes two arginine decarboxylases: SlADC1 and SlADC2, which are critical for growth, development, and immune responses against bacterial pathogens. We expressed and purified soluble SlADC1 as a recombinant protein fused with maltose-binding protein tag from E. coli Rosetta 2(DE3) cells. Using the purified fusion protein, we characterized the biochemical properties of SlADC1 in vitro and explored it as a target of the bacterial small molecule phevamine A. We confirmed that the activity of SlADC1 depends on the cofactor pyridoxal 5'-phosphate. SlADC1 is specific toward l-arginine and its kinetic parameters were measured using a liquid chromatography-mass spectrometry method. Phevamine A is a competitive inhibitor of SlADC1 and reduces the activity of SlADC1 at high micromolar concentrations. Our purification and biochemical characterization of SlADC1 sets the stage for inhibition studies of this enzyme.

Endophytic bacterium Bacillus aryabhattai induces novel transcriptomic changes to stimulate plant growth

In nature, plants interact with a wide range of microorganisms, and most of these microorganisms could induce growth through the activation of important molecular pathways. The current study evaluated whether the endophytic bacterium Bacillus aryabhattai encourages plant growth and the transcriptional changes that might be implicated in this effect. The endophytic bacterium promotes the growth of Arabidopsis and tobacco plants. The transcriptional changes in Arabidopsis plants treated with the bacterium were also identified, and the results showed that various genes, such as cinnamyl alcohol dehydrogenase, apyrase, thioredoxin H8, benzaldehyde dehydrogenase, indoleacetaldoxime dehydratase, berberine bridge enzyme-like and gibberellin-regulated protein, were highly expressed. Also, endophytic bacterial genes, such as arginine decarboxylase, D-hydantoinase, ATP synthase gamma chain and 2-hydroxyhexa-2,4-dienoate hydratase, were activated during the interaction. These findings demonstrate that the expression of novel plant growth-related genes is induced by interaction with the endophytic bacterium B. aryabhattai and that these changes may promote plant growth in sustainable agriculture.

Boosting Polyamines to Enhance Shoot Regeneration in Potato (Solanum tuberosum L.) Using AgNO3

Advancements in shoot regeneration systems support biotechnology-based tools used in the genetic improvement of plant crops. This study aims to enhance shoot regeneration in potatoes by boosting polyamine content by adding AgNO3 to the shoot regeneration medium (MS medium supplemented with 30 g L−1 sucrose, 100 mg L−1 myoinositol, and 2.25 BA mg L−1). Five concentrations of AgNO3 (2, 4, 6, 8, and 10 mg L−1) were used in addition to a control. The effect of AgNO3 on regeneration assumed a more or less concentration-dependent bell-shaped curve peaking at 4 mg L−1. Enhancements in shoot regeneration were attributed to the known role of AgNO3 as an ethylene action blocker in addition to improvements in polyamine accumulation without an increase in H2O2 content, lipid peroxidation, or DNA damage. The uncoupling of shoot regeneration and polyamine content recorded at high AgNO3 concentrations can be attributed to the consumption of polyamines to counteract the synchronized oxidative stress manifested by increases in H2O2 content, lipid peroxidation, and DNA damage.

Plant growth promotion by spermidine-producing Bacillus subtilis OKB105

The interaction between plants and plant-growth-promoting rhizobacteria (PGPR) is a complex, reciprocal process. On the one hand, plant compounds such as carbohydrates and amino acids serve as energy sources for PGPR. On the other hand, PGPR promote plant growth by synthesizing plant hormones and increasing mineral availability in the soil. Here, we evaluated the growth-promoting activity of Bacillus subtilis OKB105 and identified genes associated with this activity. The genes yecA (encoding a putative amino acid/polyamine permease) and speB (encoding agmatinase) are involved in the secretion or synthesis of polyamine in B. subtilis OKB105. Disruption of either gene abolished the growth-promoting activity of the bacterium, which was restored when polyamine synthesis was complemented. Moreover, high-performance liquid chromatography analysis of culture filtrates of OKB105 and its derivatives demonstrated that spermidine, a common polyamine, is the pivotal plant-growth-promoting compound. In addition, real-time polymerase chain reaction analysis revealed that treatment with B. subtilis OKB105 induced expansin gene (Nt-EXPA1 and Nt-EXPA2) expression and inhibited the expression of the ethylene biosynthesis gene ACO1. Furthermore, enzyme-linked immunosorbent assay analysis showed that the ethylene content in plant root cells decreased in response to spermidine produced by OKB105. Therefore, during plant interactions, OKB105 may produce and secrete spermidine, which induces expansin production and lowers ethylene levels.

Enhanced flux of substrates into polyamine biosynthesis but not ethylene in tomato fruit engineered with yeast S-adenosylmethionine decarboxylase gene

S-adenosylmethionine (SAM), a major substrate in 1-C metabolism is a common precursor in the biosynthetic pathways of polyamines and ethylene, two important plant growth regulators, which exhibit opposing developmental effects, especially during fruit ripening. However, the flux of various substrates including SAM into the two competing pathways in plants has not yet been characterized. We used radiolabeled (14)C-Arg, (14)C-Orn, L-[U-(14)C]Met, (14)C-SAM and (14)C-Put to quantify flux through these pathways in tomato fruit and evaluate the effects of perturbing these pathways via transgenic expression of a yeast SAM decarboxylase (ySAMDC) gene using the fruit ripening-specific promoter E8. We show that polyamines in tomato fruit are synthesized both from Arg and Orn; however, the relative contribution of Orn pathway declines in the later stages of ripening. Expression of ySAMDC reversed the ripening associated decline in spermidine (Spd) and spermine (Spm) levels observed in the azygous control fruit. About 2- to 3-fold higher levels of labeled-Spd in transgenic fruit (556HO and 579HO lines) expressing ySAMDC confirmed the enzymatic function of the introduced gene. The incorporation of L-[U-(14)C]Met into Spd, Spm, ethylene and 1-aminocyclopropane-1-carboxylic acid (ACC) was used to determine Met-flux into these metabolites. The incorporation of (14)C-Met into Spd/Spm declined during ripening of the control azygous fruit but this was reversed in fruits expressing ySAMDC. However, incorporation of (14)C-Met into ethylene or ACC during ripening was not altered by the expression of ySAMDC in the fruit. Taken together these results show that: (1) There is an inverse relationship between the production of higher polyamines and ethylene during fruit ripening, (2) the inverse relationship between higher polyamines and ethylene is modulated by ySAMDC expression in that the decline in Spd/Spm during fruit ripening can be reversed without significantly altering ethylene biosynthesis, and (3) cellular flux of SAM in plants is homeostatically regulated based on its demand for competing pathways.

Cadaverine: a lysine catabolite involved in plant growth and development

The cadaverine (Cad) a diamine, imino compound produced as a lysine catabolite is also implicated in growth and development of plants depending on environmental condition. This lysine catabolism is catalyzed by lysine decarboxylase, which is developmentally regulated. However, the limited role of Cad in plants is reported, this review is tempted to focus the metabolism and its regulation, transport and responses, interaction and cross talks in higher plants. The Cad varied presence in plant parts/products suggests it as a potential candidate for taxonomic marker as well as for commercial exploitation along with growth and development.

Polyamines under Abiotic Stress: Metabolic Crossroads and Hormonal Crosstalks in Plants

Polyamines are essential compounds for cell survival and have key roles in plant stress protection. Current evidence points to the occurrence of intricate cross-talks between polyamines, stress hormones and other metabolic pathways required for their function. In this review we integrate the polyamine metabolic pathway in the context of its immediate metabolic network which is required to understand the multiple ways by which polyamines can maintain their homeostasis and participate in plant stress responses.

Nitrate supply induces changes in polyamine content and ethylene production in wheat plants grown with ammonium

In order to explore the mechanisms of nitrate's beneficial effect on ammonium-grown plants, we investigated the effects of nitrate on free and conjugated polyamine plant content and ethylene biosynthesis in wheat (Triticum aestivum L.) plants grown with ammonium nutrition. Two different doses of nitrate (100 microM and 5 mM) were supplied to ammonium-fed plants, in order to determine whether the effects of nitrate require significant doses (nutritional character), or can be promoted by very low doses (pseudo-hormonal character). Our results showed that nitrate's effects on putrescine, spermidine and spermine contents of ammonium-grown plants tended to follow the pattern associated with strict nitrate nutrition. Both low (100 microM) and high (5 mM) nitrate doses caused a rapid and significant increase in free spermidine content in roots and shoots, which was well correlated with reduced root ethylene production. In shoots, this increase in free spermidine was correlated with changes in the conjugation pattern, while in roots these changes appear to be due to alternative mechanisms. On the other hand, no clear relationship between the supply of a lower dose of nitrate (100 microM) and a reduction of free putrescine content was observed. With higher doses of nitrate (5 mM) we observed a reduction of free putrescine content that was well correlated with increases in its conjugated forms. In conclusion, nitrate's effects on putrescine, spermidine and spermine contents of ammonium-fed plants tended to follow the pattern associated with strict nitrate nutrition, corroborating its beneficial effect.

Ethylene biosynthesis and endogenous polyamines in relation to development of in vitro cultured kiwifruit explants

The relationship between polyamines and ethylene is controversial because the degree of interference of one pathway with the other may differ according to species, stage of development and experimental procedure. In this paper, we modify ethylene biosynthesis by the addition of aminoethoxyvinylglicine (AVG) or 1-aminocyclopropane-1-carboxylic acid (ACC) and study how it affects polyamine content and development of kiwifruit explants (Actinidia deliciosa CS Liang. & AR Fergusson). Cultured under ventilation where ethylene did not accumulate in the culture vessels, kiwi explants had higher ACC synthase activity and lower polyamine content than those grown without ventilation. In explants cultured in the reference medium, putrescine was the more abundant polyamine and spermine was only detected in the free fraction irrespective of ventilation. Under ventilation, addition of ACC to the culture medium inhibited organogenesis, there was less spermidine and spermine was not detected. Addition of AVG to the culture medium increased both the number of shoots and the amount of polyamines, and inhibited ACC synthase, so S-adenosylmethionine (SAM) led to increasing synthesis of spermidine and spermine. The increase in putrescine is more difficult to explain on the basis of inhibition of ethylene biosynthesis. The increase in the number of shoots in kiwi explants due to AVG addition may be attributed to the lack of ethylene in the atmosphere of the vessels or the increase in free polyamines.

Effect of end-of-day irradiations on polyamine accumulation in petal cultures of Araujia sericifera

We have studied photoperiodic control and the effect of phytochrome photoconversion at the end-of-day (EOD) on polyamine (PA) accumulation in petal explants of Araujia sericifera. Petals from immature flowers were cultured under long (LD) and short (SD) days. Light was provided by Gro-lux fluorescent lamps (90-100 &mgr;mol m-2 s-1). Red (R), far red (FR), red followed by far-red (R-FR) and far-red followed by red (FR-R) light treatments were applied daily at the end of the photoperiod. The free and bound putrescine (Put), spermidine (Spd) and spermine (Spm) fractions in petal explants were determined 40 days after the beginning of the culture. We also aimed to clarify the involvement of PA changes by using two inhibitors of PA biosynthesis: D-l-alpha-difluoromethylarginine (DFMA) and methylglyoxal bis(guanylhydrazone) (MGBG). We found PA accumulation to be under photoperiodic control, and the inhibitory effect of DFMA on this accumulation suggests that arginine decarboxylase (ADC) is the major pathway for Put biosynthesis. Polyamine levels were higher under LD, mainly as a result of the accumulation of free and bound Put. FR-EOD treatment, which dramatically reduced the R : FR ratio after LD, increased the accumulation of PA, mainly as free Put and free and bound Spd. Sequential R-FR and FR-R-EOD treatments strongly increased bound Spd. The concentration of MGBG used increased total PA accumulation, mainly as Put. However, all EOD light treatments dramatically reduced Put accumulation in the presence of MGBG. This may be due to a dual role of FR light in PA accumulation: (1) FR per se stimulates PA production, probably via ADC, and (2) in the presence of MGBG, FR inhibits Put accumulation, probably via ethylene production.

Hormonal regulation of S-adenosylmethionine synthase transcripts in pea ovaries

Two cDNA clones coding for S-adenosyl-L-methionine synthase (SAMs, EC 2.5.1.6) have been isolated from a cDNA library of gibberellic acid-treated unpollinated pea ovaries. Both cDNAs were sequenced showing a high degree of identity but coding for different SAMs polypeptides. The presence of two SAMs genes in pea was further confirmed by Southern analysis. Expression of the SAMs genes in the pea plant was found at different levels in vegetative and reproductive tissues. We characterized the expression levels of SAMs genes during the development or senescence of pea ovaries. Northern analysis showed that transcription of SAMs genes in parthenocarpic fruits was upregulated by auxins in the same manner as in fruits from pollinated ovaries. In both pollinated and 2,4-dichlorophenoxyacetic acid-treated ovaries, and benzyladenine, although able to induce parthenocarpic development, did not affect SAMs mRNA levels. These data are consistent with an active participation of auxins in the upregulation of SAMs during fruit setting in pea and suggest that, at the molecular level, parthenocarpic development of pea ovaries is different for gibberellin- and cytokinin-treated ovaries than for auxin-induced parthenocarpic biosynthesis since treatment of the ovaries with aminoethoxyvinylglycine resulted in a delay of senescence and prevention of SAMs mRNA accumulation. A possible mechanism for hormonal regulation of SAMs during ovary development is discussed.

Expression of a human S-adenosylmethionine decarboxylase cDNA in transgenic tobacco and its effects on polyamine biosynthesis

S-adenosylmethionine decarboxylase (SAMDC; EC 4.1.1.50) is a key regulatory enzyme in the polyamine biosynthetic pathway. Numerous studies have shown that the enzyme activity and polyamine levels are generally correlated with cellular growth in plants, animals and bacteria. In order to gain more insight into the role of polyamines in plants, human SAMDC cDNA under control of 35S promoter of cauliflower mosaic virus, along with a neomycin phosphotransferase gene, was transferred to tobacco (Nicotiana tabacum cv.Xanthi) via Agrobacterium tumefaciens. Transgenic plants showed the presence of SAMDC mRNA and a 2-4-fold increase in SAMDC activity. In the transformed tissues, putrescine levels were significantly reduced, while spermidine content was 2-3 times higher than the control tissues. Cellular spermine content was either increased or remained unchanged. Excised leaf segments from transformed plants frequently produced shoots even on callus inducing medium.

Ethylene-Induced Polyamine Accumulation in Rice (Oryza sativa L.) Coleoptiles

Effects of ethylene on free polyamine biosynthesis in rice (Oryza sativa L. cv Taichung Native 1) coleoptiles were investigated in sealed and aerobic conditions. In sealed conditions, putrescine increased significantly and coincided with ethylene accumulation. Application of ethylene in sealed containers promoted putrescine accumulation over that in sealed controls. This ethylene-enhanced putrescine accumulation was inhibited by the ethylene action inhibitor 2,5-norbornadiene at 4000 muL/L. In aerobic conditions, ethylene and 1-aminocyclopropane-1-carboxylic acid also induced putrescine accumulation. Activity of arginine decarboxylase (EC 4.1.1.19) and S-adenosylmethionine decarboxylase (EC 4.1.1.50) increased on exposure to ethylene in aerobic conditions. Ornithine decarboxylase (EC 4.1.1.17) activity, however, remained unchanged. The ethylene-induced putrescine accumulation was inhibited by 5 x 10(-4)m alpha-difluromethylarginine, but not by 5 x 10(-4)m alpha-difluromethylornithine. Apparently, arginine decarboxylase, not ornithine decarboxylase, mediates the ethylene-induced putrescine accumulation. The increased S-adenosylmethioinine decarboxylase activity, however, did not result in a significant spermidine/spermine accumulation. In ethylene-treated coleoptiles, the accumulation of putrescine paralleled the increase of coleoptile length in both sealed and aerobic conditions. alpha-difluromethylarginine inhibited ethylene induced putrescine accumulation and coleoptile elongation. It seems that putrescine biosynthesis might be involved in the ethylene-induced elongation of rice coleoptiles.

Accumulation of wound-inducible ACC synthase transcript in tomato fruit is inhibited by salicylic acid and polyamines

Regulation of wound-inducible 1-aminocyclopropane-1-carboxylic acid (ACC) synthase expression was studied in tomato fruit (Lycopersicon esculentum cv. Pik-Red). A 70 base oligonucleotide probe homologous to published ACC synthase cDNA sequences was successfully used to identify and analyze regulation of a wound-inducible transcript. The 1.8 kb ACC synthase transcript increased upon wounding the fruit as well as during fruit ripening. Salicylic acid, an inhibitor of wound-responsive genes in tomato, inhibited the wound-induced accumulation of the ACC synthase transcript. Further, polyamines (putrescine, spermidine and spermine) that have anti-senescence properties and have been shown to inhibit the development of ACC synthase activity, inhibited the accumulation of the wound-inducible ACC synthase transcript. The inhibition by spermine was greater than that caused by putrescine or spermidine. The transcript level of a wound-repressible glycine-rich protein gene and that of the constitutively expressed rRNA were not affected as markedly by either salicylic acid or polyamines. These data suggest that salicylic acid and polyamines may specifically regulate ethylene biosynthesis at the level of ACC synthase transcript accumulation.

Polyamines in plants infected by citrus exocortis viroid or treated with silver ions and ethephon

The levels of polyamines in leaves of Gynura aurantiaca DC and tomato, Lycopersicon esculentum Mill. cv Rutgers, infected with citrus exocortis viroid (CEVd) or treated with silver nitrate or ethephon (2-chloroethylphosphonic acid) were measured by HPLC in relation to development of symptoms. Previously it had been demonstrated that treatment of G. aurantiaca plants with silver nitrate or ethephon closely mimicked the effects of viroid infection in the plants. In the studies reported here, a marked decrease in putrescine level was observed in plants infected by CEVd or treated with silver ions or ethephon. There was no significant change in either spermidine or spermine levels. Treatment of G. aurantiaca plants with specific inhibitors of ethylene biosynthesis (aminoethoxyvinylglycine, Co(2+)) or ethylene action (norbornadiene) prevented the decrease of putrescine associated with silver nitrate treatment and had no effect on spermidine or spermine levels. The development of viroid-like symptoms, the production of associated pathogenesis-related proteins, and the rise in protease activity induced by silver nitrate, were all suppressed by exogenous application of putrescine. The decreased level of putrescine as an ethylene-mediated step in the transduction of the viroid and silver or ethephon signaling is discussed.

Polyamine levels and tomato fruit development: possible interaction with ethylene

Fruits of tomato, Lycopersicon esculentum Mill. cv Liberty, ripen slowly and have a prolonged keeping quality. Ethylene production and the levels of polyamines in pericarp of cv Liberty, Pik Red, and Rutgers were measured in relation to fruit development. Depending on the stage of fruit development, Liberty produced between 16 and 38% of the ethylene produced by Pik Red and Rutgers. The polyamines putrescine, spermidine, and spermine were present in all cultivars. Cadaverine was detected only in Rutgers. Levels of putrescine and spermidine declined between the immature and mature green stages of development and prior to the onset of climacteric ethylene production. In Pik Red and Rutgers, the decline persisted, whereas in Liberty, the putrescine level increased during ripening. Ripe pericarp of Liberty contained about three and six times more free (unconjugated) polyamines than Pik Red and Rutgers, respectively. No pronounced changes in spermidine or cadaverine occurred during ripening. The increase in the free polyamine level in ripe pericarp of Liberty may account for the reduction of climacteric ethylene production, and prolonged storage life.

Changes in Two Forms of Membrane-Associated Cellulase during Ethylene-Induced Abscission

Only one form of membrane-associated cellulase was found previously in the lower petiolar pulvinus of Phaseolus vulgaris (cv Red Kidney). The cellulase has an isoelectric point (pI) of 4.5 (DE Koehler, LN Lewis 1979 Plant Physiol 63: 677-679). This enzyme was detected in abscission zones collected before the onset of abscission (control tissue), and was thought to represent a pre-secretory form of another cellulase, the abscission cellulase, which has a basic pI and is secreted during abscission. We now show that this acidic, membrane-associated cellulase is a glycoprotein, tightly bound to the membrane, with maximum activity at pH 5.1, and that it is not immunologically related to the abscission cellulase. Furthermore, when bean explants are induced to abscise with ethylene, the activity of the acidic cellulase declines rapidly to 50% of control levels in the first day. When abscission is fully developed, the membranes contain a basic form of cellulase with a pI of 8.0 to 9.0 and only trace levels of the acidic cellulase. The basic form is not a high mannose glycoprotein; it has maximum activity in a broad pH range (4.0-8.0) and is antigenically related to the abscission cellulase, which is induced during abscission and transported to the cell wall. Antibody raised against the abscission cellulase recognized two proteins in a crude membrane fraction from abscising tissue. One of those proteins comigrated with the abscission cellulase, and the other was 1 to 2 kilodaltons larger. Thus, during abscission, the acidic membrane-associated cellulase rapidly declines before the appearance of the abscission cellulase. We conclude that there is no conversion from the acidic cellulase to the basic cellulase and suggest that the acidic and basic cellulase isoenzymes are proteins derived from two different genes.

Effect of l-aminocyclopropane-l-carboxylic acid, silver nitrate, and norbornadiene on plant regeneration from maize callus cultures

The effect of the ethylene antagonists norbornadiene and silver nitrate and the ethylene precursor l-aminocyclopropane-l-carboxylic acid (ACC) on Zea mays plant regeneration was studied. A 12-fold increase in plant regeneration, as measured by number of plants obtained per gram fresh weight from callus cultures of maize inbreds Pa91 and H99, was obtained by 250 μM norbornadiene and 100 μM silver nitrate treatments. An increase in amout of nonregenerable tissue and a 68% decrease in plant regeneration were associated with callus treated with 1 mM ACC. Ethylene emanation from 1 mM ACC treated callus reached a maximum of 170 nl g(-1) h(-1) after 3 days compared to 7 nl g(-1) h(-1) for the control. The free proline content was up to 80% lower in 1 mM ACC treated callus grown for 30 days on medium with or without 12 mM proline, respectively, as compared to each control. These studies indicate that ethylene action inhibitors such as norbornadiene and silver nitrate can be used to increase plant regeneration efficiency from maize callus cultures.

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.

The effect of submergence, ethylene and gibberellin on polyamines and their biosynthetic enzymes in deepwater-rice internodes

Submergence and treatment with ethylene or gibberellic acid (GA3) stimulates rapid growth in internodes of deepwater rice (Oryza sativa L. cv. "Habiganj Aman II"). This growth is based on greatly enhanced rate of cell-division activity in the intercalary meristem (IM) and on increased cell elongation. We chose polyamine biosynthesis as a biochemical marker for cell-division activity in the IM of rice stems. Upon submergence of the plant, the activity of S-adenosylmethionine decarboxylase (SAMDC; EC 4.1.1.50) in the IM increased six- to tenfold within 8 h; thereafter, SAMDC activity declined. Arginine decarboxylase (ADC; EC 4.1.1.19) showed a similar but less pronounced increase in activity. The activity of ornithine decarboxylase (ODC; EC 4.1.1.17) in the IM was not affected by submergence. The levels of putrescine and spermidine also rose in the IM of submerged, whole plants while the concentration of spermine remained low. The increase in SAMDC activity was localized in the IM while the activity of ADC rose both in the node and the IM above it. The node also contained low levels of ODC activity which increased slightly following submergence. Increased activities of polyamine-synthesizing enzymes in the nodal region of submerged plants probably resulted from the promotion of adventitious root formation in the node. Treatment of excised rice-stem sections with ethylene or GA3 enhanced the activities of SAMDC and ADC in the IM and inhibited the decline in the levels of putrescine and spermidine. We conclude that SAMDC and perhaps also ADC may serve as biochemical markers for the enhancement of cell-division activity in the IM of deepwater rice.

Inhibition by ethylene of polyamine biosynthetic enzymes enhanced lysine decarboxylase activity and cadaverine accumulation in pea seedlings

Exposing etiolated pea seedlings to ethylene which inhibited the activity of arginine decarboxylase and S-adenosylmethionine decarboxylase caused an increase in the level of cadaverine. The elevated level of cadaverine resulted from an increase in lysine decarboxylase activity in the tissue exposed to ethylene. The hormone did not affect the apparent K(m) of the enzyme, but the apparent V(max) was increased by 96%. While lysine decarboxylase activity in the ethylene-treated plants increased in both the meristematic and the elongation zone tissue, cadaverine accumulation was observed in the latter only. The enhancement by ethylene of the enzyme activity was reversed completely 24 hours after transferring the plants to an ethylene-free atmosphere. It is postulated that the increase in lysine decarboxylase activity, and the consequent accumulation of cadaverine in ethylene-treated plants, is of a compensatory nature as a response to the inhibition of arginine and S-adenosylmethionine decarboxylase activity provoked by ethylene.