Correlations between polyamine ratios and growth patterns in seedling roots

Arbuscular mycorrhiza induced putrescine degradation into γ-aminobutyric acid, malic acid accumulation, and improvement of nitrogen assimilation in roots of water-stressed maize plants

Water shortage limits plant growth and development by inducing physiological and metabolic disorders, while arbuscular mycorrhizal (AM) symbiosis can improve plant adaptation to drought stress by altering some metabolic and signaling pathways. In this study, root growth and levels of some metabolites (polyamines, amino acids, and malic acid [MA]) and key enzymes were examined in AM-inoculated and non-inoculated (NM) maize seedlings under different water conditions. The results showed that AM symbiosis stimulated root growth and the accumulation of putrescine (Put) during initial plant growth. Root Put concentration significantly decreased in AM compared with NM plants under water stress; correspondingly, Put degradation via diamine oxidase into γ-aminobutyric acid (GABA) occurred. Moreover, glutamine concentration and the activity of N assimilation enzymes (nitrate reductase and glutamine synthetase) were higher in roots of AM than NM plants under moderate water stress. The activity of GABA transaminase and malic enzyme, and MA concentration were also higher in roots of AM than NM plants under moderate water stress. Our results indicated that Put catabolism along with improved N assimilation and the accumulation of GABA and MA were the key metabolic processes in roots of AM maize plants in response to water stress.

Polyamines cause plasma membrane depolarization, activate Ca2+-, and modulate H+-ATPase pump activity in pea roots

Polyamines regulate a variety of cation and K(+) channels, but their potential effects on cation-transporting ATPases are underexplored. In this work, noninvasive microelectrode ion flux estimation and conventional microelectrode techniques were applied to study the effects of polyamines on Ca(2+) and H(+) transport and membrane potential in pea roots. Externally applied spermine or putrescine (1mM) equally activated eosin yellow (EY)-sensitive Ca(2+) pumping across the root epidermis and caused net H(+) influx or efflux. Proton influx induced by spermine was suppressed by EY, supporting the mechanism in which Ca(2+) pump imports 2 H(+) per each exported Ca(2+). Suppression of the Ca(2+) pump by EY diminished putrescine-induced net H(+) efflux instead of increasing it. Thus, activities of Ca(2+) and H(+) pumps were coupled, likely due to the H(+)-pump inhibition by intracellular Ca(2+). Additionally, spermine but not putrescine caused a direct inhibition of H(+) pumping in isolated plasma membrane vesicles. Spermine, spermidine, and putrescine (1mM) induced membrane depolarization by 70, 50, and 35 mV, respectively. Spermine-induced depolarization was abolished by cation transport blocker Gd(3+), was insensitive to anion channels' blocker niflumate, and was dependent on external Ca(2+). Further analysis showed that uptake of polyamines but not polyamine-induced cationic (K(+)+Ca(2+)+H(+)) fluxes were a main cause of membrane depolarization. Polyamine increase is a common component of plant stress responses. Activation of Ca(2+) efflux by polyamines and contrasting effects of polyamines on net H(+) fluxes and membrane potential can contribute to Ca(2+) signalling and modulate a variety of transport processes across the plasma membrane under stress.

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 interact with hydroxyl radicals in activating Ca(2+) and K(+) transport across the root epidermal plasma membranes

Reactive oxygen species (ROS) are integral components of the plant adaptive responses to environment. Importantly, ROS affect the intracellular Ca(2+) dynamics by activating a range of nonselective Ca(2+)-permeable channels in plasma membrane (PM). Using patch-clamp and noninvasive microelectrode ion flux measuring techniques, we have characterized ionic currents and net K(+) and Ca(2+) fluxes induced by hydroxyl radicals (OH(•)) in pea (Pisum sativum) roots. OH(•), but not hydrogen peroxide, activated a rapid Ca(2+) efflux and a more slowly developing net Ca(2+) influx concurrent with a net K(+) efflux. In isolated protoplasts, OH(•) evoked a nonselective current, with a time course and a steady-state magnitude similar to those for a K(+) efflux in intact roots. This current displayed a low ionic selectivity and was permeable to Ca(2+). Active OH(•)-induced Ca(2+) efflux in roots was suppressed by the PM Ca(2+) pump inhibitors eosine yellow and erythrosine B. The cation channel blockers gadolinium, nifedipine, and verapamil and the anionic channel blockers 5-nitro-2(3-phenylpropylamino)-benzoate and niflumate inhibited OH(•)-induced ionic currents in root protoplasts and K(+) efflux and Ca(2+) influx in roots. Contrary to expectations, polyamines (PAs) did not inhibit the OH(•)-induced cation fluxes. The net OH(•)-induced Ca(2+) efflux was largely prolonged in the presence of spermine, and all PAs tested (spermine, spermidine, and putrescine) accelerated and augmented the OH(•)-induced net K(+) efflux from roots. The latter effect was also observed in patch-clamp experiments on root protoplasts. We conclude that PAs interact with ROS to alter intracellular Ca(2+) homeostasis by modulating both Ca(2+) influx and efflux transport systems at the root cell PM.

Polyamines promote root elongation and growth by increasing root cell division in regenerated Virginia pine (Pinus virginiana Mill.) plantlets

Polyamines have been demonstrated to play an important role in adventitious root formation and development in plants. Here, we present a detailed analysis of influence of exogenously added polyamines on adventitious root development and its relationship to cold tolerance in Virginia pine (Pinus virginia Mill.). Our results demonstrated that polyamines putrescine (Put), spermidine (Spd), and spermine (Spm) at 0.001 mM improve rooting frequency and promote root elongation. Put, Spd, and Spm at 0.01-1 mM decrease rooting frequency and reduce root elongation root elongation. Measurements of diamine oxidase (DAO, EC 1.4.3.6) and polyamine oxidase (PAO, EC 1.4.3.4) activities showed that higher DAO and PAO enzyme activities were obtained when high concentrations of polyamines were applied and when plantlets were treated for 5-7 week at 4 degrees C and 16 degrees C. Survival rate of plantlets increased with the treatment of polyamines at low temperature. Polyamines increased mitotic index of cells in root tips of regenerated plantlet cultured on medium containing 0.001 microM Put, Spd, or Spm, but did not increase mitotic index in tissues of needle tips of the same plantlets. These results demonstrated that polyamines promote root elongation and growth by increasing root cell division in regenerated Virginia pine plantlets.

Effects of spermidine synthase overexpression on polyamine biosynthetic pathway in tobacco plants

Transgenic tobacco plants overexpressing the Datura stramonium spermidine synthase (EC 2.5.1.16) cDNA were produced in order to understand the role of this gene in the polyamine metabolism and in particular in affecting spermidine endogenous levels. All the analysed transgenic clones displayed a high Level of overexpression of the exogenous cDNA with respect to the endogenous spermidine synthase. No relationship was detected between the mRNA expression level of S-adenosylmethionine decarboxylase (SAMDC, EC 4.1.1.50), which did not change between the negative segregant control and the transgenic plants, and spermidine synthase, suggesting the existence of an independent regulatory mechanism for transcription of the two genes. The determination of enzyme activities indicated an increased spermidine synthase and S-adenosylmethionine decarboxylase activity, with the last being mainly recovered in the particulate fraction. ODC (ODC, EC 4.1.1.17) was the most active enzyme and its activity was equally distributed between the soluble and the particulate fraction, while ADC (ADC, EC 4.1.1.19) activity in the transgenic plants did not particularly change with respect to the controls. In comparison to the controls, the transformed plants displayed an increased spermidine to putrescine ratio in the majority of the clones assayed, white the total polyamine content remained almost unchanged. These findings suggest a high capacity of the transformed plants to tightly regulate polyamine endogenous levels and provide evidence that spermidine synthase is not a limiting step in the biosynthesis of polyamines.

Spermidine metabolism in parasitic protozoa--a comparison to the situation in prokaryotes, viruses, plants and fungi

Targeting polyamines of parasitic protozoa in chemotherapy has attracted attention because polyamines might reveal novel drug targets for antiparasite therapies (Müller et al. 2001). The biological function of the triamine spermidine in parasitic protozoa has not been studied in great detail although the results obtained mainly imply three different functions, i.e., cell proliferation, cell differentiation, and biosynthesis of macromolecules. Sequence information from the malaria genome project databases and inhibitor studies provide evidence that the current status of spermidine research has to be extended since enzymes of spermidine metabolism are present in the parasite (Kaiser et al. 2001). Isolation and characterisation of these enzymes, i.e., deoxyhypusine synthase (EC 1.1.1.249) (DHS) and homospermidine synthase (EC 2.5.1.44) (HSS) might lead to valuable new targets in drug therapy. Currently research on spermidine metabolism is based on the deposition of the deoxyhypusine synthase nucleic acid sequence in GenBank while the activity of homospermidine synthase was deduced from inhibitor studies. Spermidine biosynthesis is catalyzed by spermidine synthase (EC 2.5.1.16) which transfers an aminopropyl moiety from decarboxylated S-adenosylmethionine to putrescine. Spermidine is also an important precursor in the biosynthesis of the unusual amino acid hypusine (Wolff et al. 1995) and the uncommon triamine homospermidine in eukaryotes, in particular in pyrrolizidine alkaloid-producing plants (Ober and Hartmann 2000). Hypusine is formed by a two-step enzymatic mechanism starting with the transfer of an aminobutyl moiety from spermidine to the epsilon-amino group of one of the lysine residues in the precursor protein of eukaryotic initiation factor eIF5A by DHS (Lee and Park 2000). The second step of hypusinylation is completed by deoxyhypusine hydroxylase (EC 1.14.9929) (Abbruzzese et al. 1985). Homospermidine formation in eukaryotes parallels deoxyhypusine formation in the way that in an NAD(+)-dependent reaction an aminobutyl moiety is transferred from spermidine. In the case of homospermidine synthase, however the acceptor is putrescine. Thus the triamine homospermidine consists of two symmetric aminobutyl moieties while there is one aminobutyl and one aminopropyl moiety present in spermidine. Here, we review the metabolism of the triamine spermidine with particular focus on the biosynthesis of hypusine and homospermidine in parasitic protozoa, i.e., Plasmodium, Trypanosoma and Leishmania, compared to that in prokaryotes i.e., Escherichia coli, a phytopathogenic virus and pyrrolizidine alkaloid-producing plants (Asteraceae) and fungi.

Polyamine synthesis in plants: isolation and characterization of spermidine synthase from soybean (Glycine max) axes

Spermidine synthase (EC 2.5.1.16) was purified to homogeneity for the cytosol of soybean (Glycine max) axes using ammonium sulfate fractionation and chromatography on DEAE-Sephacel, Sephacryl S-300, omega-aminooctyl-Sepharose and ATPA-Sepharose. The molecular mass of the enzyme estimated by gel filtration and SDS-PAGE is 74 kDa. Cadaverin and 1,6-diaminohexane could not replace putrescine as the aminopropyl acceptor. Kinetic behaviors of the substrate are consistent with a ping pong mechanism. The kinetic mechanism is further supported by direct evidence confirming the presence of an aminopropylated enzyme and identification of product, 5'-deoxy-5'-methylthioadenosine, prior to adding putrescine. The Km values for decarboxylated S-adenosylmethionine and putrescine are 0.43 microM and 32.45 microM, respectively. Optimum pH and temperature for the enzyme reaction are 8.5 and 37 degrees C, respectively. The enzyme activity is inhibited by N-ethylmaleimide and DTNB, but stimulated by Co2+, Cu2+ and Ca2+ significantly, suggesting that these metal ions could be the cellular regulators in polyamine biosynthesis.

Distribution of polyamines and their related catabolic enzyme in etiolated and light-grown leguminosae seedlings

Diamine-oxidase (DAO; EC 1.4.3.6) activity and di-and polyamine levels were estimated along the epicotyl and root of light-grown and etiolated lentil (Lens culinaris Medicus) and pea (Pisum sativum L.) seedlings. The activity of DAO was higher in etiolated epicotyls than in lightgrown ones. In both species there was a positive correlation between DAO activity and the diamine (putrescine and cadaverine) levels along the whole epicotyl and root. Polyamine (spermine and spermidine) distribution seemed to be associated with the meristematic and elongating zone of the epicotyl and root. The physiological function of DAO is discussed in relation to its possible role in providing hydrogen peroxide to peroxidase-dependent reactions occurring in the cell wall.