In vitro and in vivo inhibition of plant polyamine oxidase activity by polyamine analogues

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.

Cationic surfactants as antifungal agents

Fungi-in being responsible for causing diseases in animals and humans as well as environmental contaminations in health and storage facilities-represent a serious concern to health security. Surfactants are a group of chemical compounds used in a broad spectrum of applications. The recently considered potential employment of cationic surfactants as antifungal or fungistatic agents has become a prominent issue in the development of antifungal strategies, especially if such surface-active agents can be synthesized in an eco-friendly manner. In this review, we describe the antifungal effect and the reported mechanisms of action of several types of cationic surfactants and also include a discussion of the contribution of these surfactants to the inhibition of yeast-based-biofilm formation. Furthermore, the putative mechanism of arginine-based tensioactive compounds as antifungal agents and their applications are also analyzed.

Perturbation of polyamine catabolism affects grape ripening of Vitis vinifera cv. Trincadeira

Grapes are economically the most important fruit worldwide. However, the complexity of biological events that lead to ripening of nonclimacteric fruits is not fully understood, particularly the role of polyamines' catabolism. The transcriptional and metabolic profilings complemented with biochemical data were studied during ripening of Trincadeira grapes submitted to guazatine treatment, a potent inhibitor of polyamine oxidase activity. The mRNA expression profiles of one time point (EL 38) corresponding to harvest stage was compared between mock and guazatine treatments using Affymetrix GrapeGen(®) genome array. A total of 2113 probesets (1880 unigenes) were differentially expressed between these samples. Quantitative RT-PCR validated microarrays results being carried out for EL 35 (véraison berries), EL 36 (ripe berries) and EL 38 (harvest stage berries). Metabolic profiling using HPLC and (1)H NMR spectroscopy showed increase of putrescine, proline, threonine and 1-O-ethyl-β-glucoside in guazatine treated samples. Genes involved in amino acid, carbohydrate and water transport were down-regulated in guazatine treated samples suggesting that the strong dehydrated phenotype obtained in guazatine treated samples may be due to impaired transport mechanisms. Genes involved in terpenes' metabolism were differentially expressed between guazatine and mock treated samples. Altogether, results support an important role of polyamine catabolism in grape ripening namely in cell expansion and aroma development.

Over-accumulation of putrescine induced by cyclohexylamine interferes with chromium accumulation and partially restores pollen tube growth in Actinidia deliciosa

Both trivalent and hexavalent chromium, i.e., Cr(III) and Cr(VI), respectively, were previously demonstrated to affect in vitro germination and ultrastructure of kiwifruit (Actinidia deliciosa) pollen. In the present work, the response to chromium in germinating pollen was evaluated in terms of changes in the polyamine profile. Slight, though significant, increases in free spermidine and spermine occurred after exposure to Cr(III), while the levels remained almost unchanged after Cr(VI) treatment. The spermidine synthase inhibitor cyclohexylamine (CHA) caused a dramatic increase in free putrescine in both chromium-treated and untreated samples, while spermidine content was not affected. Interestingly, CHA positively affected the performance of chromium-treated pollen by partially, though significantly, restoring pollen tube growth. The major growth recovery was registered with 1 mM CHA in the presence of Cr(VI), concomitant with a considerable reduction in uptake of the metal. Conversely, endogenous calcium levels were more heavily affected in Cr(III)-treated pollen. The effect of CHA on production of reactive oxygen species also varied depending on the chromium species. The response of pollen to the CHA-induced putrescine excess was compared with that exerted by an exogenous supply of the same diamine. Results show that in Cr(III)-treated pollen, putrescine over-accumulation induced by CHA exerted similar effects as exogenous putrescine, while this was not true in the Cr(VI) treatment. It appears that the diamine was able to improve pollen tolerance to metal stress through different mechanisms, mostly depending upon the chromium species, namely via reduced metal uptake or by substituting for calcium.

Thermospermine catabolism increases Arabidopsis thaliana resistance to Pseudomonas viridiflava

This work investigated the roles of the tetraamine thermospermine (TSpm) by analysing its contribution to Arabidopsis basal defence against the biotrophic bacterium Pseudomonas viridiflava. The participation of polyamine oxidases (PAOs) in TSpm homeostasis and TSpm-mediated defence was also investigated. Exogenous supply of TSpm, as well as ectopic expression of the TSpm biosynthetic gene ACL5, increased Arabidopsis Col-0 resistance to P. viridiflava, while null acl5 mutants were less resistant than Col-0 plants. The above-mentioned increase in resistance was blocked by the PAO inhibitor SL-11061, thus demonstrating the participation of TSpm oxidation. Analysis of PAO genes expression in transgenic 35S::ACL5 and Col-0 plants supplied with TSpm suggests that PAO 1, 3, and 5 are the main PAOs involved in TSpm catabolism. In summary, TSpm exhibited the potential to perform defensive functions previously reported for its structural isomer Spm, and the relevance of these findings is discussed in the context of ACL5 expression and TSpm concentration in planta. Moreover, this work demonstrates that manipulation of TSpm metabolism modifies plant resistance to pathogens.

Involvement of calcium-mediated effects on ROS metabolism in the regulation of growth improvement under salinity

Salinity reduces Ca(2+) availability, transport, and mobility to growing regions of the plant and supplemental Ca(2+) is known to reduce salinity damages. This study was undertaken to unravel some of the ameliorative mechanisms of Ca(2+) on salt stress at the cellular and tissue levels. Zea mays L. plants were grown in nutrient solution containing 1 or 80 mM NaCl with various Ca(2+) levels. Measurements of growth and physiological parameters, such as ion imbalance, indicated that the Ca(2+)-induced alleviation mechanisms differed between plant organs. Under salinity, H(2)O(2) levels increased in the leaf-growing tissue with increasing levels of supplemental Ca(2+) and reached the levels of control plants, whereas superoxide levels remained low at all Ca(2+) levels, indicating that Ca(2+) affected growth by increasing H(2)O(2) but not superoxide levels. Salinity completely abolished apoplastic peroxidase activity. Supplemental Ca(2+) increased its activity only slightly. However, under salinity, polyamine oxidase (PAO) activity was shifted toward the leaf base probably as an adaptive mechanism aimed at restoring normal levels of reactive oxygen species (ROS) at the expansion zone where NADPH oxidase could no longer provide the required ROS for growth. Interestingly, addition of Ca(2+) shifted the PAO-activity peak back to its original location in addition to its enhancement. The increase in PAO activity in conjunction with low levels of apoplastic peroxidase is supportive of cellular growth via nonenzymatic wall loosening derived by the increase in H(2)O(2) and less supportive of the peroxidase-mediated cross-linking of wall material. Thus extracellular Ca(2+) can modulate ROS levels at specific tissue localization and developmental stages thereby affecting cellular extension.

Perturbation of spermine synthase gene expression and transcript profiling provide new insights on the role of the tetraamine spermine in Arabidopsis defense against Pseudomonas viridiflava

The role of the tetraamine spermine in plant defense against pathogens was investigated by using the Arabidopsis (Arabidopsis thaliana)-Pseudomonas viridiflava pathosystem. The effects of perturbations of plant spermine levels on susceptibility to bacterial infection were evaluated in transgenic plants (35S::spermine synthase [SPMS]) that overexpressed the SPMS gene and accumulated spermine, as well as in spms mutants with low spermine levels. The former exhibited higher resistance to P. viridiflava than wild-type plants, while the latter were more susceptible. Exogenous supply of spermine to wild-type plants also increased disease resistance. Increased resistance provided by spermine was partly counteracted by the polyamine oxidase inhibitor SL-11061, demonstrating that the protective effect of spermine partly depends on its oxidation. In addition, global changes in gene expression resulting from perturbations of spermine levels were analyzed by transcript profiling 35S::SPMS-9 and spms-2 plants. Overexpression of 602 genes was detected in 35S::SPMS-9 plants, while 312 genes were down-regulated, as compared to the wild type. In the spms-2 line, 211 and 158 genes were up- and down-regulated, respectively. Analysis of gene ontology term enrichment demonstrated that many genes overexpressed only in 35S::SPMS-9 participate in pathogen perception and defense responses. Notably, several families of disease resistance genes, transcription factors, kinases, and nucleotide- and DNA/RNA-binding proteins were overexpressed in this line. Thus, a number of spermine-responsive genes potentially involved in resistance to P. viridiflava were identified. The obtained results support the idea that spermine contributes to plant resistance to P. viridiflava.

Polyamine catabolism is involved in response to salt stress in soybean hypocotyls

The possible relationship between polyamine catabolism mediated by copper-containing amine oxidase and the elongation of soybean hypocotyls from plants exposed to NaCl has been studied. Salt treatment reduced values of all hypocotyl growth parameters. In vitro, copper-containing amine oxidase activity was up to 77-fold higher than that of polyamine oxidase. This enzyme preferred cadaverine over putrescine and it was active even under the saline condition. On the other hand, saline stress increased spermine and cadaverine levels, and the in vivo copper-containing amine oxidase activity in the elongation zone of hypocotyls. The last effect was negatively modulated by the addition of the copper-containing amine oxidase inhibitor N,N'-diaminoguanidine. In turn, plants treated with the inhibitor showed a significant reduction of reactive oxygen species in the elongation zone, even in the saline situation. In addition, plants grown in cadaverine-amended culture medium showed increased hypocotyl length either in saline or control conditions and this effect was also abolished by N,N'-diaminoguanidine. Taken together, our results suggest that the activity of the copper-containing amine oxidase may be partially contributing to hypocotyl growth under saline stress, through the production of hydrogen peroxide by polyamine catabolism and reinforce the importance of polyamine catabolism and hydrogen peroxide production in the induction of salt tolerance in plants.

Plant amine oxidases "on the move": an update

Amine oxidases (AOs) catalyse the oxidative de-amination of polyamines, ubiquitous polycationic compounds involved in important events of cell life. They include the copper-containing amine oxidases (CuAOs; EC 1.4.3.6) and the flavin-containing polyamine oxidases (PAOs; EC 1.5.3.11). The main physiological role of these moonlighting proteins has been linked to compartment-specific H2O2 synthesis in different phases of development and differentiation as well as in the course of defence mechanisms against pathogens and abiotic stress. Moreover, several studies evidenced a correlation of AO expression levels with physiological stages characterized by intense metabolism, such as cell division or organ formation, thus leaving open the hypothesis that AOs may have also a role in the regulation of cell cycle through the modulation of polyamine cellular content. This update will deal with recent reports on the involvement of CuAOs and PAOs in abiotic (salt) stress, wound-healing and host-pathogen interactions.

Polyamine oxidase activity contributes to sustain maize leaf elongation under saline stress

The possible involvement of apoplastic reactive oxygen species produced by the oxidation of free polyamines in the leaf growth of salinized maize has been studied here. Salt treatment increased the apoplastic spermine and spermidine levels, mainly in the leaf blade elongation zone. The total activity of polyamine oxidase was up to 20-fold higher than that of the copper-containing amine oxidase. Measurements of H(2)O(2), *O(2)(-), and HO* production in the presence or absence of the polyamine oxidase inhibitors 1,19-bis-(ethylamine)-5,10,15 triazanonadecane and 1,8-diamino-octane suggest that, in salinized plants, the oxidation of free apoplastic polyamines by polyamine oxidase by would be the main source of reactive oxygen species in the elongation zone of maize leaf blades. This effect is probably due to increased substrate availability. Incubation with 200 microM spermine doubled segment elongation, whereas the addition of 1,19-bis-(ethylamine)-5,10,15 triazanonadecane and 1,8-diamino-octane to 200 microM spermine attenuated and reversed the last effect, respectively. Similarly, the addition of MnCl(2) (an *O(2)(-) dismutating agent) or the HO* scavenger sodium benzoate along with spermine, annulled the elongating effect of the polyamine on the salinized segments. As a whole, the results obtained here demonstrated that, under salinity, polyamine oxidase activity provides a significant production of reactive oxygen species in the apoplast which contributes to 25-30% of the maize leaf blade elongation.

Synthesis and biological evaluation of guanidino compounds endowed with subnanomolar affinity as competitive inhibitors of maize polyamine oxidase

Previous studies on agmatine and its derivatives suggested that the presence of hydrophobic groups on the guanidine moiety was a crucial key for inhibitory activity of maize polyamine oxidase. Accordingly, new lipophilic agmatine and iminoctadine derivatives were synthesized and tested for their ability to inhibit this enzyme. Several compounds showed an affinity in the nanomolar range, while a cyclopropylmethyl derivative of iminoctadine was found to be the most potent inhibitor of maize polyamine oxidase reported so far (Ki = 0.08 nM).

Leaf expansion in grasses under salt stress

Restriction of leaf growth is among the earliest visible effects of many stress conditions, including salinity. Because leaves determine radiation interception and are the main photosynthetic organs, salinity effects on leaf expansion and function are directly related to yield constraints under saline conditions. The expanding zone of leaf blades spans from the meristem to the region in which cells reach their final length. Kinematic methods are used to describe cell division and cell expansion activities. Analyses of this type have indicated that the reduction in leaf expansion by salinity may be exerted through effects on both cell division and expansion. In turn, the components of vacuole-driven cell expansion may be differentially affected by salinity, and examination of salinity effects on osmotic and mechanical constraints to cell expansion have gradually led to the identification of the gene products involved in such control. The study of how reactive oxygen species affect cell expansion is an emerging topic in the study of salinity's regulation of leaf growth.