Presence and identification of polyamines in xylem and Phloem exudates of plants

Cell specialization and coordination in Arabidopsis leaves upon pathogenic attack revealed by scRNA-seq

Plant defense responses involve several biological processes that allow plants to fight against pathogenic attacks. How these different processes are orchestrated within organs and depend on specific cell types is poorly known. Here, using single-cell RNA sequencing (scRNA-seq) technology on three independent biological replicates, we identified several cell populations representing the core transcriptional responses of wild-type Arabidopsis leaves inoculated with the bacterial pathogen Pseudomonas syringae DC3000. Among these populations, we retrieved major cell types of the leaves (mesophyll, guard, epidermal, companion, and vascular S cells) with which we could associate characteristic transcriptional reprogramming and regulators, thereby specifying different cell-type responses to the pathogen. Further analyses of transcriptional dynamics, on the basis of inference of cell trajectories, indicated that the different cell types, in addition to their characteristic defense responses, can also share similar modules of gene reprogramming, uncovering a ubiquitous antagonism between immune and susceptible processes. Moreover, it appears that the defense responses of vascular S cells, epidermal cells, and mesophyll cells can evolve along two separate paths, one converging toward an identical cell fate, characterized mostly by lignification and detoxification functions. As this divergence does not correspond to the differentiation between immune and susceptible cells, we speculate that this might reflect the discrimination between cell-autonomous and non-cell-autonomous responses. Altogether our data provide an upgraded framework to describe, explore, and explain the specialization and the coordination of plant cell responses upon pathogenic challenge.

Effects of Excess Manganese on the Xylem Sap Protein Profile of Tomato (Solanum lycopersicum) as Revealed by Shotgun Proteomic Analysis

Metal toxicity is a common problem in crop species worldwide. Some metals are naturally toxic, whereas others such as manganese (Mn) are essential micro-nutrients for plant growth but can become toxic when in excess. Changes in the composition of the xylem sap, which is the main pathway for ion transport within the plant, is therefore vital to understanding the plant's response(s) to metal toxicity. In this study we have assessed the effects of exposure of tomato roots to excess Mn on the protein profile of the xylem sap, using a shotgun proteomics approach. Plants were grown in nutrient solution using 4.6 and 300 µM MnCl2 as control and excess Mn treatments, respectively. This approach yielded 668 proteins reliably identified and quantified. Excess Mn caused statistically significant (at p ≤ 0.05) and biologically relevant changes in relative abundance (≥2-fold increases or ≥50% decreases) in 322 proteins, with 82% of them predicted to be secretory using three different prediction tools, with more decreasing than increasing (181 and 82, respectively), suggesting that this metal stress causes an overall deactivation of metabolic pathways. Processes most affected by excess Mn were in the oxido-reductase, polysaccharide and protein metabolism classes. Excess Mn induced changes in hydrolases and peroxidases involved in cell wall degradation and lignin formation, respectively, consistent with the existence of alterations in the cell wall. Protein turnover was also affected, as indicated by the decrease in proteolytic enzymes and protein synthesis-related proteins. Excess Mn modified the redox environment of the xylem sap, with changes in the abundance of oxido-reductase and defense protein classes indicating a stress scenario. Finally, results indicate that excess Mn decreased the amounts of proteins associated with several signaling pathways, including fasciclin-like arabinogalactan-proteins and lipids, as well as proteases, which may be involved in the release of signaling peptides and protein maturation. The comparison of the proteins changing in abundance in xylem sap and roots indicate the existence of tissue-specific and systemic responses to excess Mn. Data are available via ProteomeXchange with identifier PXD021973.

What is the role of putrescine accumulated under potassium deficiency?

Biomarker metabolites are of increasing interest in crops since they open avenues for precision agriculture, whereby nutritional needs and stresses can be monitored optimally. Putrescine has the potential to be a useful biomarker to reveal potassium (K⁺ ) deficiency. In fact, although this diamine has also been observed to increase during other stresses such as drought, cold or heavy metals, respective changes are comparably low. Due to its multifaceted biochemical properties, several roles for putrescine under K⁺ deficiency have been suggested, such as cation balance, antioxidant, reactive oxygen species mediated signalling, osmolyte or pH regulator. However, the specific association of putrescine build-up with low K⁺ availability in plants remains poorly understood, and possible regulatory roles must be consistent with putrescine concentration found in plant tissues. We hypothesize that the massive increase of putrescine upon K⁺ starvation plays an adaptive role. A distinction of putrescine function from that of other polyamines (spermine, spermidine) may be based either on its specificity or (which is probably more relevant under K⁺ deficiency) on a very high attainable concentration of putrescine, which far exceeds those for spermidine and spermine. putrescine and its catabolites appear to possess a strong potential in controlling cellular K⁺ and Ca²⁺ , and mitochondria and chloroplasts bioenergetics under K⁺ stress.

Citrus Polyamines: Structure, Biosynthesis, and Physiological Functions

Polyamines (PAs) are ubiquitous biogenic amines found in all living organisms from bacteria to Archaea, and Eukaryotes including plants and animals. Since the first description of putrescine conjugate, feruloyl-putrescine (originally called subaphylline), from grapefruit leaves and juice, many research studies have highlighted the importance of PAs in growth, development, and other physiological processes in citrus plants. PAs appear to be involved in a wide range of physiological processes in citrus plants; however, their exact roles are not fully understood. Accordingly, in the present review, we discuss the biosynthesis of PAs in citrus plants, with an emphasis on the recent advances in identifying and characterizing PAs-biosynthetic genes and other upstream regulatory genes involved in transcriptional regulation of PAs metabolism. In addition, we will discuss the recent metabolic, genetic, and molecular evidence illustrating the roles of PAs metabolism in citrus physiology including somatic embryogenesis; root system formation, morphology, and architecture; plant growth and shoot system architecture; inflorescence, flowering, and flowering-associated events; fruit set, development, and quality; stomatal closure and gas-exchange; and chlorophyll fluorescence and photosynthesis. We believe that the molecular and biochemical understanding of PAs metabolism and their physiological roles in citrus plants will help citrus breeding programs to enhance tolerance to biotic and abiotic stresses and provide bases for further research into potential applications.

Proteomic changes in the xylem sap of Brassica napus under cadmium stress and functional validation

BACKGROUND

The xylem sap of vascular plants primarily transports water and mineral nutrients from the roots to the shoots and also transports heavy metals such as cadmium (Cd). Proteomic changes in xylem sap is an important mechanism for detoxifying Cd by plants. However, it is unclear how proteins in xylem sap respond to Cd. Here, we investigated the effects of Cd stress on the xylem sap proteome of Brassica napus using a label-free shotgun proteomic approach to elucidate plant response mechanisms to Cd toxicity.

RESULTS

We identified and quantified 672 proteins; 67% were predicted to be secretory, and 11% (73 proteins) were unique to Cd-treated samples. Cd stress caused statistically significant and biologically relevant abundance changes in 28 xylem sap proteins. Among these proteins, the metabolic pathways that were most affected were related to cell wall modifications, stress/oxidoreductases, and lipid and protein metabolism. We functionally validated a plant defensin-like protein, BnPDFL, which belongs to the stress/oxidoreductase category, that was unique to the Cd-treated samples and played a positive role in Cd tolerance. Subcellular localization analysis revealed that BnPDFL is cell wall-localized. In vitro Cd-binding assays revealed that BnPDFL has Cd-chelating activity. BnPDFL heterologous overexpression significantly enhanced Cd tolerance in E. coli and Arabidopsis. Functional disruption of Arabidopsis plant defensin genes AtPDF2.3 and AtPDF2.2, which are mainly expressed in root vascular bundles, significantly decreased Cd tolerance.

CONCLUSIONS

Several xylem sap proteins in Brassica napus are differentially induced in response to Cd treatment, and plant defensin plays a positive role in Cd tolerance.

Extracellular Spermine Triggers a Rapid Intracellular Phosphatidic Acid Response in Arabidopsis, Involving PLDδ Activation and Stimulating Ion Flux

Polyamines, such as putrescine (Put), spermidine (Spd), and spermine (Spm), are low-molecular-weight polycationic molecules found in all living organisms. Despite the fact that they have been implicated in various important developmental and adaptative processes, their mode of action is still largely unclear. Here, we report that Put, Spd, and Spm trigger a rapid increase in the signaling lipid, phosphatidic acid (PA) in Arabidopsis seedlings but also mature leaves. Using time-course and dose-response experiments, Spm was found to be the most effective; promoting PA responses at physiological (low μM) concentrations. In seedlings, the increase of PA occurred mainly in the root and partly involved the plasma membrane polyamine-uptake transporter (PUT), RMV1. Using a differential ³²P_i-labeling strategy combined with transphosphatidylation assays and T-DNA insertion mutants, we found that phospholipase D (PLD), and in particular PLDδ was the main contributor of the increase in PA. Measuring non-invasive ion fluxes (MIFE) across the root plasma membrane of wild type and pldδ-mutant seedlings, revealed that the formation of PA is linked to a gradual- and transient efflux of K⁺. Potential mechanisms of how PLDδ and the increase of PA are involved in polyamine function is discussed.

Collection of Phloem Sap in Phytoplasma-Infected Plants

Phytoplasmas colonize specifically the phloem sieve elements (SEs) of plants and influence effectively the plant physiology. To study and understand the interaction of phytoplasmas and host plants an access to the cellular, microscale volume of SEs is demanded. Different methods are suitable to collect phloem sap of phytoplasma-infected plants. The two most common methods are the EDTA-facilitated exudation and the stylectomy. For the EDTA-facilitated method, the cut end of a leaf is placed into an EDTA solution. The EDTA prevents and avoids the Ca²⁺ dependent (re-) occlusion of SEs by binding Ca²⁺ ions and the mass flow of SEs is restarted which results in an outflow of the SE content into the EDTA bathing solution. The advantage is on the one hand a simple application and secondly, feasible for all plant species.The stylectomy method requires piercing-sucking insects like any aphids. During phloem-sap ingestion, the stylet is severed by a microcautery device or a laser from the insect body. Due to the high turgor pressure of the SEs the phloem sap is forced out through the remaining stylet and can be collected with a glass capillary, for example. The stylectomy delivers pure phloem sap, however, the collected volumes are in the range of nano liters and the temporal and staff costs are tremendous. A third method is the spontaneous exudation in phytoplasma-infected apple trees providing only in springtime large volumes of vascular sap after cutting along the bark. For the spontaneous exudation the proportion of phloem sap is unclear. Thus, this third method still needs a closer examination in prospective surveys.

Polyamines in the life of Arabidopsis: profiling the expression of S-adenosylmethionine decarboxylase (SAMDC) gene family during its life cycle

BACKGROUND

Arabidopsis has 5 paralogs of the S-adenosylmethionine decarboxylase (SAMDC) gene. Neither their specific role in development nor the role of positive/purifying selection in genetic divergence of this gene family is known. While some data are available on organ-specific expression of AtSAMDC1, AtSAMDC2, AtSAMDC3 and AtSAMDC4, not much is known about their promoters including AtSAMDC5, which is believed to be non-functional.

RESULTS

(1) Phylogenetic analysis of the five AtSAMDC genes shows similar divergence pattern for promoters and coding sequences (CDSs), whereas, genetic divergence of 5'UTRs and 3'UTRs was independent of the promoters and CDSs; (2) while AtSAMDC1 and AtSAMDC4 promoters exhibit high activity (constitutive in the former), promoter activities of AtSAMDC2, AtSAMDC3 and AtSAMDC5 are moderate to low in seedlings (depending upon translational or transcriptional fusions), and are localized mainly in the vascular tissues and reproductive organs in mature plants; (3) based on promoter activity, it appears that AtSAMDC5 is both transcriptionally and translationally active, but based on it's coding sequence it seems to produce a non-functional protein; (4) though 5'-UTR based regulation of AtSAMDC expression through upstream open reading frames (uORFs) in the 5'UTR is well known, no such uORFs are present in AtSAMDC4 and AtSAMDC5; (5) the promoter regions of all five AtSAMDC genes contain common stress-responsive elements and hormone-responsive elements; (6) at the organ level, the activity of AtSAMDC enzyme does not correlate with the expression of specific AtSAMDC genes or with the contents of spermidine and spermine.

CONCLUSIONS

Differential roles of positive/purifying selection were observed in genetic divergence of the AtSAMDC gene family. All tissues express one or more AtSAMDC gene with significant redundancy, and concurrently, there is cell/tissue-specificity of gene expression, particularly in mature organs. This study provides valuable information about AtSAMDC promoters, which could be useful in future manipulation of crop plants for nutritive purposes, stress tolerance or bioenergy needs. The AtSAMDC1 core promoter might serve the need of a strong constitutive promoter, and its high expression in the gametophytic cells could be exploited, where strong male/female gametophyte-specific expression is desired; e.g. in transgenic modification of crop varieties.

Constituents and Antioxidant Activity of Bleeding Sap from Various Xinjiang Grapes

Objective:

Wine grape sap or bleeding sap of grapes (GBS) is commonly used in Xinjiang (China) for therapeutic aims. Do variations in composition related to region and variety affect its properties?

Methods:

GBS samples originating in various parts of Xinjiang (Turpan, Hotan, Kashgar, and Atush) were tested for phenols and polyphenols, polysaccharides, saponin, proteins, individual amino acids, and minerals. Their antioxidant activity was measured using ascorbic acid as reference.

Results:

Polyphenol content varied from 2.6 to 6.6 mg/L, polysaccharides 18.3–816 mg/L, saponin 6.25–106 mg/L, and protein 3.0–22.4 mg/L. Mineral elements and amino acids ranged from 6.20 to 201.2 mg/L and 0.06–118.7 mg/L, respectively. ·OH scavenging ability varied from 70% to over 90%, higher than Vitamin C. Grapes from Turpan had lower antioxidant activity than other grapes even though the polyphenol content was generally higher.

Conclusion:

Bleeding sap of Xinjiang grape is rich in amino acids, polysaccharides, polyphenols, and protein. The contents are different according to the origin, related possibly to species, climate, and environment. Antioxidant effects were not correlated with polyphenol content.

SUMMARY

Antioxidant activity of plants or plant extracts is often associated with polyphenols

Bleeding sap of grapes has strong antioxidant properties

Bleeding sap from different grape varieties from different parts of Xinjiang (China) had different polyphenol concentrations

There was no correlation of polyphenol concentrations with antioxidant activity.

Abbreviations used: GBS: Bleeding sap of grapes; PITC: phenyl isothiocyanate.

Effects of Fe and Mn deficiencies on the protein profiles of tomato (Solanum lycopersicum) xylem sap as revealed by shotgun analyses

The aim of this work was to study the effects of Fe and Mn deficiencies on the xylem sap proteome of tomato using a shotgun proteomic approach, with the final goal of elucidating plant response mechanisms to these stresses. This approach yielded 643 proteins reliably identified and quantified with 70% of them predicted as secretory. Iron and Mn deficiencies caused statistically significant and biologically relevant abundance changes in 119 and 118 xylem sap proteins, respectively. In both deficiencies, metabolic pathways most affected were protein metabolism, stress/oxidoreductases and cell wall modifications. First, results suggest that Fe deficiency elicited more stress responses than Mn deficiency, based on the changes in oxidative and proteolytic enzymes. Second, both nutrient deficiencies affect the secondary cell wall metabolism, with changes in Fe deficiency occurring via peroxidase activity, and in Mn deficiency involving peroxidase, Cu-oxidase and fasciclin-like arabinogalactan proteins. Third, the primary cell wall metabolism was affected by both nutrient deficiencies, with changes following opposite directions as judged from the abundances of several glycoside-hydrolases with endo-glycolytic activities and pectin esterases. Fourth, signaling pathways via xylem involving CLE and/or lipids as well as changes in phosphorylation and N-glycosylation also play a role in the responses to these stresses. Biological significance In spite of being essential for the delivery of nutrients to the shoots, our knowledge of xylem responses to nutrient deficiencies is very limited. The present work applies a shotgun proteomic approach to unravel the effects of Fe and Mn deficiencies on the xylem sap proteome. Overall, Fe deficiency seems to elicit more stress in the xylem sap proteome than Mn deficiency, based on the changes measured in proteolytic and oxido-reductase proteins, whereas both nutrients exert modifications in the composition of the primary and secondary cell wall. Cell wall modifications could affect the mechanical and permeability properties of the xylem sap vessels, and therefore ultimately affect solute transport and distribution to the leaves. Results also suggest that signaling cascades involving lipid and peptides might play a role in nutrient stress signaling and pinpoint interesting candidates for future studies. Finally, both nutrient deficiencies seem to affect phosphorylation and glycosylation processes, again following an opposite pattern.

Vacuolar Sequestration of Paraquat Is Involved in the Resistance Mechanism in Lolium perenne L. spp. multiflorum

Lolium perenne L. spp. multiflorum (Lam.) Husnot (LOLMU) is a winter annual weed, common to row crops, orchards and roadsides. Glyphosate-resistant populations of LOLMU are widespread in California. In many situations, growers have switched to paraquat or other postemergence herbicides to manage glyphosate-resistant LOLMU populations. Recently, poor control of LOLMU with paraquat was reported in a prune orchard in California where paraquat has been used several times. We hypothesize that the low efficacy observed is due to the selection of a paraquat-resistant biotype of LOLMU. Greenhouse dose-response experiments conducted with a susceptible (S) and the putative paraquat-resistant biotype (PRHC) confirmed paraquat resistance in PRHC. Herbicide absorption studies indicated that paraquat is absorbed faster in S than PRHC, although the maximum absorption estimates were similar for the two biotypes. Conversely, translocation of 14C-paraquat under light-manipulated conditions was restricted to the treated leaf of PRHC, whereas herbicide translocation out of the treated leaf was nearly 20 times greater in S. To determine whether paraquat was active within the plant cells, the photosynthetic performance was assessed after paraquat application using the parameter maximum quantum yield of photosystem II (Fv/Fm). Paraquat reaches the chloroplasts of PRHC, since there was a transitory inhibition of photosynthetic activity in PRHC leaves. However, PRHC Fv/Fm recovered to initial levels by 48 h after paraquat treatment. No paraquat metabolites were found, indicating that resistance is not due to paraquat degradation. LOLMU leaf segments were exposed to paraquat following pretreatments with inhibitors of plasma membrane- and tonoplast-localized transporter systems to selectively block paraquat intracellular movement. Subsequent evaluation of membrane integrity indicated that pre-exposure to putrescine resulted in the resistant biotype responding to paraquat similarly to S. These results strongly indicate that vacuolar sequestration is involved in the resistance to paraquat in this population of LOLMU.

Altered expression of polyamine transporters reveals a role for spermidine in the timing of flowering and other developmental response pathways

Changes in the levels of polyamines are correlated with the activation or repression of developmental response pathways, but the role of polyamine transporters in the regulation of polyamine homeostasis and thus indirectly gene expression, has not been previously addressed. Here we show that the A. thaliana and rice transporters AtPUT5 and OsPUT1 were localized to the ER, while the AtPUT2, AtPUT3, and OsPUT3 were localized to the chloroplast by transient expression in N. benthamiana. A. thaliana plants that were transformed with OsPUT1 under the control the PUT5 promoter were delayed in flowering by 16days. In contrast, put5 mutants flowered four days earlier than WT plants. The delay of flowering was associated with significantly higher levels of spermidine and spermidine conjugates in the leaves prior to flowering. A similar delay in flowering was also noted in transgenic lines with constitutive expression of either OsPUT1 or OsPUT3. All three transgenic lines had larger rosette leaves, thicker flowering stems, and produced more siliques than wild type plants. In contrast, put5 plants had smaller leaves, thinner flowering stems, and produced fewer siliques. Constitutive expression of PUTs was also associated with an extreme delay in both plant senescence and maturation rate of siliques. These experiments provide the first genetic evidence of polyamine transport in the timing of flowering, and indicate the importance of polyamine transporters in the regulation of flowering and senescence pathways.

Long-Distance Transport of Thiamine (Vitamin B1) Is Concomitant with That of Polyamines

Thiamine (vitamin B1) is ubiquitous and essential for cell energy supply in all organisms as a vital metabolic cofactor, known for over a century. In plants, it is established that biosynthesis de novo is taking place predominantly in green tissues and is furthermore limited to plastids. Therefore, transport mechanisms are required to mediate the movement of this polar metabolite from source to sink tissue to activate key enzymes in cellular energy generating pathways but are currently unknown. Similar to thiamine, polyamines are an essential set of charged molecules required for diverse aspects of growth and development, the homeostasis of which necessitates long-distance transport processes that have remained elusive. Here, a yeast-based screen allowed us to identify Arabidopsis (Arabidopsis thaliana) PUT3 as a thiamine transporter. A combination of biochemical, physiological, and genetic approaches permitted us to show that PUT3 mediates phloem transport of both thiamine and polyamines. Loss of function of PUT3 demonstrated that the tissue distribution of these metabolites is altered with growth and developmental consequences. The pivotal role of PUT3 mediated thiamine and polyamine homeostasis in plants, and its importance for plant fitness is revealed through these findings.

Polyamines in macroalgae: advances and future perspectives

Polyamines (PA) are ubiquitous, small, aliphatic cations found in all living cells. In recent years the importance of these molecules for macroalgae has become evident and a substantial body of knowledge has been accumulated over the last three decades. This review summarizes research on the PAs found in macroalgae, their transport and metabolism, and their biological significance in processes such as cell division, chloroplast development, and reproduction. The involvement of PAs in environmental stress responses in macroalgae is also addressed. The discussion of PAs in this review not only demonstrates that PAs play an important role in physiological processes in macroalgae, but also clearly demonstrates the similarities and differences between PA metabolism in macroalgae and higher plants. Key areas for future research are also discussed.

Senescence and programmed cell death in plants: polyamine action mediated by transglutaminase

Research on polyamines (PAs) in plants laps a long way of about 50 years and many roles have been discovered for these aliphatic cations. PAs regulate cell division, differentiation, organogenesis, reproduction, dormancy-break and senescence, homeostatic adjustments in response to external stimuli and stresses. Nevertheless, the molecular mechanisms of their multiple activities are still matter of research. PAs are present in free and bound forms and interact with several important cell molecules; some of these interactions may occur by covalent linkages catalyzed by transglutaminase (TGase), giving rise to "cationization" or cross-links among specific proteins. Senescence and programmed cell death (PCD) can be delayed by PAs; in order to re-interpret some of these effects and to obtain new insights into their molecular mechanisms, their conjugation has been revised here. The TGase-mediated interactions between proteins and PAs are the main target of this review. After an introduction on the characteristics of this enzyme, on its catalysis and role in PCD in animals, the plant senescence and PCD models in which TGase has been studied, are presented: the corolla of naturally senescing or excised flowers, the leaves senescing, either excised or not, the pollen during self-incompatible pollination, the hypersensitive response and the tuber storage parenchyma during dormancy release. In all the models examined, TGase appears to be involved by a similar molecular mechanism as described during apoptosis in animal cells, even though several substrates are different. Its effect is probably related to the type of PCD, but mostly to the substrate to be modified in order to achieve the specific PCD program. As a cross-linker of PAs and proteins, TGase is an important factor involved in multiple, sometimes controversial, roles of PAs during senescence and PCD.

Physiological and molecular implications of plant polyamine metabolism during biotic interactions

During ontogeny, plants interact with a wide variety of microorganisms. The association with mutualistic microbes results in benefits for the plant. By contrast, pathogens may cause a remarkable impairment of plant growth and development. Both types of plant-microbe interactions provoke notable changes in the polyamine (PA) metabolism of the host and/or the microbe, being each interaction a complex and dynamic process. It has been well documented that the levels of free and conjugated PAs undergo profound changes in plant tissues during the interaction with microorganisms. In general, this is correlated with a precise and coordinated regulation of PA biosynthetic and catabolic enzymes. Interestingly, some evidence suggests that the relative importance of these metabolic pathways may depend on the nature of the microorganism, a concept that stems from the fact that these amines mediate the activation of plant defense mechanisms. This effect is mediated mostly through PA oxidation, even though part of the response is activated by non-oxidized PAs. In the last years, a great deal of effort has been devoted to profile plant gene expression following microorganism recognition. In addition, the phenotypes of transgenic and mutant plants in PA metabolism genes have been assessed. In this review, we integrate the current knowledge on this field and analyze the possible roles of these amines during the interaction of plants with microbes.

Kinetic and phylogenetic analysis of plant polyamine uptake transporters

The rice gene Polyamine Uptake Transporter1 (PUT1) was originally identified based on its homology to the polyamine uptake transporters LmPOT1 and TcPAT12 in Leishmania major and Trypanosoma cruzi, respectively. Here we show that five additional transporters from rice and Arabidopsis that cluster in the same clade as PUT1 all function as high affinity spermidine uptake transporters. Yeast expression assays of these genes confirmed that uptake of spermidine was minimally affected by 166 fold or greater concentrations of amino acids. Characterized polyamine transporters from both Arabidopsis thaliana and Oryza sativa along with the two polyamine transporters from L. major and T. cruzi were aligned and used to generate a hidden Markov model. This model was used to identify significant matches to proteins in other angiosperms, bryophytes, chlorophyta, discicristates, excavates, stramenopiles and amoebozoa. No significant matches were identified in fungal or metazoan genomes. Phylogenic analysis showed that some sequences from the haptophyte, Emiliania huxleyi, as well as sequences from oomycetes and diatoms clustered closer to sequences from plant genomes than from a homologous sequence in the red algal genome Galdieria sulphuraria, consistent with the hypothesis that these polyamine transporters were acquired by horizontal transfer from green algae. Leishmania and Trypansosoma formed a separate cluster with genes from other Discicristates and two Entamoeba species. We surmise that the genes in Entamoeba species were acquired by phagotrophy of Discicristates. In summary, phylogenetic and functional analysis has identified two clades of genes that are predictive of polyamine transport activity.

Kinetic and phylogenetic analysis of plant polyamine uptake transporters

The rice gene Polyamine Uptake Transporter1 (PUT1) was originally identified based on its homology to the polyamine uptake transporters LmPOT1 and TcPAT12 in Leishmania major and Trypanosoma cruzi, respectively. Here we show that five additional transporters from rice and Arabidopsis that cluster in the same clade as PUT1 all function as high affinity spermidine uptake transporters. Yeast expression assays of these genes confirmed that uptake of spermidine was minimally affected by 166 fold or greater concentrations of amino acids. Characterized polyamine transporters from both Arabidopsis thaliana and Oryza sativa along with the two polyamine transporters from L. major and T. cruzi were aligned and used to generate a hidden Markov model. This model was used to identify significant matches to proteins in other angiosperms, bryophytes, chlorophyta, discicristates, excavates, stramenopiles and amoebozoa. No significant matches were identified in fungal or metazoan genomes. Phylogenic analysis showed that some sequences from the haptophyte, Emiliania huxleyi, as well as sequences from oomycetes and diatoms clustered closer to sequences from plant genomes than from a homologous sequence in the red algal genome Galdieria sulphuraria, consistent with the hypothesis that these polyamine transporters were acquired by horizontal transfer from green algae. Leishmania and Trypansosoma formed a separate cluster with genes from other Discicristates and two Entamoeba species. We surmise that the genes in Entamoeba species were acquired by phagotrophy of Discicristates. In summary, phylogenetic and functional analysis has identified two clades of genes that are predictive of polyamine transport activity.

Nitrogen under- and over-supply induces distinct protein responses in maize xylem sap

Xylem sap primarily transports water and mineral nutrients such as nitrogen (N) from roots to shoots in vascular plants. However, it remains largely unknown how nitrogenous compounds, especially proteins in xylem sap, respond to N under- or over-supply. We found that reducing N supply increased amino-N percentage of total N in maize (Zea mays L.) xylem sap. Proteomic analysis showed that 23 proteins in the xylem sap of maize plants, including 12 newly identified ones, differentially accumulated in response to various N supplies. Fifteen of these 23 proteins were primarily involved in general abiotic or biotic stress responses, whereas the other five proteins appeared to respond largely to N under- or over-supply, suggesting distinct protein responses in maize xylem upon N under- and over-supply. Furthermore, one putative xylanase inhibitor and two putative O-glycosyl hydrolases had preferential gene expression in shoots.

Thermospermine is not a minor polyamine in the plant kingdom

Thermospermine is a structural isomer of spermine, which is one of the polyamines studied extensively in the past, and is produced from spermidine by the action of thermospermine synthase encoded by a gene named ACAULIS5 (ACL5) in plants. According to recent genome sequencing analyses, ACL5-like genes are widely distributed throughout the plant kingdom. In Arabidopsis, ACL5 is expressed specifically during xylem formation from procambial cells to differentiating xylem vessels. Loss-of-function mutants of ACL5 display overproliferation of xylem vessels along with severe dwarfism, suggesting that thermospermine plays a role in the repression of xylem differentiation. Studies of suppressor mutants of acl5 that recover the wild-type phenotype in the absence of thermospermine suggest that thermospermine acts on the translation of specific mRNAs containing upstream open reading frames (uORFs). Thermospermine is a novel type of plant growth regulator and may also serve in the control of wood biomass production.

Functional analysis of OsPUT1, a rice polyamine uptake transporter

Polyamines are nitrogenous compounds found in all eukaryotic and prokaryotic cells and absolutely essential for cell viability. In plants, they regulate several growth and developmental processes and the levels of polyamines are also correlated with the plant responses to various biotic and abiotic stresses. In plant cells, polyamines are synthesized in plastids and cytosol. This biosynthetic compartmentation indicates that the specific transporters are essential to transport polyamines between the cellular compartments. In the present study, a phylogenetic analysis was used to identify candidate polyamine transporters in rice. A full-length cDNA rice clone AK068055 was heterologously expressed in the Saccharomyces cerevisiae spermidine uptake mutant, agp2∆. Radiological uptake and competitive inhibition studies with putrescine indicated that rice gene encodes a protein that functioned as a spermidine-preferential transporter. In competition experiments with several amino acids at 25-fold higher levels than spermidine, only methionine, asparagine, and glutamine were effective in reducing uptake of spermidine to 60% of control rates. Based on those observations, this rice gene was named polyamine uptake transporter 1 (OsPUT1). Tissue-specific expression of OsPUT1 by semiquantitative RT-PCR showed that the gene was expressed in all tissues except seeds and roots. Transient expression assays in onion epidermal cells and rice protoplasts failed to localize to a cellular compartment. The characterization of the first plant polyamine transporter sets the stage for a systems approach that can be used to build a model to fully define how the biosynthesis, degradation, and transport of polyamines in plants mediate developmental and biotic responses.

Evaluation of automated sample preparation, retention time locked gas chromatography-mass spectrometry and data analysis methods for the metabolomic study of Arabidopsis species

In this paper, automated sample preparation, retention time locked gas chromatography-mass spectrometry (GC-MS) and data analysis methods for the metabolomics study were evaluated. A miniaturized and automated derivatisation method using sequential oximation and silylation was applied to a polar extract of 4 types (2 types×2 ages) of Arabidopsis thaliana, a popular model organism often used in plant sciences and genetics. Automation of the derivatisation process offers excellent repeatability, and the time between sample preparation and analysis was short and constant, reducing artifact formation. Retention time locked (RTL) gas chromatography-mass spectrometry was used, resulting in reproducible retention times and GC-MS profiles. Two approaches were used for data analysis. XCMS followed by principal component analysis (approach 1) and AMDIS deconvolution combined with a commercially available program (Mass Profiler Professional) followed by principal component analysis (approach 2) were compared. Several features that were up- or down-regulated in the different types were detected.

Pumpkin eIF5A isoforms interact with components of the translational machinery in the cucurbit sieve tube system

In yeast, eIF5A, in combination with eEF2, functions at the translation step, during the protein elongation cycle. This result is of significance with respect to functioning of the enucleate sieve tube system, as eIF5A was recently detected in Cucurbita maxima (pumpkin) phloem sap. In the present study, we further characterized four CmeIF5A isoforms, encoding three proteins, all of which were present in the phloem sap. Although hypusination of CmeIF5A was not necessary for entry into the sieve elements, this unique post-translational modification was necessary for RNA binding. The two enzymes required for hypusination were detected in pumpkin phloem sap, where presumably this modification takes place. A combination of gel-filtration chromatography and protein overlay assays demonstrated that, as in yeast, CmeIF5A interacts with phloem proteins, like eEF2, known to be involved in protein synthesis. These findings are discussed in terms of a potential role for eIF5A in regulating protein synthesis within the enucleate sieve tube system of the angiosperms.

Role of polyamines in plant vascular development

Several pieces of evidence suggest a role for polyamines in the regulation of plant vascular development. For instance, polyamine oxidase gene expression has been shown to be associated with lignification, and downregulation of S-adenosylmethionine decarboxylase causes dwarfism and enlargement of the vasculature. Recent evidence from Arabidopsis thaliana also suggests that the active polyamine in the regulation of vascular development is the tetraamine thermospermine. Thermospermine biosynthesis is catalyzed by the aminopropyl transferase encoded by ACAULIS5, which is specifically expressed in xylem vessel elements. Both genetic and molecular evidence support a fundamental role for thermospermine in preventing premature maturation and death of the xylem vessel elements. This safeguard action of thermospermine has significant impact on xylem cell morphology, cell wall patterning and cell death as well as on plant growth in general. This manuscript reviews recent reports on polyamine function and places polyamines in the context of the known regulatory mechanisms that govern vascular development.

Metabolomic and proteomic changes in the xylem sap of maize under drought

Plants produce compounds in roots that are transported to shoots via the xylem sap. Some of these compounds are vital for signalling and adaptation to environmental stress such as drought. In this study, we screened the xylem sap using mass spectrometry to quantify the changes in new and previously identified sap constituents under extended drought. We detected and quantified the changes in the concentration of 31 compounds present in the xylem sap under progressively increasing drought stress. We found changes in the hormones abscisic acid (ABA) and cytokinin, and the presence of high concentrations of the aromatic cytokinin 6-benzylaminopurine (BAP). Several phenylpropanoid compounds (coumaric, caffeic and ferulic acids) were found in xylem sap. The concentrations of some of these phenylpropanoid compounds changed under drought. In parallel, an analysis of the xylem sap proteome was conducted. We found a higher abundance of cationic peroxidases, which with the increase in phenylpropanoids may lead to a reduction in lignin biosynthesis in the xylem vessels and could induce cell wall stiffening. The application of new methodologies provides insights into the range of compounds in sap and how alterations in composition may lead to changes in development and signalling during adaptation to drought.

Characterization of a tobacco TPK-type K+ channel as a novel tonoplast K+ channel using yeast tonoplasts

The tonoplast K(+) membrane transport system plays a crucial role in maintaining K(+) homeostasis in plant cells. Here, we isolated cDNAs encoding a two-pore K(+) channel (NtTPK1) from Nicotiana tabacum cv. SR1 and cultured BY-2 tobacco cells. Two of the four variants of NtTPK1 contained VHG and GHG instead of the GYG signature sequence in the second pore region. All four products were functional when expressed in the Escherichia coli cell membrane, and NtTPK1 was targeted to the tonoplast in tobacco cells. Two of the three promoter sequences isolated from N. tabacum cv. SR1 were active, and expression from these was increased approximately 2-fold by salt stress or high osmotic shock. To determine the properties of NtTPK1, we enlarged mutant yeast cells with inactivated endogenous tonoplast channels and prepared tonoplasts suitable for patch clamp recording allowing the NtTPK1-related channel conductance to be distinguished from the small endogenous currents. NtTPK1 exhibited strong selectivity for K(+) over Na(+). NtTPK1 activity was sensitive to spermidine and spermine, which were shown to be present in tobacco cells. NtTPK1 was active in the absence of Ca(2+), but a cytosolic concentration of 45 microM Ca(2+) resulted in a 2-fold increase in the amplitude of the K(+) current. Acidification of the cytosol to pH 5.5 also markedly increased NtTPK1-mediated K(+) currents. These results show that NtTPK1 is a novel tonoplast K(+) channel belonging to a different group from the previously characterized vacuolar channels SV, FV, and VK.

Involvement of inorganic elements in tissue reunion in the hypocotyl cortex of Cucumis sativus

Cucumber (Cucumis sativus L.) hypocotyls were transversely cut to half their diameter, and morphological analyses of the tissue-reunion process in the cortex were conducted to elucidate the involvement of root-derived factors. Cell division in the cortex commenced 3 days after cutting, and the cortex was nearly fully united within 7 days. In shoots from which the roots were removed and which were cultured in water, cell division occurred during tissue reunion; however, thick-wall layer formed in the reunion region, and intrusive cell elongation and interdigitation of cortex cells at the cut surface did not occur, even after 7 days. Interdigitation of cells, followed by normal tissue reunion, was observed in shoots from which the roots were removed and which were cultured in squash xylem sap or Murashige and Skoog (MS) medium. The same effect was observed with the simultaneous application of B, Mn, and Zn, which are the major inorganic microelements of MS medium. Our results suggest that application of these inorganic elements, which are taken up from the soil and transferred to the xylem sap, are required for interdigitation of cells during tissue reunion in the cortex of cucumber hypocotyls, possibly because they are required for cell wall function and metabolism.

Levels of polyamines and kinetic characterization of their uptake in the soybean pathogen Phytophthora sojae

Polyamines are ubiquitous biologically active aliphatic cations that are at least transiently available in the soil from decaying organic matter. Our objectives in this study were to characterize polyamine uptake kinetics in Phytophthora sojae zoospores and to quantify endogenous polyamines in hyphae, zoospores, and soybean roots. Zoospores contained 10 times more free putrescine than spermidine, while hyphae contained only 4 times as much free putrescine as spermidine. Zoospores contained no conjugated putrescine, but conjugated spermidine was present. Hyphae contained both conjugated putrescine and spermidine at levels comparable to the hyphal free putrescine and spermidine levels. In soybean roots, cadaverine was the most abundant polyamine, but only putrescine efflux was detected. The selective efflux of putrescine suggests that the regulation of polyamine availability is part of the overall plant strategy to influence microbial growth in the rhizosphere. In zoospores, uptake experiments with [1,4-(14)C]putrescine and [1,4-(14)C]spermidine confirmed the existence of high-affinity polyamine transport for both polyamines. Putrescine uptake was reduced by high levels of exogenous spermidine, but spermidine uptake was not reduced by exogenous putrescine. These observations suggest that P. sojae zoospores express at least two high-affinity polyamine transporters, one that is spermidine specific and a second that is putrescine specific or putrescine preferential. Disruption of polyamine uptake or metabolism has major effects on a wide range of cellular activities in other organisms and has been proposed as a potential control strategy for Phytophthora. Inhibition of polyamine uptake may be a means of reducing the fitness of the zoospore along with subsequent developmental stages that precede infection.

Organic substances in xylem sap delivered to above-ground organs by the roots

Squash (Cucurbita maxima) xylem sap, an apoplastic fluid, contains t-zeatin riboside, glutamine, methylglycine, myo-inositol, fructose, oligosaccharides of arabinogalactan, glucan, galacturonan, and pectins (rhamnogalacturonan-I and rhamnogalacturonan-II), as well as various proteins, including arabinogalactan and pathogen-related proteins. These substances are mainly produced in stele (xylem) parenchyma and the pericycle in the root-hair zone where ion transporter genes are expressed. Glycine-rich protein genes (CRGRPs) cloned by antiserum raised against whole xylem sap of cucumber (Cucumis sativus) were abundantly expressed in the parenchyma cells surrounding xylem vessels in the root-hair zone. CRGRP proteins accumulated and immobilized in the lignified walls of metaxylem vessels and perivascular fibers in shoots, suggesting a systemic delivery mechanism of wall materials via xylem sap. A major 30-kDa protein (XSP30) found in cucumber xylem sap was homologous to the B chains of a lectin (ricin) and bound to a nonfucosylated core N-acetylglucosamine dimer of N-linked glycoproteins abundant in leaf parenchyma cells. XSP30 gene expression, abundant in root xylem parenchyma and pericycle, and the level of XSP30 protein fluctuated diurnally under the control of a circadian clock, and the amplitude was up-regulated by gibberellic acid produced in young leaves, suggesting a long-distance control system between organs.

Genomic organization and expression analyses of putrescine pathway genes in soybean

Putrescine is synthesized using one of two alternative pathways in plants, from arginine by arginine decarboxylase (ADC) or from ornithine by ornithine decarboxylase (ODC) and is catabolized by diamine oxidase (DAO). A survey of approximately 310,000 expressed sequenced tags (ESTs) in soybean EST libraries identified diverse representation of ADC, ODC, and DAO ESTs, with ODC being least frequent and DAO ESTs most abundant. Southern analysis suggested that ADC and ODC belong to small gene families, and DAO is the most divergent. Using three bacterial artificial chromosome (BAC) libraries, 26X genome equivalents, two common loci for ADC and DAO and one independent DAO locus were identified. ADC and DAO are physically linked in the soybean genome within approximately 150 kb. Identification of genomic regions encoding ODC proved difficult and required using additional BAC libraries, increasing genome coverage to approximately 40X. Using Real Time reverse transcriptase-polymerase chain reaction (RT-PCR), higher steady-state levels of ADC than ODC in roots, leaves, shoot apices, and dry seeds suggested that ADC is the predominant pathway for putrescine biosynthesis in soybean. However, organ-specific expression showed that root is the major site of ODC transcription. Significantly elevated accumulation of ADC mRNA and elevated putrescine content in seeds of the fasciation mutant compared with the wild type may stimulate cell divisions and establishment of enlarged apical meristem during early mutant ontogeny. The DAO frequent representation in EST libraries constructed from root tissue and elevated steady-state levels in roots compared to above ground tissues show DAO is critical for regulation of putrescine content in soybean roots.

Effect of salt and osmotic stress on changes in polyamine content and arginine decarboxylase activity in Lupinus luteus seedlings

The effects of NaCl (260 mM) and sorbitol (360 mM) isoosmotic stresses on polyamine titers in lupin (Lupinus luteus L. var. Ventus) in relation to organ-specific responses were investigated. Analysis showed that during the first few hours (4 h) of salt and osmotic stress higher amounts of putrescine (Put) and spermidine (Spd) were accumulated in the roots and leaves of lupin seedlings. After exposing the plants to a longer duration (24 h) of exposure to NaCl, the level of free Put decreased in roots and cotyledons by about 48% and 54%, respectively, and increased in hypocotyls and leaves by about 27% and 73%, respectively. The Level of free Spd also decreased in roots by about 50%, in contrast to the increase of Spd observed in hypocotyls and leaves by about 50% and 70%, respectively. The effect of non-ionic stress on the level of Put and Spd in studied organs of lupin was similar to that of NaCl. Free spermine was at an undetectable level in examined organs. However, in the roots of lupin growing for 24 h in the presence of NaCl and/or sorbitol, the activity of arginine decarboxylase (ADC) (EC 4.1.1.19) increased by about 66% and 80%, respectively. ADC activity in leaves was similar to that observed in the control. Additionally, in the roots and leaves of lupin growing under the stress condition (NaCl or sorbitol), a higher level of polyamines (PAs) bound to microsomal membranes was observed. It is probable that PAs bound to microsomal membranes prevent stress-induced damage. We conclude that both stresses induce biosynthesis of Put and other PAs in the roots, as well as Put accumulation in the leaves, and this may indicate translocation of Put from the roots to the shoot. The possible role of PAs in adaptive mechanisms to stress is discussed.

Analysis of polyamine metabolism in soybean seedlings using 15N-labelled putrescine

The translocation and metabolism of polyamines during soybean germination were studied using 15N-labelled putrescine as a precursor. Both 15N-labelled and unlabelled polyamines were simultaneously detected using a novel application of ionspray ionization-mass spectrometry. 15N-putrescine was rapidly transported to the shoots and roots, where it was converted to spermidine and spermine. The main 15N-polyamine that accumulated in the root was 15N-spermine. It was found that there were differences in the way endogenous putrescine and exogenous 15N-putrescine were metabolized in soybean seedlings.

Analysis of sugars in squash xylem sap

Xylem sap contains organic and inorganic compounds that might be involved in root-to-shoot communication. To clarify the physiological functions of sugars in xylem sap, we characterized the sugar compounds of the xylem sap. The 80% ethanol-soluble fraction of xylem sap contained mainly myo-inositol and oligosaccharides. The 80% ethanol precipitate was solubilized with cyclohexanediamine tetraacetate and fractionated using anion exchange chromatography. The non-bound fraction from the anion-exchange column reacted with Yariv reagent and was rich in arabinogalactan, indicating the presence of arabinogalactan proteins (AGP). The bound fraction eluted with 50 mM ammonium formate buffer and separated using size exclusion chromatography producing the pectins rhamnogaracturonan (RG)-I and RG-II with apparent molecular masses of 15000 and 11000, respectively. These results indicate that the AGP, RG-I, borate cross-linked RG-II dimer and oligosaccharides produced by root tissues are transported to above-ground organs via xylem sap.

Genetic manipulation of the metabolism of polyamines in poplar cells. The regulation of putrescine catabolism

We investigated the catabolism of putrescine (Put) in a non-transgenic (NT) and a transgenic cell line of poplar (Populus nigra x maximowiczii) expressing a mouse (Mus musculus) ornithine (Orn) decarboxylase (odc) cDNA. The transgenic cells produce 3- to 4-fold higher amounts of Put than the NT cells. The rate of loss of Put from the cells and the initial half-life of cellular Put were determined by feeding the cells with [U-(14)C]Orn and [1,4-(14)C]Put as precursors and following the loss of [(14)C]Put in the cells at various times after transfer to label-free medium. The amount of Put converted into spermidine as well as the loss of Put per gram fresh weight were significantly higher in the transgenic cells than the NT cells. The initial half-life of exogenously supplied [(14)C]Put was not significantly different in the two cell lines. The activity of diamine oxidase, the major enzyme involved in Put catabolism, was comparable in the two cell lines even though the Put content of the transgenic cells was severalfold higher than the NT cells. It is concluded that in poplar cells: (a) exogenously supplied Orn enters the cells and is rapidly converted into Put, (b) the rate of Put catabolism is proportional to the rate of its biosynthesis, and (c) the increased Put degradation occurs without significant changes in the activity of diamine oxidase.

Genetic manipulation of the metabolism of polyamines in poplar cells. The regulation of putrescine catabolism

We investigated the catabolism of putrescine (Put) in a non-transgenic (NT) and a transgenic cell line of poplar (Populus nigra x maximowiczii) expressing a mouse (Mus musculus) ornithine (Orn) decarboxylase (odc) cDNA. The transgenic cells produce 3- to 4-fold higher amounts of Put than the NT cells. The rate of loss of Put from the cells and the initial half-life of cellular Put were determined by feeding the cells with [U-(14)C]Orn and [1,4-(14)C]Put as precursors and following the loss of [(14)C]Put in the cells at various times after transfer to label-free medium. The amount of Put converted into spermidine as well as the loss of Put per gram fresh weight were significantly higher in the transgenic cells than the NT cells. The initial half-life of exogenously supplied [(14)C]Put was not significantly different in the two cell lines. The activity of diamine oxidase, the major enzyme involved in Put catabolism, was comparable in the two cell lines even though the Put content of the transgenic cells was severalfold higher than the NT cells. It is concluded that in poplar cells: (a) exogenously supplied Orn enters the cells and is rapidly converted into Put, (b) the rate of Put catabolism is proportional to the rate of its biosynthesis, and (c) the increased Put degradation occurs without significant changes in the activity of diamine oxidase.

Equilibrium between basic nitrogen compounds in lupin seeds with differentiated alkaloid content

The results of studies on the content of the nitrogen basic compounds, viz. quinolizidine alkaloids, biogenic polyamines and basic amino acids in lupin seeds are presented. The investigations concerned three lupin species (Lupinus angustifolius L., Lupinus albus L. and Lupinus luteus L.) and 10 bitter and sweet cultivated varieties. Content of quinolizidine alkaloids in L. angustifolus ranged from 11.4 to 19.6 microg mg(-1) dw (bitter cultivars), from 0.18 to 0.47 microg mg(-1) dw (sweet), in L. albus from 0.58 microg mg(-1) dw (sweet) to 29.6 microg mg(-1) dw (bitter) and in L. luteus from 0.59 (sweet) to 14.7 microg mg(-1) dw (bitter). Total biogenic polyamine content ranged in L. angustifolius from 2,773.9 to 3,180.2 pmol mg(-1) dw (bitter) and from 315.0 to 599.0 pmol mg(-1) dw (sweet), in L. albus from 432.6 pmol mg(-1) dw (sweet) to 1,832.0 pmol mg(-1) dw (bitter) and in L. luteus from 506.9 pmol mg(-1) dw (sweet) to 2,091.8 pmol mg(-1) dw (bitter). Total basic amino acids varied in L. angustifolus from 1,034.3 to 1,704.6 pmol mg(-1) dw (bitter) and from 1,761.9 to 2,101.9 pmol mg(-1) dw (sweet), in L. albus from 696.9 pmol mg(-1) dw (bitter) to 1,269.2 pmol mg(-1) dw (sweet) and in L. luteus from 927.6 pmol mg(-1) dw (bitter) to 1,598.3 pmol mg(-1) dw (sweet). We found a close dependence between alkaloid content and level of biogenic polyamines and basic amino acids in all three lupin species tested. All bitter lupin seeds also contain high level of biogenic polyamines but a low content of basic amino acids. The reverse relationship in sweet lupin seeds was found. The findings demonstrate that lupin nitrogen basic compounds are in steady equilibrium and that change of content in one compound leads to corresponding change in the content of another.

Transport Interactions between Paraquat and Polyamines in Roots of Intact Maize Seedlings

Interactions between absorption of paraquat and the polyamines putrescine, cadaverine, and spermine in roots of intact maize (Zea mays L. cv 3377 Pioneer) seedlings were examined. Concentration-dependent kinetics for paraquat and putrescine influx were similar and both kinetic curves could be resolved into a linear and a saturable component. The linear component was previously shown to represent cell wall/membrane binding. The saturable components for paraquat and putrescine uptake, which represent influx across the plasmalemma, had K(m) values of 98 and 120 micromolar, respectively, and V(max) values of 445 and 456 nanomoles per gram fresh weight per hour, respectively. Lineweaver-Burk transformation of the saturable component of paraquat influx in the presence of varying concentrations of putrescine indicated that the diamine competitively inhibited the saturable component of paraquat uptake. Reciprocal experiments similarly demonstrated that paraquat competitively inhibited the saturable component of putrescine uptake. Competitive inhibition of both paraquat and putrescine influx could also be demonstrated with the diamine cadaverine, which has a charge distribution similar to that of paraquat and putrescine. In contrast, the larger, tetravalent polyamine spermine appeared to noncompetitively inhibit the influx of paraquat and putrescine. These results strongly suggest that paraquat enters maize root cells via a carrier system that normally functions in the transport of diamines with a charge distribution similar to that of paraquat.

Effect of inorganic cations and metabolic inhibitors on putrescine transport in roots of intact maize seedlings

The specificity and regulation of putrescine transport was investigated in roots of intact maize (Zea mays L.) seedlings. In concentration-dependent transport studies, the kinetics for putrescine uptake could be resolved into a single saturable component that was noncompetitively inhibited by increasing concentrations of Ca(2+) (50 micromolar to 5 millimolar). Similarly, other polyvalent cations, including Mg(2+) (1.8 millimolar) and La(3+) (200 micromolar), almost completely abolished the saturable component for putrescine uptake. This suggests that putrescine does not share a common transport system with other divalent or polyvalent inorganic cations. Further characterization of the putrescine transport system indicated that 0.3 millimolar N-ethyl-maleimide had no effect on putrescine uptake, and 2 millimolar p-chloromercuribenzene sulfonic acid only partially inhibited transport of the diamine (39% inhibition). Metabolic inhibitors, including carbonylcyanide-m-chlorphenylhydrazone (20 micromolar) and KCN (0.5 millimolar), also partially inhibited the saturable component for putrescine uptake (V(max) reduced 48-60%). Increasing the time of exposure to carbonylcyanide-m-chlorphenylhydrazone from 30 minutes to 2 hours did not significantly increase the inhibition of putrescine uptake. Electrophysiological evidence indicates that the inhibitory effect on putrescine uptake by these inhibitors is correlated to a depolarization of the membrane potential, suggesting that the driving force for putrescine uptake is the transmembrane electrical potential across the plasmalemma.

Transport kinetics and metabolism of exogenously applied putrescine in roots of intact maize seedlings

Putrescine metabolism, uptake, and compartmentation were studied in roots of hydroponically grown intact maize (Zea mays L.) seedlings. In vivo analysis of exogenously applied putrescine indicated that the diamine is primarily metabolized by a cell wall-localized diamine oxidase. Time-dependent kinetics for putrescine uptake could be resolved into a rapid phase of uptake and binding within the root apoplasm, followed by transport across the plasma membrane that was linear for 30 to 40 minutes. Concentration-dependent kinetics for putrescine uptake (between 0.05 and 1.0 millimolar putrescine) appeared to be nonsaturating but could be resolved into a saturable (V(max) 0.397 micromoles per gram fresh weight per hour; K(m) 120 micromolar) and a linear component. The linear component was determined to be cell wall-bound putrescine that was not removed during the desorption period following uptake of [(3)H]putrescine. These results suggest that a portion of the exogenously applied putrescine can be metabolized in maize root cell walls by diamine oxidase activity, but the bulk of the putrescine is transported across the plasmalemma by a carrier-mediated process, similar to that proposed for animal systems.

Electron-microscopic cytochemical localization of diamine and polyamine oxidases in pea and maize tissues

An electron-microscopic cytochemical method was used to localize diamine oxidase (DAO) in pea and polyamine oxidase (PAO) in maize (Zea mays L.). The method, based on the precipitation of amine-oxidase-generated H2O2 by CeCl3, was shown to be specific for DAO and PAO and permitted their localization in plant tissues with a high degree of resolution. Both enzymes are localized exclusively in the cell wall. Both DAO- and PAO-activity staining is most intense in the middle lamellar region of the wall and in cells exhibiting highly lignified walls. The oxidases could provide H2O2 for peroxidase-mediated cross-linking reactions in the cell wall and may, in this capacity, play a role in the regulation of plant growth.

Spatial and functional correlation between diamine-oxidase and peroxidase activities and their dependence upon de-etiolation and wounding in chick-pea stems

The activities of diamine oxidase (DAO, EC 1.4.3.6) and peroxidase (POD, EC 1.11.1.7) were determined along the stems of light-grown Cicer arietinum L. (chick-pea) seedlings. Enzyme activities were evaluated in the soluble, lightly bound (salt extraction) and tightly bound (Driselase digestion) wall fractions, and in residual fractions obtained from the different internodes. Apparent tissue distributions of both enzymes and lignin depositions were visualised by means of histochemical and immunohistochemical techniques. A close relationship was found between DAO and POD activities in the soluble and wall fractions along the stem. The biochemical activities of both enzymes decreased from the base to the apex of the stem in parallel with the distribution pattern of lignifying tissues in this organ. A similar activity gradient was found for each enzyme along the epidermis of the whole organ. Moreover, deetiolation elicited a rise in the activities of both enzymes in this tissue. Wounding chick-pea stems induced parallel increases in DAO and POD activities in the soluble and wall fractions. In-situ histochemical detection of both enzymes demonstrated the parallel occurrence of the DAO/POD system and lignosuberised depositions in the cell walls adjacent to the wound site. The patterns of POD isoforms resulting from the wound-healing process were determined by means of starch-gel electrophoresis. In addition to changes in relative intensity of enzyme bands in soluble and wall fractions, a new POD isoform, possibly related to the wounding response, appeared in the soluble fraction. This isoform was shown to be lightly bound to cell walls as it could be detected in the extracellular fluids obtained from wound-healed seedlings. On the basis of the above-mentioned results, a strict spatial and functional correlation can be inferred between DAO and POD in chick-pea, and probably in other Leguminosae species, in accordance with previous evidence indicating an integrated role for these enzymes in the apoplast.

Spermidine Uptake by Mitochondria of Helianthus tuberosus

In the present work evidence is provided that spermidine, a polyamine largely present in plant tissues, may be transported, at physiological concentrations, into the matrix space of mitochondria isolated from tubers of Helianthus tuberosus L. cv OB1 (Jerusalem artichoke). It is concluded that the movement of spermidine strictly depends on membrane potential, since it is drastically blocked by valinomycin and only slightly sensitive to nigericin. Mg(2+) and K(+) inhibit the transport of spermidine in line with the general concept that these cations compete for the same binding sites on the mitochondrial membrane. In contrast to previous data on mammalian mitochondria, spermidine uptake by plant mitochondria does not depend on the presence of inorganic phosphate. This latter result, along with evidence that Ca(2+) does not affect accumulation of spermidine, indicates that the control of the polyamine uptake mechanism in plant mitochondria is distinct from that of mammalian systems.

Putrescine-induced wounding and its effects on membrane integrity and ion transport processes in roots of intact corn seedlings

Interactions between putrescine and membrane function were examined with the use of a recently developed microelectrode system that enables us simultaneously to quantify membrane potentials and net K(+) fluxes associated with individual cells at the root surface of an intact corn (Zea mays L.) seedling. In contrast to the results of others, our analyses indicate that exogenous putrescine (0.5 millimolar), in the absence of calcium, does not maintain membrane stability. In addition, putrescine caused a wound response characterized by a gradual depolarization of the membrane potential and a considerable net efflux of K(+) from the root. In the presence of calcium, both short term (20 minutes) and long term (24 hours) exposure to a high concentration of exogenous putrescine (5 millimolar) also caused a reduction in the resting membrane potential and a significant K(+) efflux. However, preincubating corn roots in a solution containing the antioxidant ascorbate ameliorated the wounding effects of putrescine and slightly increased potassium uptake. A similar preincubation in the absence of calcium did not protect membranes against putrescine-induced damage. The ameliorating effect of ascorbate on putrescine-induced membrane damage suggests that the wounding response of high putrescine levels in corn roots involves the catabolism of the polyamine by a cell wall diamine oxidase, with the concomitant production of hydrogen peroxide and free radicals resulting in peroxidative damage of the plasmalemma.

Transport and subcellular localization of polyamines in carrot protoplasts and vacuoles

Putrescine and spermidine uptake in carrot (Daucus carota L., cv "Tip top") protoplasts and isolated vacuoles was studied. Protoplasts and vacuoles accumulated polyamines very quickly, with maximum absorption within 1 to 2 minutes. The insertion of a washing layer containing 100 millimolar unlabeled putrescine or spermidine did not change this pattern, but strongly reduced the uptake of putrescine and spermidine in protoplasts and in vacuoles. The dependence of spermidine uptake on the external concentration was linear up to the highest concentrations tested in protoplasts, while that in vacuoles showed saturation kinetics below 1 millimolar (K(m) = 61.8 micromolar) and a linear component from 1 to 50 millimolar. Spermidine uptake in protoplasts increased linearly between pH 5.5 and 7.0, while there was a distinct optimum at pH 7.0 for vacuoles. Preincubation of protoplasts with 1 millimolar Ca(2+) affected only surface binding but not transport into the cells. Nonpermeant polycations such as La(3+) and polylysine inhibited spermidine uptake into protoplasts. Compartmentation studies showed that putrescine and spermidine were partly vacuolar in location and that exogenously applied spermidine could be recovered inside the cells. The characteristics of the protoplast and vacuolar uptake system induce us to put forward the hypothesis of a passive influx of polyamines through the plasmalemma and of the presence of a carrier-mediated transport system localized in the tonoplast.