Improvement of plant abiotic stress tolerance through modulation of the polyamine pathway

Polyamines(mainly putrescine(Put),spermidine(Spd),and spermine(Spm))have been widely found in a range of physiological processes and in almost all diverse environmental stresses.In various plant species,abiotic stresses modulated the accumulation of polyamines and related gene expression.Studies using loss-of-function mutants and transgenic overexpression plants modulating polyamine metabolic pathways confirmed protective roles of polyamines during plant abiotic stress responses,and indicated the possibility to improve plant tolerance through genetic manipulation of the polyamine pathway.Additionally,putative mechanisms of polyamines involved in plant abiotic stress tolerance were thoroughly discussed and crosstalks among polyamine,abscisic acid,and nitric oxide in plant responses to abiotic stress were emphasized.Special attention was paid to the interaction between polyamine and reactive oxygen species,ion channels,amino acid and carbon metabolism,and other adaptive responses.Further studies are needed to elucidate the polyamine signaling pathway,especially polyamine-regulated downstream targets and the connections between polyamines and other stress responsive molecules.     

Improvement of plant abiotic stress tolerance through modulation of the polyamine pathway FA简

Polyamines （mainly putrescine （Put）, spermidine （Spd）, and spermine （Spin）） have been widely found in a range of physiological processes and in almost all diverse environ- mental stresses. In various plant species, abiotic stresses modulated the accumulation of polyamines and related gene expression. Studies using loss-of-function mutants and transgenic overexpression plants modulating polyamine metabolic pathways confirmed protective roles of polyamines during plant abiotic stress responses, and indicated the possibility to improve plant tolerance through genetic manipulation of the polyamine pathway. Additionally, puta- tive mechanisms of polyamines involved in plant abiotic stress tolerance were thoroughly discussed and crosstalks among polyamine, abscisic acid, and nitric oxide in plant responses to abiotic stress were emphasized. Special attention was paid to the interaction between polyamine and reactive oxygen species, ion channels, amino acid and carbon metabolism, and other adaptive responses. Further studies are needed to elucidate the polyamine signaling pathway, especially polyamine-regulated downstream tar- gets and the connections between polyamines and other stress responsive molecules.     

Plant polyamine catabolism: The state of the art

Polyamines have long been implicated in plant growth and development, as well as adaptation to abiotic and biotic stress. As a general rule of thumb the higher the polyamine titers the better. However, their molecular roles in plant stress responses still remain obscure. It has been postulated that they could act through their catabolism, which generates molecules which may act as secondary messengers signalling networks of numerous developmental and stress adaptation processes. Recently it was shown that plant and mammalian polyamine catabolism share critical features, giving new insight in plant polyamine catabolism. In this review, the advances in genes and proteins of polyamine catabolism in plants is presented and compared to other models.Key words: polyamines, polyamine catabolism, polyamine oxidase, abiotic stress, ROS signaling     

Ornithine decarboxylase transgene in tobacco affects polyamines,in vitro-morphogenesis and response to salt stress

Transgenic tobacco plants expressing the putrescine synthesis gene ornithine decarboxylase from mouse were raised to study the effects of up-regulation of a metabolic pathway as critical as the polyamine biosynthesis on the plant growth and development, in vitro-morphogenesis and their response to salt stress. Further, the response of the alternate pathway (arginine decarboxylase) for putrescine synthesis to the modulation of the ornithine decarboxylase pathway has also been investigated. The over-expression of the odc gene and increased levels of putrescine in tobacco led to a delay in plant regeneration on selection medium which could be overcome by the exogenous application of polyamine biosynthesis inhibitors and spermidine. Further, the lines generated had a variable in vitro morphogenic potential, which could be correlated to the shifts in their polyamine metabolism. These studies have brought forward the critical role played by polyamines in the normal development of plants and also their role in plant regeneration. Since polyamines are known to accumulate in cells under abiotic stress conditions, the tolerance of the transgenics to salt stress was also investigated and the transgenics with their polyamine metabolism up-graded showed increased tolerance to salt stress.     

Involvement of polyamines in plant response to abiotic stress

Environmental stresses are the major cause of crop loss worldwide. Polyamines are involved in plant stress responses. However, the precise role(s) of polyamine metabolism in these processes remain ill-defined. Transgenic approaches demonstrate that polyamines play essential roles in stress tolerance and open up the possibility to exploit this strategy to improve plant tolerance to multiple environmental stresses. The use of Arabidopsis as a model plant enables us to carry out global expression studies of the polyamine metabolic genes under different stress conditions, as well as genome-wide expression analyses of insertional-mutants and plants over-expressing these genes. These studies are essential to dissect the polyamine mechanism of action in order to design new strategies to increase plant survival in adverse environments.     

Role of polyamines in the ontogeny of plants and their biotechnological applications

Recent developments in the metabolism and function of polyamines in plants is presented. Polyamines appear to be involved in a wide range of plant processes, however their exact role is not completely understood. In this review, the metabolic pathways involved in polyamine biosynthesis and degradation are explained, along with the transport and conjugation of these compounds. The studies involved in the understanding of function(s) of polyamines using metabolic inhibitors, as well as genetic and molecular approaches are described. Polyamine metabolism and profound changes in polyamine titres in response to infection by pathogens has been presented. Its role in adaptation of plants to stress is also presented. Molecular understanding of polyamines and their modulation in transgenics is also discussed. Further line of work in the understanding of the role of polyamines has also been focussed.     

多胺与环境胁迫关系研究进展

多胺是植物对胁迫响应的重要物质,可以抵消胁迫引起的负效应.多胺预处理可缓解胁迫引起的伤害,通过转基因技术过量表达多胺可提高植物胁迫耐性.本文综述了生物胁迫和非生物胁迫条件下,多胺的合成、代谢、功能及其作为抗氧化剂减少胁迫诱导氧化损伤的研究现状.重点综述了病虫胁迫、盐胁迫、重金属胁迫、渗透胁迫,也简要的综述了其它胁迫如低氧胁迫、冷胁迫、酸胁迫、辐射胁迫等条件下植物体内多胺合成的变化及功能.     

The role of polyamines during <Emphasis Type="Italic">in vivo</Emphasis> and <Emphasis Type="Italic">in vitro</Emphasis> development

Polyamines are ubiquitous polycationic compounds that mediate fundamental aspects of cell growth, differentiation, and cell death in eukaryotic and prokaryotic organisms. In plants, polyamines are implicated in a variety of growth and developmental processes, in addition to abiotic and biotic stress responses. In the last decade, mutant studies conducted predominantly in Arabidopsis thaliana revealed an obligatory requirement for polyamines in zygotic and somatic embryogenesis. Moreover, our appreciation for the intricate spatial and temporal regulation of intracellular polyamine levels has advanced considerably. The exact molecular mechanism(s) through which polyamines exert their physiological response remains somewhat enigmatic and likely serves as a major area for future research efforts. In the following review, we discuss recent advances in the plant polyamine field, which range from metabolism and mutant characterization to molecular genetics and potential mode(s) of polyamine action during growth and development in vitro and in vivo. This review will also focus on the specific role of polyamines during embryogenesis and organogenesis.     

Polyamines and abiotic stress tolerance in plants

Environmental stresses including climate change, especially global warming, are severely affecting plant growth and productivity worldwide. It has been estimated that two-thirds of the yield potential of major crops are routinely lost due to the unfavorable environmental factors. On the other hand, the world population is estimated to reach about 10 billion by 2050, which will witness serious food shortages. Therefore, crops with enhanced vigour and high tolerance to various environmental factors should be developed to feed the increasing world population. Maintaining crop yields under adverse environmental stresses is probably the major challenge facing modern agriculture where polyamines can play important role. Polyamines (PAs)(putrescine, spermidine and spermine) are group of phytohormone-like aliphatic amine natural compounds with aliphatic nitrogen structure and present in almost all living organisms including plants. Evidences showed that polyamines are involved in many physiological processes, such as cell growth and development and respond to stress tolerance to various environmental factors. In many cases the relationship of plant stress tolerance was noted with the production of conjugated and bound polyamines as well as stimulation of polyamine oxidation. Therefore, genetic manipulation of crop plants with genes encoding enzymes of polyamine biosynthetic pathways may provide better stress tolerance to crop plants. Furthermore, the exogenous application of PAs is also another option for increasing the stress tolerance potential in plants. Here, we have described the synthesis and role of various polyamines in abiotic stress tolerance in plants.Key words: abiotic stress tolerance, putrescine, spermidine, spermine, polyamines     

Polyamines and abiotic stress: recent advances

Summary. In this review we will concentrate in the results published the last years regarding the involvement of polyamines in the plant responses to abiotic stresses, most remarkably on salt and drought stress. We will also turn to other types of abiotic stresses, less studied in relation to polyamine metabolism, such as mineral deficiencies, chilling, wounding, heavy metals, UV, ozone and paraquat, where polyamine metabolism is also modified. There is a great amount of data demonstrating that under many types of abiotic stresses, an accumulation of the three main polyamines putrescine, spermidine and spermine does occur. However, there are still many doubts concerning the role that polyamines play in stress tolerance. Several environmental challenges (osmotic stress, salinity, ozone, UV) are shown to induce ADC activity more than ODC. The rise in Put is mainly attributed to the increase in ADC activity as a consequence of the activation of ADC genes and their mRNA levels. On the other hand, free radicals are now accepted as important mediators of tissue injury and cell death. The polycationic nature of polyamines, positively charged at physiological pH, has attracted the attention of researchers and has led to the hypothesis that polyamines could affect physiological systems by binding to anionic sites, such as those associated with nucleic acids and membrane phospholipids. These amines, involved with the control of numerous cellular functions, including free radical scavenger and antioxidant activity, have been found to confer protection from abiotic stresses but their mode of action is not fully understood yet. In this review, we will also summarize information about the involvement of polyamines as antioxidants against the potential abiotic stress-derived oxidative damage. Authors’ address: Dr. María Patricia Benavides, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, Buenos Aires 1113, Argentina     

Polyamines: essential factors for growth and survival

Polyamines are low molecular weight, aliphatic polycations found in the cells of all living organisms. Due to their positive charges, polyamines bind to macromolecules such as DNA, RNA, and proteins. They are involved in diverse processes, including regulation of gene expression, translation, cell proliferation, modulation of cell signalling, and membrane stabilization. They also modulate the activities of certain sets of ion channels. Because of these multifaceted functions, the homeostasis of polyamines is crucial and is ensured through regulation of biosynthesis, catabolism, and transport. Through isolation of the genes involved in plant polyamine biosynthesis and loss-of-function experiments on the corresponding genes, their essentiality for growth is reconfirmed. Polyamines are also involved in stress responses and diseases in plants, indicating their importance for plant survival. This review summarizes the recent advances in polyamine research in the field of plant science compared with the knowledge obtained in microorganisms and animal systems.     

Comparative roles of brassinosteroids and polyamines in salt stress tolerance

Salt stress is among the major abiotic stresses that adversely affect the global crop production and its adverse impacts are getting more serious in the regions where saline water is used for irrigation. It induces reactive oxygen species, alters the activity of antioxidant system and adversely affects the process of photosynthesis. Various strategies have been employed to mitigate the deleterious effects of salt stress. Presently, the recommended strategies to overcome the adverse effects of salt stress include the use of tolerant cultivars, ameliorative water management and diverse cultural practices. However, none of these approaches have been found to be fully effective under salt stress conditions. An alternative and technically simpler approach to induce salt stress tolerance is the exogenous application of plant growth regulators (PGRs). This technique has gained significant importance during the past decade. PGRs have been implicated to regulate a wide range of metabolic and physiological activities in plants, ranging from cell division and organogenesis to protection against biotic and abiotic stresses. One of the important factors for enhanced plant productivity by PGRs is their efficiency to overcome the salt-induced stress conditions. Recent findings on the effects of brassinosteroids and polyamines on the salt stress tolerance of crops open new avenues to address the salinity problems. This review enlightens the role of brassinosteroids and polyamines in different plant processes like their role in regulation of photosynthesis, antioxidant systems and other related aspects, thereby improving overall performance of plants.     

In vivo role of Arabidopsis arginase in arginine metabolism and abiotic stress response

Nitric oxide (NO) and polyamines play essential roles in many developmental processes and abiotic stress responses in plants. NO and polyamines are metabolized from arginine through NO synthase (NOS) and arginine decarboxylase (ADC), respectively. Function of arginase, another important enzyme involved in arginine metabolism, in abiotic stress remains largely unknown. In the recent study, we have dissected the impact of arginase on arginine metabolism and abiotic stress responses through manipulating AtARGAHs expression. The results suggested that manipulation of arginase expression modulated accumulation of arginine and direct downstream products of arginine catabolism. AtARGAHs knockout lines exhibited increased accumulation of polyamines and NO and enhanced abiotic stress tolerance, while AtARGAHs overexpressing lines displayed the opposite results. Notably, we highlighted that Arabidopsis arginase plays distinctive and dual roles in the crosstalk between polyamines and NO signaling during abiotic stress responses, mediating both arginine metabolism and reactive oxygen species (ROS) accumulation. It is likely that accumulation of both NO and polyamines might activate abiotic stress responses in the plant.     

Role of Polyamines in Apoptosis and Other Recent Advances in Plant Polyamines

Numerous citations in the literature indicate that polyamines are intensively studied in plants. Polyamines are implicated in many functions of the plant cell. Excellent recent reviews cover much of this original research. This article is focused primarily on literature that relates research on the role of polyamines in apoptosis and programmed cell death in both plants and animals. Apoptosis and programmed cell death are considerably better studied in animal systems, and this review demonstrates that the role of polyamines in these processes in plant systems are remarkably congruent with what is known in animal systems. In addition, key recent research reports are reviewed that describe the functional analysis of key polyamine biosynthesis genes in plants in relation to responses to environmental stress signals. Molecular analysis is providing strong evidence for the polyamine biosynthetic pathways to play major roles in ameliorating plant responses to abiotic stresses.     

Metabolism and function of polyamines in plants: recent development (new approaches)

A review is presented of the recent developments in the metabolism andfunction of polyamines in plants. Polyamines appear to be involved in a widerange of plant processes so their exact role is not completely understood. Inthis review, the metabolic pathways involved in polyamine biosynthesis anddegradation are explained, along with the transport and conjugation of thesecompounds. The methodologies involved in the analysis of polyamine functionusing metabolic inhibitors and genetic and molecular approaches are described.The occurrence and distribution of polyamine-derived alkaloids are also dealtwith. The direction of future research in the study of plant polyamines isindicated.     

Polyamines, polyamine oxidases and nitric oxide in development, abiotic and biotic stresses

Nitric oxide (NO), polyamines (PAs), diamine oxidases (DAO) and polyamine oxidases (PAO) play important roles in wide spectrum of physiological processes such as germination, root development, flowering and senescence and in defence responses against abiotic and biotic stress conditions. This functional overlapping suggests interaction of NO and PA in signalling cascades. Exogenous application of PAs putrescine, spermidine and spermine to Arabidopsis seedlings induced NO production as observed by fluorimetry and fluorescence microscopy using the NO-binding fluorophores DAF-2 and DAR-4M. The observed NO release induced by 1 mM spermine treatment in the Arabidopsis seedlings was very rapid without apparent lag phase. These observations pave a new insight into PA-mediated signalling and NO as a potential mediator of PA actions. When comparing the functions of NO and PA in plant development and abiotic and biotic stresses common to both signalling components it can be speculated that NO may be a link between PA-mediated stress responses filing a gap between many known physiological effects of PAs and amelioration of stresses. NO production indicated by PAs could be mediated either by H₂O₂, one reaction product of oxidation of PAs by DAO and PAO, or by unknown mechanisms involving PAs, DAO and PAO.     

Functions of amine oxidases in plant development and defence

Copper amine oxidases and flavin-containing amine oxidases catalyse the oxidative de-amination of polyamines, which are ubiquitous compounds essential for cell growth and proliferation. Far from being only a means of degrading cellular polyamines and, thus, contributing to polyamine homeostasis, amine oxidases participate in important physiological processes through their reaction products. In plants, the production of hydrogen peroxide (H(2)O(2)) deriving from polyamine oxidation has been correlated with cell wall maturation and lignification during development as well as with wound-healing and cell wall reinforcement during pathogen invasion. As a signal molecule, H(2)O(2) derived from polyamine oxidation mediates cell death, the hypersensitive response and the expression of defence genes. Furthermore, aminoaldehydes and 1,3-diaminopropane from polyamine oxidation are involved in secondary metabolite synthesis and abiotic stress tolerance.     

Selective regulation of polyamine metabolism with methylated polyamine analogues

Polyamine metabolism is intimately linked to the physiological state of the cell. Low polyamines levels promote growth cessation, while increased concentrations are often associated with rapid proliferation or cancer. Delicately balanced biosynthesis, catabolism, uptake and excretion are very important for maintaining the intracellular polyamine homeostasis, and deregulated polyamine metabolism is associated with imbalanced metabolic red/ox state. Although many cellular targets of polyamines have been described, the precise molecular mechanisms in these interactions are largely unknown. Polyamines are readily interconvertible which complicate studies on the functions of the individual polyamines. Thus, non-metabolizable polyamine analogues, like carbon-methylated analogues, are needed to circumvent that problem. This review focuses on methylated putrescine, spermidine and spermine analogues in which at least one hydrogen atom attached to polyamine carbon backbone has been replaced by a methyl group. These analogues allow the regulation of both metabolic and catabolic fates of the parent molecule. Substituting the natural polyamines with methylated analogue(s) offers means to study either the functions of an individual polyamine or the effects of altered polyamine metabolism on cell physiology. In general, gem-dimethylated analogues are considered to be non-metabolizable by polyamine catabolizing enzymes spermidine/spermine-N ¹-acetyltransferase and acetylpolyamine oxidase and they support short-term cellular proliferation in many experimental models. Monomethylation renders the analogues chiral, offering some advantage over gem-dimethylated analogues in the specific regulation of polyamine metabolism. Thus, methylated polyamine analogues are practical tools to meet existing biological challenges in solving the physiological functions of polyamines.