Volume 1 Number 1 2007

CONTENTS AND ABSTRACTS

Boris B. Vartapetian (Russia), Robert M.M. Crawford (UK) The International Society for Plant Anaerobiosis: History, Functions and Activity (pp 1-3)

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John M. Cheeseman (USA) Hydrogen Peroxide and Plant Stress: A Challenging Relationship (pp 4-15)

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Special Feature: The relationship between plants and hydrogen peroxide is a challenging one: H₂O₂ has many essential roles in plant metabolism but at the same time, accumulation related to virtually any environmental stress is potentially damaging. In this review, I consider H₂O₂ physiology broadly, both as a stress and as a developmentally and physiologically important metabolite, including its sources and mobility, and the vexing question of tissue level concentrations. I then consider problems associated with H₂O₂ as a signaling molecule, including mechanisms of H₂O₂ sensing, signaling, and response networks. Finally, I discuss recent advances in transcript network modeling, and complex systems approaches to understanding the interactions between the transcriptome, proteome and metabolome in responses to H₂O₂.

Markus Wunderlich, Jasmin Doll, Wolfgang Busch, Christiane Katja Kleindt, Christian Lohmann, Fritz Schöffl (Germany) Heat Shock Factors: Regulators of Early and Late Functions in Plant Stress Response (pp 16-22)

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Invited Mini-Review: Heat shock factors (HSFs) among others are of great importance regarding the regulation of increased stress tolerance. Based on structural characteristics and phylogenetic comparison plant HSFs are subdivided into 3 classes and several subgroups. Recent studies showed that different HSFs play important roles during early and late stages of stress response. In this review, we focus mainly on the functional characterisation of class A HSFs of Arabidopsis, which are known to function as transcriptional activators of stress target genes. Recent evidence obtained from the identification of HSF-knockout mutants and microarray expression profiling indicates that different early and late HSF regulate large numbers of partially overlapping sets of target genes. Meta-analysis of microarray data generated from different experimental setup may have the potential to verify known and/or to identify novel HSF target genes. In addition, we will summarise recent work on the potential roles of oxidative stress leading to the activation of HSFs and the induction of the heat stress response.

Alex Boyko, Igor Kovalchuk (Canada) Genetic and Epigenetic Nature of Transgenerational Changes in Stressed Plants (pp 23-31)

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Invited Review: Plants, as sedentary organisms, are constantly exposed to a variety of abiotic and biotic factors. The ability for quick adaptation is perhaps the major reason for the diversity of plant species on our planet. The fact that plants are able to adapt within a single generation upon exposure to stress suggests the involvement of epigenetic mechanisms of inheritance. Changes in genome methylation and histone acetylation/methylation, being a part of epigenetic regulation, lead to a differential ability of certain areas of the genome to rearrange. If directed to a particular genomic region, epigenetic changes could result in an increased frequency of rearrangements leading to appearance of novel genes, thus new traits. We believe that epigenetic alterations are a general mechanism of plant adaptation to stress, and are the initial mechanism of permanent genomic changes leading to genome evolution. Here we present several examples of the influence of various abiotic and biotic factors on plant genome stability and plant tolerance to stress. We describe the influence of viral and bacterial pathogens on tobacco (Nicotiana tabacum) and Arabidopsis (Arabidopsis thaliana) genomes. Our experiments suggest that exposure of plants to pathogen stress triggers the production of a plant-derived signal, named the systemic recombination signal (SRS), that is capable of changing the stability of the plant genome. Infected plants “propagate” the information about pathogen infection by passing the signal to meiotic tissue. Progeny of infected plants show changes in global genome and loci-specific methylation patterns, indicating the epigenetic nature of the signal. This leads to multiple changes in plant physiology, including higher tolerance to stress and increased instability of resistance gene loci. Similar results were also obtained after exposure to several unrelated abiotic stresses. In this review we introduce a novel theory of stress-induced plant genome evolution and discuss the mechanisms behind such a phenomenon.

M.B. Arnao, J. Hernández-Ruiz (Spain) Recommendations for Determining Antioxidant Activity to Study Redox Status and Plant Stress (pp 32-36)

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Invited Mini-Review: Antioxidant activity is a very useful parameter for characterizing the potential of biological samples to scavenge reactive oxygen and nitrogen species and other dangerous free radicals in specific reaction media. This parameter has been extensively used in fields such as phytochemistry, food chemistry, food science and technology, human and animal physiology, dietetics and nutrition. It has also been used in plant physiology, but to a lesser extent. Several methodological approaches for measuring antioxidative capacity in plant extracts are presented and the advantages and disadvantages of the most relevant methods from a physiological point of view are discussed. The discrimination between hydrophilic and lipophilic antioxidant activities is very important for identifying the specific antioxidants present in plant samples. The plant redox status of different tissues and its relationship with plant stress situations can be studied by reference to the antioxidant activity, which is an interesting parameter that permits us to investigate the overall antioxidative potential, its distribution, its evolution and its adaptation to different environmental situations. Possible future applications are also presented.

Francisco J. Corpas, Alfonso Carreras, Raquel Valderrama, Mounira Chaki, José M. Palma, Luis A. del Río, Juan B. Barroso (Spain) Reactive Nitrogen Species and Nitrosative Stress in Plants (pp 37-41)

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Invited Mini-Review: Nitric oxide (^.NO) is a gaseous free radical which can have two opposite physiological roles in higher plants. While a high cellular production of ^.NO can bring about extensive cellular damage, at low levels this compound is involved as a signal molecule in many important physiological processes. ^.NO and a family of related molecules, including peroxynitrite (ONOO^-), S-nitrosoglutathione (GSNO) and nitrotyrosine (nTyr), among others, are designated with the term reactive nitrogen species (RNS). Under stress conditions, plants can undergo a de-regulated synthesis or overproduction of ^.NO and NO-derived products that can have toxic physiological consequences. This situation is known as nitrosative stress, due to its similarities with animal systems, and can produce important changes in plant cells. In this article the current knowledge of these effects of RNS on the physiology of plants under stress conditions is briefly reviewed.

Young-Su Seo (USA), Jung-Il Cho, Sang-Kyu Lee, Hak-Seung Ryu, Muho Han, Tae-Ryong Hahn (Korea), Uwe Sonnewald (Germany), Jong-Seong Jeon (Korea) Current Insights into the Primary Carbon Metabolic Flux that Occurs in Plants Undergoing a Defense Response (pp 42-49)

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Invited Mini-Review: The precise control of photoassimilate production, partitioning, and storage is a crucial process during plant growth and development. An excess of carbohydrates mediates important regulatory processes, including the down-regulation of source-specific genes and the up-regulation of sink-specific gene repertoires. Such source-to-sink transitions occur also in plant cells infected with biotrophic pathogens. A growing body of evidence now indicates that successful plant defense responses are accomplished by the reprogramming of a diverse set of cellular pathways that are associated with an increased demand for energy. Notably, it is frequently observed that cell wall-bound invertase (CW-INV) activity is rapidly induced at the infection site, indicating an early metabolic transition of host cells to overcome the invading pathogen. The shift from housekeeping to defense metabolism is also evident on the basis of microarray-based global transcript analysis. However, the intimate relationship between the changes in primary carbon metabolism and defense responses in plants remains poorly understood. In our present review, we focus on the current knowledge of this phenomenon with respect to the reprogramming of primary carbon metabolism and its potential role in the reinforcement of defense mechanisms in infected plants.

Vladimir V. Kuznetsov, Nina I. Shevyakova (Russia) Polyamines and Stress Tolerance of Plants (pp 50-71)

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Invited Review: Polyamines are universal organic polycations implicated in a wide array of fundamental processes in plants ranging from triggering the cell cycle, genome expression, signaling, plant growth and development to plant adaptation toward abiotic stresses. Stress-induced accumulation of polyamines often correlates with the improvement of plant tolerance that has been shown by modulation of the polyamine biosynthetic pathway in some transgenic plants. Genes for several key biosynthetic and catabolic enzymes have been cloned from various plant species. Polyamines can modulate functions of RNA, DNA, nucleotide triphosphates, and proteins and protect macromolecules under stress. Polyamines are also the modulators of stress-regulated gene expression and exhibit antioxidant properties. Taken together, these recent findings have promoted intense efforts to characterize in detail the mechanisms of polyamine homeostasis regulation and to elucidate realization of their multifunctional role in plants under environmental stress. However, molecular mechanisms underlying polyamine participation in plant adaptation to stress are not completely understood. Plant adaptation to various abiotic stresses is a complex process involving numerous changes, including the increased expression of many stress-related genes responsible for the accumulation of compatible solutes, expression of antioxidant enzymes, and supression of energy-consuming pathways. Recent reviews did not summarize data concerning the correlation between polyamine functions and other adaptive mechanisms in plants. Therefore in this review, particular emphasis is placed on discussion on protective mechanisms used by polyamines during different stages of the adaptation process.

Jill M. Farrant, Wolf Brandt, George G. Lindsey (South Africa) An Overview of Mechanisms of Desiccation Tolerance in Selected Angiosperm Resurrection Plants (pp 72-84)

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Invited Mini-Review: The vegetative tissues of resurrection plants, like seeds, can tolerate desiccation to 5% relative water content (RWC) for extended periods and yet resume full metabolic activity on re-watering. In this review we will illustrate how this is achieved in a variety of angiosperm resurrection plants, our studies ranging from the ecophysiological to the biochemical level. At the whole plant level, leaf folding and other anatomical changes serve to minimise light and mechanical stress associated with drying and rehydration. The mechanisms of cell wall folding are described for Craterostigma wilmsii and Myrothanmus flabellifolia. Free radicals, radical oxygen species (ROS) usually generated under water-deficit stress by photosynthesis, are minimised by either homoiochlorophylly (e.g. C. wilmsii and M. flabellifolia) or poikilochlorophylly (e.g. Xerophyta sp.). The antioxidant systems of these plants effectively deal with ROS generated by other metabolic processes. In addition to antioxidants common to most plants, resurrection plants also accumulate polyphenols such as 3, 4, 5 tri-o-galloylquinic acid in M. flabellifolia, and seed-associated antioxidants (e.g. 1-cys-peroxiredoxin and metallothionines) as effective ROS scavengers. Sucrose accumulates at low RWC, presumably protecting the sub-cellular milieu against desiccation-induced macromolecular denaturation.

Ron Porat (Israel), Charles L. Guy (USA) Arabidopsis as a Model System to Study Chilling Tolerance Mechanisms in Plants (pp 85-92)

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Invited Mini-Review: Many plants of tropical and subtropical origin, including a large number of economically important crops, such as tomato, rice, cotton, cucumber and maize, are severely damaged when exposed to temperatures between 2 and 15°C (chilling temperatures). The symptoms of these chilling injuries include cessation of growth, wilting, chlorosis, and necrosis. In contrast with chilling-sensitive species, the cruciferous plant Arabidopsis thaliana is chilling tolerant, and is able to grow to maturity even at a low temperature of 4°C. Therefore, at the genetic level, Arabidopsis may provide a useful model plant system for the identification of chilling-tolerance traits. Taking a mutational approach several ethyl methanesulphonate (EMS) and T-DNA insertion chilling-sensitive mutants have been identified that show wild-type phenotypes when grown at normal temperatures, but are severely damaged following transfer to low temperatures. These mutants provide valuable genetic sources for the identification of structural or regulatory genes that are crucial for plant survival at chilling temperatures. Furthermore, it has been reported that a number of mutations at several genetic loci involved in fatty acid biosynthesis (fab1) and fatty acid desaturation (fad2, fad5 and fad6) resulted in reduced-growth and chlorosis phenotypes at low temperatures, thus providing direct evidence for the contribution of lipid polyunsaturation to low-temperature fitness. Arabidopsis has also proven to be an efficient model system for the identification of major biochemical mechanisms involved in protection of the photosynthesis system from photooxidative damage following exposure to excess light energy at low temperatures. DNA microarray studies have revealed new insights into the complex network of transcriptional regulation at low temperatures and the possible interrelationships between cold-regulated gene expression and acquisition of chilling tolerance but this work is just beginning. At last, recently, Arabidopsis is also being used as a main model plant system to study possible genetic linkages between the programmed cell death (PCD) mechanism and development of necrotic lesions following exposure to biotic and abiotic stresses, including chilling. Overall, it is concluded that Arabidopsis can potentially be an ideal model system for basic studies on chilling stress and for identification of key components of chilling-tolerance traits in plants.

Ana Fita, Belén Picó, Fernando Nuez (Spain) Melon Roots under Stress: Melon Vine Decline (pp 93-104)

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Invited Review: Melon Vine Decline is a severe root rot disease of increasing worldwide importance, characterized by a sudden plant collapse at harvest time. Monosporascus cannonballus Pollack et Uecker is the main causal agent, but other soilborne pathogens, certain stressful cultural practices and environmental conditions enhance disease symptoms. Due to its complexity, etiological studies as well as methodologies that detect and assess the disease (ranging from visual lesion scoring to real-time PCR) have been needed to select the best control methods. As vine decline depends on the soil inoculum, on the susceptibility of the plant and on the hydraulic balance of the plant, control methods have been focused on the following three main directions: I) Reducing/inactivating the soil inoculum: achieved only partially through chemical control, biological control and cultural practices; II) Increasing the resistance to root lesions: certain cultivars suffer fewer root lesions, and some breeding lines derived from the resistant accession Pat 81 (C. melo subsp. agrestis) are about to be released; III) Improving the hydraulic balance of the plant: Pat 81 has shown to be useful through grafting or by breeding for improved root systems due to its large and branched root system. Improving root systems is crucial not only in overcoming melon vine decline but also in overcoming many soil stresses. New in vitro culture techniques along with root image analysis allow accurate in vivo studies of root development. The combined use of these technologies has led to an adequate control of the disease. In addition, the generation of new genomic tools for melon is allowing a deeper knowledge of the biological/genetic mechanism involved in the disease.

S.J. Tabatabaei (Iran) Salinity Stress and Olive: An Overview (pp 105-112)

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Invited Review: Olive (Olea europaea L.) is a schleropyllous evergreen tree which is an important tree crop with a large distribution in the Mediterranean and Middle East regions. The environmental adaptability of the olive tree and its tolerance to drought and salinity has made it possible for most of these new plantations to be established in arid and marginal areas. In many such areas the only water available for irrigation is saline. Recent research indicates that certain olive cultivars are able to tolerate salinity of 5800 mg l^-1 (EC ?8 dS m^-1) producing new growth at a leaf Na concentration of 4-6 mg g^-1 Dwt. Salt tolerance in olives significantly depends on the cultivar and is most likely due to control of salt translocation to the shoots. Many studies show that the mechanism of salt tolerance is placed in the roots preventing the translocation of toxic ions, rather than absorption. The exchange of K⁺-Na⁺ at the plasmalemma membrane seems to promote the modulation of Na⁺ transport to the shoot. A high level of NaCl salinity significantly reduces the concentration of N, NO₃, K and nitrate reductase in the leaves, leading to an alteration in nutritional status. In salt tolerant cultivars, either a low or moderate salinity have a negligible effect on the growth of olive. However, in salt sensitive cultivars it reduces olive growth, which is associated with the reduction of CO₂ assimilation rate, stomatal and mesophyll conductance. Salinity tends to reduce fruit size, oil content and the ratio of unsaturated/saturated fatty acids but it has no effect on total phenol content. Salt tolerance in olive cultivars is associated with effective mechanisms of ion exclusion and retention of Na⁺ and Cl⁻ in the roots. It should be possible to establish new cultivation in arid and saline lands by understanding the physiology of tolerance to salinity, screening salt tolerant cultivars and utilizing advanced agro-techniques in saline conditions.

Daisuke Matsuoka, Toto Hadiarto, Takashi Nanmori (Japan) Cell Signaling and Response Via Mitogen-Activated Protein Kinase (MAPK) Cascade in Arabidopsis (pp 113-117)

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Invited Mini-Review: Plant cells respond specifically to environmental conditions such as temperature, light, pH and parasite attacks. The involvement of signal transduction is inevitable in relation to activated chains of intracellular signaling responses. The intracellular signal processing depends on specific interactions between proteins. Protein phosphorylation is amongst events that play significant roles in the protein-protein communication to make up signal relay. The mitogen-activated protein kinase (MAPK) is one of many kinds of plant protein kinases that have been reported in the past decade. MAPK cascade plays essential roles in the signal transduction process. In plants, the cascade has been implicated in relaying signal of various plant hormones and stress stimuli. It consists of MAPK, MAPK kinase (MAPKK) and MAPKK kinase (MAPKKK). Activated MAPKKK phosphorylates MAPKK, thus activated MAPKK in turn activates MAPK through phosphorylation. The extracellular signaling is relayed through this MAPK cascade resulting in switching gene expression on/off or activation/inactivation of cell response matters, and by doing so physiological and morphological changes to adapt external situation are fulfilled.  In Arabidopsis thaliana, genome analysis reveals 20 different genes encoding MAPKs, 10 MAPKK genes and 60 MAPKKK genes, suggesting complicated signal networks of this cascade. Recently, each set of plant MAPK cascade begins to be investigated and several evidences are shown. We have done research projects especially on Arabidopsis MAPKK (AtMEK1) and showed AtMEKK1-AtMEK1-AtMPK4 cascade that becomes active and works on a wounding stimulus. This review will discuss the mechanism and roles of plant protein phosphorylation via three-component MAPK cascade, focus especially on Arabidopsis MAPKKs and encompass a recent review of this field.

Masashi Miyama, Nobutaka Hanagata (Japan) Microarray Gene Expression Profiling for Salt Tolerant Gene Selection (pp 118-122)

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Invited Mini-Review: Salt stress is serious threat to agriculture and sustainability of world food supply. The generation of transgenic crops with increased salt tolerance would contribute to address the problem. In this article, we argue that the microarray expression profiling for global salt-tolerant gene selection towards a generation of transgenic plants that can tolerate high levels of salinity. Although there have been several successes in producing transgenic plants with increased salt tolerance, no genes so far have been from microarray gene selection. Microarray systematic gene selection can be a rapid and effective way to identify the gene that confers high salt tolerance. We especially focus on salt tolerant study on halophytes. Most of salt tolerant studies have been on glycophyte, lacking the genetic basis of high-salinity tolerant. Study of halophyte may be instructive. The gene resource of halophytes may have unique salt tolerant determinants that are absent in model glycophyte plants, and are expected to have novel genes that could increase salt tolerance in transgenic plants.