ROS signalling--specificity is required

Transcriptomic Response of Chinese Yew (Taxus chinensis) to Cold Stress

Taxus chinensis is a rare and endangered shrub, highly sensitive to temperature changes and widely known for its potential in cancer treatment. How gene expression of T. chinensis responds to low temperature is still unknown. To investigate cold response of the genus Taxus, we obtained the transcriptome profiles of T. chinensis grown under normal and low temperature (cold stress, 0°C) conditions using Illumina Miseq sequencing. A transcriptome including 83,963 transcripts and 62,654 genes were assembled from 4.16 Gb of reads data. Comparative transcriptomic analysis identified 2,025 differently expressed (DE) isoforms at p < 0.05, of which 1,437 were up-regulated by cold stress and 588 were down-regulated. Annotation of DE isoforms indicated that transcription factors (TFs) in the MAPK signaling pathway and TF families of NAC, WRKY, bZIP, MYB, and ERF were transcriptionally activated. This might have been caused by the accumulation of secondary messengers, such as reactive oxygen species (ROS) and Ca²⁺. While accumulation of ROS will have caused damages to cells, our results indicated that to adapt to low temperatures T. chinensis employed a series of mechanisms to minimize these damages. The mechanisms included: (i) cold-enhanced expression of ROS deoxidant systems, such as peroxidase and phospholipid hydroperoxide glutathione peroxidase, to remove ROS. This was further confirmed by analyses showing increased activity of POD, SOD, and CAT under cold stress. (ii) Activation of starch and sucrose metabolism, thiamine metabolism, and purine metabolism by cold-stress to produce metabolites which either protect cell organelles or lower the ROS content in cells. These processes are regulated by ROS signaling, as the "feedback" toward ROS accumulation.

Chemical control of flowering time

Flowering at the right time is of great importance; it secures seed production and therefore species survival and crop yield. In addition to the genetic network controlling flowering time, there are a number of much less studied metabolites and exogenously applied chemicals that may influence the transition to flowering as well as flower opening. Increased emphasis on research within this area has the potential to counteract the negative effects of global warming on flowering time, especially in perennial crop plants. Perennial crops have a requirement for winter chill, but winters become increasingly warm in temperate regions. This has dramatic effects on crop yield. Different strategies are therefore being developed to engineer flowering time to match local growing conditions. The majority of these efforts are within plant breeding, which benefits from a substantial amount of knowledge on the genetic aspects of flowering time regulation in annuals, but less so in perennials. An alternative to plant breeding approaches is to engineer flowering time chemically via the external application of flower-inducing compounds. This review discusses a variety of exogenously applied compounds used in fruit farming to date, as well as endogenous growth substances and metabolites that can influence flowering time of annuals and perennials.

Nitric oxide-polyamines cross-talk during dormancy release and germination of apple embryos

Nitric oxide (NO) and polyamines (PAs) belong to plant growth and development regulators. These compounds play a key role in numerous physiological processes e.g. seed germination. Based on the suggestion of overlapping of NO and PAs biosynthetic pathways, we demonstrated a cross-talk of NO and PAs in regulation of embryonic dormancy release. The aim of the work was to investigate an impact of PAs (Put, Spd and Spm) or NO short-term fumigation on nitrite, urea, Arg and ornithine (Orn) content, NO synthase-like (NOS-like) and arginase activity in axes of apple (Malus domestica Borkh.) embryos during dormancy alleviation and at the stage of termination of germination sensu stricto. NO, Put/Spd induced dormancy breakage and germination of apple embryos corresponded to stimulation of urea cycle and high free Arg pool in seedlings roots. After two days of the culture Put and Spd stimulated Arg dependent NO formation, inhibition of which was observed after Spm application. Put or Spd application as well as NO short-term pretreatment of apple embryos influenced level of ubiquitin-conjugated proteins. Higher abundance of such modified proteins correlated well to the declined content of nitrated proteins, suggesting their important role in regulation of embryo germination. NO led to stimulation of embryos germination by increasing level of free PAs (mostly Put). While transcriptomic approach showed down regulation of Spm synthesis and up-regulation of Spm degradation by NO, confirming negative role of Spm over-accumulation in embryo dormancy removal. Our data clearly indicate positive relationship of NO-Put/Spd acting as dormancy removing factors.

The role of mitochondria in plant development and stress tolerance

Eukaryotic cells require orchestrated communication between nuclear and organellar genomes, perturbations in which are linked to stress response and disease in both animals and plants. In addition to mitochondria, which are found across eukaryotes, plant cells contain a second organelle, the plastid. Signaling both among the organelles (cytoplasmic) and between the cytoplasm and the nucleus (i.e. nuclear-cytoplasmic interactions (NCI)) is essential for proper cellular function. A deeper understanding of NCI and its impact on development, stress response, and long-term health is needed in both animal and plant systems. Here we focus on the role of plant mitochondria in development and stress response. We compare and contrast features of plant and animal mitochondrial genomes (mtDNA), particularly highlighting the large and highly dynamic nature of plant mtDNA. Plant-based tools are powerful, yet underutilized, resources for enhancing our fundamental understanding of NCI. These tools also have great potential for improving crop production. Across taxa, mitochondria are most abundant in cells that have high energy or nutrient demands as well as at key developmental time points. Although plant mitochondria act as integrators of signals involved in both development and stress response pathways, little is known about plant mtDNA diversity and its impact on these processes. In humans, there are strong correlations between particular mitotypes (and mtDNA mutations) and developmental differences (or disease). We propose that future work in plants should focus on defining mitotypes more carefully and investigating their functional implications as well as improving techniques to facilitate this research.

Disulfiram chelated with copper promotes apoptosis in human breast cancer cells by impairing the mitochondria functions

Disulfiram (DSF) has been proved to have broad-spectrum anti-alcoholism effects, and it is also found to show stronger anti-tumor effects after chelating with Cu²⁺ to form DSF-Cu complex. In this work, we studied the anti-tumor activity of DSF-Cu in MCF-7 cells by flow cytometry, confocal laser scanning microscope, and atomic force microscopy to clarify the underlying anti-tumor mechanisms. MCF-7 cells were incubated with 50, 100, 150, 200, and 250 nM DSF chelated with 10 µM CuCl₂ for 24 h. The results showed that DSF-Cu could induce the accumulation of MCF-7 cells in G2/M phase and apoptosis in a concentration-dependent manner. Additionally, atomic force microscope (AFM) analysis at nanoscale level showed that the morphology of cell was significantly shrunk with destroyed filopodia and ultrastructure presented many irregular protuberances on the cell membrane after DSF-Cu treatment, which was closely associated with the re-arrangement of cytoskeleton. DSF-Cu induced the production of reactive oxygen species (ROS), increased the concentration of intracellular Ca²⁺ and decreased the mitochondrial membrane potential (MMP) in MCF-7 cells resulting in a mitochondria-dependent apoptosis pathway. The results indicated that DSF-Cu has a potential anti-tumor activity in breast cancer by impairing the mitochondria functions. SCANNING 38:825-836, 2016. © 2016 Wiley Periodicals, Inc.

Modification of the endogenous NO level influences apple embryos dormancy by alterations of nitrated and biotinylated protein patterns

NO donors and Arg remove dormancy of apple embryos and stimulate germination. Compounds lowering NO level (cPTIO, L -NAME, CAN) strengthen dormancy. Embryo transition from dormancy state to germination is linked to increased nitric oxide synthase (NOS)-like activity. Germination of embryos is associated with declined level of biotin containing proteins and nitrated proteins in soluble protein fraction of root axis. Pattern of nitrated proteins suggest that storage proteins are putative targets of nitration. Nitric oxide (NO) acts as a key regulatory factor in removal of seed dormancy and is a signal necessary for seed transition from dormant state into germination. Modulation of NO concentration in apple (Malus domestica Borkh.) embryos by NO fumigation, treatment with NO donor (S-nitroso-N-acetyl-D,L-penicillamine, SNAP), application of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), N ω-nitro-L-arginine methyl ester (L-NAME), canavanine (CAN) or arginine (Arg) allowed us to investigate the NO impact on seed dormancy status. Arg analogs and NO scavenger strengthened embryo dormancy by lowering reactive nitrogen species level in embryonic axes. This effect was accompanied by strong inhibition of NOS-like activity, without significant influence on tissue NO2 (-) concentration. Germination sensu stricto of apple embryos initiated by dormancy breakage via short term NO treatment or Arg supplementation were linked to a reduced level of biotinylated proteins in root axis. Decrease of total soluble nitrated proteins was observed at the termination of germination sensu stricto. Also modulation of NO tissue status leads to modification in nitrated protein pattern. Among protein bands that correspond to molecular mass of approximately 95 kDa, storage proteins (legumin A-like and seed biotin-containing protein) were identified, and can be considered as good markers for seed dormancy status. Moreover, pattern of nitrated proteins suggest that biotin containing proteins are also targets of nitration.

ROS signalling in a destabilised world: A molecular understanding of climate change

Climate change results in increased intensity and frequency of extreme abiotic and biotic stress events. In plants, reactive oxygen species (ROS) accumulate in proportion to the level of stress and are major signalling and regulatory metabolites coordinating growth, defence, acclimation and cell death. Our knowledge of ROS homeostasis, sensing, and signalling is therefore key to understanding the impacts of climate change at the molecular level. Current research is uncovering new insights into temporal-spatial, cell-to-cell and systemic ROS signalling pathways, particularly how these affect plant growth, defence, and more recently acclimation mechanisms behind stress priming and long term stress memory. Understanding the stabilising and destabilising factors of ROS homeostasis and signalling in plants exposed to extreme and fluctuating stress will concomitantly reveal how to address future climate change challenges in global food security and biodiversity management.

Lysine acetylation in mitochondria: From inventory to function

Cellular signaling pathways are regulated in a highly dynamic fashion in order to quickly adapt to distinct environmental conditions. Acetylation of lysine residues represents a central process that orchestrates cellular metabolism and signaling. In mitochondria, acetylation seems to be the most prevalent post-translational modification, presumably linked to the compartmentation and high turnover of acetyl-CoA in this organelle. Similarly, the elevated pH and the higher concentration of metabolites in mitochondria seem to favor non-enzymatic lysine modifications, as well as other acylations. Hence, elucidating the mechanisms for metabolic control of protein acetylation is crucial for our understanding of cellular processes. Recent advances in mass spectrometry-based proteomics have considerably increased our knowledge of the regulatory scope of acetylation. Here, we review the current knowledge and functional impact of mitochondrial protein acetylation across species. We first cover the experimental approaches to identify and analyze lysine acetylation on a global scale, we then explore both commonalities and specific differences of plant and animal acetylomes and the evolutionary conservation of protein acetylation, as well as its particular impact on metabolism and diseases. Important future directions and technical challenges are discussed, and it is pointed out that the transfer of knowledge between species and diseases, both in technology and biology, is of particular importance for further advancements in this field.

The proteome of higher plant mitochondria

Plant mitochondria perform a wide range of functions in the plant cell ranging from providing energy and metabolic intermediates, via coenzyme biosynthesis and their own biogenesis to retrograde signaling and programmed cell death. To perform these functions, they contain a proteome of >2000 different proteins expressed in some cells under some conditions. The vast majority of these proteins are imported, in many cases by a dedicated protein import machinery. Recent proteomic studies have identified about 1000 different proteins in both Arabidopsis and potato mitochondria, but even for energy-related proteins, the most well-studied functional protein group in mitochondria, <75% of the proteins are recognized as mitochondrial by even one of six of the most widely used prediction algorithms. The mitochondrial proteomes contain proteins representing a wide range of different functions. Some protein groups, like energy-related proteins, membrane transporters, and de novo fatty acid synthesis, appear to be well covered by the proteome, while others like RNA metabolism appear to be poorly covered possibly because of low abundance. The proteomic studies have improved our understanding of basic mitochondrial functions, have led to the discovery of new mitochondrial metabolic pathways and are helping us towards appreciating the dynamic role of the mitochondria in the responses of the plant cell to biotic and abiotic stress.

What is hot in plant mitochondria?

In this overview of recent trends in plant mitochondrial research, four questions are considered: (1) How large is the mitochondrial proteome? It appears to be in excess of 1500 proteins in a tissue at any given time. It is proposed that the fusion-fission frequently observed for plant mitochondria provides a vital mixing function ensuring that all low-abundance proteins are present in each mitochondrion at least some of the time. (2) What is the significance of posttranslational modifications (PTM) of proteins? As a result of PTM, many proteins are present in a very large number of slightly different forms. The most well-studied PTMs, such as protein phosphorylation, acetylation and reversible cysteine oxidation, are known to regulate mitochondrial function. Recent studies have provided examples of the importance of this regulation, but it remains a research area with a massive growth potential. (3) What is the role(s) of pentatricopeptide repeat (PPR) proteins in plant mitochondria? There is general agreement that PPR proteins are involved in RNA metabolism such as RNA editing. Recent comprehensive proteomic studies raise the question of how many of the potential 250-300 mitochondrial PPR proteins encoded in the nuclear DNA are required to be present for a mitochondrion to be able to grow and divide. (4) What is the mechanism(s) of retrograde signal transduction from the mitochondria to the nucleus? The nature of the signal transduction molecule is still unknown, but calcium ions, hydrogen peroxide and/or oxidized peptides are potential candidates. Recent results place a receptor for the activation of a group of nuclear genes on the endoplasmic reticulum, possibly close to ER-mitochondrial contact points.

Spreading the news: subcellular and organellar reactive oxygen species production and signalling

As plants are sessile organisms that have to attune their physiology and morphology continuously to varying environmental challenges in order to survive and reproduce, they have evolved complex and integrated environment-cell, cell-cell, and cell-organelle signalling circuits that regulate and trigger the required adjustments (such as alteration of gene expression). Although reactive oxygen species (ROS) are essential components of this network, their pathways are not yet completely unravelled. In addition to the intrinsic chemical properties that define the array of interaction partners, mobility, and stability, ROS signalling specificity is obtained via the spatiotemporal control of production and scavenging at different organellar and subcellular locations (e.g. chloroplasts, mitochondria, peroxisomes, and apoplast). Furthermore, these cellular compartments may crosstalk to relay and further fine-tune the ROS message. Hence, plant cells might locally and systemically react upon environmental or developmental challenges by generating spatiotemporally controlled dosages of certain ROS types, each with specific chemical properties and interaction targets, that are influenced by interorganellar communication and by the subcellular location and distribution of the involved organelles, to trigger the suitable acclimation responses in association with other well-established cellular signalling components (e.g. reactive nitrogen species, phytohormones, and calcium ions). Further characterization of this comprehensive ROS signalling matrix may result in the identification of new targets and key regulators of ROS signalling, which might be excellent candidates for engineering or breeding stress-tolerant plants.

The influence of alternative pathways of respiration that utilize branched-chain amino acids following water shortage in Arabidopsis

During dark-induced senescence isovaleryl-CoA dehydrogenase (IVDH) and D-2-hydroxyglutarate dehydrogenase (D-2HGDH) act as alternate electron donors to the ubiquinol pool via the electron-transfer flavoprotein/electron-transfer flavoprotein:ubiquinone oxidoreductase (ETF/ETFQO) pathway. However, the role of this pathway in response to other stresses still remains unclear. Here, we demonstrated that this alternative pathway is associated with tolerance to drought in Arabidopsis. In comparison with wild type (WT) and lines overexpressing D-2GHDH, loss-of-function etfqo-1, d2hgdh-2 and ivdh-1 mutants displayed compromised respiration rates and were more sensitive to drought. Our results demonstrated that an operational ETF/ETFQO pathway is associated with plants' ability to withstand drought and to recover growth once water becomes replete. Drought-induced metabolic reprogramming resulted in an increase in tricarboxylic acid (TCA) cycle intermediates and total amino acid levels, as well as decreases in protein, starch and nitrate contents. The enhanced levels of the branched-chain amino acids in loss-of-function mutants appear to be related to their increased utilization as substrates for the TCA cycle under water stress. Our results thus show that mitochondrial metabolism is highly active during drought stress responses and provide support for a role of alternative respiratory pathways within this response.

Inactivation of Mitochondrial Complex I Induces the Expression of a Twin Cysteine Protein that Targets and Affects Cytosolic, Chloroplastidic and Mitochondrial Function

At12Cys-1 (At5g64400) and At12Cys-2 (At5g09570) are two closely related isogenes that encode small, twin cysteine proteins, typically located in mitochondria. At12Cys-2 transcript is induced in a variety of mutants with disrupted mitochondrial proteins, but an increase in At12Cys protein is only detected in mutants with reduced mitochondrial complex I abundance. Induction of At12Cys protein in mutants that lack mitochondrial complex I is accompanied by At12Cys protein located in mitochondria, chloroplasts, and the cytosol. Biochemical analyses revealed that even single gene deletions, i.e., At12cys-1 or At12cys-2, have an effect on mitochondrial and chloroplast functions. However, only double mutants, i.e., At12cys-1:At12cys-2, affect the abundance of protein and mRNA transcripts encoding translation elongation factors as well as rRNA abundance. Blue native PAGE showed that At12Cys co-migrated with mitochondrial supercomplex I + III. Likewise, deletion of both At12cys-1 and At12cys-2 genes, but not single gene deletions, results in enhanced tolerance to drought and light stress and increased anti-oxidant capacity. The induction and multiple localization of At12Cys upon a reduction in complex I abundance provides a mechanism to specifically signal mitochondrial dysfunction to the cytosol and then beyond to other organelles in the cell.

Oxidative stress and antioxidative systems: recipes for successful data collection and interpretation

Oxidative stress and reactive oxygen species (ROS) are common to many fundamental responses of plants. Enormous and ever-growing interest has focused on this research area, leading to an extensive literature that documents the tremendous progress made in recent years. As in other areas of plant biology, advances have been greatly facilitated by developments in genomics-dependent technologies and the application of interdisciplinary techniques that generate information at multiple levels. At the same time, advances in understanding ROS are fundamentally reliant on the use of biochemical and cell biology techniques that are specific to the study of oxidative stress. It is therefore timely to revisit these approaches with the aim of providing a guide to convenient methods and assisting interested researchers in avoiding potential pitfalls. Our critical overview of currently popular methodologies includes a detailed discussion of approaches used to generate oxidative stress, measurements of ROS themselves, determination of major antioxidant metabolites, assays of antioxidative enzymes and marker transcripts for oxidative stress. We consider the applicability of metabolomics, proteomics and transcriptomics approaches and discuss markers such as damage to DNA and RNA. Our discussion of current methodologies is firmly anchored to future technological developments within this popular research field.

Stress-triggered redox signalling: what's in pROSpect?

Reactive oxygen species (ROS) have a profound influence on almost every aspect of plant biology. Here, we emphasize the fundamental, intimate relationships between light-driven reductant formation, ROS, and oxidative stress, together with compartment-specific differences in redox buffering and the perspectives for their analysis. Calculations of approximate H2 O2 concentrations in the peroxisomes are provided, and based on the likely values in other locations such as chloroplasts, we conclude that much of the H2 O2 detected in conventional in vitro assays is likely to be extracellular. Within the context of scant information on ROS perception mechanisms, we consider current knowledge, including possible parallels with emerging information on oxygen sensing. Although ROS can sometimes be signals for cell death, we consider that an equally important role is to transmit information from metabolism to allow appropriate cellular responses to developmental and environmental changes. Our discussion speculates on novel sensing mechanisms by which this could happen and how ROS could be counted by the cell, possibly as a means of monitoring metabolic flux. Throughout, we place emphasis on the positive effects of ROS, predicting that in the coming decades they will increasingly be defined as hallmarks of viability within a changing and challenging environment.

Hydrogen Peroxide, Signaling in Disguise during Metal Phytotoxicity

Plants exposed to excess metals are challenged by an increased generation of reactive oxygen species (ROS) such as superoxide ([Formula: see text]), hydrogen peroxide (H2O2) and the hydroxyl radical ((•)OH). The mechanisms underlying this oxidative challenge are often dependent on metal-specific properties and might play a role in stress perception, signaling and acclimation. Although ROS were initially considered as toxic compounds causing damage to various cellular structures, their role as signaling molecules became a topic of intense research over the last decade. Hydrogen peroxide in particular is important in signaling because of its relatively low toxicity, long lifespan and its ability to cross cellular membranes. The delicate balance between its production and scavenging by a plethora of enzymatic and metabolic antioxidants is crucial in the onset of diverse signaling cascades that finally lead to plant acclimation to metal stress. In this review, our current knowledge on the dual role of ROS in metal-exposed plants is presented. Evidence for a relationship between H2O2 and plant metal tolerance is provided. Furthermore, emphasis is put on recent advances in understanding cellular damage and downstream signaling responses as a result of metal-induced H2O2 production. Finally, special attention is paid to the interaction between H2O2 and other signaling components such as transcription factors, mitogen-activated protein kinases, phytohormones and regulating systems (e.g. microRNAs). These responses potentially underlie metal-induced senescence in plants. Elucidating the signaling network activated during metal stress is a pivotal step to make progress in applied technologies like phytoremediation of polluted soils.

When Bad Guys Become Good Ones: The Key Role of Reactive Oxygen Species and Nitric Oxide in the Plant Responses to Abiotic Stress

The natural environment of plants is composed of a complex set of abiotic stresses and their ability to respond to these stresses is highly flexible and finely balanced through the interaction between signaling molecules. In this review, we highlight the integrated action between reactive oxygen species (ROS) and reactive nitrogen species (RNS), particularly nitric oxide (NO), involved in the acclimation to different abiotic stresses. Under stressful conditions, the biosynthesis transport and the metabolism of ROS and NO influence plant response mechanisms. The enzymes involved in ROS and NO synthesis and scavenging can be found in different cells compartments and their temporal and spatial locations are determinant for signaling mechanisms. Both ROS and NO are involved in long distances signaling (ROS wave and GSNO transport), promoting an acquired systemic acclimation to abiotic stresses. The mechanisms of abiotic stresses response triggered by ROS and NO involve some general steps, as the enhancement of antioxidant systems, but also stress-specific mechanisms, according to the stress type (drought, hypoxia, heavy metals, etc.), and demand the interaction with other signaling molecules, such as MAPK, plant hormones, and calcium. The transduction of ROS and NO bioactivity involves post-translational modifications of proteins, particularly S-glutathionylation for ROS, and S-nitrosylation for NO. These changes may alter the activity, stability, and interaction with other molecules or subcellular location of proteins, changing the entire cell dynamics and contributing to the maintenance of homeostasis. However, despite the recent advances about the roles of ROS and NO in signaling cascades, many challenges remain, and future studies focusing on the signaling of these molecules in planta are still necessary.

Global Plant Stress Signaling: Reactive Oxygen Species at the Cross-Road

Current technologies have changed biology into a data-intensive field and significantly increased our understanding of signal transduction pathways in plants. However, global defense signaling networks in plants have not been established yet. Considering the apparent intricate nature of signaling mechanisms in plants (due to their sessile nature), studying the points at which different signaling pathways converge, rather than the branches, represents a good start to unravel global plant signaling networks. In this regard, growing evidence shows that the generation of reactive oxygen species (ROS) is one of the most common plant responses to different stresses, representing a point at which various signaling pathways come together. In this review, the complex nature of plant stress signaling networks will be discussed. An emphasis on different signaling players with a specific attention to ROS as the primary source of the signaling battery in plants will be presented. The interactions between ROS and other signaling components, e.g., calcium, redox homeostasis, membranes, G-proteins, MAPKs, plant hormones, and transcription factors will be assessed. A better understanding of the vital roles ROS are playing in plant signaling would help innovate new strategies to improve plant productivity under the circumstances of the increasing severity of environmental conditions and the high demand of food and energy worldwide.

Global Proteome Analyses of Lysine Acetylation and Succinylation Reveal the Widespread Involvement of both Modification in Metabolism in the Embryo of Germinating Rice Seed

Regulation of rice seed germination has been shown to mainly occur at post-transcriptional levels, of which the changes on proteome status is a major one. Lysine acetylation and succinylation are two prevalent protein post-translational modifications (PTMs) involved in multiple biological processes, especially for metabolism regulation. To investigate the potential mechanism controlling metabolism regulation in rice seed germination, we performed the lysine acetylation and succinylation analyses simultaneously. Using high-accuracy nano-LC-MS/MS in combination with the enrichment of lysine acetylated or succinylated peptides from digested embryonic proteins of 24 h after imbibition (HAI) rice seed, a total of 699 acetylated sites from 389 proteins and 665 succinylated sites from 261 proteins were identified. Among these modified lysine sites, 133 sites on 78 proteins were commonly modified by two PTMs. The overlapped PTM sites were more likely to be in polar acidic/basic amino acid regions and exposed on the protein surface. Both of the acetylated and succinylated proteins cover nearly all aspects of cellular functions. Ribosome complex and glycolysis/gluconeogenesis-related proteins were significantly enriched in both acetylated and succinylated protein profiles through KEGG enrichment and protein-protein interaction network analyses. The acetyl-CoA and succinyl-CoA metabolism-related enzymes were found to be extensively modified by both modifications, implying the functional interaction between the two PTMs. This study provides a rich resource to examine the modulation of the two PTMs on the metabolism pathway and other biological processes in germinating rice seed.

Canavanine Alters ROS/RNS Level and Leads to Post-translational Modification of Proteins in Roots of Tomato Seedlings

Canavanine (CAN), a structural analog of arginine (Arg), is used as a selective inhibitor of inducible NOS in mammals. CAN is incorporated into proteins' structure in the place of Arg, leading to the formation of aberrant compounds. This non-protein amino acid is found in legumes, e.g., Canavalia ensiformis (L.) DC. or Sutherlandia frutescens (L.) R.Br. and acts as a strong toxin against herbivores or plants. Tomato (Solanum lycopersicum L.) seedlings were treated for 24-72 h with CAN (10 or 50 μM) inhibiting root growth by 50 or 100%, without lethal effect. We determined ROS level/production in root extracts, fluorescence of DAF-FM and APF derivatives corresponding to RNS level in roots of tomato seedlings and linked CAN-induced restriction of root growth to the post-translational modifications (PTMs) of proteins: carbonylation and nitration. Both PTMs are stable markers of nitro-oxidative stress, regarded as the plant's secondary response to phytotoxins. CAN enhanced H2O2 content and superoxide radicals generation in extracts of tomato roots and stimulated formation of protein carbonyl groups. An elevated level of carbonylated proteins was characteristic for the plants after 72 h of the culture, mainly for the roots exposed to 10 μM CAN. The proteolytic activity was stimulated by tested non-protein amino acid. CAN treatment led to decline of fluorescence of DAF-FM derivatives, and transiently stimulated fluorescence of APF derivatives. Short-term exposure of tomato seedlings to CAN lowered the protein nitration level. Activity of peroxidase, polyamine oxidase and NADPH oxidase, enzymes acting as modulators of H2O2 concentration and governing root architecture and growth were determined. Activities of all enzymes were stimulated by CAN, but no strict CAN concentration dependence was observed. We conclude, that although CAN treatment led to a decline in the nitric oxide level, PTMs observed in roots of plants exposed to CAN are linked rather to the formation of carbonyl groups than to nitration, and are detected particularly after 24 h. Thus, oxidative stress and oxidative modifications of proteins seems to be of significant importance in the rapid response of plants to CAN.

Reactive Oxygen Species (ROS): Beneficial Companions of Plants' Developmental Processes

Reactive oxygen species (ROS) are generated inevitably in the redox reactions of plants, including respiration and photosynthesis. In earlier studies, ROS were considered as toxic by-products of aerobic pathways of the metabolism. But in recent years, concept about ROS has changed because they also participate in developmental processes of plants by acting as signaling molecules. In plants, ROS regulate many developmental processes such as cell proliferation and differentiation, programmed cell death, seed germination, gravitropism, root hair growth and pollen tube development, senescence, etc. Despite much progress, a comprehensive update of advances in the understanding of the mechanisms evoked by ROS that mediate in cell proliferation and development are fragmentry and the matter of ROS perception and the signaling cascade remains open. Therefore, keeping in view the above facts, an attempt has been made in this article to summarize the recent findings regarding updates made in the regulatory action of ROS at various plant developmental stages, which are still not well-known.

Molecular cloning and characterization of two manganese superoxide dismutases from Miscanthus × giganteus

Six MnSOD genes were isolated from five Miscanthus species. MgMnSOD1 functions in mitochondria and MgMnSOD1 seems to be the main MnSOD gene involved in stress response of M. × giganteus. Miscanthus × giganteus is a promising biomass energy crop with advantages of vigorous growth, high yield, low fertilizer and pesticide inputs. However, poor overwinter ability limits its widespread cultivation. Moreover, narrow genetic base may increase the risk of susceptibility to diseases and pests. Manganese superoxide dismutase (MnSOD), an important antioxidant enzyme involved in stress tolerance is able to protect plant cells from accumulated reactive oxygen species by converting superoxide to peroxide and oxygen. In many plants, overexpression of MnSOD has shown the ability to enhance the resistance to various stresses. This article describes the studies performed in an attempt to elucidate the molecular and enzymatic properties of MnSODs in M. × giganteus. MnSOD genes from M. × giganteus (MgMnSOD1, MgMnSOD2), M. lutarioriparia (MlMnSOD), M. sacchariflora (MsaMnSOD), M. sinensis (MsiMnSOD), and M. floridulus (MfMnSOD) were cloned and sequenced. The sequence analysis and expression patterns of MgMnSOD1 and MgMnSOD2 suggest that they were orthologous genes which were inherited from the two parents, M. sacchariflora and M. sinensis, respectively. In addition, MgMnSOD1 is predicted to be the main MnSOD gene involved in stress response of M. × giganteus. The activity of purified recombinant MgMnSOD1 was 1854.79 ± 39.98 U mg(-1) (mean ± SD). Further enzymatic assays revealed that the protein exhibited an outstanding thermal stability. MgMnSOD1 is predicted to be targeted to mitochondria and involved in removing the superoxide radical generated by respiration. The presence and sequences of other SOD isozymes transcripts were also investigated in this study.

Switch from heterotrophy to autotrophy of apple cotyledons depends on NO signal

NO accelerates transition of germinated embryos from heterotrophy to autotrophy by stimulation of chloroplasts maturation. NO-mediated autotrophy of apple seedlings correlates to increased content of RuBisCO small subunit and improvement of parameters of chlorophyll a fluorescence. Nitric oxide (NO) acts as signaling molecule involved in regulation of various physiological processes in plants, although its involvement in cotyledons greening is poorly recognized. To identify the importance of NO signal for plant growth and development we investigated the effects of short-term application of NO at various developmental stages of seedlings of apple (Malus domestica Borkh.) on cotyledons' chlorophyll a to b ratio, chlorophyll a fluorescence, photosynthetic activity, carbohydrates and RuBisCO both subunits content. NO-dependent biochemical alterations were linked to cytological observation of developing plastids in cotyledons of apple plants. Abnormal plantlets developing from dormant apple embryos are characterized by anatomical malformations of cotyledons. Short-term pre-treatment with NO of isolated embryos or seedlings with developmental anomalies resulted in formation of plants with cotyledons of equal size and chlorophyll content; these responses were blocked by NO scavenger. NO independently of time point of application accelerated embryos transition from heterotrophy to autotrophy by stimulation of photosynthetic activity, improvement of parameters of chlorophyll a fluorescence (F v/F m, F v/F 0) and increased content of RuBisCO small subunit. Further analysis showed that NO application modified glucose and hydrogen peroxide concentration in cotyledons. Beneficial effect of NO on development of seedlings without any abnormalities was manifested at ultrastructural level by decline in amount of proplastids and induction of formation and maturation of chloroplasts. Our data suggest that progress of autotrophy of young seedlings is governed by NO acting as stimulator of chloroplast-to-nucleus signaling.

Succinate dehydrogenase (mitochondrial complex II) is a source of reactive oxygen species in plants and regulates development and stress responses

Reactive oxygen species (ROS) are signaling molecules that regulate plant development and responses to stresses. Mitochondria are the source of most ROS in heterotrophic cells, and mitochondrial complex I and complex III are regarded as the main sites of ROS production in plant mitochondria. Recent studies have demonstrated that succinate dehydrogenase (SDH) also contributes to mitochondrial ROS production. However, the ability of SDH to generate ROS in plants is unclear. The aim of this study was to evaluate the role of SDH in mitochondrial ROS production. Our results demonstrated that SDH is a direct source of ROS in Arabidopsis thaliana and Oryza sativa, and the induction of ROS production by specific SDH inhibitors impaired plant growth. In addition, this effect was accompanied by the down-regulation of cell cycle genes and the up-regulation of stress-related genes. However, the partial inhibition of SDH by a competitive inhibitor decreased ROS production, which was associated with increased shoot and root growth, and prevented the down-regulation of cell cycle genes and the induction of stress-related genes by noncompetitive inhibitors. In conclusion, SDH plays an important role in ROS production, being a direct source of ROS in plant mitochondria and regulating plant development and stress responses.

The fungal endophyte Epichloë typhina improves photosynthesis efficiency of its host orchard grass (Dactylis glomerata)

MAIN CONCLUSION

According to the results presented in this paper the fungal endophyte Epichloë typhina significantly improves the growth, PSII photochemistry and C assimilation efficiency of its host Dactylis glomerata. In this paper, we present a comprehensive study of the impact of the endophytic fungi Epichloë typhina on its plant hosts' photosynthesis apparatus. Chlorophyll a fluorescence, gas exchange, immuno-blotting and spectrophotometric measurements were employed to assess photosynthetic performance, changes in pigment content and mechanisms associated with light harvesting, carbon assimilation and energy distribution in Dactylis glomerata colonized with Epichloë typhina. According to the results presented in this study, colonization of D. glomerata results in improved photosynthesis efficiency. Additionally, we propose a new mechanism allowing plants to cope with the withdrawal of a significant fraction of its energy resources by the endophytic fungi. The abundance of LHCI, LHCII proteins as well as chlorophyll b was significantly higher in E+ plants. Malate export out of the chloroplast was shown to be increased in colonized plants. To our knowledge, we are the first to report this phenomenon. Epichloë colonization improved PSII photochemistry and C assimilation efficiency. Elevated energy demands of E+ D. glomerata plants are met by increasing the rate of carbon assimilation and PSII photochemistry.

Peroxisomes sense and respond to environmental cues by regulating ROS and RNS signalling networks

BACKGROUND

Peroxisomes are highly dynamic, metabolically active organelles that used to be regarded as a sink for H2O2 generated in different organelles. However, peroxisomes are now considered to have a more complex function, containing different metabolic pathways, and they are an important source of reactive oxygen species (ROS), nitric oxide (NO) and reactive nitrogen species (RNS). Over-accumulation of ROS and RNS can give rise oxidative and nitrosative stress, but when produced at low concentrations they can act as signalling molecules.

SCOPE

This review focuses on the production of ROS and RNS in peroxisomes and their regulation by antioxidants. ROS production is associated with metabolic pathways such as photorespiration and fatty acid β-oxidation, and disturbances in any of these processes can be perceived by the cell as an alarm that triggers defence responses. Genetic and pharmacological studies have shown that photorespiratory H2O2 can affect nuclear gene expression, regulating the response to pathogen infection and light intensity. Proteomic studies have shown that peroxisomal proteins are targets for oxidative modification, S-nitrosylation and nitration and have highlighted the importance of these modifications in regulating peroxisomal metabolism and signalling networks. The morphology, size, number and speed of movement of peroxisomes can also change in response to oxidative stress, meaning that an ROS/redox receptor is required. Information available on the production and detection of NO/RNS in peroxisomes is more limited. Peroxisomal homeostasis is critical for maintaining the cellular redox balance and is regulated by ROS, peroxisomal proteases and autophagic processes.

CONCLUSIONS

Peroxisomes play a key role in many aspects of plant development and acclimation to stress conditions. These organelles can sense ROS/redox changes in the cell and thus trigger rapid and specific responses to environmental cues involving changes in peroxisomal dynamics as well as ROS- and NO-dependent signalling networks, although the mechanisms involved have not yet been established. Peroxisomes can therefore be regarded as a highly important decision-making platform in the cell, where ROS and RNS play a determining role.

Antioxidative and proteolytic systems protect mitochondria from oxidative damage in S-deficient Arabidopsis thaliana

We examined the functioning of the antioxidative defense system in Arabidopsis thaliana under sulphur (S) deficiency with an emphasis on the role of mitochondria. In tissue extracts and in isolated mitochondria from S-deficient plants, the concentration of non-protein thiols declined but protein thiols did not change. Superoxide anion and hydrogen peroxide were accumulated in leaf blades and the generation of superoxide anion by isolated mitochondria was higher. Lower abundance of reduced (GSH) plus oxidized (GSSG) glutathione in the leaf and root tissues, and leaf mitochondria from S-deficient plants was accompanied by a decrease in the level of GSH and the changes in the GSH/GSSG ratios. In the chloroplasts, the total level of glutathione decreased. Lower levels of reduced (AsA) and oxidized (DHA) ascorbate were reflected in much higher ratios of AsA/DHA. Sulphur deficiency led to an increase in the activity of cytosolic, mitochondrial and chloroplastic antioxidative enzymes, peroxidases, catalases and superoxide dismutases. The protein carbonyl level was higher in the leaves of S-deficient plants and in the chloroplasts, while in the roots, leaf and root mitochondria it remained unchanged. Protease activity in leaf extracts of S-deficient plants was higher, but in root extracts it did not differ. The proteolytic system reflected subcellular specificity. In leaf and root mitochondria the protease activity was higher, whereas in the chloroplasts it did not change. We propose that the preferential incorporation of S to protein thiols and activation of antioxidative and proteolytic systems are likely important for the survival of S-deficient plants and that the mitochondria maintain redox homeostasis.

Mitochondrial electron transport protects floating leaves of long leaf pondweed (Potamogeton nodosus Poir) against photoinhibition: comparison with submerged leaves

Investigations were carried to unravel mechanism(s) for higher tolerance of floating over submerged leaves of long leaf pondweed (Potamogeton nodosus Poir) against photoinhibition. Chloroplasts from floating leaves showed ~5- and ~6.4-fold higher Photosystem (PS) I (reduced dichlorophenol-indophenol → methyl viologen → O2) and PS II (H2O → parabenzoquine) activities over those from submerged leaves. The saturating rate (V max) of PS II activity of chloroplasts from floating and submerged leaves reached at ~600 and ~230 µmol photons m(-2) s(-1), respectively. Photosynthetic electron transport rate in floating leaves was over 5-fold higher than in submerged leaves. Further, floating leaves, as compared to submerged leaves, showed higher F v/F m (variable to maximum chlorophyll fluorescence, a reflection of PS II efficiency), as well as a higher potential to withstand photoinhibitory damage by high light (1,200 µmol photons m(-2) s(-1)). Cells of floating leaves had not only higher mitochondria to chloroplast ratio, but also showed many mitochondria in close vicinity of chloroplasts. Electron transport (NADH → O2; succinate → O2) in isolated mitochondria of floating leaves was sensitive to both cyanide (CN(-)) and salicylhydroxamic acid (SHAM), whereas those in submerged leaves were sensitive to CN(-), but virtually insensitive to SHAM, revealing the presence of alternative oxidase in mitochondria of floating, but not of submerged, leaves. Further, the potential of floating leaves to withstand photoinhibitory damage was significantly reduced in the presence of CN(-) and SHAM, individually and in combination. Our experimental results establish that floating leaves possess better photosynthetic efficiency and capacity to withstand photoinhibition compared to submerged leaves; and mitochondria play a pivotal role in protecting photosynthetic machinery of floating leaves against photoinhibition, most likely by oxidation of NAD(P)H and reduction of O2.

Lipid Peroxide-Derived Short-Chain Carbonyls Mediate Hydrogen Peroxide-Induced and Salt-Induced Programmed Cell Death in Plants

Lipid peroxide-derived toxic carbonyl compounds (oxylipin carbonyls), produced downstream of reactive oxygen species (ROS), were recently revealed to mediate abiotic stress-induced damage of plants. Here, we investigated how oxylipin carbonyls cause cell death. When tobacco (Nicotiana tabacum) Bright Yellow-2 (BY-2) cells were exposed to hydrogen peroxide, several species of short-chain oxylipin carbonyls [i.e. 4-hydroxy-(E)-2-nonenal and acrolein] accumulated and the cells underwent programmed cell death (PCD), as judged based on DNA fragmentation, an increase in terminal deoxynucleotidyl transferase dUTP nick end labeling-positive nuclei, and cytoplasm retraction. These oxylipin carbonyls caused PCD in BY-2 cells and roots of tobacco and Arabidopsis (Arabidopsis thaliana). To test the possibility that oxylipin carbonyls mediate an oxidative signal to cause PCD, we performed pharmacological and genetic experiments. Carnosine and hydralazine, having distinct chemistry for scavenging carbonyls, significantly suppressed the increase in oxylipin carbonyls and blocked PCD in BY-2 cells and Arabidopsis roots, but they did not affect the levels of ROS and lipid peroxides. A transgenic tobacco line that overproduces 2-alkenal reductase, an Arabidopsis enzyme to detoxify α,β-unsaturated carbonyls, suffered less PCD in root epidermis after hydrogen peroxide or salt treatment than did the wild type, whereas the ROS level increases due to the stress treatments were not different between the lines. From these results, we conclude that oxylipin carbonyls are involved in the PCD process in oxidatively stressed cells. Our comparison of the ability of distinct carbonyls to induce PCD in BY-2 cells revealed that acrolein and 4-hydroxy-(E)-2-nonenal are the most potent carbonyls. The physiological relevance and possible mechanisms of the carbonyl-induced PCD are discussed.

He-Ne laser preillumination improves the resistance of tall fescue (Festuca arundinacea Schreb.) seedlings to high saline conditions

In this paper, we explored the protective effect and physiochemical mechanism of He-Ne laser preillumination in enhancement of tall fescue seedlings tolerance to high salt stress. The results showed that salt stress greatly reduced plant growth, plant height, biomass, leaf development, ascorbate acid (AsA) and glutathione (GSH) concentration, the enzymatic activities, and gene expression levels of antioxidant enzymes such as catalase (CAT) and glutathione reductase (GR) and enhanced hydrogen peroxide (H2O2) content, superoxide radical (O2 (·-)) generation rates, membrane lipid peroxidation, relative electrolyte leakage, the enzymatic activities, and gene expression levels of superoxide dismutase (SOD), ascorbate peroxidase (APX), and peroxidase (POD), compared with controls. However, He-Ne laser preillumination significantly reversed plant growth retardation, biomass loss, and leaves development decay induced by salt stress. And the values of the physiochemical parameters observed in salt-stressed plants were partially reverted or further increased by He-Ne laser. Salt stress had no obvious effect on the transcriptional activity of phytochromeB, whereas He-Ne laser markedly enhanced its transcriptional level. Preillumination with white fluorescent lamps (W), red light (RL) of the same wavelength, or RL, then far-red light (FRL) had not alleviated the inhibitory effect of salt stress on plant growth and antioxidant enzymes activities, suggesting that the effect of He-Ne laser on improved salt tolerance was most likely attributed to the induction of phytochromeB transcription activities by the laser preillumination, but not RL, FRL or other light sources. In addition, we also utilized sodium nitroprusside (SNP) as NO donor to pre-treat tall fescue seedlings at the same conditions, and further evaluated the differences of physiological effects between He-Ne laser and NO in increasing salt resistance of tall fescue. Taken together, our data illustrated that He-Ne laser preillumination contributed to conferring an increased tolerance to salt stress in tall fescue seedlings due to alleviating oxidative damage through scavenging free radicals and inducing transcriptional activities of some genes involved in plant antioxidant system, and the induction of phytochromeB transcriptional level by He-Ne laser was probably correlated with these processes. Moreover, this positive physiochemical effect seemed more effective with He-Ne laser than NO molecule.

Products of lipid, protein and RNA oxidation as signals and regulators of gene expression in plants

Reactive oxygen species (ROS) are engaged in several processes essential for normal cell functioning, such as differentiation, anti-microbial defense, stimulus sensing and signaling. Interestingly, recent studies imply that cellular signal transduction and gene regulation are mediated not only directly by ROS but also by the molecules derived from ROS-mediated oxidation. Lipid peroxidation leads to non-enzymatic formation of oxylipins. These molecules were shown to modulate expression of signaling associated genes including genes encoding phosphatases, kinases and transcription factors. Oxidized peptides derived from protein oxidation might be engaged in organelle-specific ROS signaling. In turn, oxidation of particular mRNAs leads to decrease in the level of encoded proteins and thus, contributes to the post-transcriptional regulation of gene expression. Present mini review summarizes latest findings concerning involvement of products of lipid, protein and RNA oxidation in signal transduction and gene regulation.

Sugars as hydroxyl radical scavengers: proof-of-concept by studying the fate of sucralose in Arabidopsis

Substantial formation of reactive oxygen species (ROS) is inevitable in aerobic life forms. Due to their extremely high reactivity and short lifetime, hydroxyl radicals are a special case, because cells have not developed enzymes to detoxify these most dangerous ROS. Thus, scavenging of hydroxyl radicals may only occur by accumulation of higher levels of simple organic compounds. Previous studies have demonstrated that plant-derived sugars show hydroxyl radical scavenging capabilities during Fenton reactions with Fe(2+) and hydrogen peroxide in vitro, leading to formation of less detrimental sugar radicals that may be subject of regeneration to non-radical carbohydrates in vivo. Here, we provide further evidence for the occurrence of such radical reactions with sugars in planta, by following the fate of sucralose, an artificial analog of sucrose, in Arabidopsis tissues. The expected sucralose recombination and degradation products were detected in both normal and stressed plant tissues. Oxidation products of endogenous sugars were also assessed in planta for Arabidopsis and barley, and were shown to increase in abundance relative to the non-oxidized precursor during oxidative stress conditions. We concluded that such non-enzymatic reactions with hydroxyl radicals form an integral part of plant antioxidant mechanisms contributing to cellular ROS homeostasis, and may be more important than generally assumed. This is discussed in relation to the recently proposed roles for Fe(2+) and hydrogen peroxide in processes leading to the origin of metabolism and the origin of life.

Biomarkers of ecotoxicological oxidative stress in an urban environment: using evergreen plant in industrial areas

Plants react to air pollution by increased production of reactive oxygene species and oxidative stress, which triggers multiple defense mechanisms. In this study, some parameters that serve as biomarkers for antioxidative defense, such as glutathione S-transferase (GST) activity, glutathione (GSH), malondialdehyde, chlorophyll and total soluble protein contents, were investigated on the needles of Cedrus libani (A. Rich.) grown around two industrial areas in Eskisehir. The measurements revealed that metabolism in needles of C. libani trees is largely directed towards defence against ROS, due to effects of air pollution in the sampling areas. We observed significant increases in all parameters, except chlorophyll contents, which were strongly decreased. However, these sharp changes were also prominent not only between sampling sites and control site, but also among the areas investigated, suggesting the quantitative influence of the extent of pollution. Together with total soluble protein contents, the correlation between GST activities and GSH contents suggests that damage due to oxidative stress was most probably reduced due to the increased antioxidant capacity. Therefore, we can suggest C. libani as a good model for biomonitoring atmospheric quality with the oxidative stress parameters providing an effective measure for early environmental assessment due to their sensitivities of even low levels of pollution.

The metabolomics of oxidative stress

Oxidative stress resulting from increased availability of reactive oxygen species (ROS) is a key component of many responses of plants to challenging environmental conditions. The consequences for plant metabolism are complex and manifold. We review data on small compounds involved in oxidative stress, including ROS themselves and antioxidants and redox buffers in the membrane and soluble phases, and we discuss the wider consequences for plant primary and secondary metabolism. While metabolomics has been exploited in many studies on stress, there have been relatively few non-targeted studies focused on how metabolite signatures respond specifically to oxidative stress. As part of the discussion, we present results and reanalyze published datasets on metabolite profiles in catalase-deficient plants, which can be considered to be model oxidative stress systems. We emphasize the roles of ROS-triggered changes in metabolites as potential oxidative signals, and discuss responses that might be useful as markers for oxidative stress. Particular attention is paid to lipid-derived compounds, the status of antioxidants and antioxidant breakdown products, altered metabolism of amino acids, and the roles of phytohormone pathways.

The production, localization and spreading of reactive oxygen species contributes to the low vitality of long-term stored common beech (Fagus sylvatica L.) seeds

The common beech (Fagus sylvatica L.) is propagated by seeds, but the seed set is irregular with five to ten years in between crops. It is therefore necessary to store the seeds. However, beech seeds lose germinability during long-term storage. In this study, beech seeds were stored at -10°C under controlled conditions for 2, 5, 8, 11 and 13 years. Our results show that beech seeds lose germinability during storage in proportion to the duration of storage. The decrease in germinability correlated with increased electrolyte leakage and accumulation of superoxide anion radicals, hydrogen peroxide and hydroxyl radicals. Furthermore, a strong positive correlation was observed among the releases of superoxide anion radicals, hydrogen peroxide and hydroxyl radicals. In situ localization showed that superoxide anion radicals and hydrogen peroxide were first detectable in root cap cells. When the seed storage time was extended, the reactive oxygen species fluorescence expanded to more areas of the radicle, reaching the root apical meristem. A storage time-dependent decrease in catalase activity, observed in both embryonic axes and cotyledons, was also positively correlated with germinability. DNA fragmentation was observed in beech seeds during storage and occurred predominantly in embryonic axes stored for 5 years and more. Altogether, these results suggest that the loss of germinability in beech seeds during long-term storage depends on several factors, including strong of reactive oxygen species accumulation accompanied by reduced catalase activity as well as membrane injury and DNA alternations, which may be aging-related and ROS-derived. We suggest that the accumulating reactive oxygen species that spread to the root apical meristem are key factors that affect seed germinability after long-term storage.

Reactive oxygen species, abscisic acid and ethylene interact to regulate sunflower seed germination

Sunflower (Helianthus annuus L.) seed dormancy is regulated by reactive oxygen species (ROS) and can be alleviated by incubating dormant embryos in the presence of methylviologen (MV), a ROS-generating compound. Ethylene alleviates sunflower seed dormancy whereas abscisic acid (ABA) represses germination. The purposes of this study were to identify the molecular basis of ROS effect on seed germination and to investigate their possible relationship with hormone signalling pathways. Ethylene treatment provoked ROS generation in embryonic axis whereas ABA had no effect on their production. The beneficial effect of ethylene on germination was lowered in the presence of antioxidant compounds, and MV suppressed the inhibitory effect of ABA. MV treatment did not alter significantly ethylene nor ABA production during seed imbibition. Microarray analysis showed that MV treatment triggered differential expression of 120 probe sets (59 more abundant and 61 less abundant genes), and most of the identified transcripts were related to cell signalling components. Many transcripts less represented in MV-treated seeds were involved in ABA signalling, thus suggesting an interaction between ROS and ABA signalling pathways at the transcriptional level. Altogether, these results shed new light on the crosstalk between ROS and plant hormones in seed germination.

Heme-heme oxygenase 1 system is involved in ammonium tolerance by regulating antioxidant defence in Oryza sativa

Despite substantial evidence showing the ammonium-altered redox homeostasis in plants, the involvement and molecular mechanism of heme-heme oxygenase 1 (heme-HO1), a novel antioxidant system, in the regulation of ammonium tolerance remain elusive. To fill in these gaps, the biological function of rice HO1 (OsSE5) was investigated. Results showed that NH4 Cl up-regulated rice OsSE5 expression. Oxidative stress and subsequent growth inhibition induced by excess NH4 Cl was partly mitigated by pretreatment with carbon monoxide (CO, a by-product of HO1 activity) or intensified by zinc protoporphyrin (ZnPP, a potent inhibitor of HO1 activity). Pretreatment with HO1 inducer hemin, not only up-regulated OsSE5 expression and HO activity, but also rescued the down-regulation of antioxidant transcripts, total and related isozymatic activities, thus significantly counteracting the excess NH4 Cl-triggered reactive oxygen species overproduction, lipid peroxidation and growth inhibition. OsSE5 RNAi transgenic rice plants revealed NH4 Cl-hypersensitive phenotype with impaired antioxidant defence, both of which could be rescued by CO but not hemin. Transgenic Arabidopsis plants over-expressing OsSE5 also exhibited enhanced tolerance to NH4 Cl, which might be attributed to the up-regulation of several antioxidant transcripts. Altogether, these results illustrated the involvement of heme-HO1 system in ammonium tolerance by enhancing antioxidant defence, which may improve plant tolerance to excess ammonium fertilizer.

Growth and physiological changes in continuously cropped eggplant (Solanum melongena L.) upon relay intercropping with garlic (Allium sativum L.)

Relay intercropping represents an alternative for sustainable production of vegetables, but the changes of internally antioxidant defense combined with the growth and yield are not clear. Field experiment was carried out to investigate the malondialdehyde (MDA) content and activity levels of superoxide dismutase (SOD), peroxidase (POD), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL) in eggplant (Solanum melongena L.) and plant height, stem diameter, maximal leaf area, and yield of eggplant grown under successive cropping in the year 2011 and 2012 to see if relay intercropping with garlic (Allium sativum L.) could benefit to eggplant growth and yield. Three experimental treatments with three repeats in each were carried out (completely randomized block design): eggplant monoculture (CK), eggplant relay intercropping with normal garlic (NG), and eggplant relay intercropping with green garlic (GG). In both years, the MDA content was significantly lower and SOD and POD activities were generally lower in NG and GG compared with CK in most sampling dates. PPO activity trends were generally opposite to those of POD. The general trend of PAL activity was similar to MDA. The plant height and stem of eggplant was lower, but the maximal leaf area was larger in NG and GG in 2011; in 2012 the plant growth was stronger in relay intercropping treatments. For eggplant yield in 2011, NG was 2.85% higher than CK; after the time for the green garlic pulled out was moved forward in 2012, the yield was increased by 6.26 and 7.80%, respectively, in NG and GG. The lower MDA content and enzyme activities in relay intercropping treatments showed that the eggplant suffered less damage from environment and continuous cropping obstacles, which promoted healthier plant. Thus from both the growth and physiological perspective, it was concluded that eggplant/garlic relay intercropping is a beneficial cultivation practice maintaining stronger plant growth and higher yield.

Convergent signaling pathways--interaction between methionine oxidation and serine/threonine/tyrosine O-phosphorylation

Oxidation of methionine (Met) to Met sulfoxide (MetSO) is a frequently found reversible posttranslational modification. It has been presumed that the major functional role for oxidation-labile Met residues is to protect proteins/cells from oxidative stress. However, Met oxidation has been established as a key mechanism for direct regulation of a wide range of protein functions and cellular processes. Furthermore, recent reports suggest an interaction between Met oxidation and O-phosphorylation. Such interactions are a potentially direct interface between redox sensing and signaling, and cellular protein kinase/phosphatase-based signaling. Herein, we describe the current state of Met oxidation research, provide some mechanistic insight into crosstalk between these two major posttranslational modifications, and consider the evolutionary significance and regulatory potential of this crosstalk.

Proteomics of seed development, desiccation tolerance, germination and vigor

Proteomics, the large-scale study of the total complement of proteins in a given sample, has been applied to all aspects of seed biology mainly using model species such as Arabidopsis or important agricultural crops such as corn and rice. Proteins extracted from the sample have typically been separated and quantified by 2-dimensional polyacrylamide gel electrophoresis followed by liquid chromatography and mass spectrometry to identify the proteins in the gel spots. In this way, qualitative and quantitative changes in the proteome during seed development, desiccation tolerance, germination, dormancy release, vigor alteration and responses to environmental factors have all been studied. Many proteins or biological processes potentially important for each seed process have been highlighted by these studies, which greatly expands our knowledge of seed biology. Proteins that have been identified to be particularly important for at least two of the seed processes are involved in detoxification of reactive oxygen species, the cytoskeleton, glycolysis, protein biosynthesis, post-translational modifications, methionine metabolism, and late embryogenesis-abundant (LEA) proteins. It will be useful for molecular biologists and molecular plant breeders to identify and study genes encoding particularly interesting target proteins with the aim to improve the yield, stress tolerance or other critical properties of our crop species.

Universal Stress Protein Exhibits a Redox-Dependent Chaperone Function in Arabidopsis and Enhances Plant Tolerance to Heat Shock and Oxidative Stress

Although a wide range of physiological information on Universal Stress Proteins (USPs) is available from many organisms, their biochemical, and molecular functions remain unidentified. The biochemical function of AtUSP (At3g53990) from Arabidopsis thaliana was therefore investigated. Plants over-expressing AtUSP showed a strong resistance to heat shock and oxidative stress, compared with wild-type and Atusp knock-out plants, confirming the crucial role of AtUSP in stress tolerance. AtUSP was present in a variety of structures including monomers, dimers, trimers, and oligomeric complexes, and switched in response to external stresses from low molecular weight (LMW) species to high molecular weight (HMW) complexes. AtUSP exhibited a strong chaperone function under stress conditions in particular, and this activity was significantly increased by heat treatment. Chaperone activity of AtUSP was critically regulated by the redox status of cells and accompanied by structural changes to the protein. Over-expression of AtUSP conferred a strong tolerance to heat shock and oxidative stress upon Arabidopsis, primarily via its chaperone function.

BcRISP1, isolated from non-heading Chinese cabbage, decreases the seed set of transgenic Arabidopsis

Mitochondria are the energy sources of plant cells and are involved in regulating cell development. Ubiquinol-cytochrome c reductase iron-sulfur protein, which is necessary for mitochondrial respiration, is a subunit of mitochondrial electron transport chain multimeric enzyme complexes. To better understand the biological function of the ubiquinol-cytochrome c reductase iron-sulfur protein, the full-length cDNA of BcRISP1 was cloned; it was found to contain 810 base pairs and encode 269 amino acids. Unusually, high expression of the BcRISP1 gene in the archesporial cell stages was determined by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis of cytoplasmic male sterile lines and maintainer lines. The seed set was affected by the overexpression of BcRISP1, and shorter siliques with lower seed sets were observed in 35S::BcRISP1 Arabidopsis plants. These characteristics may have resulted from the reduced formation of pollen and impaired pollen tube growth. qRT-PCR results revealed that in 35S::BcRISP1 plants, the expression levels of the mitochondrial respiratory chain-related genes, COX10 and RIP1, were enhanced, whereas the expression levels of QCR7 and SDH2-1 were reduced. This result implies that overexpression of BcRISP1 in transgenic Arabidopsis plants may disrupt the mitochondrial electron transport chain by affecting the expression of mitochondrial respiratory chain-related genes and therefore, reducing the seed set.