Comparative proteome analysis of differentially expressed proteins induced by K+ deficiency inArabidopsis thaliana

A Plant Based Modified Biostimulant (Copper Chlorophyllin), Mediates Defense Response in Arabidopsis thaliana under Salinity Stress

To date, managing salinity stress in agriculture relies heavily on development of salt tolerant plant varieties, a time-consuming process particularly challenging for many crops. Plant based biostimulants (PBs) that enhance plant defenses under stress can potentially address this drawback, as they are not crop specific and are easy to apply in the field. Unfortunately, limited knowledge about their modes of action makes it harder to utilize them on a broader scale. Understanding how PBs enhance plant defenses at cellular and molecular levels, is a prerequisite for the development of sustainable management practices utilizing biostimulants to improve crop health. In this study we elucidated the protective mechanism of copper chlorophyllin (Cu-chl), a PB, under salinity stress. Our results indicate that Cu-chl exerts protective effects primarily by decreasing oxidative stress through modulating cellular H₂O₂ levels. Cu-chl treated plants increased tolerance to oxidative stress imposed by an herbicide, methyl viologen dichloride hydrate as well, suggesting a protective role against various sources of reactive oxygen species (ROS). RNA-Seq analysis of Cu-chl treated Arabidopsis thaliana seedlings subjected to salt stress identified genes involved in ROS detoxification, and cellular growth.

Genome-wide analysis and metabolic profiling unveil the role of peroxidase CsGPX3 in theaflavin production in black tea processing

Plucked tea leaves can be processed into black tea (Camellia sinensis), which is rich in health-promoting molecules, including flavonoid antioxidants. During black tea processing, theaflavins (TFs) and thearubigins (TRs) are generated via the successive oxidation of catechins by endogenous polyphenol oxidase (PPO)- or peroxidase (POD)-mediated reactions. This process must be well controlled to achieve the proper TF/TR ratio, which is an important quality parameter of the tea beverage. However, little is known about the POD/PPO catalyzed TF formation process at the molecular genetic level. Here, we identified and characterized the POD genes responsible for TF production in tea. Genome-wide analysis of POD/PPO family genes, metabolite profiling, and expression analysis of PPO/POD genes in tea leaves enabled us to select several PPO/POD genes potentially involved in TF production. Differential gene expression in plant tissues and enzyme activity in several tea varieties traditionally used for processing of various beverage types indicate that black tea processing primarily depends on PPO/POD activity. Among these POD/PPO genes, the POD CsGPX3 is involved in the generation of TFs during black tea processing. The capacity of PPO/POD-catalysed TF production is potentially used for controlling catechin oxidation during black tea processing and could be used to create molecular markers for breeding of tea plant varieties suitable for the production of high-quality black tea beverages.

Physiology and proteomic analysis reveals root, stem and leaf responses to potassium deficiency stress in alligator weed

Alligator weed is reported to have a strong ability to adapt to potassium deficiency stress. Proteomic changes in response to this stress are largely unknown in alligator weed seedlings. In this study, we performed physiological and comparative proteomics of alligator weed seedlings between normal growth (CK) and potassium deficiency (LK) stress using 2-DE techniques, including root, stem and leaf tissues. Seedling height, soluble sugar content, PGK activity and H₂O₂ contents were significantly altered after 15 d of LK treatment. A total of 206 differentially expressed proteins (DEPs) were identified. There were 72 DEPs in the root, 79 in the stem, and 55 in the leaves. The proteomic results were verified using western blot and qRT-PCR assays. The most represented KEGG pathway was "Carbohydrate and energy metabolism" in the three samples. The "Protein degradation" pathway only existed in the stem and root, and the "Cell cycle" pathway only existed in the root. Protein-protein interaction analysis demonstrated that the interacting proteins detected were the most common in the stem, with 18 proteins. Our study highlights protein changes in alligator weed seedling under LK stress and provides new information on the comprehensive analysis of the protein network in plant potassium nutrition.

The synergistic effects of sodium and potassium on the xerophyte Apocynum venetum in response to drought stress

Apocynum venetum is an eco-economic plant species with high adaptability to saline and arid environments. Our previous work has found that A. venetum could absorb large amount of Na⁺ and maintain high K⁺ level under saline conditions. To investigate whether K⁺ and Na⁺ could simultaneously enhance drought resistance in A. venetum, seedlings were exposed to osmotic stress (-0.2 MPa) in the presence or absence of additional 25 mM NaCl under low (0.01 mM) and normal (2.5 mM) K⁺ supplying conditions, respectively. The results showed that A. venetum should be considered as a typical K⁺-efficient species since its growth was unimpaired and possessed a strong K⁺ uptake and prominent K⁺ utilization efficiency under K⁺ deficiency condition. Leaf K⁺ concentration remained stable or was even significantly increased under osmotic stress in the presence or absence of NaCl, compared with that under control condition, regardless of whether the K⁺ supply was sufficient or not, and the contribution of K⁺ to leaf osmotic potential consistently exceeded 37%, indicating K⁺ is the uppermost contributor to osmotic adjustment of A. venetum. Under osmotic stress, the addition of 25 mM NaCl significantly increase Na⁺ accumulation in leaves and the contribution of Na⁺ to osmotic adjustment, thus improving the relative water content, concomitantly, promoting the photosynthetic activity resulting in an enhancement of overall plant growth. These findings suggested that, K⁺ and Na⁺ simultaneously play crucial roles in the osmotic adjustment and the maintenance of water status and photosynthetic activity, which is beneficial for A. venetum to cope with drought stress.

Physiological Analysis and Proteome Quantification of Alligator Weed Stems in Response to Potassium Deficiency Stress

The macronutrient potassium is essential to plant growth, development and stress response. Alligator weed (Alternanthera philoxeroides) has a high tolerance to potassium deficiency (LK) stress. The stem is the primary organ responsible for transporting molecules from the underground root system to the aboveground parts of the plant. However, proteomic changes in response to LK stress are largely unknown in alligator weed stems. In this study, we investigated the physiological and proteomic changes in alligator weed stems under LK stress. First, the chlorophyll and soluble protein content and SOD and POD activity were significantly altered after 15 days of LK treatment. The quantitative proteomic analysis suggested that a total of 296 proteins were differentially abundant proteins (DAPs). The functional annotation analysis revealed that LK stress elicited complex proteomic alterations that were involved in oxidative phosphorylation, plant-pathogen interactions, glycolysis/gluconeogenesis, sugar metabolism, and transport in stems. The subcellular locations analysis suggested 104 proteins showed chloroplastic localization, 81 proteins showed cytoplasmic localization and 40 showed nuclear localization. The protein–protein interaction analysis revealed that 56 proteins were involved in the interaction network, including 9 proteins involved in the ribosome network and 9 in the oxidative phosphorylation network. Additionally, the expressed changes of 5 DAPs were similar between the proteomic quantification analysis and the PRM-MS analysis, and the expression levels of eight genes that encode DAPs were further verified using an RT-qPCR analysis. These results provide valuable information on the adaptive mechanisms in alligator weed stems under LK stress and facilitate the development of efficient strategies for genetically engineering potassium-tolerant crops.

Physiological and quantitative proteomic analyses unraveling potassium deficiency stress response in alligator weed (Alternanthera philoxeroides L.) root

Physiological and iTRAQ based proteomic analysis provided new insights into potassium deficiency stress response in alligator weed root. Alligator weed (Alternanthera philoxeroides) has a strong ability to adapt to potassium deficiency (LK) stress. Proteomic changes in response to this stress are largely unknown in alligator weed. In this study, we investigated physiological and molecular mechanisms under LK using isobaric tags for relative and absolute quantitation to characterize proteome-level changes in this plant. First, root physiology, 2, 3, 5-Triphenyl-trazolium chloride (TTC) assay and peroxidase activity were significantly altered after 10 and 15 days of LK treatment. The comparative proteomic analysis suggested a total of 375 proteins were differential abundance proteins. The proteomic results were verified by western blot assays and quantitative real-time PCR. Correlation analysis of transcription and proteomics suggested protein processing in the endoplasmic reticulum, endocytosis, and spliceosome pathways were significantly enriched. The protein responsible for energy metabolism, signal sensing and transduction and protein degradation played crucial roles in this stress. Twelve ubiquitin pathway related proteins were identified in our study, among them 11 proteins were up-regulated. All protein ubiquitination of lysine using pan antibodies were also increased after LK treatment. Our study provide a valuable insights of molecular mechanism underlying LK stress response in alligator weed roots and afford a vital basis to further study potassium nutrition molecular breeding of other plant species.

Cerium Improves Growth of Maize Seedlings via Alleviating Morphological Structure and Oxidative Damages of Leaf under Different Stresses

It had been indicated that cerium (Ce) could promote maize growth involving photosynthetic improvement under potassium (K) deficiency, salt stress, and combined stress of K⁺ deficiency and salt stress. However, whether the improved growth is related to leaf morphological structure, oxidative stress in maize leaves is not well understood. The present study showed that K⁺ deficiency, salt stress, and their combined stress inhibited growth of maize seedlings, affecting the formation of appendages of leaf epidermal cells, and stomatal opening, which may be due to increases in H₂O₂ and malondialdehyde levels, and reductions in Ca²⁺ content, ratios of glutathione/oxidized glutathione, ascorbic acid/dehydroascorbic acid, and the activities of superoxide dismutase, catalase, ascorbic acid peroxidase, guaiacol peroxidase, and glutathione reductase in leaves under different stresses. The adverse effects caused by combined stress were higher than those of single stress. Furthermore, our findings demonstrated that adding Ce³⁺ could significantly promote seedling growth, and alleviate morphological and structural damage of leaf, decrease oxidative stress and increase antioxidative capacity in maize leaves caused by different stresses.

Large-scale Proteomics Combined with Transgenic Experiments Demonstrates An Important Role of Jasmonic Acid in Potassium Deficiency Response in Wheat and Rice

Potassium (K⁺) is the most abundant inorganic cation in plants, and molecular dissection of K⁺ deficiency has received considerable interest in order to minimize K⁺ fertilizer input and develop high quality K⁺-efficient crops. However, the molecular mechanism of plant responses to K⁺ deficiency is still poorly understood. In this study, 2-week-old bread wheat seedlings grown hydroponically in Hoagland solution were transferred to K⁺-free conditions for 8 d, and their root and leaf proteome profiles were assessed using the iTRAQ proteome method. Over 4000 unique proteins were identified, and 818 K⁺-responsive protein species showed significant differences in abundance. The differentially expressed protein species were associated with diverse functions and exhibited organ-specific differences. Most of the differentially expressed protein species related to hormone synthesis were involved in jasmonic acid (JA) synthesis and the upregulated abundance of JA synthesis-related enzymes could result in the increased JA concentrations. Abundance of allene oxide synthase (AOS), one key JA synthesis-related enzyme, was significantly increased in K⁺-deficient wheat seedlings, and its overexpression markedly increased concentrations of K⁺ and JA, altered the transcription levels of some genes encoding K⁺-responsive protein species, as well as enhanced the tolerance of rice plants to low K⁺ or K⁺ deficiency. Moreover, rice AOS mutant (osaos) exhibited more sensitivity to low K⁺ or K⁺ deficiency. Our findings could highlight the importance of JA in K⁺ deficiency, and imply a network of molecular processes underlying plant responses to K⁺ deficiency.

Quantitative Proteomic Analysis of the Response to Zinc, Magnesium, and Calcium Deficiency in Specific Cell Types of Arabidopsis Roots

The proteome profiles of specific cell types have recently been investigated using techniques such as fluorescence activated cell sorting and laser capture microdissection. However, quantitative proteomic analysis of specific cell types has not yet been performed. In this study, to investigate the response of the proteome to zinc, magnesium, and calcium deficiency in specific cell types of Arabidopsis thaliana roots, we performed isobaric tags for relative and absolute quantification (iTRAQ)-based quantitative proteomics using GFP-expressing protoplasts collected by fluorescence-activated cell sorting. Protoplasts were collected from the pGL2-GFPer and pMGP-GFPer marker lines for epidermis or inner cell lines (pericycle, endodermis, and cortex), respectively. To increase the number of proteins identified, iTRAQ-labeled peptides were separated into 24 fractions by OFFGFEL electrophoresis prior to high-performance liquid chromatography coupled with mass spectrometry analysis. Overall, 1039 and 737 proteins were identified and quantified in the epidermal and inner cell lines, respectively. Interestingly, the expression of many proteins was decreased in the epidermis by mineral deficiency, although a weaker effect was observed in inner cell lines such as the pericycle, endodermis, and cortex. Here, we report for the first time the quantitative proteomics of specific cell types in Arabidopsis roots.

Comparative proteome analysis of the response of ramie under N, P and K deficiency

Ramie is an important natural fiber. There has been little research on the molecular mechanisms of ramie related to the absorption, utilization and metabolism of nitrogen (N), phosphorus (P) and potassium (K). One approach to reveal the mechanisms of N, P and K (NPK) utilization and metabolism in ramie is comparative proteome analysis. The differentially expressed proteins in the leaves of ramie were analyzed by proteome analysis after 6 days of N- and K-deficient treatments and 3 days of P-deficient treatment using MALDI-TOF/TOF mass spectrometry and 32, 27 and 51 differential proteins were obtained, respectively. These proteins were involved in photosynthesis, protein destination and storage, energy metabolism, primary metabolism, disease/defense, signal transduction, cell structure, transcription, secondary metabolism and protein synthesis. Ramie responded to NPK stress by enhancing secondary metabolism and reducing photosynthesis and energy metabolism to increase endurance. Specifically, ramie adapted to NPK deficiency by increasing signal transduction pathways, enhancing the connection between glycolysis and photosynthesis, promoting the intracellular flow of carbon and N; promoting the synthesis cysteine and related hormones and upregulating actin protein to promote growth of the root system. The experimental results provide important information for further study on the high-efficiency NPK utilization mechanism of ramie.

Proteomics dissection of plant responses to mineral nutrient deficiency

Plants require at least 17 essential nutrients to complete their life cycle. Except for carbon, hydrogen, and oxygen, other essential nutrients are mineral nutrients, which are mainly acquired from soils by roots. In natural soils, the availability of most essential mineral nutrients is very low and hard to meet the demand of plants. Developing crops with high nutrient efficiency is essential for sustainable agriculture, which requires more understandings of crop responses to mineral nutrient deficiency. Proteomic techniques provide a crucial and complementary tool to dissect molecular mechanisms underlying crop adaptation to mineral nutrient deficiency in the rapidly processing postgenome era. This review gives a comparative overview about identification of mineral nutrient deficiency responsive proteins using proteomic analysis, and discusses the current status for crop proteomics and its challenges to be integrated into systems biology approaches for developing crops with high mineral nutrient efficiency.

Genes encoding plant-specific class III peroxidases are responsible for increased cold tolerance of the brassinosteroid-insensitive 1 mutant

We previously reported that one of the brassinosteroidinsensitive mutants, bri1-9, showed increased cold tolerance compared with both wild type and BRI1-overexpressing transgenic plants, despite its severe growth retardation. This increased tolerance in bri1-9 resulted from the constitutively high expression of stress-inducible genes under normal conditions. In this report, we focused on the genes encoding class III plant peroxidases (AtPrxs) because we found that, compared with wild type, bri1-9 plants contain higher levels of reactive oxygen species (ROS) that are not involved with the activation of NADPH oxidase and show an increased level of expression of a subset of genes encoding class III plant peroxidases. Treatment with a peroxidase inhibitor, salicylhydroxamic acid (SHAM), led to the reduction of cold resistance in bri1-9. Among 73 genes that encode AtPrxs in Arabidopsis, we selected four (AtPrx1, AtPrx22, AtPrx39, and AtPrx69) for further functional analyses in response to cold temperatures. T-DNA insertional knockout mutants showed increased sensitivity to cold stress as measured by leaf damage and ion leakage. In contrast, the overexpression of AtPrx22, AtPrx39, and AtPrx69 increased cold tolerance in the BRI1-GFP plants. Taken together, these results indicate that the appropriate expression of a particular subset of AtPrx genes and the resulting higher levels of ROS production are required for the cold tolerance.

14-3-3 proteins in plant physiology

Plant 14-3-3 isoforms, like their highly conserved homologues in mammals, function by binding to phosphorylated client proteins to modulate their function. Through the regulation of a diverse range of proteins including kinases, transcription factors, structural proteins, ion channels and pathogen defense-related proteins, they are being implicated in an expanding catalogue of physiological functions in plants. 14-3-3s themselves are affected, both transcriptionally and functionally, by the extracellular and intracellular environment of the plant. They can modulate signaling pathways that transduce inputs from the environment and also the downstream proteins that elicit the physiological response. This review covers some of the key emerging roles for plant 14-3-3s including their role in the response to the plant extracellular environment, particularly environmental stress, pathogens and light conditions. We also address potential key roles in primary metabolism, hormone signaling, growth and cell division.

A multidisciplinary study on the effects of phloem-limited viruses on the agronomical performance and berry quality of Vitis vinifera cv. Nebbiolo

Viral infections are known to have a detrimental effect on grapevine yield and performance, but there is still a lack of knowledge about their effect on the quality and safety of end products. Vines of Vitis vinifera cv. Nebbiolo clone 308, affected simultaneously by Grapevine leafroll-associated virus 1 (GLRaV-1), Grapevine virus A (GVA), and Rupestris stem pitting associated virus (RSPaV), were subjected to integrated analyses of agronomical performance, grape berry characteristics, instrumental texture profile, and proteome profiling. The comparison of performance and grape quality of healthy and infected vines cultivated in a commercial vineyard revealed similar shoot fertility, number of clusters, total yield, with significant differences in titratable acidity, and resveratrol content. Also some texture parameters such as cohesiveness and resilience were altered in berries of infected plants. The proteomic analysis of skin and pulp visualized about 400 spots. The ANOVA analysis on 2D gels revealed significant differences among healthy and virus-infected grape berries for 12 pulp spots and 7 skin spots. Virus infection mainly influenced proteins involved in the response to oxidative stress in the berry skin, and proteins involved in cell structure metabolism in the pulp.

Specific functions of individual class III peroxidase genes

In higher plants, class III peroxidases exist as large multigene families (e.g. 73 genes in Arabidopsis thaliana). The diversity of processes catalysed by peroxidases as well as the large number of their genes suggests the possibility of a functional specialization of each isoform. In addition, the fact that peroxidase promoter sequences are very divergent and that protein sequences contain both highly conserved domains and variable regions supports this hypothesis. However, two difficulties are associated with the study of the function of specific peroxidase genes: (i) the modification of the expression of a single peroxidase gene often results in no visible mutant phenotype, because it is compensated by redundant genes; and (ii) peroxidases show low substrate specificity in vitro resulting in an unreliable indication of peroxidase specific activity unless complementary data are available. The generalization of molecular biology approaches such as whole transcriptome analysis and recombinant DNA combined with biochemical approaches provide unprecedented tools for overcoming these difficulties. This review highlights progress made with these new techniques for identifying the specific function of individual class III peroxidase genes taking as an example the model plant A. thaliana, as well as discussing some other plants.

14-3-3 and FHA domains mediate phosphoprotein interactions

Many aspects of plant growth and development require specific protein interactions to carry out biochemical and cellular functions. Several proteins mediate these interactions, two of which specifically recognize phosphoproteins: 14-3-3 proteins and proteins with FHA domains. These are the only phosphobinding domains identified in plants. Both domains are present in animals and plants, and are used by plant proteins to regulate metabolic, developmental, and signaling pathways. 14-3-3s regulate sugar metabolism, proton gradients, and control transcription factor localization. FHA domains are modular domains often found in multidomain proteins that are involved in signal transduction and plant development.

Plant proteomics: concepts, applications, and novel strategies for data interpretation

Proteomics is an essential source of information about biological systems because it generates knowledge about the concentrations, interactions, functions, and catalytic activities of proteins, which are the major structural and functional determinants of cells. In the last few years significant technology development has taken place both at the level of data analysis software and mass spectrometry hardware. Conceptual progress in proteomics has made possible the analysis of entire proteomes at previously unprecedented density and accuracy. New concepts have emerged that comprise quantitative analyses of full proteomes, database-independent protein identification strategies, targeted quantitative proteomics approaches with proteotypic peptides and the systematic analysis of an increasing number of posttranslational modifications at high temporal and spatial resolution. Although plant proteomics is making progress, there are still several analytical challenges that await experimental and conceptual solutions. With this review I will highlight the current status of plant proteomics and put it into the context of the aforementioned conceptual progress in the field, illustrate some of the plant-specific challenges and present my view on the great opportunities for plant systems biology offered by proteomics.

Comparative proteome analysis of differentially expressed proteins induced by Al toxicity in soybean

Phytotoxic aluminum (Al) is a limiting factor for crop production on acid soils. The molecular mechanism, however, underlying Al toxicity and responses in plants is still not well understood. We report here the characterization of comparative proteome of aluminum-stress-responsive proteins in a known Al-resistant soybean cultivar, Baxi 10 (BX10). To investigate time-dependent responses, 1-week-old soybean seedlings were exposed to 50 microM AlCl3 for 24, 48 and 72 h, and total proteins extracted from roots were separated by two-dimensional electrophoresis. More than 1200 root proteins of the soybean BX10 seedling were reproducibly resolved on the gels. A total of 39 differentially expressed spots in abundance were identified by mass spectrometry, with 21 upregulated, 13 newly induced and 5 downregulated. The heat shock protein, glutathione S-transferase, chalcone-related synthetase, GTP-binding protein and ABC transporter ATP-binding protein were previously detected at the transcriptional or translational level in other plants. Other proteins, identified in this study, are new Al-induced proteins. Soybean BX10 roots under aluminum stress could be characterized by the cellular activities involved in stress/defense, signal transduction, transport, protein folding, gene regulation, and primary metabolisms, which are critical for plant survival under Al toxicity. This present study expands our understanding of differentially expressed proteins associated with aluminum stress on soybean BX10.

Proteomics-based dissection of stress-responsive pathways in plants

Abiotic stress has an ability to alter the levels of a number of proteins, which may be soluble or structural in nature or which may exist before and after folding in the plant cell. The most crucial function of plant cell is to respond to stress by developing defence mechanisms. This defence is brought about by alteration in the pattern of gene expression. This leads to modulation of certain metabolic and defensive pathways. Owing to gene expression altered under stress, qualitative and quantitative changes in proteins are obvious. These proteins might play a role in signal transduction, antioxidative defence, antifreezing, heat shock, metal binding, antipathogenesis or osmolyte synthesis. A significant part of the literature shows the quantitative and qualitative changes in proteins, mainly employing western analysis, enzymatic kinetics, fraction isolation, one-dimensional SDS-PAGE electrophoresis, etc. Fortunately, recent developments in sensitivity and accuracy for proteome analysis have provided new dimensions to assess the changes in protein types and their expression levels under stress. The novel aim of this review is to do a side-by-side comparison of the proteins that are induced or overexpressed under abiotic stress, examining those from biochemical literature and the ones observed, sequenced and identified using the advanced proteomics and bioinformatic techniques.

Proteomic analysis of roots growth and metabolic changes under phosphorus deficit in maize (Zea mays L.) plants

Phosphorus (P) deficiency is a major limitation for plant growth and development. Plants can respond defensively to this stress, modifying their metabolic pathways and root morphology, and this involves changes in their gene expression. To better understand the low P adaptive mechanism of crops, we conducted the comparative proteome analysis for proteins isolated from maize roots treated with 1000 microM (control) or 5 microM KH2PO4 for 17 days. The results showed that approximately 20% of detected proteins on 2-DE gels were increased or decreased by two-fold or more under phosphate (Pi) stress. We identified 106 differentially expressed proteins by MALDI-TOF MS. Analysis of these P starvation responsive proteins suggested that they were involved in phytohormone biosynthesis, carbon and energy metabolisms, protein synthesis and fate, signal transduction, cell cycle, cellular organization, defense, secondary metabolism, etc. It could be concluded that they may play important roles in sensing the change of external Pi concentration and regulating complex adaptation activities for Pi deprivation to facilitate P homeostasis. Simultaneously, as a basic platform, the results would also be useful for the further characterization of gene function in plant P nutrition.

How do plants respond to nutrient shortage by biomass allocation?

Plants constantly sense the changes in their environment; when mineral elements are scarce, they often allocate a greater proportion of their biomass to the root system. This acclimatory response is a consequence of metabolic changes in the shoot and an adjustment of carbohydrate transport to the root. It has long been known that deficiencies of essential macronutrients (nitrogen, phosphorus, potassium and magnesium) result in an accumulation of carbohydrates in leaves and roots, and modify the shoot-to-root biomass ratio. Here, we present an update on the effects of mineral deficiencies on the expression of genes involved in primary metabolism in the shoot, the evidence for increased carbohydrate concentrations and altered biomass allocation between shoot and root, and the consequences of these changes on the growth and morphology of the plant root system.

Metabolomic, proteomic and biophysical analyses of Arabidopsis thaliana cells exposed to a caesium stress. Influence of potassium supply

The incorporation and localisation of 133Cs in a plant cellular model and the metabolic response induced were analysed as a function of external K concentration using a multidisciplinary approach. Sucrose-fed photosynthetic Arabidopsis thaliana suspension cells, grown in a K-containing or K-depleted medium, were submitted to a 1 mM Cs stress. Cell growth, strongly diminished in absence of K, was not influenced by Cs. In contrast, the chlorophyll content, affected by a Cs stress superposed to K depletion, did not vary under the sole K depletion. The uptake of Cs was monitored in vivo using 133Cs NMR spectroscopy while the final K and Cs concentrations were determined using atomic absorption spectrometry. Cs absorption rate and final concentration increased in a K-depleted external medium; in vivo NMR revealed that intracellular Cs was distributed in two kinds of compartment. Synchrotron X-ray fluorescence microscopy indicated that one could be the chloroplasts. In parallel, the cellular response to the Cs stress was analysed using proteomic and metabolic profiling. Proteins up- and down-regulated in response to Cs, in presence of K+ or not, were analysed by 2D gel electrophoresis and identified by mass spectrometry. No salient feature was detected excepting the overexpression of antioxidant enzymes, a common response of Arabidopsis cells stressed whether by Cs or by K-depletion. 13C and 31P NMR analysis of acid extracts showed that the metabolome impact of the Cs stress was also a function of the K nutrition. These analyses suggested that sugar metabolism and glycolytic fluxes were affected in a way depending upon the medium content in K+. Metabolic flux measurements using 13C labelling would be an elegant way to pursue on this line. Using our experimental system, a progressively stronger Cs stress might point out other specific responses elicited by Cs.

Proteomic dissection of plant development

Plant development is controlled by complex endogenous genetic programs and responses to environmental cues. Proteome analyses have recently been introduced to plant biology to identify proteins instrumental in these developmental processes. To date most plant proteome studies have been employed to generate reference maps of the most abundant soluble proteins of plant organs at a defined developmental stage. However, proteomics is now also utilized for genetic studies comparing the proteomes of different plant genotypes, for physiological studies analyzing the influences of exogenous signals on a particular plant organ, and developmental studies investigating proteome changes during development. Technical advances are now beginning to allow a proteomic dissection of individual cell types, thus greatly increasing the information revealed by proteome analyses.