Showing papers by "Christine H. Foyer published in 2011"

Ascorbate and glutathione: the heart of the redox hub.

Abstract: The discovery that there is a close relationship between ascorbate and glutathione dates from soon after the characterization of the chemical formulae of the two molecules ([Szent-Gyorgyi, 1931][1]; [Hopkins and Morgan, 1936][2]). Similarly, it has long been known that thylakoids can generate

Understanding Oxidative Stress and Antioxidant Functions to Enhance Photosynthesis

Abstract: Photosynthesis is a well-established source of reactive oxygen species (ROS) in plants. The photosynthetic electron transport chain (PET) operates in an aerobic environment; thus, regulatory systems are required to minimize ROS production. Moreover, an efficient antioxidant network is also essential

Enhancing drought tolerance in C4 crops

Abstract: Adaptation to abiotic stresses is a quantitative trait controlled by many different genes. Enhancing the tolerance of crop plants to abiotic stresses such as drought has therefore proved to be somewhat elusive in terms of plant breeding. While many C4 species have significant agronomic importance, most of the research effort on improving drought tolerance has focused on maize. Ideally, drought tolerance has to be achieved without penalties in yield potential. Possibilities for success in this regard are highlighted by studies on maize hybrids performed over the last 70 years that have demonstrated that yield potential and enhanced stress tolerance are associated traits. However, while our understanding of the molecular mechanisms that enable plants to tolerate drought has increased considerably in recent years, there have been relatively few applications of DNA marker technologies in practical C4 breeding programmes for improved stress tolerance. Moreover, until recently, targeted approaches to drought tolerance have concentrated largely on shoot parameters, particularly those associated with photosynthesis and stay green phenotypes, rather than on root traits such as soil moisture capture for transpiration, root architecture, and improvement of effective use of water. These root traits are now increasingly considered as important targets for yield improvement in C4 plants under drought stress. Similarly, the molecular mechanisms underpinning heterosis have considerable potential for exploitation in enhancing drought stress tolerance. While current evidence points to the crucial importance of root traits in drought tolerance in C4 plants, shoot traits may also be important in maintaining high yields during drought.

Respiration and nitrogen assimilation: targeting mitochondria-associated metabolism as a means to enhance nitrogen use efficiency

Abstract: Considerable advances in our understanding of the control of mitochondrial metabolism and its interactions with nitrogen metabolism and associated carbon/nitrogen interactions have occurred in recent years, particularly highlighting important roles in cellular redox homeostasis. The tricarboxylic acid (TCA) cycle is a central metabolic hub for the interacting pathways of respiration, nitrogen assimilation, and photorespiration, with components that show considerable flexibility in relation to adaptations to the different functions of mitochondria in photosynthetic and non-photosynthetic cells. By comparison, the operation of the oxidative pentose phosphate pathway appears to represent a significant limitation to nitrogen assimilation in non-photosynthetic tissues. Valuable new insights have been gained concerning the roles of the different enzymes involved in the production of 2-oxoglutarate (2-OG) for ammonia assimilation, yielding an improved understanding of the crucial role of cellular energy balance as a broker of co-ordinate regulation. Taken together with new information on the mechanisms that co-ordinate the expression of genes involved in organellar functions, including energy metabolism, and the potential for exploiting the existing flexibility for NAD(P)H utilization in the respiratory electron transport chain to drive nitrogen assimilation, the evidence that mitochondrial metabolism and machinery are potential novel targets for the enhancement of nitrogen use efficiency (NUE) is explored.

The transcription factor ABI4 is required for the ascorbic acid-dependent regulation of growth and regulation of jasmonate-dependent defense signaling pathways in Arabidopsis.

Abstract: Cellular redox homeostasis is a hub for signal integration. Interactions between redox metabolism and the ABSCISIC ACID-INSENSITIVE-4 (ABI4) transcription factor were characterized in the Arabidopsis thaliana vitamin c defective1 (vtc1) and vtc2 mutants, which are defective in ascorbic acid synthesis and show a slow growth phenotype together with enhanced abscisic acid (ABA) levels relative to the wild type (Columbia-0). The 75% decrease in the leaf ascorbate pool in the vtc2 mutants was not sufficient to adversely affect GA metabolism. The transcriptome signatures of the abi4, vtc1, and vtc2 mutants showed significant overlap, with a large number of transcription factors or signaling components similarly repressed or induced. Moreover, lincomycin-dependent changes in LIGHT HARVESTING CHLOROPHYLL A/B BINDING PROTEIN 1.1 expression were comparable in these mutants, suggesting overlapping participation in chloroplast to nucleus signaling. The slow growth phenotype of vtc2 was absent in the abi4 vtc2 double mutant, as was the sugar-insensitive phenotype of the abi4 mutant. Octadecanoid derivative-responsive AP2/ERF-domain transcription factor 47 (ORA47) and AP3 (an ABI5 binding factor) transcripts were enhanced in vtc2 but repressed in abi4 vtc2, suggesting that ABI4 and ascorbate modulate growth and defense gene expression through jasmonate signaling. We conclude that low ascorbate triggers ABA- and jasmonate-dependent signaling pathways that together regulate growth through ABI4. Moreover, cellular redox homeostasis exerts a strong influence on sugar-dependent growth regulation.

Perturbations of amino acid metabolism associated with glyphosate-dependent inhibition of shikimic acid metabolism affect cellular redox homeostasis and alter the abundance of proteins involved in photosynthesis and photorespiration

Abstract: The herbicide glyphosate inhibits the shikimate pathway of the synthesis of amino acids such as phenylalanine, tyrosine, and tryptophan. However, much uncertainty remains concerning precisely how glyphosate kills plants or affects cellular redox homeostasis and related processes in glyphosate-sensitive and glyphosate-resistant crop plants. To address this issue, we performed an integrated study of photosynthesis, leaf proteomes, amino acid profiles, and redox profiles in the glyphosate-sensitive soybean (Glycine max) genotype PAN809 and glyphosate-resistant Roundup Ready Soybean (RRS). RRS leaves accumulated much more glyphosate than the sensitive line but showed relatively few changes in amino acid metabolism. Photosynthesis was unaffected by glyphosate in RRS leaves, but decreased abundance of photosynthesis/photorespiratory pathway proteins was observed together with oxidation of major redox pools. While treatment of a sensitive genotype with glyphosate rapidly inhibited photosynthesis and triggered the appearance of a nitrogen-rich amino acid profile, there was no evidence of oxidation of the redox pools. There was, however, an increase in starvation-associated and defense proteins. We conclude that glyphosate-dependent inhibition of soybean leaf metabolism leads to the induction of defense proteins without sustained oxidation. Conversely, the accumulation of high levels of glyphosate in RRS enhances cellular oxidation, possibly through mechanisms involving stimulation of the photorespiratory pathway.

Acclimation to high CO2 in maize is related to water status and dependent on leaf rank

Abstract: The responses of C(3) plants to rising atmospheric CO(2) levels are considered to be largely dependent on effects exerted through altered photosynthesis. In contrast, the nature of the responses of C(4) plants to high CO(2) remains controversial because of the absence of CO(2) -dependent effects on photosynthesis. In this study, the effects of atmospheric CO(2) availability on the transcriptome, proteome and metabolome profiles of two ranks of source leaves in maize (Zea mays L.) were studied in plants grown under ambient CO(2) conditions (350 +/- 20 µL L(-1) CO(2) ) or with CO(2) enrichment (700 +/- 20 µL L(-1) CO(2) ). Growth at high CO(2) had no effect on photosynthesis, photorespiration, leaf C/N ratios or anthocyanin contents. However, leaf transpiration rates, carbohydrate metabolism and protein carbonyl accumulation were altered at high CO(2) in a leaf-rank specific manner. Although no significant CO(2) -dependent changes in the leaf transcriptome were observed, qPCR analysis revealed that the abundance of transcripts encoding a Bowman-Birk protease inhibitor and a serpin were changed by the growth CO(2) level in a leaf rank specific manner. Moreover, CO(2) -dependent changes in the leaf proteome were most evident in the oldest source leaves. Small changes in water status may be responsible for the observed responses to high CO(2,) particularly in the older leaf ranks.

Dorsoventral variations in dark chilling effects on photosynthesis and stomatal function in Paspalum dilatatum leaves

Abstract: The effects of dark chilling on the leaf-side-specific regulation of photosynthesis were characterized in the C(4) grass Paspalum dilatatum. CO(2)- and light-response curves for photosynthesis and associated parameters were measured on whole leaves and on each leaf side independently under adaxial and abaxial illumination before and after plants were exposed to dark chilling for one or two consecutive nights. The stomata closed on the adaxial sides of the leaves under abaxial illumination and no CO(2) uptake could be detected on this surface. However, high rates of whole leaf photosynthesis were still observed because CO(2) assimilation rates were increased on the abaxial sides of the leaves under abaxial illumination. Under adaxial illumination both leaf surfaces contributed to the inhibition of whole leaf photosynthesis observed after one night of chilling. After two nights of chilling photosynthesis remained inhibited on the abaxial side of the leaf but the adaxial side had recovered, an effect related to increased maximal ribulose-1,5-bisphosphate carboxylation rates (V(cmax)) and enhanced maximal electron transport rates (J(max)). Under abaxial illumination, whole leaf photosynthesis was decreased only after the second night of chilling. The chilling-dependent inhibition of photosynthesis was located largely on the abaxial side of the leaf and was related to decreased V(cmax) and J(max), but not to the maximal phosphoenolpyruvate carboxylase carboxylation rate (V(pmax)). Each side of the leaf therefore exhibits a unique sensitivity to stress and recovery. Side-specific responses to stress are related to differences in the control of enzyme and photosynthetic electron transport activities.

Nitrogen metabolism in plants in the post-genomic era

Abstract: Contributors. Preface. 1 Nitrogen Assimilation and its Relevance to Crop Improvement (Peter J. Lea and Ben J. Miflin). 1.1 Introduction. 1.2 The assimilation of ammonia. 1.3 Crop improvement through manipulating genes for nitrogen metabolism. 1.4 Conclusions. Acknowledgements. References. 2 Transcriptional Profiling Approaches for Studying Nitrogen. Use Efficiency (Malcolm J. Hawkesford and Jonathan R. Howarth). 2.1 N-responsive genes. 2.2 Nitrogen and crop production. 2.3 Targeting NUtE processes in crop plants. 2.4 Validating candidate genes by correlating gene expression with complex traits. 2.5 Prospects. Acknowledgements. References. 3 Energetics of Nitrogen Acquisition (Arnold J. Bloom). 3.1 Availability of nitrogen in the environment. 3.2 Curiosities. 3.3 Mineral nitrogen. 3.4 Plant growth and development. 3.5 Future of plant nitrogen. References. 4 Transport Systems for NO-3 and NH+4 (Mathilde Orsel and Anthony J. Miller). 4.1 Nitrogen forms available to plants. 4.2 Nitrogen transport steps and mechanisms. 4.3 Arabidopsis as a model. 4.4 Ammonium transporters. 4.5 Nitrate transporters. 4.6 Plastid transport. 4.7 Conclusions and future. Acknowledgements. References. 5 Nitric Oxide Synthase-Like Activities in Plants (Hideo Yamasaki, Ryuuichi D. Itoh, Jos'ee N. Bouchard, Ata Allah Dghim, Khurshida K. Hossain, Sushma Gurung and Michael F. Cohen). 5.1 Introduction. 5.2 Lifetime of nitric oxide. 5.3 An overview of NO-dependent signalling systems. 5.4 Mammalian-type NOS - ghost enzymes in plants. 5.5 Comparative NO-related signalling. 5.6 Algal nitric oxide synthesis - an echo from water. 5.7 Nitric oxide synthase in plant-associated bacteria: its occurrence and functions. 5.8 Prospects for NO-dependent signal transduction systems in plants. 5.9 Concluding remarks. Acknowledgements. References. 6 Nitrate Reductase and Nitric Oxide (Werner M. Kaiser, Elisabeth Planchet and Stefan Rumer). 6.1 Introduction. 6.2 Structure, basic functions and regulation of NR. 6.3 NR-dependent NO formation in vivo, measured as NO emission. 6.4 NO production by NR in vitro. 6.5 Physiological effects of NR-derived NO. 6.6 Conclusions and open questions. Acknowledgements. References . 7 Nitric Oxide Signalling in Plants: Cross-Talk With Ca2+,Protein Kinases and Reactive Oxygen Species (J'eremy Astier, Ang'elique Besson-Bard, Izabela Wawer, Claire Parent, Sumaira Rasul, Sylvain Jeandroz, James Dat and David Wendehenne). 7.1 Basic concepts of NO signalling in animals. 7.2 NO signalling in plants. 7.3 Interplays between NO and ROS. 7.4 Conclusion. Acknowledgements. References. 8 Theanine: Its Occurrence and Metabolism in Tea (Ning Li and Jacquie de Silva). 8.1 Introduction. 8.2 Physiological benefits of theanine. 8.3 Chemical properties and characteristics of theanine in tea. 8.4 Role of theanine in tea. 8.5 Metabolism of theanine in tea. 8.6 Theanine synthase. 8.7 Theanine hydrolase. 8.8 The site of synthesis and transport of theanine in tea. 8.9 Other enzymes capable of synthesizing theanine. 8.10 Nitrogen uptake and transport. 8.11 Nitrate transporters. 8.12 Ammonium transporters. 8.13 Nitrogen assimilation by GS (glutamine synthetase) - GOGAT (glutamate synthase). 8.14 Biochemical properties of glutamine synthetase in plants. 8.15 Gene families of glutamine synthetase. 8.16 Regulation of plant glutamine synthetase. 8.17 Glutamate synthase (GOGAT) in plants. 8.18 Glutamate dehydrogenase in plants. 8.19 Regulation of theanine - genotypic factors . 8.20 Regulation of theanine - agronomic factors. 8.21 Summary. Acknowledgements. References. 9 Legume Nitrogen Fixation and Soil Abiotic Stress: From Physiology to Genomics and Beyond (Alex J. Valentine, Vagner A. Benedito and Yun Kang). 9.1 Introduction. 9.2 Legume nitrogen fixation under drought stress. 9.3 Soil acidity. 9.4 Phosphate deficiency. 9.5 Legume biology is taking off. 9.6 Beyond genomics: prospects for legume genetic breeding . References. 10 Metabolomics Approaches to Advance Understanding of Nitrogen Assimilation and Carbon-Nitrogen Interactions (Aaron Fait, Agata Sienkiewicz-Porzucek and Alisdair R. Fernie). 10.1 Introduction. 10.2 Methods for analysing the plant metabolome. 10.3 Uptake and assimilation of nitrate and ammonium. 10.4 Cross-talk between N and secondary metabolism . 10.5 Summary. References. 11 Morphological Adaptations of Arabidopsis Roots to Nitrogen Supply (Hanma Zhang and David J. Pilbeam). 11.1 Introduction. 11.2 N-related morphological adaptations in Arabidopsis roots. 11.3 The developmental context of N-related morphological adaptations in Arabidopsis roots. 11.4 Mechanisms of N-related morphological adaptations in Arabidopsis roots. 11.5 Role of NO3- transporters in N-related morphological adaptations. 11.6 Biological significance of the localized stimulatory effect. 11.7 Concluding remarks. References. 12 Mitochondrial Redox State, Nitrogen Metabolism and Signalling (Christine H. Foyer). 12.1 Introduction. 12.2 The Nicotiana sylvestris mitochondrial cytoplasmic male sterile II mutant. 12.3 Metabolite profiling in CMSII leaves reveals an N-rich phenotype. 12.4 Mitochondrial redox cycling is a key player in determining the rate of nitrate assimilation. 12.5 Regulation of pyridine nucleotide metabolism in CMSII leaves. 12.6 CMSII is an N-sensing/signalling mutant. 12.7 Regulation of gibberellin metabolism and signalling in the CMSII mutant. 12.8 Concluding remarks. References. 13 The Utilization of Nitrogen by Plants: A Whole Plant Perspective (David J. Pilbeam). 13.1 Introduction. 13.2 Nitrogen and plant growth. 13.3 Nitrogen, biomass partitioning and yield. 13.4 Partitioning of nitrogen into metabolites. 13.5 Acquisition of nitrogen by plants. 13.6 Plants, nitrogen and environment. 13.7 Conclusions. References. Index.

Identification and Application of Phenotypic and Molecular Markers for Abiotic Stress Tolerance in Soybean

Abstract: Soybean is a sub-tropical crop, however, its present cultivation range extends from temperate regions to the tropics. The sustainability and predictability of soybean crop production can therefore be severely restricted by environmental stresses. Of these, drought stress is considered to be the cause of major limitations in yield, particularly for soybean crops grown in rain-fed areas (Manavalan et al., 2009; Siddique et al., 2001). The detrimental effects of drought on plant metabolism arise largely from osmotic constraints particularly to the cytoplasm (Lopes et al., 2011). Varieties that are able to grow well under stressful conditions and retain high yields have therefore great potential economic importance. Ideally, therefore, such varieties must be able to sustain growth under limited water supply, conditions that also cause nutrient deprivation and exacerbate the production of reactive oxygen species (Lopes et al., 2011; Foyer & Shigeoka, 2011). The production of drought-tolerant soybean varieties is a major goal of many plant breeders but progress to date remains slow. Intensive research efforts have identified a variety of genes and processes that are affected by drought in soybean (see for example, Chen et al., 2007 a, b). Similarly, much is known about how drought-induced changes in plant metabolism and gene expression influence plant growth, development and yield. However, sustained increases in soybean yield under stressful conditions will require improved crop management practices as well as new soybean varieties with enhanced drought tolerance. Many research groups world-wide are involved in the identification of phenotypic and molecular markers for application in marker-assisted breeding programs. A range of robust phenotypic and molecular markers are required to assist cultivar evaluation for stress tolerance. Ideally, any selected markers should be able to discriminate between stresstolerant and sensitive soybean cultivars using rapid, inexpensive methods. It is an advantage to have markers that do not require destruction of the plants or plant organs, particularly as the assessment of non-destructive markers allows greater consistency in measurements over time. The routine use of molecular markers in soybean breeding