Showing papers by "Christine H. Foyer published in 2008"
TL;DR: expression of GS genes in leaves was developmentally regulated, with both GS2 and GS1 assimilating or recycling ammonia in leaves during the period of grain development and filling, suggesting major roles in assimilating ammonia during the critical phases of remobilisation of nitrogen to the grain.
Abstract: We present the first cloning and study of glutamine synthetase (GS) genes in wheat (Triticum aestivum L.). Based on sequence analysis, phylogenetic studies and mapping data, ten GS sequences were classified into four sub-families: GS2 (a, b and c), GS1 (a, b and c), GSr (1 and 2) and GSe (1 and 2). Phylogenetic analysis showed that the wheat GS sub-families together with the GS genes from other monocotyledonous species form four distinct clades. Immunolocalisation studies in leaves, stems and rachis in plants at flowering showed GS protein to be present in parenchyma, phloem companion and perifascicular sheath cells. In situ localisation confirmed that GS1 transcripts were present in the perifascicular sheath cells whilst those for GSr were confined to the vascular cells. Studies of the expression and protein profiles showed that all GS sub-families were differentially expressed in the leaves, peduncle, glumes and roots. Expression of GS genes in leaves was developmentally regulated, with both GS2 and GS1 assimilating or recycling ammonia in leaves during the period of grain development and filling. During leaf senescence the cytosolic isozymes, GS1 and GSr, were the predominant forms, suggesting major roles in assimilating ammonia during the critical phases of remobilisation of nitrogen to the grain. A preliminary analysis of three different wheat genotypes showed that the ratio of leaf GS2 protein to GS1 protein was variable. Use of this genetic variation should inform future efforts to modulate this enzyme for pre-breeding efforts to improve nitrogen use in wheat.
165 citations
TL;DR: Results demonstrate that CPs are involved in Rubisco turnover in leaves under optimal and stress conditions and that extra-plastidic RVB bodies are present even in young source leaves, and form the basis for a new model of Rubisco protein turnover involving CPs and RVBs.
Abstract: The roles of cysteine proteinases (CP) in leaf protein accumulation and composition were investigated in transgenic tobacco (Nicotiana tabacum L.) plants expressing the rice cystatin, OC-1. The OC-1 protein was present in the cytosol, chloroplasts, and vacuole of the leaves of OC-1 expressing (OCE) plants. Changes in leaf protein composition and turnover caused by OC-1-dependent inhibition of CP activity were assessed in 8-week-old plants using proteomic analysis. Seven hundred and sixty-five soluble proteins were detected in the controls compared to 860 proteins in the OCE leaves. A cyclophilin, a histone, a peptidyl-prolyl cis-trans isomerase, and two ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase isoforms were markedly altered in abundance in the OCE leaves. The senescence-related decline in photosynthesis and Rubisco activity was delayed in the OCE leaves. Similarly, OCE leaves maintained higher leaf Rubisco activities and protein than controls following dark chilling. Immunogold labelling studies with specific antibodies showed that Rubisco was present in Rubisco vesicular bodies (RVB) as well as in the chloroplasts of leaves from 8-week-old control and OCE plants. Western blot analysis of plants at 14 weeks after both genotypes had flowered revealed large increases in the amount of Rubisco protein in the OCE leaves compared to controls. These results demonstrate that CPs are involved in Rubisco turnover in leaves under optimal and stress conditions and that extra-plastidic RVB bodies are present even in young source leaves. Furthermore, these data form the basis for a new model of Rubisco protein turnover involving CPs and RVBs.
135 citations
TL;DR: An asymmetric surface-specific regulation of photosynthesis and stomatal conductance was observed with respect to light orientation and this was not caused by dorso-ventral variations in leaf structure, the distribution of phosphoenolpyruvate carboxylase and ribulose 1,5-bisphosphate car boxylase/oxygenase proteins or light absorptance, transmittance or reflectance.
Abstract: Whole-plant morphology, leaf structure and composition were studied together with the effects of light orientation on the dorso-ventral regulation of photosynthesis and stomatal conductance in Paspalum dilatatum cv. Raki plants grown for 6 wk at either 350 or 700 µl l?1 CO2. Plant biomass was doubled as a result of growth at high CO2 and the shoot:root ratio was decreased. Stomatal density was increased in the leaves of the high CO2-grown plants, which had greater numbers of smaller stomata and more epidermal cells on the abaxial surface. An asymmetric surface-specific regulation of photosynthesis and stomatal conductance was observed with respect to light orientation. This was not caused by dorso-ventral variations in leaf structure, the distribution of phosphoenolpyruvate carboxylase (PEPC) and ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) proteins or light absorptance, transmittance or reflectance. Adaxial/abaxial specification in the regulation of photosynthesis results from differential sensitivity of stomatal opening to light orientation and fixed gradients of enzyme activation across the leaf.
69 citations
TL;DR: It is proposed that a deficiency in protein glycosylation is responsible for the observed cell death phenotype of the temperature-sensitive Arabidopsis thaliana pmm-12 mutant.
61 citations
TL;DR: A model in which the amine/nitrate ratio interacts with GA signalling and respiratory pathways to regulate the partitioning of biomass between shoots and roots is proposed.
Abstract: Mitochondrial electron transport pathways exert effects on carbon-nitrogen (C/N) relationships. To examine whether mitochondria-N interactions also influence plant growth and development, we explored the responses of roots and shoots to external N supply in wild-type (WT) Nicotiana sylvestris and the cytoplasmic male sterile II (CMSII) mutant, which has a N-rich phenotype. Root architecture in N. sylvestris seedlings showed classic responses to nitrate and sucrose availability. In contrast, CMSII showed an altered 'nitrate-sensing' phenotype with decreased sensitivity to C and N metabolites. The WT growth phenotype was restored in CMSII seedling roots by high nitrate plus sugars and in shoots by gibberellic acid (GA). Genome-wide cDNA-amplified fragment length polymorphism (AFLP) analysis of leaves from mature plants revealed that only a small subset of transcripts was altered in CMSII. Tissue abscisic acid content was similar in CMSII and WT roots and shoots, and growth responses to zeatin were comparable. However, the abundance of key transcripts associated with GA synthesis was modified both by the availability of N and by the CMSII mutation. The CMSII mutant maintained a much higher shoot/root ratio at low N than WT, whereas no difference was observed at high N. Shoot/root ratios were strikingly correlated with root amines/nitrate ratios, values of <1 being characteristic of high N status. We propose a model in which the amine/nitrate ratio interacts with GA signalling and respiratory pathways to regulate the partitioning of biomass between shoots and roots.
60 citations
TL;DR: It is concluded that Robusta accumulates less sucrose than Arabica for two reasons:Robusta has higher sucrose synthase and acid invertase activities early in grain development - the expression of CcSS1 and CcInv2 appears to be crucial at this stage and RobUSTa has a lower SPS activity and low CcSPS1 expression at the final stages of grain development and hence has less capacity for sucrose re-synthesis.
Abstract: * Coffea arabica (Arabica) and Coffea canephora (Robusta) are the two main cultivated species used for coffee bean production. Arabica genotypes generally produce a higher coffee quality than Robusta genotypes. Understanding the genetic basis for sucrose accumulation during coffee grain maturation is an important goal because sucrose is an important coffee flavor precursor. * Nine new Coffea genes encoding sucrose metabolism enzymes have been identified: sucrose phosphate synthase (CcSPS1, CcSPS2), sucrose phosphate phosphatase (CcSP1), cytoplasmic (CaInv3) and cell wall (CcInv4) invertases and four invertase inhibitors (CcInvI1, 2, 3, 4). * Activities and mRNA abundance of the sucrose metabolism enzymes were compared at different developmental stages in Arabica and Robusta grains, characterized by different sucrose contents in mature grain. * It is concluded that Robusta accumulates less sucrose than Arabica for two reasons: Robusta has higher sucrose synthase and acid invertase activities early in grain development - the expression of CcSS1 and CcInv2 appears to be crucial at this stage and Robusta has a lower SPS activity and low CcSPS1 expression at the final stages of grain development and hence has less capacity for sucrose re-synthesis. Regulation of vacuolar invertase CcInv2 activity by invertase inhibitors CcInvI2 and/or CcInvI3 during Arabica grain development is considered.
56 citations
01 Jan 2008
TL;DR: Ascorbate, glutathione, and tocopherol are the three major low molecular weight antioxidants of plant cells as mentioned in this paper, and the degree of redox coupling between these antioxidants has profound implications for regulation, function, and signaling associated with the two major energy-generating systems.
Abstract: Ascorbate, glutathione, and tocopherol are the three major low molecular weight antioxidants of plant cells. While tocopherol is hydrophobic and is found only in lipid membranes, ascorbate and glutathione are hydrophilic, accumulating to high concentrations in the chloroplast stroma and other compartments of the plant cell. Ascorbate and glutathione not only limit photo-oxidative damage but can also act independently as signal-transducing molecules regulating defense gene expression. Both metabolites transmit information concerning oxidative load and redoxbuffering capacity. Ascorbate modifies the expression of chloroplast genes. Net glutathione synthesis during stress restores the cellular redox state and allows orchestration of systemic acquired resistance. The degree of redox coupling between these antioxidants has profound implications for regulation, function, and signaling associated with the two major energy-generating systems, i.e. photosynthesis and respiration. Tocopherol fulfills an essential protective function, counter-acting the harmful effects of singlet oxygen production at photosystem II. Ascorbate reduces and thus regenerates oxidized tocopherol, but flux through this reaction is not sufficient to maintain the reduced tocopherol pool under high light stress. This may be because tocopherol regeneration draws on the ascorbate pool of the chloroplast lumen, which may be depleted under stress. Moreover, while glutathione always reduces oxidized ascorbate (dehydroascorbate), the degree of coupling between the ascorbate and glutathione redox couples is variable. The flexibility of coupling between these antioxidant pools is crucial to differential redox signaling, particularly by ascorbate and glutathione.
39 citations
TL;DR: In this paper, the authors examined nodule structure, carbon-nitrogen interactions, and respiration in two soybean genotypes that differ in chilling sensitivity: PAN809 (PAN) and Highveld Top (HT) which is more chilling resistant.
Abstract: Symbiotic nitrogen fixation is sensitive to dark chilling (7°C–15°C)-induced inhibition in soybean (Glycine max). To characterize the mechanisms that cause the stress-induced loss of nodule function, we examined nodule structure, carbon-nitrogen interactions, and respiration in two soybean genotypes that differ in chilling sensitivity: PAN809 (PAN), which is chilling sensitive, and Highveld Top (HT), which is more chilling resistant. Nodule numbers were unaffected by dark chilling, as was the abundance of the nitrogenase and leghemoglobin proteins. However, dark chilling decreased nodule respiration rates, nitrogenase activities, and NifH and NifK mRNAs and increased nodule starch, sucrose, and glucose in both genotypes. Ureide and fructose contents decreased only in PAN nodules. While the chilling-induced decreases in nodule respiration persisted in PAN even after return to optimal temperatures, respiration started to recover in HT by the end of the chilling period. The area of the intercellular spaces in the nodule cortex and infected zone was greatly decreased in HT after three nights of chilling, an acclimatory response that was absent from PAN. These data show that HT nodules are able to regulate both respiration and the area of the intercellular spaces during chilling and in this way control the oxygen diffusion barrier, which is a key component of the nodule stress response. We conclude that chilling-induced loss of symbiotic nitrogen fixation in PAN is caused by the inhibition of respiration coupled to the failure to regulate the oxygen diffusion barrier effectively. The resultant limitations on nitrogen availability contribute to the greater chilling-induced inhibition of photosynthesis in PAN than in HT.
33 citations
TL;DR: Effective and accurate methods for the measurement of changes in the cellular ascorbate and glutathione pools and the activities of related enzymes such poly (ADP-ribose) polymerase during mitosis and cell expansion are provided, particularly in cell suspension cultures.
Abstract: Reactive oxygen species (ROS) and low molecular weight antioxidants, such as glutathione and ascorbate, are powerful signaling molecules that participate in the control of plant growth and development, and modulate progression through the mitotic cell cycle. Enhanced reactive oxygen species accumulation or low levels of ascorbate or glutathione cause the cell cycle to arrest and halt progression especially through the G1 checkpoint. Plant cell suspension cultures have proved to be particularly useful tools for the study of cell cycle regulation. Here we provide effective and accurate methods for the measurement of changes in the cellular ascorbate and glutathione pools and the activities of related enzymes such poly (ADP-ribose) polymerase during mitosis and cell expansion, particularly in cell suspension cultures. These methods can be used in studies seeking to improve current understanding of the roles of redox controls on cell division and cell expansion.
18 citations
TL;DR: A novel morphological mechanism is reported that allows C4 monocotyledonous leaves to regulate photosynthesis independently on each surface with respect to incident light allowing better adaptation to water deficits and light stress and how this regulation confers a survival advantage to the C4 relative to C3 leaves.
Abstract: Photosynthesis is an important driver of ecosystem sustainability in the face of climate change. Monocotyledonous crop species with C4 photosynthesis such as maize (Zea mays L; corn) and sugar cane are crucial for future food security and biofuel crop requirements, while C4 pasture grasses such as Paspalum are central to natural ecosystems. The global demand for corn will exceed that for wheat and rice by 2020, making it the world's most important crop. Light-driven photosynthesis supports plant biomass production, but plants have also evolved safety valve mechanisms that attenuate the absorption of potentially lethal levels of excess light. The array of survival responses that enables leaves to evade photoinhibition is complex and involves chloroplast and leaf movement as well as the molecular rearrangements that facilitate thermal energy dissipation. Here we report a novel morphological mechanism that allows C4 monocotyledonous leaves to regulate photosynthesis independently on each surface with respect to incident light allowing better adaptation to water deficits and light stress. We show that under abaxial illumination as occurs when monocotyledonous leaves curl in response to water stress the stomata close and photosynthetic metabolism shuts down on the adaxial surface of C4 leaves but these parameters increase in function to the abaxial surface. We discuss how this regulation confers a survival advantage to the C4 relative to C3 leaves which are unable to regulate their dorso-ventral functions in relation to light.
01 Jan 2008
TL;DR: In Chinese free-air CO2 enrichment experiments, the net photosynthetic rate (P n) was significantly lower in CO2-enriched rice but not in the CO2enriched Rice offspring grown in ambient air when measured at comparable CO2 concentrations, indicating that no down-regulation of photosynthesis occurred in the offspring of CO2enhanced rice as discussed by the authors.
Abstract: Rising CO2 increases photosynthesis in C3 plants owing to the increase of its substrate concentration and inhibition of photorespiration. After long-term exposure to elevated CO2, however, the stimulatory effect decreases gradually in many C3 plants so that the net photosynthetic rate (P n) is lower than that in plants grown in ambient air when measured at the same CO2 concentration. This phenomenon, the so called down-regulation of photosynthesis, is often reported in CO2-enriched current generation plants. It has not been known whether the down-regulation is preserved or eliminated in the offspring from seeds of plants grown at elevated CO2. In Chinese free-air CO2 enrichment experiments the leaf Pn was significantly lower in CO2-enriched rice but not in the CO2-enriched rice offspring grown in ambient air when measured at comparable CO2 concentrations, indicating that no down-regulation of photosynthesis occurred in the offspring of CO2-enriched rice.
01 Jan 2008
TL;DR: It is proposed that a deficiency in protein glycosylation is responsible for the observed cell death phenotype of the temperature-sensitive Arabidopsis thaliana pmm-12 mutant.
Abstract: Eukaryotic phosphomannomutases (PMMs) catalyze the interconversion of mannose 6-phosphate to mannose 1-phosphate and are essential to the biosynthesis of GDP-mannose. As such, plant PMMs are involved in ascorbic acid (AsA) biosynthesis and N-glycosylation. We report on the conditional phenotype of the temperature-sensitive Arabidopsis thaliana pmm-12 mutant. Mutant seedlings were phenotypically similar to wild type seedlings when grown at 16 –18 °C but died within several days after transfer to 28 °C. This phenotype was observed throughout both vegetative and reproductive development. Protein extracts derived from pmm-12 plants had lower PMM protein and enzyme activity levels. In vitro biochemical analysis of recombinant proteins showed that the mutant PMM protein was compromised in its catalytic efficiency (Kcat/Km). Despite significantly decreased AsA levels in pmm-12 plants, AsA deficiency could not account for the observed phenotype. Since, at restrictive temperature, total glycoprotein patterns were altered and glycosylation of protein-disulfide isomerase was perturbed, we propose that a deficiency in protein glycosylation is responsible for the observed cell death phenotype.