44 research outputs found
Métabolisme des fructanes chez <em>Lolium perenne</em> L. : identification de deux gènes codant des fructanes exohydrolases (FEHs) et étude de la régulation de l'activité FEH par les sucres solubles
No full textMitochondrial complex I dysfunction increases CO₂ efflux and reconfigures metabolic fluxes of day respiration in tobacco leaves
No full textMutants affected in complex I are useful to understand the role played by mitochondrial electron transport and redox metabolism in cellular homeostasis and signaling. However, their respiratory phenotype is incompletely described and a specific examination of day respiration (Rd) is lacking. Here, we used isotopic methods and metabolomics to investigate the impact of complex I dysfunction on Rd in two respiratory mutants of forest tobacco (Nicotiana sylvestris): cytoplasmic male sterile II (CMSII) and nuclear male sterile 1 (NMS1), previously characterized for complex I disruption. Rd was higher in mutants and the inhibition of leaf respiration by light was lower. Higher Rd values were caused by increased (phosphoenol)pyruvate (PEP) metabolism at the expense of anaplerotic (PEP carboxylase (PEPc) ‐catalyzed) activity. De novo synthesis of Krebs cycle intermediates in the light was larger in mutants than in the wild‐type, although numerically small in all genotypes. Carbon metabolism in mutants involved alternative pathways, such as alanine synthesis, and an increase in amino acid production with the notable exception of aspartate. Our results show that the alteration of NADH re‐oxidation activity by complex I does not cause a general inhibition of catabolism, but rather a re‐orchestration of fluxes in day respiratory metabolism, leading to an increased CO2 efflux
Nitrogen metabolism in plants under low oxygen stress
No full textMore frequent flooding and waterlogging events due to more heavy precipitation are expected worldwide in the context of climate change. Accordingly, adaptation of plants to oxygen limitation at both cellular and whole plant levels should be investigated thoroughly, that derived knowledge could be taken into account in breeding programs and agronomical practices for saving plant fitness, growth and development even when oxygen availability is low. In the present review, we highlight current knowledge on essential aspects of low oxygen stress-induced changes in nitrogen metabolism. The involvement of two possible pathways for NO production either via the reaction catalyzed by nitrate reductase or at Complex III or IV of the mitochondrial electron transport chain, thus contributing to ATP synthesis via the so-called nitrite-NO respiration, is discussed. NO is proposed to be scavenged by non-symbiotic hemoglobin (Hb) in a Hb/NO cycle, in which NAD(P)H is oxidized for the conversion of NO into NO3(-). The investigation of an additional adaptation to the decrease in oxygen availability via transcriptional and posttranslational regulation of amino acid synthesis pathways, using publicly available transcriptome and translatome data for Arabidopsis thaliana and rice is also discussed
<i>In silico</i> analysis of 3 expansin gene promoters reveals 2 hubs controlling light and cytokinins response during bud outgrowth
No full textBud outgrowth is under the intricate control of environmental and endogenous factors. In a recent paper,1 Roman H, Girault T, Barbier F, Péron T, Brouard N, Pěnčík A, Novák O, Vian A, Sakr S, Lothier J, et al. Cytokinins are initial targets of light in the control of bud outgrowth. Plant Physiol 2016; 172:489-509; PMID:27462085; http://dx.doi.org/10.1104/pp.16.00530[Crossref], [PubMed], [Web of Science ®], [Google Scholar] we demonstrated that light perceived by Rosa buds triggers cytokinins (CK) synthesis within 3 hours in the adjacent node followed by their transport to the bud. There, CK control expression of a set of major genes (strigolactones-, auxin-, sugar sink strength-, cells division and elongation-related genes) leading to bud outgrowth in light. Conversely, under dark condition, CK accumulation and transport to the bud are repressed and no bud outgrowth occurs. In this paper, we show that the 3 expansin genes RhEXPA1,2,3 are under the control of both light and CK during bud outgrowth. In silico analysis of promoter sequences highlights 2 regions enriched in light and CK cis-regulatory elements as well as a specific cis-element in pRhEXPA3, potentially responsible for the expression patterns observed in response to CK and light
Modelling temporal variation of parameters used in two photosynthesis models: influence of fruit load and girdling on leaf photosynthesis in fruit-bearing branches of apple
No full textBackground and Aims: Several studies have found seasonal and temporal variability in leaf photosynthesis parameters in different crops. This variability depends upon the environment, the developmental stage of the plant and the presence or absence of sinks. Girdling involves the removal of the bark and phloem down to the youngest xylem all around the stem and prevents export of photoassimilates out of the stem. The load of developing fruits has often been reported to influence the individual net leaf photosynthesis rate (Pn) in tree crops. In this study, we chose (1) to model the key parameters of photosynthesis models of leaves (Pgmax, Rd, α and θ) as a function of time and using these two means (girdling and low fruit load) to alter the source-sink balance and (2) to compare three models: the rectangular and non-rectangular hyperbola model by Thornley, as well as the non-rectangular hyperbola model by Marshall and Biscoe.
Methods: Six-year-old fruit-bearing branches of 10-year-old apple trees were used to study and model the seasonal variation of photosynthetic parameters in leaves of vegetative shoots, as a function of global fruit load (at the branch level), with or without girdling, during the growing season of 2015. Three treatments were applied: control, low load (LL) or low load + girdling (LLG). For each fruit-bearing branch, light-response curves of Pn for two leaves of vegetative shoots were measured at two different positions, proximal and distal.
Key Results: The model of Marshall and Biscoe was the most accurate for the simulation of Pn in fruit-bearing branches of apple trees with time (season) and the three treatments applied.
Conclusion: The present study proposed a way to model the photosynthesis rate by temporal and environmental variables only. A proper validation of this model will be necessary to extend its utilization and appreciate its predictive capacity fully
Hypoxic respiratory metabolism in plants: reorchestration of nitrogen and carbon metabolisms
No full textHexokinase-dependent sugar signaling represses fructan exohydrolase activity in Lolium perenne
No full textDefoliation of perennial ryegrass (Lolium perenne L.) by grazing animals leads to fructan mobilisation via an increase of fructan exohydrolase (FEH) activity. To highlight the regulation of fructan metabolism in perennial ryegrass, the role of sugars as signalling molecules for regulation of FEH activity after defoliation was evaluated. We used an original approach in planta by spraying stubble of defoliated plants (sugar starved plants) during 24 h with metabolisable sugars (glucose, fructose, sucrose) and sugar analogues (3-O-methylglucose, mannose, lactulose, turanose, palatinose). Metabolisable sugar (glucose, fructose, sucrose) supply following defoliation led to the repression of FEH activity increase. The supply of mannose, which is phosphorylated by hexokinase but not further metabolisable, led to the same repressive effect, whereas 3-O-methylglucose, which is not a substrate for hexokinase, had no effect. These results indicate that hexoses could be sensed by hexokinase, triggering a chain of events leading to the repression of FEH activity. By contrast, it was not possible to determine the role of sucrose as a signal since the supply of sucrose analogues (lactulose, turanose and palatinose) enhanced internal hexose content
– roles of glutamate synthases and carbamoylphosphate synthetase in leaves
No full textInternational audienceThis study was aimed at investigating the physiological role of ferredoxin-glutamate synthases (EC 1.4.1.7), NADH-glutamate synthase (EC 1.4.1.14) and carbamoylphosphate synthetase (EC 6.3.5.5) in Arabidopsis. Phenotypic analysis revealed a high level of photorespiratory ammonium, glutamine/glutamate and asparagine/aspartate in the GLU1 mutant lacking the major ferredoxin-glutamate synthase, indicating that excess photorespiratory ammonium was detoxified into amino acids for transport out of the veins. Consistent with these results, promoter analysis and in situ hybridization demonstrated that GLU1 and GLU2 were expressed in the mesophyll and phloem companion cell-sieve element complex. However, these phenotypic changes were not detected in the GLU2 mutant defective in the second ferredoxin-glutamate synthase gene. The impairment in primary ammonium assimilation in the GLT mutant under nonphotorespiratory high-CO(2) conditions underlined the importance of NADH-glutamate synthase for amino acid trafficking, given that this gene only accounted for 3% of total glutamate synthase activity. The excess ammonium from either endogenous photorespiration or the exogenous medium was shifted to arginine. The promoter analysis and slight effects on overall arginine synthesis in the T-DNA insertion mutant in the single carbamoylphosphate synthetase large subunit gene indicated that carbamoylphosphate synthetase located in the chloroplasts was not limiting for ammonium assimilation into arginine. The data provided evidence that ferredoxin-glutamate synthases, NADH-glutamate synthase and carbamoylphosphate synthetase play specific physiological roles in ammonium assimilation in the mesophyll and phloem for the synthesis and transport of glutamine, glutamate, arginine, and derived amino acids
Nitrogen Management at the Whole Plant Level for Better Nitrogen Use Efficiency
No full textInternational audienceNitrogen fertilizers are used worldwide and are essential to obtain good yields in cereals, oilseed rape and maize. However, nitrogen fertilizers have a negative impact on the carbon balance and in some case on environment. Decreasing fertilizer needs without affecting yield would be beneficial to farmers’ costs and to environment. Then understanding how plants uptake fertilizers, their preference amongst the different nitrogen sources, how they assimilate inorganic nitrogen forms and how they recycle and reuse nitrogen all along their lifespan is essential for better use efficiency (NUE). This keynote lecture will focus on nitrogen assimilation, recycling and remobilization in plant and will show how our recent knowledge led us to propose breeding solutions to improve NUE and plant adaptation to environment.Chen, Q., Soulay, F., Saudemont, B., Elmayan, T., Marmagne, A., and Masclaux-Daubresse, C.(2019): Overexpression of ATG8 in Arabidopsis Stimulates Autophagic Activity and Increases NitrogenRemobilization Efficiency and Grain Filling, Plant and Cell Physiology (60), 343-352.Guiboileau, A., Yoshimoto, K., Soulay, F., Bataille, M.P., Avice, J.C., and Masclaux-Daubresse, C.(2012): Autophagy machinery controls nitrogen remobilization at the whole-plant level under bothlimiting and ample nitrate conditions in Arabidopsis, New Phytologist (194), 732-740.James, M., Masclaux-Daubresse, C., Marmagne, A., Azzopardi, M., Laine, P., Goux, D., Etienne, P.,and Trouverie, J. (2019): A New Role for SAG12 Cysteine Protease in Roots of Arabidopsis thaliana.Frontiers in Plant Science (9).James, M., Poret, M., Masclaux-Daubresse, C., Marmagne, A., Coquet, L., Jouenne, T., Chan, P.,Trouverie, J., and Etienne, P. (2018): SAG12, a Major Cysteine Protease Involved in NitrogenAllocation during Senescence for Seed Production in Arabidopsis thaliana, Plant and Cell Physiology(59), 2052-2063.Masclaux-Daubresse, C., Chen, Q., and Havé, M. (2017): Regulation of nutrient recycling viaautophagy, Current Opinion in Plant Biology (39), 8-17.Moison, M., Marmagne, A., Dinant, S., Soulay, F., Azzopardi, M., Lothier, J., Citerne, S., Morin, H.,Legay, N., Chardon, F., Avice, J.C., Reisdorf-Cren, M., and Masclaux-Daubresse, C. (2018): Threecytosolic glutamine synthetase isoforms localized in different-order veins act together for Nremobilization and seed filling in Arabidopsis, Journal of Experimental Botany (69), 4379-4393.Tegeder, M., and Masclaux-Daubresse, C. (2018): Source and sink mechanisms of nitrogen transportand use, New Phytologist (217), 35-53
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