48 research outputs found
Assessment of the physio-biochemical performance of Tunisian barley landraces under deficit saline-irrigation during grain filling stage
Salinity is one of the main and important abiotic stresses that adversely affects crop growth, development and production. In this study, two barley (Hordeum vulgare L.) landraces were subjected to three treatments of deficit saline-irrigation (12 dS/cm) (T0 = 100%ETc, T1 = 75%ETc, and T2 = 50%ETc) during grain filling stage. Carbon isotope discrimination (Δ13C) was associated with some physio-biochemical parameters to evaluate barley response to saline conditions. Results of this study showed that deficit saline-irrigation significantly (p < 0.05) decreases Δ13C in both barley landraces. Moreover, photosynthetic rate (A), transpiration (E), stomatal conductance (gs), and instantaneous water use efficiency (iWUE) were significantly affected by treatments. Relative water content (RWC), chlorophyll a, and chlorophyll (SPAD) value were significantly (p < 0.01 and p < 0.001) were affected by deficit saline-irrigation. In addition, phenolic compounds were affected by treatments and landraces (except syringic and p-coumaric acids), and their interactions (except syringic acid). Moreover, high correlations were noticed between Δ13C and physio-biochemical parameters. Results suggested that both barley landraces make a higher iWUE, and a weak variation in phenolic compounds. Moreover, Δ13C associated with physio-biochemical traits can also be good criteria for screening of salt-tolerance of barley during grain filling stage. Taken together, our study suggests that the response to deficit saline-irrigation in barley landraces involves an interplay between various physiological and biochemical mechanisms mainly related to Δ13C
Photosynthese et relations hydriques de la fetuque elevee sous carence azotee : effet d'un cycle de dessechement-rehydratation
SIGLECNRS T 60062 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
DISCRIMINATION ISOTOPIQUE DU CARBONE ( 1 3C/ 1 2C) CHEZ LES PLANTES C3 LORS DE LA RESPIRATION A L'OBSCURITE DANS DIFFERENTES CONDITIONS D'ENVIRONNEMENT
ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF
Etude de la respiration et de la gestion des réserves foliaires à l'obscurité chez Phaseolus vulgaris L. à l'aide des isotopes stables du carbonne
Les plantes terrestres discriminent contre le 13CO2 lors de l'assimilation photosynthétique, de telle sorte que la matière organique des plantes en C3 est appauvrie de 20% en 13C par rapport au CO2 de l'air. Il a été montré que le CO2 rejeté par la respiration foliaire à l'obscurité est en général enrichi en 13C par rapport à la matière organique, mais il demeure une importante variabilité. C'est pourquoi la teneur naturelle en 13C dans le CO2 produit par la respiration est étudiée dans ce travail de façon systématique, en relation avec l'état métabolique des feuilles comme la disponibilité en substrats, et la température. L'ensemble des données collectées indique qu'il existe une relation linéaire forte entre la teneur en 13C du CO2 et le quotient respiratoire (CO2/02), ce qui montre que les variations d'abondance isotopique sont simplement expliquées par des changements de substrats respiratoires. Néanmoins, même lorsque les substrats respiratoires sont déterminés expérimentalement comme étant des carbohydrates, l'origine précise des atomes de carbone (c'est-à-dire l'identité du pool métabolique) retrouvés dans le CO2 n'est pas connue avec précision. C'est pourquoi cette étude est complétée par des marquages isotopiques à la lumière avec du CO2 à très basse teneur en 13C, afin de voir si l'abondance en 13C du CO2 produit par la respiration après l'illumination reflète tout à la fois la contribution des réserves et celle des assimilats récemment fabriqués lors du marquage. Les résultats indiquent que le carbone récemment fixé ne contribue que très peu à l'alimentation de la respiration.Carbon assimilation of terrestrial plants discriminates against 13CO2 and consequently, plant organic matter is on average 13C-depleted by 20 per mil compared to atmospheric CO2. It has been previously shown that leaf dark-respired CO2 is generally 13C-enriched, but this enrichment is quite variable. That is why the natural abundance of 13C in CO2 evolved in darkness is precisely studied here as a function of the metabolic status of leaves (that is, the substrate availability) and temperature. Taken as a whole, the data obtained in the experiments indicate that there lies a strong linear relationship between the 13C-abundance in dark-respired CO2 and the respiratory quotient (RQ=CO2/02). In other words, the variations of the 13C-abundance in CO2 evolved in darkness are explained by shifts of respiratory substrate. However, the origin of the carbon atoms that are found in respired CO2 that is, the identity of the metabolic pool feeding dark-respiratory decarboxylations, is not precisely known even when the respiratory substrates are carbohydrates, as given by RQ=1. Thus, in order to investigate the contribution of recently fixed carbon and storage carbon to CO2 production, isotopic labelling is conducted in illuminated leaves with strongly 13C-depleted CO2. It is found that recent photosynthates only hardly feed respiration in darkness after illumination, with a contribution value as low as 50% after a 24 h-iabelling period. Clearly, 'old' storage carbon is the major component of the dark-respiratory metabolic pool.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF
Approche isotopique du métabolisme respiratoire des racines chez Phaseolus vulgaris L.
La photosynthèse discrimine contre le 13C d en moyenne 20 chez les plantes en C3, de telle sorte que leur matière organique est appauvrie en 13C par rapport au CO2 atmosphérique. Cependant, d autres discriminations susceptibles de modifier le 13C de la matière organique des plantes interviennent en aval de la photosynthèse, notamment au cours de la respiration à l obscurité. Il a ainsi été montré que les feuilles rejettent du CO2 enrichi en 13C par rapport à la matière organique. Il semble être appauvri dans le cas des racines, mais les données à ce sujet sont éparses. L origine de l abondance naturelle en 13C du CO2 respiré par des racines intactes de haricot à donc été étudiée, en relation avec la disponibilité en substrat au cours de l obscurité prolongée. Les résultats obtenus montrent qu à l inverse des feuilles, le CO2 respiré par les racines est appauvri en 13C par rapport au saccharose, et que le 13C n est pas corrélé au quotient respiratoire (c.a.d. la nature des substrats respirés). Cette divergence isotopique du CO2 respiratoire des feuilles et des racines apparaît lorsque les feuilles deviennent autotrophes. En outre, des marquages isotopiques révèlent que l appauvrissement en 13C du CO2 respiré provient d une part de la contribution du cycle des pentoses phosphate (CPP) au dégagement de CO2 (22%), et d autre part de la relation quasi-stoechiométrique entre la PDH et le cycle de Krebs. A l obscurité prolongée, le ralentissement du cycle de Krebs est compensé par le maintien du CPP, ainsi que par le recyclage des lipides pauvres en 13C, conduisant à la stabilité du 13C du CO2. En revanche, les protéines ne semblent pas recyclées et de façon concordante, les données de RMN, de 15N et de métabolomique suggèrent que l assimilation des nitrates se poursuit. Ceci est rendu possible par le maintien de l activité PEP-carboxylase qui alimente la synthèse du glutamate. Pris globalement, ces résultats indiquent qu aux variations près de la discrimination photosynthétique, le signal 13CO2 des racines est relativement insensible aux alternances jour/nuit, contribuant à tamponner les variations isotopiques journalières des écosystèmes.C3 photosynthesis discriminates against 13C so that plant organic matter is on average 13C-depleted by 20 compared to atmospheric CO2. However, other post-photosynthetic discriminations (e.g. during dark respiration) occur that may modify the 13C of plant organic matter. While leaf dark respiration has been shown to produce 13C-enriched CO2, root respiration, though unwell documented, seems to produce 13C-depleted CO2. In the present study, the origin of the 13C-natural abundance in respired CO2 of intact bean roots was investigated in relation to substrate availability under continuous darkness. In contrast to leaves, root-respired CO2 is 13C-depleted as compared to sucrose, and the 13C-signal does not correlate at all with the respiratory quotient (that is, the type of respired substrates). Such an isotopic divergence between leaves and roots appears when leaves turn to autotrophy. Isotopic labeling data demonstrate that the 13C-depletion in respired CO2 is caused by both the contribution of the pentose phosphate pathway (PPP) to the CO2 efflux (22%), and the quasi-stochiometric relationship between the PDH and the Krebs cycle fluxes. Under continuous darkness, the relative PPP flux is kept constant and the consumption of (13C-depleted) lipids compensates for the decrease of the flux associated with the Krebs cycle. Such a pattern results in an invariant 13C of respired CO2. Noteworthy, proteins do not seem to be reclycled in darkness, and such a view is consistent with NMR and 15N data and metabolomics, that suggest nitrate assimilation is maintained as well as glutamate synthesis, thanks to the anaplerotic PEP-carboxylase activity. Taken as a whole, it is concluded that, unless the 13C photosynthetic fractionation varies at the leaf level, the root 13C-signal does not change under natural environmental conditions throughout a circadian day/night cycle, thereby buffering isotopic daily variations in ecosystems.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF
Carbon isotope discrimination during photosynthesis and dark respiration in intact leaves of Nicotiana sylvestris: comparisons between wild type and mitochondrial mutant plants
Carbon Isotope Fractionation in Plant Respiration
Carbon isotopes have long been used to dissect metabolic pathways. More recently, stable isotopes have become an important tool in modeling global fluxes in the biosphere, and notably CO2 isofluxes. The accuracy of these models relies partly on the knowledge of fractionations associated with each individual flux component. This has led to the observation that carbon isotope fractionation occurs during respiration in plants, and exhibits large temporal and spatial variations. Despite important advances in the area, metabolic features underlying such variability remain to be fully elucidated. The present chapter summarizes available data on plant respiratory fractionation, and presents a critical discussion about the metabolic origin of its variation, in the light of recent developments in understanding the compartmentation and plasticity of plant respiration. It emphasizes the need for refining existing frameworks, and points out knowledge gaps that need to be filled so as to achieve a more quantitative modeling of respiratory fractionation