Jean-François Morot-Gaudry : témoignage

National audienc

Jean-François Morot-Gaudry : témoignage

National audienc

Plant nitrogen

407p. ; 24 c

Influence de l'age sur les caracteristiques photosynthetiques de la feuille de mais , Zea mays L.

National audienceLeaf apparent photosynthetic rates (N) as a function of carbon-dioxide concentration (C02) were studied in three maize genotypes (F7EP1, W64A and F7F2) during growth, flowering and cob-formation stages. The shape of the C02-assimilation curves obtained with increasing C02 concentration under non-light-limiting conditions was very useful in determining the resistances to C02 diffusion (ra : the boundary layer resistance ; rs the stomatal resistance and ri, the intracellular resistance). It also helped in determining the level of the plateau (Pm) of the curve at light and C02 saturation resulting in a limitation of photosynthesis by biochemical processes. A model of photosynthesis versus external C02 (C) is presented. Maximum leaf apparent photosynthesis (N max) - corresponding to the light and CO2 saturation plateau (Pm) minus the respiration - remained relatively constant during vegetative growth, anthesis and early grain filling. After the milky-doughy grain stage and throughout kernel development and maturation, maximum photosynthesis decreased and was limited by leaf C02 diffusive resistances (especially rs). Thus, it appears that the stomatal resistances (rs) which increased during the later stage of kernel development are not the cause of the photosynthetic decrease but rather the consequence of the fall in net assimilation previously shown by RASCHKE (1975) and WONG et al. (1979). Nevertheless, the potential for stomatal aperture (rs determined at CO2 concentration near Т) remained constant irrespective of age or genotype.L’assimilation nette maximale (N max) du maïs, Zea mays L., rapportée à l’unité de surface foliaire et de temps, reste stationnaire de juillet à août puis décroît de septembre à octobre durant le remplissage du grain. L’examen des courbes d’assimilation nette en fonction de la concentration en C02, sous éclairement saturant, montre que jusqu’au stade grain laiteux-pâteux, la photosynthèse maximale du maïs dépend du niveau du plateau de double saturation en C02 et en lumière (Pm). Du stade remplissage du grain à la récolte, c’est la diffusion du C02 qui devient le principal facteur limitant. Nous montrons (fig. 4 et 5) que la fermeture des stomates, responsable de l’augmentation de la résistance à la diffusion du C02, est en fait une conséquence de la baisse de photosynthèse, confirmant ainsi les travaux de RASCHKE et de WONG et al. Par ailleurs, les potentialités d’ouverture stomatique - résistance stomatique (rs) mesurée pour une concentration en C02 voisine de Т - demeurent invariantes tant en fonction de l’âge qu’en fonction du génotype

Influence de l'age sur les caracteristiques photosynthetiques de la feuille de mais , Zea mays L.

National audienceLeaf apparent photosynthetic rates (N) as a function of carbon-dioxide concentration (C02) were studied in three maize genotypes (F7EP1, W64A and F7F2) during growth, flowering and cob-formation stages. The shape of the C02-assimilation curves obtained with increasing C02 concentration under non-light-limiting conditions was very useful in determining the resistances to C02 diffusion (ra : the boundary layer resistance ; rs the stomatal resistance and ri, the intracellular resistance). It also helped in determining the level of the plateau (Pm) of the curve at light and C02 saturation resulting in a limitation of photosynthesis by biochemical processes. A model of photosynthesis versus external C02 (C) is presented. Maximum leaf apparent photosynthesis (N max) - corresponding to the light and CO2 saturation plateau (Pm) minus the respiration - remained relatively constant during vegetative growth, anthesis and early grain filling. After the milky-doughy grain stage and throughout kernel development and maturation, maximum photosynthesis decreased and was limited by leaf C02 diffusive resistances (especially rs). Thus, it appears that the stomatal resistances (rs) which increased during the later stage of kernel development are not the cause of the photosynthetic decrease but rather the consequence of the fall in net assimilation previously shown by RASCHKE (1975) and WONG et al. (1979). Nevertheless, the potential for stomatal aperture (rs determined at CO2 concentration near Т) remained constant irrespective of age or genotype.L’assimilation nette maximale (N max) du maïs, Zea mays L., rapportée à l’unité de surface foliaire et de temps, reste stationnaire de juillet à août puis décroît de septembre à octobre durant le remplissage du grain. L’examen des courbes d’assimilation nette en fonction de la concentration en C02, sous éclairement saturant, montre que jusqu’au stade grain laiteux-pâteux, la photosynthèse maximale du maïs dépend du niveau du plateau de double saturation en C02 et en lumière (Pm). Du stade remplissage du grain à la récolte, c’est la diffusion du C02 qui devient le principal facteur limitant. Nous montrons (fig. 4 et 5) que la fermeture des stomates, responsable de l’augmentation de la résistance à la diffusion du C02, est en fait une conséquence de la baisse de photosynthèse, confirmant ainsi les travaux de RASCHKE et de WONG et al. Par ailleurs, les potentialités d’ouverture stomatique - résistance stomatique (rs) mesurée pour une concentration en C02 voisine de Т - demeurent invariantes tant en fonction de l’âge qu’en fonction du génotype

Modifications dans les premières étapes de l'assimilation photosynthétique du carbone chez le maïs sous l'effet du génotype

L’étude des réactions de carboxylations photosynthétiques chez les maïs « WH x WJ » et « INRA 508 » montre qu’une baisse de l’activité photosynthétique chez le maïs « WH x WJ », par rapport au maïs « INRA 508 », s’accompagne de déviations métaboliques au sein des premières réactions qui assurent le transfert du carbone du CO2 atmosphérique vers les composés du cycle de CALVIN-BENSON, via les acides malique et aspartique. Le même comportement métabolique en relation avec la photosynthèse avait déjà été observé antérieurement chez le maïs « W64A » mutant opaque-2 comparé au maïs « W64A » normal, plus productif.A compared study of the C4 photosynthetic pathway carried out on different maize genotypes (« WH x WJ » and « INRA 508 »), showed that in « WH x WJ» maize an important decrease of the photosynthetic rate was associated with marked metabolic deviations. From short pulse and chase experiments with 14CO2 under steady-state photosynthesis it was evidenced that the transfer of carbon from the dicarboxylic acids to CALVIN-BENSON cycle components was decelerated in maize « WH x WJ » as compared with « INRA 508 ». Aspartate was more heavily labeled in « WH x WJ » than in the « INRA 508 » leaves. Conversely the incorporations of 14C into malate and 3-phosphoglycerate were always higher in the « INRA 508 » than in the « WH x WJ » leaves. Previously the same pattern of the 14C distribution was observed in maize mutant « W64A » opaque-2 known to differ from maize « W64A » normal in CO2 uptake rate and dry matter production

Biologie Végétale - Nutrition et Métabolisme

Biologie Végétale - Nutrition et Métabolism

L'assimilation nette du dioxyde de carbone à l'échelle du couvert végétal

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Absorption et assimilation du nitrate et recyclage de l'azote organique chez les plantes: interet pour le colza

CABI:20073191056International audienceBrassica napus (winter oilseed rape) is an important agricultural crop cultivated for oil, which can be used as an edible product or for industrial application, bioester for example. Despite the very high capacity of oilseed rape to take up nitrate, many authors have reported a very low recovery of nitrogen in field-grown crops whatever the level of N fertilizer applied. In this manuscript we describe the main biochemical and molecular mechanisms involved in nitrate uptake, reduction, assimilation and N recycling during the reproductive period to gain sufficient knowledge to determine the relative importance of environmental and genetic factors determining N management in plants. This understanding will provide the necessary background for improvement of oilseed rape varieties

Characterization of Markers to Determine the Extent and Variability of Leaf Senescence in Arabidopsis. A Metabolic Profiling Approach

Comparison of the extent of leaf senescence depending on the genetic background of different recombinant inbred lines (RILs) of Arabidopsis (Arabidopsis thaliana) is described. Five RILs of the Bay-0 × Shahdara population showing differential leaf senescence phenotypes (from early senescing to late senescing) were selected to determine metabolic markers to discriminate Arabidopsis lines on the basis of senescence-dependent changes in metabolism. The proportion of γ-aminobutyric acid, leucine, isoleucine, aspartate, and glutamate correlated with (1) the age and (2) the senescence phenotype of the RILs. Differences were observed in the glycine/serine ratio even before any senescence symptoms could be detected in the rosettes. This could be used as predictive indicator for plant senescence behavior. Surprisingly, late-senescing lines appeared to mobilize glutamine, asparagine, and sulfate more efficiently than early-senescing lines. The physiological basis of the relationship between leaf senescence and flowering time was analyzed