RÉSUMÉ
Nitrogen fixation of the nodule of soybean is highly sensitive to oxygen deficiency such as provoked by waterlogging of the root system. This study aimed to evaluate the effects of flooding on N metabolism in nodules of soybean. Flooding resulted in a marked decrease of asparagine (the most abundant amino acid) and a concomitant accumulation of γ-aminobutyric acid (GABA). Flooding also resulted in a strong reduction of the incorporation of (15)N2 in amino acids. Nodule amino acids labelled before flooding rapidly lost (15)N during flooding, except for GABA, which initially increased and declined slowly thereafter. Both nitrogenase activity and the expression of nifH and nifD genes were strongly decreased on flooding. Expression of the asparagine synthetase genes SAS1 and SAS2 was reduced, especially the former. Expression of genes encoding the enzyme glutamic acid decarboxylase (GAD1, GAD4, GAD5) was also strongly suppressed except for GAD2 which increased. Almost all changes observed during flooding were reversible after draining. Possible changes in asparagine and GABA metabolism that may explain the marked fluctuations of these amino acids during flooding are discussed. It is suggested that the accumulation of GABA has a storage role during flooding stress.
Sujet(s)
Asparagine/métabolisme , Régulation de l'expression des gènes végétaux , Glycine max/physiologie , Azote/métabolisme , Nodules racinaires de plante/métabolisme , Amino-butyrates/métabolisme , Aspartate-ammonia ligase/génétique , Aspartate-ammonia ligase/métabolisme , Inondations , Glutamate decarboxylase/génétique , Glutamate decarboxylase/métabolisme , Protéines végétales/génétique , Protéines végétales/métabolisme , Nodules racinaires de plante/génétique , Glycine max/enzymologie , Glycine max/génétique , Stress physiologiqueRÉSUMÉ
BACKGROUND: Lectins are mainly described as simple carbohydrate-binding proteins. Previous studies have tried to identify other binding sites, which possible recognize plant hormones, secondary metabolites, and isolated amino acid residues. We report the crystal structure of a lectin isolated from Canavalia gladiata seeds (CGL), describing a new binding pocket, which may be related to pathogen resistance activity in ConA-like lectins; a site where a non-protein amino-acid, alpha-aminobutyric acid (Abu), is bound. RESULTS: The overall structure of native CGL and complexed with alpha-methyl-mannoside and Abu have been refined at 2.3 A and 2.31 A resolution, respectively. Analysis of the electron density maps of the CGL structure shows clearly the presence of Abu, which was confirmed by mass spectrometry. CONCLUSION: The presence of Abu in a plant lectin structure strongly indicates the ability of lectins on carrying secondary metabolites. Comparison of the amino acids composing the site with other legume lectins revealed that this site is conserved, providing an evidence of the biological relevance of this site. This new action of lectins strengthens their role in defense mechanisms in plants.
Sujet(s)
Canavalia/composition chimique , Lectines végétales/composition chimique , Graines/composition chimique , Amino-butyrates/composition chimique , Amino-butyrates/métabolisme , Sites de fixation , Cristallographie aux rayons X , Interactions hydrophobes et hydrophiles , Modèles moléculaires , Lectines végétales/métabolisme , Liaison aux protéines , Conformation des protéines , Structure tertiaire des protéines , Spectrométrie de masse ESIRÉSUMÉ
En timocitos de ratas adrenoprivas (Ax) y adrenoprivas-diabéticas (AxD) se estudió la presencia de receptores de insulina y la acción de la hormona "in vitro" e "in vivo" sobre el transporte de ácido alfa -aminoisobutírico (AIB). En ambos grupos la insulina "in vivo" incrementó el transporte dee AIB, mientras que "in vitro" no tuvo ningún efecto. El hecho de que los timocitos carecieran de receptores de insulina se correlaciona con la falta de acción "in vitro", mientras que el efecto "in vivo" sugeriría que la hormona ejercería sobre los timocitos de animales adultos un efecto indirecto a través de alteraciones metabólicas
Sujet(s)
Rats , Animaux , Mâle , Femelle , Amino-butyrates/métabolisme , Surrénalectomie , Diabète expérimental/métabolisme , Insuline/pharmacologie , Thymus (glande)/cytologie , Sites de fixation , Récepteur à l'insuline/analyseRÉSUMÉ
En timocitos de ratas adrenoprivas (Ax) y adrenoprivas-diabéticas (AxD) se estudió la presencia de receptores de insulina y la acción de la hormona "in vitro" e "in vivo" sobre el transporte de ácido alfa -aminoisobutírico (AIB). En ambos grupos la insulina "in vivo" incrementó el transporte dee AIB, mientras que "in vitro" no tuvo ningún efecto. El hecho de que los timocitos carecieran de receptores de insulina se correlaciona con la falta de acción "in vitro", mientras que el efecto "in vivo" sugeriría que la hormona ejercería sobre los timocitos de animales adultos un efecto indirecto a través de alteraciones metabólicas (AU)