COMPORTEMENT DES SPORES DE BACTÉRIES ANAÉROBIES FERMENTANT LE LACTATE DANS LE TRACTUS DIGESTIF DU RUMINANT. I. — VARIATIONS AVEC LE RÉGIME DE LA CONCENTRATION EN SPORES DANS LE RUMEN ET LES FÈCES

International audienc

Expression of Leaf Nitrate Reductase Genes from Tomato and Tobacco in Relation to Light-Dark Regimes and Nitrate Supply

The influence of light-dark cycles and nitrate supply on nitrate reductase (NR) mRNA levels was studied in two plant species, tobacco (Nicotiana tabacum) and tomato (Lycopersicon esculentum) using specific NR DNA probes. In the same series of experiments, changes in the levels of NR protein (NRP) by enzyme-linked immunosorbent assay and changes in the level of NADH-nitrate reductase activity (NRA) were also followed. During a light-dark cycle, it was found that in both tomato and tobacco, NR mRNA accumulation increased rapidly during the dark period and reached a maximum at the beginning of the day, while NRP reached a peak 2 and 4 hours after mRNA peaked, for tomato and tobacco, respectively. At the end of the day, the amount of mRNA was decreased by a factor of at least 100 compared to sunrise in both species. These results demonstrate that light is involved, although probably not directly, in the regulation of the NR gene expression at the mRNA level. The peak of NRA in tobacco coincided with the peak in NR mRNA accumulation (i.e. sunrise), whereas in tomato the peak of NRA was approximately 5 to 6 hours after sunrise. There is no obvious correlation between NRP and NRA levels during the day. In nitrogen starvation experiments, a rapid decrease of NRP and NRA was detected, while NR mRNA levels were not significantly altered. Upon nitrate replenishment, nitrogen-starved plants accumulated NR mRNA rapidly. These results suggest that the availability of nitrogen affects the expression of NR activity at the transcriptional as well as at the post-transcriptional levels

ENSILAGES « GNOTOXÉNIQUES » DE FOURRAGES. I. — ÉTUDE CINÉTIQUE DU DÉVELOPPEMENT BACTÉRIEN DANS DES ENSILAGES « GNOTOXÉNIQUES » DE LUZERNE, FÉTUQUE ET RAY-GRASS

International audienc

COMPORTEMENT DES SPORES DE BACTÉRIES ANAÉROBIES FERMENTANT LE LACTATE DANS LE TRACTUS DIGESTIF DU RUMINANT. II. — ÉVOLUTION DU NOMBRE DE SPORES DE C. TYROBUTYRICUM INTRODUITES AU NIVEAU DU RUMEN, AU COURS DU TRANSIT DIGESTIF CHEZ LE RUMINANT

International audienc

CONSERVATION PAR ENSILAGE OU DÉSHYDRATATION D'UNE ORGE ET D'UN MAÏS IMMATURES

International audienc

ENSILAGES « GNOTOXÉNIQUES » DE FOURRAGES. II. — CATABOLISME DES GLUCIDES ET MÉTABOLISME FERMÉNTAIRÉ DANS DES ENSILAGES « GNOTOXÉNIQUES » DE LUZERNE, FÉTUQUE ET RAY-GRASS

International audienc

The Arabidopsis ATNRT2.7 Nitrate Transporter Controls Nitrate Content in Seeds[W]

In higher plants, nitrate is taken up by root cells where Arabidopsis thaliana NITRATE TRANSPORTER2.1 (ATNRT2.1) chiefly acts as the high-affinity nitrate uptake system. Nitrate taken up by the roots can then be translocated from the root to the leaves and the seeds. In this work, the function of the ATNRT2.7 gene, one of the seven members of the NRT2 family in Arabidopsis, was investigated. High expression of the gene was detected in reproductive organs and peaked in dry seeds. β-Glucuronidase or green fluorescent protein reporter gene expression driven by the ATNRT2.7 promoter confirmed this organ specificity. We assessed the capacity of ATNRT2.7 to transport nitrate in Xenopus laevis oocytes or when it is expressed ectopically in mutant plants deficient in nitrate transport. We measured the impact of an ATNRT2.7 mutation and found no difference from the wild type during vegetative development. By contrast, seed nitrate content was affected by overexpression of ATNRT2.7 or a mutation in the gene. Finally, we showed that this nitrate transporter protein was localized to the vacuolar membrane. Our results demonstrate that ATNRT2.7 plays a specific role in nitrate accumulation in the seed

The Arabidopsis ATNRT2.7 Nitrate Transporter Controls Nitrate Content in Seeds[W]

In higher plants, nitrate is taken up by root cells where Arabidopsis thaliana NITRATE TRANSPORTER2.1 (ATNRT2.1) chiefly acts as the high-affinity nitrate uptake system. Nitrate taken up by the roots can then be translocated from the root to the leaves and the seeds. In this work, the function of the ATNRT2.7 gene, one of the seven members of the NRT2 family in Arabidopsis, was investigated. High expression of the gene was detected in reproductive organs and peaked in dry seeds. β-Glucuronidase or green fluorescent protein reporter gene expression driven by the ATNRT2.7 promoter confirmed this organ specificity. We assessed the capacity of ATNRT2.7 to transport nitrate in Xenopus laevis oocytes or when it is expressed ectopically in mutant plants deficient in nitrate transport. We measured the impact of an ATNRT2.7 mutation and found no difference from the wild type during vegetative development. By contrast, seed nitrate content was affected by overexpression of ATNRT2.7 or a mutation in the gene. Finally, we showed that this nitrate transporter protein was localized to the vacuolar membrane. Our results demonstrate that ATNRT2.7 plays a specific role in nitrate accumulation in the seed