PRELIMINARY INVESTIGATIONS ON INDIGENOUS STRAINS OF RHIZOBIUM NODULATING YAM BEAN (Pachyrhizus erosus Urban) IN GUADELOUPE

Yam bean plants formed efficient nodules with indigenous strains of Rhizobium living in vertisols (pH 8.4), in neutral ferralitic soils (pH 6.9) but not in.acid ferrallitic soils (pH 4.6). Mineral amendments imploying Urea, basic slag, lime incorporation in the acid soils overcome the pH inhibition of nodule formation. Rhizobium strains from the different soils were isolated and characterized. Apparent rate of growth (ARG) and rate of nodulation in gibson tubes (RNG) were determined. Their aptitude to use sugars and other compounds was assessed by API STAPH tests. The efficiency of the symbiosis of each strain of Rhizobium-Pachyrhizus was measured by estimating the biomass produced in gibson tubes and by determining carbohydrates, ureides and amino-compounds in the nodules of the plant. ----- Le dolique tubéreux forme des nodosités efficientes avec des souches de Rhizobium indigènes des vertisols (pH 8) et des sols ferralitiques neutres (pH 6.9). La nodulation est inexistante dans les sols ferralitiques acides (pH 4.6). L'incorporation des amendements minéraux (urée, scories de déphosphoration, chaux) capables d'élever le pH permet de lever l'inhibition de la formation des nodosités dans ces derniers sols. Les souches de Rhizobiumont été sélectionnées et caractérisées. Les vitesses de croissance apparente et de nodulation en tubes Gibson ont été déterminées. Leur aptitude à utiliser les sucres et d'autres composés ont été mis en évidence par les tests API STAPH. L'efficience de chaque souche a été estimée par la matière organique produite en tubes Gibson, les quantités de sucres solubles, d'uréides, et composés aminés des nodosités

CONSEQUENCES OF PURINE DEGRADATION INHIBITION INDUCED BY ALLOPURINOL ON GROWTH, NITROGENOUS COMPOUNDS AND CARBOHYDRATES IN YAM BEAN (Pachyrhizus erosus Urban)

Allopurinol effects on Xanthine dehydrogenase (XDH) and uricase, the key enzymes of conversion of fixed nitrogen in ureides (allantoin and allantoate), exporting forms of ammonia from nodules to leaves, where investigated on growth, amino-compounds and carbohydrates in yam bean. Allopurinol decreased XDH and uricase activities in the nodules. As a consequence, ureides dropped down in nodules, tubers, stems and leaves. Aminocompounds declined in nodules and leaves but not in tubers or stems. Proteins were unaffected. Allopurinol also caused sucrose and starch accumulation in the nodules. In the tuber it did not affect sucrose level but decreased glucose, fructose and starch. The relationships between the enzyme activities, different metabolites and plant growth were discussed. ----- Les effets de Pallopurinol sur la Xanthine déshydrogénase (XDH)etl'uricase, les enzymes clés de la transformation de l'ammoniac en uréides (allantoine et allantoate), forme de transport d'azote chez le dolique tubéreux, ont été étudiés sur la croissance, les composés aminés et les glucides. Allopurinol réduit les activités Xanthine déshydrogénase et uricase dans les nodosités. Il s'ensuit une chute des uréides dans les nodosités, tubercules, tiges et feuilles. Les aminoacides baissent dans les nodosités et dans les feui'les mais pas dans les tubercules et dans les tiges. Les protéines restent inchangées. Allopurinol provoque l'accumulation de saccharose et de l'amidon dans les nodosités. Dans les tubercules il n'affecte pas le saccharose mais diminue le niveau du fructose et de l'amidon. Les relations entre les différents métabolites et la croissance des plantes sont discutées

Gibberellic acid and CCC effects on sugar composition and tuber yield in Yam Bean (Pachyrhizus erosus, Urban)

Yam bean is a tropical tuber and grain legume that needs to be better known as a crop for human consumption and animal feed. The seeds are poisonous but can be used for planting. The tuber is edible and can be eaten as a fresh vegetable or cooked. Large tubers and better fruiting occurred when the growing season coincided with long days, but marketable tubers were produced, especially under short days. In all cases tuber production competes with seed production. Investigations were undertaken to study the effects of foliar application of GA3 and CCC on growth, sugar composition and tuber yield of yam bean under short days. GA3 promoted shoot growth, tuber enlargement,. yield increase, sucrose accumulation and starch content increase. CCC did not consistently affect growth, but reduced tuber size, increased starch content, therefore reduced tuber and starch yields per plant. Foliar applications of GA3 might be used to increase tuber and starch yields per plant under short days. This result was obtained because of a partial or total inhibition of flowering and seed set by that growth substance

The soil affects both the differential accumulation of iron between wild type and ferritin over-expressor tobacco plants and the sensitivity of their rhizosphere bacterioflora to iron stress.

Transgenic tobacco P6 over-expressing ferritin is known to activate iron transport systems and to have increased iron content. Iron phytoextraction by this transgene is then expected to be higher than that of the wild-type (WT). In the present study, the possibility to modify iron availability for bacteria via the cultivation of the transgene P6 was explored by comparing the sensitivity to iron stress of bacteria isolated from the rhizosphere of the two plant genotypes (WT and P6). This sensitivity was evaluated by measuring the bacterial density when plated on a solid media depleted (supplemented with 8-hydroxiquinoline) or not (supplemented with Fe-8-hydroxyquinoline) in iron. The experimental conditions favorable to the di.erential iron accumulation between the wild-type and transgenic tobacco were identi.ed. The two plant genotypes were grown in three soils (Hervau, Thory and Oudun) chosen for their di.erences in iron content, and the plants were yielded at three stages (vegetative, .oral bud and .owering). The highest di.erential accumulation of iron in favor of the over-expressing transgene was found in the plants at the .oral bud stage when cultivated in the Oudun and Thory soils. Since at that stage, the plant growth was signi.cantly higher in the Oudun soil, the phytoextraction of iron was the highest in this soil. At the .oral bud stage, bacteria isolated from the rhizosphere of the transgene cultivated in the Oudun and Thory soils appeared to be less susceptible to iron stress than those from the wild-type. Bacterial density recovered on agar medium depleted in iron was signi.cantly the highest in the rhizosphere of the transgene cultivated in the Oudun soil. Altogether, these data indicate that the over-expressing ferritin transgenic plants, that accumulate and extract more iron from the rhizosphere than the wild-type plants, select in their rhizosphere bacteria less susceptible to iron stress compared to those selected by the wild-type plants

Mobilization of vacuolar iron by AtNRAMP3 and AtNRAMP4 is essential for seed germination on low iron

Iron (Fe) is necessary for all living cells, but its bioavailability is often limited. Fe deficiency limits agriculture in many areas and affects over a billion human beings worldwide. In mammals, NRAMP2/DMT1/DCT1 was identified as a major pathway for Fe acquisition and recycling. In plants, AtNRAMP3 and AtNRAMP4 are induced under Fe deficiency. The similitude of AtNRAMP3 and AtNRAMP4 expression patterns and their common targeting to the vacuole, together with the lack of obvious phenotype in nramp3-1 and nramp4-1 single knockout mutants, suggested a functional redundancy. Indeed, the germination of nramp3 nramp4 double mutants is arrested under low Fe nutrition and fully rescued by high Fe supply. Mutant seeds have wild type Fe content, but fail to retrieve Fe from the vacuolar globoids. Our work thus identifies for the first time the vacuole as an essential compartment for Fe storage in seeds. Our data indicate that mobilization of vacuolar Fe stores by AtNRAMP3 and AtNRAMP4 is crucial to support Arabidopsis early development until efficient systems for Fe acquisition from the soil take over

Consequences physiologiques et morphologiques de l'expression du gene rolA dans les plantes de tabac

International audienc

Consequences physiologiques et morphologiques de l'expression du gene rolA dans les plantes de tabac

National audienc