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.
Résumé
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.