Soil-dependent variability of leaf iron accumulation in transgenic tobaccooverexpressing ferritin

Ferritin overexpression in transgenic plants has been recently reported to increase leaf and seed iron content. We investigated the influence of vario us soil conditions on this increase in leaf iron content. One control trans genic tobacco and two transgenic tobaccos overexpressing ferritin in the pl astids or in the cytoplasm, respectively, were grown on five different soil s, two of them being amended with sewage sludge. Although a significant inc rease in leaf iron concentration was measured in transgenics overexpressing ferritin grown on three out of five soils, this increase was not a general rule. On some soils, leaf iron concentration of control plants was as high as in transgenics grown on other soils. In addition, an increased phosphor us concentration in the two sewage sludge amended soils correlated with a h igh leaf iron concentration in control plants, similar to the one measured in ferritin transformed plants. Indeed, growing plants in vitro with variou s increasing phosphate concentrations revealed a direct P involvement in ir on loading of control plants, at a similar level as overexpressing ferritin plants. Also, with one of the soil tested, not only iron but also manganes e, zinc and cadmium, and to a much lesser extent copper, nickel and lead we re found more abundantly in ferritin transformed plants than in control pla nts. These data indicate that the iron fortification of leaves, based on fe rritin overexpression, could be limited in its biotechnological application because of its high soil dependence. (C) 2000 Editions scientifiques et me dicales Elsevier SAS.