Cadmium (Cd) is naturally occurring in soils that are also enriched by human activity. Cd contaminates food crops because of its absorption by plant roots. Because it is a toxic element for living organisms, its concentrations in food and feed plant products are subjected to regulatory limits. Therefore, it is necessary to understand the transfer of this metal from the soil to the edible plant part, especially for sunflower (Helianthus annuus L.), our model plant that can accumulate more Cd than other crop species. This study tested the hypothesis that the amount of Cd absorbed by sunflower was related to the root architecture. We characterized, at the individual roots level, a longitudinal variation of the influx of Cd2+ absorption in relation with the culture medium, the order and the age of roots. These variations were attributed to the development of apoplastic barriers (cellulose, lignin and suberin deposition) that restrict the absorption of Cd2+ into the cytosol. By simulation, it has been shown that these variations could theoritically impact the total absorption of Cd2+ in hydroponics depending on the root architecture while in solid substrate (sand) the impact was much more limited. Furthermore, a comparison of 14 sunflower cultivars showed that the variability in Cd concentrations in shoots was rather due to differences in absorption independent of root architecture and in variations in the root to shoot distribution. The longitudinal variation in the Cd root influx can then be considered of minor importance compared to the between cultivar variability in Cd uptake, the origin of which remains to be determined. In the perspective of modelling the total uptake of Cd in soil conditions, it could then be possible to assume a global mean influx of Cd independent of the root architecture
