Cadmium uptake and partitioning during the vegetative growth of sunflower exposed to low Cd2+ concentrations in hydroponics

Aim To characterize the response of sunflower to the low levels of Cd exposure encountered in agricultural soils. Methods Plants were exposed in hydroponics to low concentrations of Cd (2.5 nM or 20 nM) and sampled at four vegetative stages (6, 9, 14 and 19 expanded leaves). Plant growth, root Cd absorbing properties and Cd partitioning between organs were monitored along with Cd content in the xylem sap. Results Sunflower growth was not limited when exposed to 20 nM Cd. The amount of Cd taken up by the plant roots as well as the rate of Cd loading in xylem sap increased in direct proportion to the concentration of Cd2+ in the nutrient solution, suggesting that neither the root Cd absorbing capacities nor the root-to-shoot translocation of Cd were impacted by the level of Cd exposure. The partitioning of Cd between stem and leaves followed that of dry matter, regardless of the Cd treatment. The root-to-shoot partitioning of Cd at early growth stages differed from that prevailing later on. Conclusions In an agricultural context, the partitioning of Cd between sunflower organs does not appear to be affected by the level of Cd exposure during vegetative growth.