Sulfur deficiency affects the accumulation and the allocation to shoots of cadmium and of some macro- (P, K, Ca, Mg) and micro-nutrients (Cu, Mn, Mo, Zn) in durum wheat at heading.

Cadmium (Cd), which is naturally present in soils, is transferred to durum wheat grains at levels that have worrying consequences for food safety. There have been some reports that adding sulfur (S) to plants reduces Cd accumulation in shoots by increasing its retention in roots due to complexation of Cd by S-containing ligands. Consequently, low S availability in some agricultural soils could favor Cd contamination of durum wheat grains. We conducted a greenhouse experiment to test whether S deficiency would reduce Cd retention in roots, thus favoring its allocation to shoots. Durum wheat was grown in a nutrient solution containing a low level of Cd (100 nM) with sufficient (+ S) or deficient (-S) sulfate levels and harvested at heading. Surprisingly, in the -S treatment, more Cd was retained in roots and less allocated to shoots than in the + S treatment, and the same applied to P, K, Ca, Mg, Cu, Mn, Mo, and Zn. The reduced aboveground biomass resulting from S deficiency explained both the reduced net uptake (i.e., the total quantities of elements in the plant) and the reduced allocation of elements to shoots. Depending on the relative effects of S deficiency on shoot biomass compared to the effects of a reduction in S uptake and allocation to shoots, the reduced supply of S increased the concentrations of Cd and of P, K, Mn, Mo, and Zn in the shoot, whereas the concentration of Cu decreased, and that of Ca and Mg remained unchanged. The higher concentration of Cd in the shoots of S-deficient plants suggests that attention should be paid to the consequences of insufficient S for Cd contamination of durum wheat.