CHLORIDE INCREASES CADMIUM UPTAKE IN SWISS-CHARD IN A RESIN-BUFFERED NUTRIENT SOLUTION

One of the possible hypotheses to explain the high Cd availability at elevated Cl concentration in soil is that chloro-complexes of Cd are a vailable for root uptake, In order to test this hypothesis, Swiss char d [Beta vulgaris ssp, cicla (L.) Koch, cv, Fordhook Giant) was grown i n nutrient solution continuously recirculated over a chelating resin ( Chelex-100) partially loaded with Cd, Treatments were increasing conce ntrations of CI (0.01, 40, 80, and 120 mM) in the nutrient solution wi th Fourfold replication. Solution Na concentrations and ionic strength s were equalized in all treatments by compensating with NaNO3, Increas ing CI concentrations in solution did not affect dry weights of either roots or shoots, Activity of Cd2+ in solution was well buffered durin g plant growth using the resin system. Complexation of Cd2+ by Cl incr eased soluble Cd in culture solutions but the calculated activity of C d2+ was not significantly affected by increasing concentrations of Cl in solution, As solution CI concentration increased, Cd concentrations in plant shoots increased from 6.5 to 17.3 mg kg(-1) and in roots fro m 47 to 106 mg kg(-1). We concluded that enhancement of Cd uptake by C I in soils need not be related only to enhanced diffusion of Cd2+ thro ugh soil to the root but that (i) CdCln2-n (in addition to Cd2+) speci es in solution are phytoavailable and/or (ii) Cl enhances diffusion of Cd2+ through the unstirred liquid layer adjacent to the root surface or through the apoplast to sites of Cd uptake within the root itself.