Cadmium tolerance and accumulation in Excluder Thlaspi arvense and various accessions of hyperaccumulator Noccaea caerulescens

Cadmium (Cd) accumulation and tolerance were analyzed in hyperaccumulator Noccaea caerulescens F.K. Mey and excluder Thlaspi arvense L.. Five accessions of N. caerulescens (La Calamine (LC, Belgium), Saint F,lix de Palli,res (SF, France), Col du Mas de l'Aire (CMA, France), Ganges (GA, France) from metalliferous soils and Lellingen (LE, Luxembourg) from nonmetalliferous soils) were grown in halfstrength Hoagland solution for 8 weeks in the presence of 1, 5, 25, and 50 mu M Cd(NO3)(2) and T. arvense in the presence of 0.1, 0.2, 1.0, and 5.0 mu M Cd(NO3)(2). The toxic effect of Cd was assessed by changes in root and shoot dry weight. The content of Cd in roots and shoots was determined by atomic absorption spectrophotometry and expressed in mg/kg dry weight of plant material and calculated per plant root system or shoot. The tolerance of N. caerulescens to Cd was higher than that of T. arvense and increased in various accessions of N. caerulescens in the row GA < CMA < LE < SF a parts per thousand LC. The ability to accumulate Cd in roots of N. caerulescens accessions increased in the row LC < LE a parts per thousand GA < CMA a parts per thousand SF, while that in shoots were in the row LC < LE a parts per thousand GA < SF < CMA. Reduction in accumulation of root biomass of hyperaccumulator N. caerulescens started at lower Cd content in them compared with that in shoots, while an opposite pattern was observed for excluder T. arvense. Thus, accessions of hyperaccumulator N. caerulescens, having a higher tolerance to Cd compared with excluder T. arvense, differed significantly from each other not only in their capacity to accumulate heavy metals but also in tolerance to them. LC accession from calamine soils accumulated less Cd and, possibly, this was the reason why it was more tolerant than the other accessions. SF accession, also growing on calamine soils, was characterized both by high Cd tolerance and accumulation, which is probably due to more efficient mechanisms of Cd detoxification. The results obtained suggest that there are differences in the mechanisms and causes of tolerance to Cd in various accessions of hyperaccumulator N. caerulescens.