Cadmium tolerance and hyperaccumulation by Thlaspi caerulescens populations grown in hydroponics are related to plant uptake characteristics in the field

Abstract

In order to fully understand the hyperaccumulation process and to increase the potential of plants for phytoextraction purposes, there is a need for more investigation of hyperaccumulating species or populations. Five Swiss populations of Thlaspi caerulescens J. & C. Presl originating from non-metalliferous but naturally Cd-rich soils (1.1–9.2 mg Cd kg–1) were compared with Ganges and Prayon populations and a non-accumulating species, Thlaspi perfoliatum (L.) F.K. Meyer, for their tolerance (shoot and root dry weight and root length) and Cd hyperaccumulation in hydroponics (0, 1, 5, 10, 20 and 50 µm Cd). In the field, the Swiss populations accumulated Zn and clearly hyperaccumulated Cd (up to 505 mg Cd kg–1 dry weight). The general response was significantly different between populations but in general an increasing Cd concentration in solution led to a decrease in dry weight production and an increase in Cd concentration in shoots. The shoot dry weight was a more discriminating parameter for tolerance than root dry weight and total root length. The Swiss populations behaved similarly to the Ganges population but differently from the Prayon population. Cadmium concentrations in shoots were above 100 mg kg–1 when plants were grown in 1 µm Cd, except for the Prayon population and T. perfoliatum. In addition, as 1 µm Cd did not induce any visible toxicity symptoms, it was found to be adequate to test Cd hyperaccumulation. However, the most striking feature was the positive linear relationship observed between the transfer factor (TF) calculated in the field and the response of a population to increasing Cd concentrations in solution, indicating that plant uptake in the field had an influence on the plant response in solution.