Zinc and cadmium accumulation in controlled crosses between metallicolous and nonmetallicolous populations of Thlaspi caerulescens (Brassicaceae)

• Growth and heavy metal (Zn and Cd) hyperaccumulation were investigated in metallicolous and nonmetallicolous Mediterranean populations of Thlaspi caerulescens (Brassicaceae), and in offspring from controlled crosses between these populations. • Seeds for the growth and crossing experiments were collected from a number of sites varying in heavy metal contamination. Tissue Zn and Cd content was determined by atomic absorption spectrophotometry. • Offspring from crosses between nonmetallicolous populations had the highest Zn concentration ( c . 30 000 μg g − 1 ), compared with 20 000 μg g − 1 for the nonmetallicolous parents. The metallicolous parents and the other crosses had only 10 000 μg g − 1 . Offspring from crosses including a nonmetallicolous parent still had a significantly higher Zn uptake than the metallicolous parents. A trend towards a higher Cd uptake was observed in offspring from crosses with a metallicolous parent. • We suggest that the most probable hypothesis is that the differences in Zn hyperaccumulation between crosses could be explained by a monogenic system with two alleles. The dominant allele would restrict Zn hyperaccumulation at 10 000 μg g − 1