Cadmium partitioning and gene expression studies in Nicotiana tabacum and Nicotiana rustica

To better understand the differences in cadmium (Cd) uptake, partitioning and gene regulation between Nicotiana tabacum and Nicotiana rustica, we compared these two species for root and leaf Cd concentrations after different Cd exposures, 109Cd root‐to‐shoot transport, Cd tolerance as well as differential gene expression in roots exposed or not to CdCl2 using reverse transcriptase–PCR (RT‐PCR). When grown in 1 μM CdCl2 for 7 days, N. rustica exhibited higher root and lower leaf Cd contents than N. tabacum. Data were confirmed by radiolabeling experiments, which further showed that some 109Cd accumulated in the distal part of lateral roots in N. rustica. Visual inspection of leaves suggested that N. rustica was somewhat more tolerant to high Cd exposure (50 μM CdCl2) compared with N. tabacum. At such a high Cd concentration, Cd toxic effects on N. tabacum leaves were apparently not directly related to the homeostasis of Fe and Mn. However, the Zn levels were different in N. rustica compared with N. tabacum in absence and presence of Cd treatments. Root growth experiments revealed that N. tabacum, but not N. rustica, root length was reduced in bactoagar medium containing 20 μM CdCl2. Complementary DNA microarrays were used as a screening approach to demonstrate by RT‐PCR that some gene products were differentially regulated by Cd in N. rustica and in N. tabacum. In addition, “NtIRT1,”NtMTP1a, “NtHMA3” and “NtNAS3” were inducible by Cd in N. tabacum. Interestingly “NtIRT1” and NtMTP1a were differently expressed between the two species. Our results suggest different pathways for Cd sequestration and transport between these two species.