There is described a mutant, non-naturally occurring or transgenic plant or plant cell comprising (a) a polynucleotide selected from the group consisting of: (i) a polynucleotide comprising, consisting or consisting essentially of a sequence having at least 71 % sequence identity to SEQ ID NOs: 1, 2, 27, 28 or 29 or 51； or (ii)a polynucleotide comprising, consisting or consisting essentially of a sequence having at least 65 % sequence identity to any of SEQ ID NOs: 3 to 23 or 30 to 50； or (iii) a polynucleotide encoding a NtMRP polypeptide comprising, consisting or consisting essentially of a sequence having at least 65% sequence identity to any of SEQ ID NOs. 24 to 26 or 52, and wherein the polypeptide has heavy metal transporter activity； or (b) a polynucleotide construct of at least 15 contiguous nucleotides in length that is at least 65 % identical to a region of any of SEQ ID NOs: 1 to 23 or 27 to 51； or (c) a double-stranded RNA comprising at least two sequences that are at least partially complementary to each other and wherein a sense strand comprises a first sequence and an antisense strand comprises a second sequence and wherein at least one of the sequences comprises at least 10 contiguous nucleotides of NtMRP RNA； or (d) an expression vector comprising the polynucleotide as set forth in (i), (ii) or (iii) or the polynucleotide construct as set forth in (b).
