Enhancement of cadmium tolerance and accumulation by introducing Perilla frutescens (L.) Britt var. frutescens genes in Nicotiana tabacum L. plants

The tobacco has the genetic potential to remove toxic metals from the soil. To develop hyperaccumulating tobacco plants, distant hybridization between tobacco (Nicotiana tabacum L.), a high-biomass crop, and Perilla frutescens (L.) Britt var. frutescens, a newfound Cd-hyperaccumulator species, was carried out using a novel method viz. pollination following grafting. Their hybrid nature was preliminarily confirmed by phenotype, isozyme pattern, random amplified polymorphic DNA (RAPD) and metabolites analysis. About 120 putative F-2 hybrids derived from the cross-combination [(N. sylvestris Speg. & Comes rootstock+N. tabacum L. var. 78-04 scion) x P. frutescens (L.) Britt var. frutescens] were then subjected to up to 300 mu M CdCl2 in hydroponic conditions for 10 days. Results showed five seedlings were more resistant to Cd than female parent and accumulated 314.6 +/- 99.9 mg kg(-1) Cd in their aerial biomass, which was 5.7 times greater than that in "78-04"tobacco (47.2 +/- 3.56mg kg(-1)) (P <= 0.05). Two of these seedlings exceeded male parent P. frutescens in the Cd concentration of shoots and reached 424 and 396 mg kg(-1), which was 13 % and 6 % greater for that of perilla (374.2 +/- 10.38 mg kg(-1)), respectively. Compared with parents, two other F2 hybrids tended to accumulate more Cd in the root with bioconcentration factor (BCF) 7.05 and 5.17, respectively. Only one hybrid showed lower Cd concentration but transferred Cd more effectively from the root to the shoot than parents and other F-2 hybrids, with the maximum translocation factor (TF) value 1.37. These indicated that the introduction of P. frutescens genes could obviously enhance the cadmium tolerance and accumulation of superior individuals.