Publication
Some plants able to take up heavy metals from contaminated soils offer a possibility to clean up sites contaminated with heavy metals. Plants thus act as a solar driven pump, which can extract and concentrate heavy metals from the environment. Since most of the metal hyperaccumulating wild plants only produce very low biomass and most of plants producing high biomass accumulate only moderate amounts of metals, the current research is mainly focused on the overcoming of this deficiency to optimise metal phytoextraction. The main goal of this EC financed study was aimed at improvement of phytoextraction through improved metal extraction of high yielding oil crops, such as Helianthus annuus L. and Brassica juncea L. producing a high biomass. The use of their oil and biomass for technical purpose (lubricants, biogas and energy) allows to produce an additional value from this in situ decontamination technique and to improve the economical balance of phytoextraction. The enhancement of metal accumulation properties of sunflower and Indian mustard by non-GMO approach and of stimulated metal bioavailability in the soil were the main milestones of the present study. Classical fertilisers were used to lower soil pH, increasing metal availability from the soil and conventional biotechnological approaches were used as an alternative to genetic engineering to enhance both metal accumulation and extraction efficiency of oil crops. The first field experimentation (2002) was mainly focused on the screening of 15 commercial sunflower cultivars growing on a contaminated field in Rafz (Switzerland) to select the cultivar with the naturally highest potential to accumulate and extract metals from contaminated soil, and to assess the effect of classical fertilisers on metal accumulation/extraction of the sunflower cultivars. Highly significant differences of heavy metal accumulation and extraction were found between cultivars. Cadmium extraction varied by a factor of 4, Zn extraction by factor of 3 and Pb extraction by a factor of 14 between the cultivars with the highest and lowest metal extraction treated with the same fertiliser. Sulphate fertilisation significantly enhanced Zn and Pb extraction, whereas ammonium nitrate enhanced Cd extraction by most of the sunflower cultivars. Cultivar Salut showed the highest Cd, Zn and Pb extraction and was chosen for the next mutation breeding. Classical mutation breeding techniques were assumed to be efficient to improve the efficiency of metal accumulation of high yielding crops. Therefore, in vitro breeding was used to improve metal uptake of Indian mustard and chemical mutagenesis using ethyl methanesulphonate (EMS) was additionally applied for sunflowers, hybrid cultivar Salut and genetically homogenous inbred lines. Somaclonal variation of tissue culture was used as a source of genetic variability to increase the potential of metal accumulation in Indian mustard. After the selection of B. juncea callus cultures on a medi