Transgenic Citrate-Producing Plants for Lead Phytoremediation

In this Phase II project, Edenspace Systems Corporation seeks to demonstrate the use of transgenic plants that exude significant amounts of a rapidly biodegradable chelator-citric acid-from their roots, enabling a cost savings of more than 70 percent in lead phytoextraction. A citrate synthase (CS) transgene was placed under the control of different plant promoters to overexpress the gene in roots. In Phase I, 100 lines of CS-transgenic tobacco, Nicotiana tabacum, were created and tested. Preliminary results with five hemizygous strains are promising, suggesting that higher-performing homozygous strains created at the end of Phase I may hyperaccumulate lead from soil (bioconcentration factor >1). Significantly, little soluble lead remained in the soil, indicating that the plants may successfully address leaching concerns. In Phase II, the highest performing transgenic lines will be demonstrated at a small arms firing range in Maryland and a residential site in Massachusetts. Phase II objectives also include concentrating lead in harvested plants to facilitate disposal or recycling, and mating transgenic lines of a proven lead-accumulating plant species, Brassica juncea.At many sites, applying rapidly biodegradable citric acid precisely at the root/soil interface where metal uptake occurs may eliminate the need for expensive chelating agents and liners. Attainment of the project's goals therefore may reduce the substantial public health hazard of soil lead by realizing phytoremediation's low-cost potential.