Poster: Heavy metals & phytoremediation

Abs # 61: Enhanced lead accumulation through transgenic expression of citrate synthase

Presenter:	Poynton, Charissa Y., charissa@oneant.com
Authors	Poynton, Charissa Y. (A)   Vallee, Nathalee  (B)   Ayalew, Mentewab  (B)   Stewart, Jr., C. Neal  (B)   Elless, Mark P. (A)
Affiliations:	(A): Edenspace Systems Corporation (B): Department of Plant Sciences, University of Tennessee
Web Site:	http://www.edenspace.com

Lead contamination of soil is a widely recognized problem and exposure can have harmful human health effects. Phytoremediation is a promising technology and relies on successful combinations of plants and chelators that facilitate higher metal uptake rates. However, the significant cost of standard chelators, coupled with potential off-site migration of chelated lead, limits their use. A novel approach is to use plants that exude a rapidly biodegradable chelator, such as citric acid, from their roots. Many aluminum-tolerant plants exude organic acids from their roots. Transgenic plants expressing a citrate synthase gene had increased citrate production and increased tolerance to toxic Al³⁺ relative to wild type plants (de la Fuente et al., 1997, Science 276: 1566). However, there has been controversy over the effectiveness of this approach, as a second group was unable to repeat the findings (Delhaize et al., 2001, Plant Phys. 125: 2059). We have expressed a citrate synthase gene from Pseudomonas aeruginosa in tobacco, under the control of both the constitutive 35S and a root-specific promoter, potato Ubi7. Our aims are firstly, to investigate whether high citrate synthase expression does lead to increased citrate exudation, secondly to determine whether citrate exudation is influenced by certain environmental conditions and finally, to investigate if plants with increased citrate exudation accumulate more lead or other metals when grown in lead contaminated soil. The advantages of this approach are that the citrate will be present in the root zone, precisely where it is most effective, the cost of exogenous chelator application will be removed, and the potential of off-site migration will be reduced because of the rapid biodegradation of citrate.