ENHANCED PHYTOREMEDIATION EFFICIENCY THROUGH PLANT BIOTECHNOLOGY
1
Elizabeth A.H. Pilon-Smits, 2Yong Liang Zhu, 3Kerry Hale, 3Marinus Pilon, and 4Norman Terry
1,3
Department of Biology, Colorado State University, A/Z Building, Fort Collins, CO 80523; 2,4Department
of Plant and Microbial Biology, University of California at Berkeley, 111 Koshland Hall, Berkeley, CA
94720; 1Phone: (970) 491-4991, 1E-mail: epsmits@lamar.colostate.edu; 4E-mail:
nterry@nature.berkeley.edu.
Phytoremediation, i.e. the use of plants for environmental cleanup, offers an attractive and cost-effective
approach to remediate metal-polluted soils and waters. The goal of these studies is to use genetic
engineering to increase metal tolerance and accumulation in plants, so as to create better plants for metal
phytoremediation. In one of our studies, we have overproduced the metal-binding peptides glutathione and
phytochelatins. Glutathione plays several important roles in the defense of plants against environmental
stresses, and is the precursor for phytochelatins (PCs): heavy metal-binding peptides involved in metal
tolerance and sequestration. Glutathione is synthesized in two enzymatic reactions, catalyzed by glutamylcysteine synthetase (ECS), and glutathione synthetase (GS), respectively. To obtain plants with superior
metal accumulation and tolerance, we overexpressed the E. coli ECS and GS enzymes in Brassica juncea
(Indian mustard), a particularly suitable plant species for heavy metal remediation. The transgenic ECS and
GS plants contained higher levels of glutathione and phytochelatins than the wildtype plants. The ECS and
GS plants accumulated up to 3-fold more cadmium in their shoots than wildtype plants, and also showed
enhanced cadmium tolerance. In another study, we overexpressed the key enzyme of the sulfate
assimilation pathway, i.e. ATP sulfurylase (APS). The resulting APS plants accumulated significantly (up
to 3-fold) more selenium, molybdenum, and sulfur than wildtype plants. We conclude that plant genetic
engineering is a promising strategy for the production of plants with superior phytoremediation capacity.
These transgenic plants are presently analyzed with respect to their tolerance and accumulation of other
metals, and used in phytoremediation studies of metal-polluted mine drainage in Leadville.
Key words: phytoremediation, metals, selenium, phytochelatins