title: Arsenic and mercury tolerance and cadmium sensitivity in Arabidopsis plants expressing bacterial gamma-glutamylcysteine synthetase.
abstract: Cysteine sulfhydryl-rich peptide thiols are believed to play important roles in the detoxification of many heavy metals and metalloids such as arsenic, mercury, and cadmium in plants. The gamma-glutamylcysteine synthetase (gamma-ECS) catalyzes the synthesis of the dipeptidethiol gamma-glu-cys (gamma-EC), the first step in the biosynthesis of phytochelatins (PCs). Arabidopsis thaliana, engineered to express the bacterial gamma-ECS gene under control of a strong constitutive actin regulatory sequence (A2), expressed gamma-ECS at levels approaching 0.1% of total protein. In response to arsenic, mercury, and cadmium stresses, the levels of gamma-EC and its derivatives, glutathione (GSH) and PCs, were increased in the A2::ECS transgenic plants to three- to 20-fold higher concentrations than the increases that occurred in wild-type (WT). Compared to cadmium and mercury treatments, arsenic treatment most significantly increased levels of gamma-EC and PCs in both the A2::ECS transgenic and WT plants. The A2::ECS transgenic plants were highly resistant to arsenic and weakly resistant to mercury. Although exposure to cadmium produced three- to fivefold increases in levels of gamma-EC-related peptides in the A2::ECS lines, these plants were significantly more sensitive to Cd(II) than WT and trace levels of Cd(II) blocked resistance to arsenic and mercury. A few possible mechanisms for gamma-ECS-enhanced arsenic and mercury resistance and cadmium hypersensitivity are discussed.
authors.affiliation: Department of Genetics, University of Georgia, Athens, Georgia 30602-7223, USA.
authors.forename: Yujing
authors.initials: Y
authors.lastname: Li
authors.forename: Om Parkash
authors.initials: OP
authors.lastname: Dhankher
authors.forename: Laura
authors.initials: L
authors.lastname: Carreira
authors.forename: Rebecca S
authors.initials: RS
authors.lastname: Balish
authors.forename: Richard B
authors.initials: RB
authors.lastname: Meagher
mesh_terms: D017360:Arabidopsis / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D001151:Arsenic / Q000493:pharmacokinetics / Q000633:toxicity; D020261:Arsenic Poisoning / Q000235:genetics / Q000378:metabolism / Q000517:prevention & control*; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D002104:Cadmium / Q000493:pharmacokinetics / Q000633:toxicity; D002105:Cadmium Poisoning / Q000235:genetics / Q000378:metabolism / Q000517:prevention & control*; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics; D005721:Glutamate-Cysteine Ligase / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005978:Glutathione / Q000096:biosynthesis / Q000378:metabolism; D008628:Mercury / Q000493:pharmacokinetics / Q000633:toxicity; D008630:Mercury Poisoning / Q000235:genetics / Q000378:metabolism / Q000517:prevention & control*; D054811:Phytochelatins; D010935:Plant Diseases / Q000139:chemically induced / Q000235:genetics; D030821:Plants, Genetically Modified / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D002104:Cadmium; D054811:Phytochelatins; D005721:Glutamate-Cysteine Ligase; D008628:Mercury; D005978:Glutathione; D001151:Arsenic