Overexpression of Enzymes Involved in Glutathione Synthesis Enhances Tolerance to Organic Pollutants in Brassica juncea

ABSTRACT

Transgenic Indian mustard (Brassica juncea) overexpressing γ-glutamylcysteine synthetase (ECS) or glutathione synthetase (GS) were shown previously to have two-fold higher levels of glutathione and total nonprotein thiols, as well as enhanced cadmium tolerance and accumulation. Here, the hypothesis was tested that these transgenics have enhanced tolerance to organic pollutants, based on the reasoning that many organic xenobiotics are detoxified via conjugation to glutathione. Both the ECS and GS transgenics showed enhanced tolerance to atrazine: while root growth of wildtype seedlings was inhibited 50% by 100 mg L⁻¹ atrazine, ECS and GS root growth was inhibited 20–30% (P < 0.05). The tolerance of the transgenics to CDNB (1-chloro-2,4-dinitrobenzene), metolachlor, and phenanthrene was also somewhat higher than wild type, but these differences were not as pronounced. Each of the organics treatments significantly enhanced total nonprotein thiol levels in all plant types (2 to 12-fold). Overall, these results suggest that GSH biosynthesis is limiting for atrazine detoxification in Indian mustard and that overexpression of enzymes involved in GSH biosynthesis offers a promising approach to create plants with the enhanced capacity to tolerate not only heavy metals, but also certain organics.

Keywords:

• Brassica juncea
• Indian mustard
• γ-glutamylcysteine synthetase
• glutathione synthetase
• glutathione
• phytoremediation
• herbicides.

ACKNOWLEDGEMENTS

This work was supported financially by the Environmental Protection Agency Research Grant number G8A11586 awarded, to E.A.H.P.S., and a graduate scholarship from Fundación Antorchas for CG Flocco. The authors would like to thank Ashley Ackley for help with the thiol analyses.