Overexpression of glutathione reductase in Brassica juncea: Effects on cadmium accumulation and tolerance

Abstract

To determine the importance of glutathione reductase (GR, EC 1.6.4.2) for heavy metal accumulation and tolerance, a bacterial GR was expressed in Indian mustard (Brassica juncea L.), targeted to the cytosol or the plastids. GR activity in the cytosolic transgenics (cytGR) was about two times higher compared to wild‐type plants; in the plastidic transgenics (cpGR) the activity was up to 50 times higher. When treated with 100 μM CdSO4, cytGR plants did not differ from wild type in cadmium tolerance or accumulation. CpGR plants, however, showed enhanced cadmium tolerance at the chloroplast level: in contrast to wild‐type plants they showed no chlorosis, and their chlorophyll fluorescence parameters Fv/Fm and photochemical quenching were higher. Cadmium tolerance at the whole‐plant level (plant growth) was not affected. The lower cadmium stress experienced by the cpGR chloroplasts may be the result of reduced cadmium uptake and/or translocation: cadmium levels in shoots of cpGR plants were half as high as those in wild‐type shoots. These differences in cadmium tolerance and accumulation may result from increased root glutathione levels, which were up to two times higher in cpGR plants than in the wild type.