Cadmium induces two waves of reactive oxygen species in Glycine max (L.) roots

Abstract

Cadmium (Cd) is a non-essential heavy metal that may be toxic or even lethal to plants as it can be easily taken up by the roots and loaded into the xylem to the leaves. Using soybean roots (Glycine maxL.) DM 4800, we have analysed various parameters related to reactive oxygen metabolism and nitric oxide (NO) during a 6 day Cd exposure. A rise in H2O2 and NO, and to a lesser extent O2·- content was observed after 6h exposure with a concomitant increase in lipid peroxidation and carbonyl group content. Both oxidative markers were significantly reduced after 24h. A second, higher wave of O2·- production was also observed after 72h of exposure followed by a reduction until the end of the treatment. NOX and glicolate oxidase activity might be involved in the initial Cd-induced reactive oxygen species (ROS) production and it appears that other sources may also participate. The analysis of antioxidative enzymes showed an increase in glutathione-S-transferase activity and in transcript levels and activity of enzymes involved in the ascorbate-glutathione cycle and the NADPH-generating enzymes. These results suggest that soybean is able to respond rapidly to oxidative stress imposed by Cd by improving the availability of NADPH necessary for the ascorbate-glutathione cycle. Different pieces of evidence suggest a role for ROS, and NO in cadmium toxicity, although evolution through the treatment is not so analysed. In this work the response of soybean roots over 6 d Cd treatment was analysed. From the very beginning an increase in ROS and NO production was observed besides an initial oxidative damage on lipids and proteins. Then, the roots recover quickly thanks to the induction of its antioxidant enzymes mainly those involved in the ascorbate-glutathione cycle and the NADPH generating enzymes suggesting a key role for NADPH availability in plant acclimation to Cd stress. © 2014 John Wiley & Sons Ltd.