High Peroxide Level May Be a Characteristic Trait of a Hyperaccumulator

Under various abiotic stresses, plants overproduce reactive oxygen species (ROS) such as superoxide anion (O-2(center dot-)), hydroxyl radical (OH center dot), and hydrogen peroxide (H2O2). When in excess, these highly reactive molecules cause oxidative stress, thus damaging proteins, lipids, and DNA. Therefore, plants evolved an enzymatic defense machinery that involves such enzymes as superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APOX). Various plant families, species and even specimens differ in their ability to withstand the abiotic stress. A study has been undertaken to assess the differences in response to trace metals between two species : a resistant hyperaccumulator Indiana mustard (Brassica juncea) and a metal-sensitive pea (Pisum sativum). We observed that trace elements (Cu, Zn, Cd, Pb) changed the activity of antioxidative enzymes (SOD, APOX, CAT) and the rate of ROS generation. However, in the control plants and at a point 0' of the treatment, we have noticed a large disproportion in the hydrogen peroxide level, with B. juncea maintaining naturally higher H2O2 level (up to 40 times higher). We believe that this may be a distinguishing trait common to plants being resistant to oxidative stress.