Evidence of a new Hg-tolerant ecotype of Rumex induratus from Almaden ( Ciudad Real, Spain)

Mercury tolerance in wild vascular plants has hardly been studied and a tolerant ecotype is not known. In order to confirm the tolerance to Hg of Rumex induratus naturally growing in the biggest Hg mine in the world (Almaden population), the population was compared in a hydroponic experiment with another population from a non-Hg-contaminated area (Colmenar). The plants were exposed to different doses of Hg and a dose of As to establish whether the tolerance to Hg coincides with tolerance to other trace elements. Plants from Colmenar reached up to 1322gHgg(-1) in roots and 65gHgg(-1) in shoots and showed a significant decrease in biomass due to Hg exposure, whilst Almaden accumulated only 812gHgg(-1) and 56gHgg(-1) in roots and shoots, respectively. The Almaden population showed a higher tolerance to intense exposure to Hg, but not to As. Plants from Almaden exposed to Hg showed higher capacity to synthesise thiols in the root and to control oxidative stress and Zn starvation. Our findings suggest that R. induratus could be used to enhance understanding of the mechanisms of Hg tolerance in plants.