Ecological Characteristics Of Cadmium-hyperaccumulators And Their Mechanism Analysis Of Pollution Endurance

Among the group of the known metal-hyperaccumulators, Cd-hyperaccumulators are relatively scarce. Although remediation of contaminated soils using Cd-hyperaccumulators is regarded as an economic and green method, the lack of understanding basic biochemical, physiological, ecological, and molecular mechanisms involved in Cd-hyperaccumulation has an adverse effect on the optimization of the phytoextraction technique and obstructs its further commercial application. The main aims of this study were to explore ecological characteristics and analyze pollution-tolerance mechanisms of Cd-hyperaccumulators Solanum nigrum L. and Rorippa globosa(Turcz.) Thell., in comparison with a closely related species Solanum melongena L. and Rorippa islandica(Oeder.) Borb..Solanum nigrum was considerably higher tolerant and hyperaccumulative to Cd than S. melongena. Similarly, Rorippa globosa was higher tolerant and hyperaccumulative to Cd than R. islandica. The growth inhibition of R. globosa stems was the unique ecological character as the Cd-hyperaccumulator.The synergism between the activity of SOD and CAT in the roots and the activity of POD and CAT in the leaves of S. nigrum, the synergism between the activity of SOD and CAT in the leaves of R. globosa represent effective defense strategies. Antioxidative defenses in the Cd hyperaccumulator might play an important role in Cd tolerance.The stress of Cd pollution could significantly increase the level of free proline in S. nigrum and R. globosa. It could be suggested that free proline might play an important protective roles against Cd stress. Free proline in the leaves had the stronger ability than that in the roots. Acetic and citric acids in the leaves of S. nigrum might be related to its Cd hyperaccumulation. Tartaric and malic acids in the leaves of R. globosa might be related to its Cd hyperaccumulation. Organic acids may play an important role in Cd tolerance and hyperaccumulation. High level of organic acids is not likely primary reason of Cd hyperaccumulation and hypertolerance.PCs may be an important biomarker of Cd hyperaccumulation. PCs do not appear to be involved in Cd tolerance in the hyperaccumulators. PCs do not play an important role in Cd tolerance of S. nigrum and R. globosa.