Characteristics of cadmium accumulation and tolerance in novel Cd-accumulating crops, Avena strigosa and Crotalaria juncea.

Characteristics of accumulation and tolerance of cadmium (Cd) in green manure crops were investigated to identify Cd-accumulating crops and to clarify the mechanisms involved in Cd accumulation and tolerance. Seedlings of eight crop species were treated with Cd (1 mg l(-1) or 5 mg l(-1)) in the growing medium for 4 d. Cd concentration in leaves of Avena strigosa Schreb. cv. New-oat, Crotalaria juncea L. and Tagetes erecta L. cv. African-tall was greater than values used to define Cd-hyperaccumulation (>100 mg Cd kg(-1) DW). However, in leaves of T. erecta, lipid peroxidation level increased significantly, and the activities of superoxide dismutase, ascorbate peroxidase, glutathione reductase, and catalase were depressed by both Cd treatments. By contrast, A. strigosa and C. juncea exhibited high Cd tolerance. Avena strigosa leaves showed higher activities of antioxidative enzymes such as superoxide dismutase and ascorbate peroxidase than those of other species tested. Crotalaria juncea showed higher amounts of total soluble phenolics which, in leaves, were doubled by 5 mg l(-1) Cd treatment. When two Cd-tolerant accumulators (A. strigosa and C. juncea) and the non-accumulator (C. spectabilis) were treated with lower Cd concentrations for 4 weeks, A. strigosa and C. juncea exhibited superior Cd accumulation in the shoots with greater biomass production compared with C. spectabilis. These results indicate that A. strigosa and C. juncea possess the greater potential for Cd accumulation and tolerance than common crops.