title: Does cadmium play a physiological role in the hyperaccumulator Thlaspi caerulescens?
abstract: The southern French (Ganges) ecotype of Thlaspi caerulescens J & C Presl is able to hyperaccumulate several thousand mg Cd kg(-1) shoot dry weight without suffering from phytotoxicity. We investigated the effect of Cd on growth and the activity of carbonic anhydrase (CA), a typical Zn-requiring enzyme, of T. caerulescens in soil and hydroponic experiments. In one of the hydroponic experiments, T. caerulescens was compared to the non-accumulator Thlaspi ferganense N. Busch. In the soil experiment, additions of Cd at 5-500 mg kg(-1) soil increased the growth of T. caerulescens significantly. In the hydroponic experiments, exposure to Cd at 1-50 microM for three weeks had no significant effect on the growth of T. caerulescens, but decreased the growth of T. ferganense markedly even at the lowest concentration of Cd (1muM). Cadmium exposure significantly increased the CA activity in T. caerulescens, but decreased it in T. ferganense. The CA activity in T. caerulescens correlated positively with the Cd concentration in the shoots up to 6000 mg kg(-1), even though shoot Zn concentration was decreased by the Cd treatments. For comparison, Cd treatments had no consistent effect on the activity of superoxide dismutase in T. caerulescens. The results suggest that Cd may play a physiological role in the Cd-hyperaccumulating ecotype of T. caerulescens by enhancing the activities of some enzymes such as CA. Further research is needed to establish whether a Cd-requiring CA exists in T. caerulescens.
authors.affiliation: Key Laboratory of Plant-Soil Interactions of Ministry of Education, College of Resources and Environmental Sciences, China Agricultural University, Beijing 100094, China.
authors.forename: Mei-Qing
authors.initials: MQ
authors.lastname: Liu
authors.forename: Junta
authors.initials: J
authors.lastname: Yanai
authors.forename: Rong-Feng
authors.initials: RF
authors.lastname: Jiang
authors.forename: Fusuo
authors.initials: F
authors.lastname: Zhang
authors.forename: Steve P
authors.initials: SP
authors.lastname: McGrath
authors.forename: Fang-Jie
authors.initials: FJ
authors.lastname: Zhao
mesh_terms: D002104:Cadmium / Q000494:pharmacology*; D002256:Carbonic Anhydrases / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D018521:Plant Physiological Phenomena / Q000187:drug effects*; D018520:Plant Shoots / Q000201:enzymology / Q000254:growth & development; D013482:Superoxide Dismutase / Q000378:metabolism; D031227:Thlaspi / Q000201:enzymology* / Q000254:growth & development*
chemical_list: D002104:Cadmium; D013482:Superoxide Dismutase; D002256:Carbonic Anhydrases