Plant Response to Heavy Metal Toxicity: Comparative Study Between the Hyperaccumulator Thlaspi caerulescens (Ecotype Ganges) and Nonaccumulator Plants: Lettuce, Radish, and Alfalfa Saoussen Benzarti, Shino Mohri, Yoshiro Ono The Graduate School of Environmental Science, Okayama University. 3-1-1, Tsushimanaka, Okayama 700-8530, Japan Received 22 October 2007; revised 30 January 2008; accepted 16 April 2008 ABSTRACT: Thlaspi caerulescens (alpine pennycress) is one of the best-known heavy metal (HM) hyperaccumulating plant species. It exhibits the ability to extract and accumulate various HM at extremely high concentrations. In this hydroponic study, the performance of T. caerulescens (ecotype Ganges) to accumulate Cd, Zn, and Cu was compared with that of three nonaccumulator plants: alfalfa (Medicago sativa), radish (Raphanus sativus), and lettuce (Lactuca sativa). Plants were exposed to the separately dissolved HM salts for 7 days at a wide range of increasing concentrations: 0 (con- trol: 1/5 Hoagland nutrient solution), 0.1, 1, 10, 100, and 1000 lM. The comparative study combined chemical, physiological, and ecotoxicological assessments. Excessive concentrations of HM (100 and 1000 lM) affected plant growth, photosynthesis, and phytoaccumulation efficiency. Root exudation for all plant species was highly and significantly correlated to HM concentration in exposure solutions and proved its importance to counter effect toxicity. T. caerulescens resisted better the phytotoxic effects of Cd and Zn (at 1000 lM each), and translocated them significantly within tissues (366 and 1290 lgg 21 , respectively). At the same HM level, T. caerulescens exhibited lower performances in accumulating Cu when compared with the rest of plant species, mainly alfalfa (298 lgg 21 ). Root elongation inhibition test confirmed the selective aptitude of T. caerulescens to better cope with Cd and Zn toxicities. MetPLATE bioassay showed greater sensitivity to HM toxicity with much lower EC 50 values for b-galactosidase activity in E. coli. Nevertheless, exaggerated HM concentrations coupled with relatively short exposure time did not allow for an efficient metal phytoextraction thus a signifi- cant reduction of ecotoxicity. # 2008 Wiley Periodicals, Inc. Environ Toxicol 23: 607–616, 2008. Keywords: heavy metals; hydroponics; phytoaccumulation; T. caerulescens; nonaccumulator plants INTRODUCTION The environmental pollution with toxic heavy metals (HM), owing primarily to anthropogenic activities, has become a global issue (Ghosh and Singh, 2005; Tandy et al., 2006). HM are hazardous compounds that tend to bioaccumulate in living organisms over time via food, water, and air pathways. Unlike organic compounds they cannot be degraded or destroyed under biotic conditions. Correspondence to: S. Benzarti; e-mail: dev18310@cc.okayama-u. ac.jp and sbenzarti@yahoo.fr Contract grant sponsor: Ministry of Education, Culture, Sports, Science and Technology, Japan. Published online 4 June 2008 in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/tox.20405  C 2008 Wiley Periodicals, Inc. 607