Ca 2þ -dependent plant response to Pb 2þ is regulated by LCT1 S. Wojas a , A. Ruszczyn ´ska b , E. Bulska b , M. Wojciechowski b , D.M. Antosiewicz a, * a University of Warsaw, Faculty of Biology, Department of Ecotoxicology, Miecznikowa street 1, 02-096 Warszawa, Poland b University of Warsaw, Faculty of Chemistry, Pasteura street 1, 02-093 Warszawa, Poland Received 20 April 2006; received in revised form 8 September 2006; accepted 6 October 2006 Ca 2þ -dependent Pb 2þ detoxification and uptake was regulated by TaLCT1. Abstract Tobacco plants transformed with TaLCT1 were cultured on Knop’s medium with modified calcium concentrations (0.01e3 mM) in the pres- ence of Pb 2þ , and in soil contaminated by lead. A 4e5 mM Pb 2þ administered in the presence of 1 mM Ca 2þ inhibited the root growth of trans- genic plants to much lesser degree than of control plants, whereas in the presence of 3 mM Ca 2þ no differences were found between the studied lines. The reduction of Pb 2þ toxicity in the presence of 1 mM Ca 2þ was not accompanied by a change in the lead tissue concentration. However, when Ca 2þ level in the medium was lowered to 0.01 mM, several fold higher root/shoot Pb ratio in transgenic plants was observed, twofold increase in the total amount of metal accumulated, and lower concentration of Pb in the xylem sap. Results suggest the involvement of TaLCT1 in the regulation of Ca-dependent Pb-detoxification, and under conditions of low calcium in lead uptake and distribution. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Lead tolerance; Calcium; Tobacco; LCT1 1. Introduction Lead and cadmium occur widely in the environment but they have no known biological role. Numerous factors deter- mine how toxic these elements are to living organisms. That Pb/Cd tolerance depends on calcium has been known for years, since the harmful effects of Pb 2þ and Cd 2þ on plants are ameliorated as soil Ca concentrations increase. This depen- dence has also been found for other heavy metals (e.g. Zn 2þ , Cu 2þ , Ni 2þ , as well as Al 3þ or even Na þ ) despite the differ- ences in their chemical properties (Antosiewicz, 2005; Anto- siewicz and Hennig, 2004; Epstein, 1998; Garland and Wilkins, 1981; Maksymiec and Baszyn ´ski, 1998; Rashid and Popovic, 1990; Woolhouse, 1983). Experiments demonstrating Ca-dependent Pb/Cd tolerance have been performed on many types of plants, both crop and wild species (Garland and Wil- kins, 1981; Karataglis, 1981; Sko ´rzyn ´ska-Polit et al., 1998; Sko ´rzyn ´ska-Polit and Baszyn ´ski, 2000). Calcium-dependent tolerance to heavy metals is not, therefore, a species-specific trait. Studies have shown that at higher calcium levels, heavy metal inhibition of growth and development of whole plants is weaker, and on the cellular level, the inhibition of enzyme activity (e.g. of nitrogenase), synthesis of photosynthetic pig- ments and photosystem II is reduced (Sko ´rzyn ´ska-Polit et al., 1998; Sko ´rzyn ´ska-Polit and Baszyn ´ski, 2000). The mechanism of Ca-dependent Pb/Cd tolerance remains unknown. It is believed, however, that regulation of metal up- take and accumulation is not the only process involved since amelioration of Pb 2þ /Cd 2þ toxicity by increasing Ca 2þ con- centrations can be associated not only with a reduction in the tissue content of the metals, but also with their unchanged or even increased levels (Antosiewicz, 2005; Antosiewicz and Hennig, 2004; Chen et al., 2000; Sko ´rzyn ´ska-Polit et al., 1998). Thus, the involvement of many processes is postulated. Increased efficacy of a plant’s defense mechanisms, including more effective detoxification of metal ions taken up into the cell, may be one of them. It has been found that under low * Corresponding author. Tel.: þ48 22 55 42 005; fax: þ48 22 55 42 022. E-mail address: dma@biol.uw.edu.pl (D.M. Antosiewicz). 0269-7491/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2006.10.012 Environmental Pollution 147 (2007) 584e592 www.elsevier.com/locate/envpol