Lead distribution in tobacco plants experimentally exposed to the heavy metal
In order to evaluate lead distribution in the different parts of the tobacco plant, a greenhouse trial of experimental exposure to the heavy metal was performed in year 2000 and replicated in 2001. Six tobacco varieties were grown in pots, where lead had been supplied to the peat at the rates of 0 (Pb0), 4 (Pb1) and 8 g/kg (Pb2). During tobacco growth five primings were collected and at the end of the vegetative cycle, plants were divided into stalks and roots, keeping individual plants separated. Lead content was measured on lamina and midrib of the five primings, on the upper, median and lower stalk, on the root base, the small root and the large root. For each year, data of individual plants (3 replications) were submitted to the analysis of variance (3 lead rates, 16 plant parts, 6 varieties). Significant effects of lead rate, plant part and variety on lead content were revealed. Concerning lead rate, significant differences between lead rates Pb1 and Pb2 were observed in the year 2000, but not in 2001. As regards the parts of the plant, significant differences were registered both among the different organs and among the parts of the same organ. Concerning the varieties assayed, a different ranking order was revealed in 2000 with respect to the year 2001. In spite of the differences observed between the two experiments, the same behaviour was highlighted as regards to lead distribution in the different parts of tobacco plant. Lead content in the root depended on lead rate and the major sequestration of the heavy metal occurred in the small roots. In the stalk, lead content changed little from the bottom to the top of the plant and it was almost always the lowest, with respect to the other parts of the plant. Lamina lead content showed significant differences among the primings, and it seemed to depend not only on the lead rate but also on other factors, such as lead exposure time and physiological stage.* This research was carried out with the financial support of the Commission of the European Community, Tobacco and Information and Research Fund, project 96/T/35 "Monitoring and minimizing heavy metal contents in tobacco". It does not necessarily reflect the views of the Commission and in no way anticipates its future in this area.