Effect of Cd, Cr, Cu, Mn, Ni, Pb and Zn on seed germination and seedling growth of two lettuce cultivars (Lactuca sativa L.)

In this study, the effect of different concentrations of Cd, Cr, Cu, Mn, Ni, Pb and Zn on seed germination and seedling growth at an early stage of two lettuce cultivars (one with green and the other with red leaves) was evaluated. The inhibitory effects of these metals on germination rate, viable seedlings, shoot and root biomass, root length, seedling vigor and root tolerance index was determined. Globally, a decrease was observed in these variables with increasing concentrations of the metals. The present results indicate that seedling growth was more sensitive than germination. Lactuca sativa seeds were usually tolerant for all metals during the germination process and this probably occurred due to barrier effect of seed coat that prevented the metals to come in contact with the developing embryo. The inhibitory effects of these metals on seedling growth varied. In general, the presence of low Ni and Cr concentrations stimulated the growth of green-leaf lettuce seedlings. Low concentrations of Zn promoted the growth of red-leaf lettuce which is less tolerant to Cd. In this study it was verified that Lactuca sativa seedlings can survive in contaminated media, however, it was more sensitive to Cd and Cu and tolerant to Mn.