The aim of this study was to evaluate the effects of increasing concentrations of lead (Pb) in the nutrient solution on growth and macronutrient and organic solute contents of Helianthus annuus plants. The experimental design was completely randomized with four replications. The dry mass yield was not affected by the treatments up to a Pb concentration of 0.6 mM, indicating that H. annuus was tolerant to this Pb concentration in the growth medium. The reductions in leaf, stem and root dry masses at a Pb concentration of 0.8 mM were 74, 84 and 85%, respectively. Lead stress did not reduce the levels of nitrogen (N), phosphorus (P) and potassium (K), indicating that the growth reduction observed at 0.8 mM Pb could not be attributed to deficiencies of these nutrients. On the other hand, Pb significantly reduced calcium (Ca) and magnesium (Mg) contents in leaves, stems and roots, which might, at least in part, explain the Pb-induced growth reduction in the H. annuus plants. Pb increased soluble carbohydrate, free amino acid and proline contents in leaves, and soluble protein and proline contents in roots, showing stress-induced changes in cell metabolism. The data also suggest that Ca and Mg concentrations may be used as nutritional indicators and the proline content may be used as a biochemical indicator of Pb toxicity in H. annuus.

Growth and volatile compounds of Martianthus leucocephalus exposed to heavy metal stress.Ciência Rural, v.46, n.12, dez, 2016. Cd (15, 30, ), Cu (30, 60, ) and Zn (150, 300, ) levels on the growth of this species and its volatile compounds production. Apical cuttings were placed in plastic trays containing 6.0L nutrient solution, and after rooting, they were submitted to Cd, Cu and Zn treatments for 15 days. All the metals evaluated reduced the succulence and growth of all parts of M. ABSTRACT Martianthus leucocephalus is found in the semi-arid Northeast of Brazil and has high pharmacological potential due to the production of volatile compounds. This study aimed to evaluate the leucocephalus. This effect was accompanied by the increase of Cd, Cu and Zn concentrations in all plant tissues. Volatile compounds content produced by M. leucocephalus was increased only by Zn (86%).Key words: Lamiaceae, metals, relative growth. Cd (15, 30, ), Cu (30, 60, ) e Zn (150, 300, 450 and 600µmol L -1 RESUMO Martianthus leucocephalus é encontrada no semiárido nordestino e possui potencial farmacológico atribuído à produção de compostos voláteis. Este trabalho objetivou avaliar o efeito de doses de