RESUMO
Lead (Pb) is known by its toxicity both for animals and plants. In order to evaluate its toxicity, plants of Brachiaria brizantha were cultivated on nutritive solution of Hoagland during 90 days and submitted to different concentrations of Pb. The content of macro and micronutrients was evaluated and there was a reduction on root content of Ca, besides the lowest dosages of Pb had induced an increase of N, S, Mn, Cu, Zn and Fe. The cell ultrastructure of leaves and roots were analyzed by transmission electronic microscopy (TEM). Among the main alterations occurred there were invaginations on cell walls, the presence of crystals on the root cells, accumulation of material on the interior of cells and vacuolar compartmentalization. On the leaves the degradation of chloroplasts was observed, as well as the increase of vacuoles. Structures for the formation of oxalate crystals were proposed through molecular modeling and thermodynamic stability. Calculi suggest the formation of highly stable metal-oxalate complexes.
Assuntos
Brachiaria/metabolismo , Brachiaria/ultraestrutura , Cálcio/metabolismo , Complexos de Coordenação/metabolismo , Chumbo/metabolismo , Oxalatos/metabolismo , Chumbo/toxicidade , Modelos Moleculares , Folhas de Planta/metabolismo , Folhas de Planta/ultraestrutura , Raízes de Plantas/metabolismo , Raízes de Plantas/ultraestrutura , TermodinâmicaRESUMO
Com o objetivo de avaliar o efeito da aplicação de cádmio (Cd) e chumbo (Pb) na cultura da mostarda (Brassica juncea) e sua relação com o desenvolvimento das plantas, os teores, o acúmulo e a translocação nas raízes e na parte aérea, plantas de mostarda em solução nutritiva de Clark foram cultivadas e submetidas a doses crescentes de Cd (0,00; 0,25; 1,00; 5,00 e 10,00 mg.L-1) e de Pb (0,00; 2,50; 10,00; 50,00 e 100,00 mg.L-1). O Cd mostrou significativa translocação na planta, o que se deve à formação de um complexo entre essa espécie química e a fitoquelatina; a baixa translocação de Pb e o efeito deletério se devem a depósitos radiculares de quelatos estáveis de Pb.
With the objective of evaluating the effect of cadmium (Cd) and lead (Pb) in the culture of mustard (Brassica juncea) and its relationship with plant development, levels, accumulation and translocation in roots and shoots, mustard plants were grown in Clark nutrient solution and subjected to increasing doses of Cd (0.00; 0.25; 1.00; 5.00 and 10.00 mg.L-1) and Pb (0.00; 2.50; 10.00; 50.00 and 100.00 mg.L-1). Cd showed a significant translocation into the plant, which is due to the formation of a complex between the chemical species and phytochelatin; the low translocation of Pb and deleterious effects are due to root deposits of Pb stable chelates.