Toxicidade por metais pesados em pinhão-manso e mamona cultivadas em solução nutritiva.

Abstract

The work was carried out to study the response of jatropha (Jatropha curcas L.) and castor bean (Ricinus communis) to Cd, Zn, and Pb assessed by X-ray chlorophyll fluorescence. The effect of the metal doses on phytotoxicity, metal tolerance, nutrients composition, enzymes activity, soluble proteins and photosynthetic pigments were studied. Five experiments were conducted in greenhouse, being three of them using jatropha and two studying castor bean plants. Each experiment had five doses of each metal and a control (no metal addition). Given its essentiality, the experiment with Zn utilized a 0,380 μmol L-1 of Zn as a control. All the experiments were carried out in randomized block design with three replicates. The metals were applied and the experiments conducted during different periods. The following characteristics were evaluated: biomass of roots, stem and leaves, concentration of metals and nutrients (N, P, K, Ca, Mg, Fe, Cu, Zn, Mn, Mo and B), antioxidative enzymes activity, soluble protein, pigments as well as X-ray chlorophyll fluorescence. The results showed that chlorophyll fluorescence was efficient in determining the time alterations caused by Cd, Zn and Pb phytotoxicities. Jatropha showed a relative tolerance to Cd and did not present deleterious effects on the Fe contents and chlorophyll “a”. The visual symptoms of Cd toxicity were chlorosis in newest leaves, plant growth reduction, besides darkening and restrict growth of roots. The 227 μmol L-1 of Zn was equivalent to a 50% reduction in jatropha biomass. Both the toxicity and deficiency of Zn provoked nutritional imbalance and diminished the pigments concentration in jatropha leaves. The Pb doses also caused changes in the chemical composition of plants with reduction of N, P, Cu and Zn in leaves. The Pb toxicity did not change the concentrations of Fe, Mg and foliar pigments in jatropha. In spite of the decreased nutritional status, with reduction of Fe and Mg in leaves, castor bean did show tolerance to Zn toxicity with no effects on photosynthetic pigments. The Pb doses did not provoke changes on the plants mineral composition as well as on castor bean photosynthetic pigments. The doses of Cd, Zn and Pb did not change the activities of antioxidant enzymes neither the soluble proteins for both plant species. Owing to their relative tolerance to the studied metals, castor bean and jatropha can be environmental and economic alternatives to phytostabilization and phytoattenuation of contaminated areas with additional advantage of oil utilization in industry and bioenergy production during the remediation.