Changes in antioxidant enzyme activities in Eichhornia crassipes (Pontederiaceae) and Pistia stratiotes (Araceae) under heavy metal stress

Whole plants of Eichhornia crassipes and Pistia stratiotes were exposed to various concentrations (0, 0.1, 0.3, 0.5, 1.0, 3.0 and 5.0 mM) of 8 heavy metals (Ag, Cd, Cr, Cu, Hg, Ni, Pb and Zn) hydroponically for 21 days. Spectrometric assays for the total activity of catalase, peroxidase, and superoxide dismutase in the leaves were studied. At the end of the experimental period, data referred to metal treated plants were compared to data of untreated ones (control). Heavy metals increased the activity of catalase, peroxidase and superoxide dismutase in both species and there was differential inducement among metals. Overall, Zn had the least inducement of antioxidant enzymes in both species while Hg had the highest inducement. The increase in antioxidant enzymes in relation to the control plants was more in E. crassipes than P. stratiotes. The results showed that E. crassipes tolerated higher metal concentrations in a greater number of metals than P. stratiotes. Rev. Biol. Trop. 55 (3-4): 815-823. Epub 2007 December, 28.<br>Plantas completas de Eichhornia crassipes y Pistia stratiotes fueron expuestas a varias concentraciones (0, 0.1, 0.3, 0.5, 1.0, 3.0 and 5.0 mM) de metales pesados (Ag, Cd, Cr, Cu, Hg, Ni, Pb and Zn) utilizando hidroponía, por 21 días. Se realizaron análisis espectrométricos en las hojas para determinar la actividad total de la catalasa, peroxidasa y dismutasa superóxida. Al final del periodo experimental, se comparó con plantas no tratadas (control). Los metales pesados incrementan la actividad de la catalasa, peroxidasa y la dismutasa superóxida para ambas especies y hay diferencias entre los metales. El Zn produce el menor estímulo para enzimas antioxidantes en ambas especies; Hg produce el mayor estímulo. El incremento de las enzimas antioxidantes en relación con las plantas control fue mayor en E. crassipes que P. stratiotes. E. crassipes tolera altas concentraciones de metal en un gran número de ellos, mientras que la tolerancia en P. stratiotes es menor.