Toxicidade do chumbo em cultivares de Vigna unguiculata (L.) Walp: enzimas antioxidantes e potencial fitorremediador

Abstract

The contamination of different ecosystems with lead is a major global concern, since it has a cumulative effect on the environment and in living organisms, it is recalcitrant and that, even at low concentrations; it presents toxic effects to all living beings. One of the effects caused by lead in plants is to cause the excessive production and accumulation of reactive species of oxygen (ROS), which in turn causes cell damage. Phytoremediation is an important technique recently created with the objective of exploring the ability of plants to decontaminate different ecosystems. Therefore, there is need to investigate the potential of different plants to be used in this technique and to understand the mechanisms that underlie the ability of plants to remove, accumulate and tolerate the adverse effects that these pollutants cause. To avoid this accumulation, several antioxidant enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT), are responsible for removing the excess of those species. Thus, plants that naturally exhibit high antioxidant activity of these enzymes have one of the necessary characteristics for application in phytoremediation of heavy metals as lead. The aim of this work was to evaluate the activity profile and transcription of antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT) in roots and leaves of Vigna unguiculata (L.) Walp, cultivars Sempre Verde (SV) and Setentão (SET), subjected to lead stress and to evaluate the potential of these cultivars for use in phytoremediation. The SV cultivar showed higher lead concentration in the roots, whereas SET showed higher concentration in leaves. When comparing the treatment groups, SV was the cultivar with the highest antioxidant activity in roots for the three enzymes evaluated, while SET had the highest activity in the leaves. It is noteworthy that SV showed no reduction in expression of the enzymes evaluated in roots and that SET had reduced expression in leaves for two genes tested Vu-APX1 and Vu-APX5. In both cultivars, no morphological change was observed in roots, but there was an increase in the distribution of waxes in leaves and reduction in stomatal aperture for SV, whereas these changes in SET were less pronounced. Based on all results it is suggested that SV shows more tolerance to the stress caused by Pb and that both cultivars showed no potential for phytoremediation.