Parâmetros de crescimento, bioquímicos e ecofisiológicos em plantas de milho cultivadas em solos multicontaminados com Cd e Zn

Abstract

Agricultural species face several biotic and abiotic stresses that are the main limiting factors for crop production. In this context, contamination by trace-elements is characterized as an abiotic stress, representing an environmental issue. Cadmium is a powerful enzyme inhibitor and, given that it is a non-essential element, it can damage plant cells, even in low concentrations. Plant exposure to this trace-element results in many damages to plant physiological metabolism and injures the photosynthetic system, triggering the production of oxygen reactive species in photosynthetically active tissues. Zinc is a co-factor for several enzymes, and is involved in both regulation and activation of such molecules. In addition, it is also involved in the regulation processes of signal transcription, translation, and transduction. Because of its importance for plant metabolism, the concentration of this element must be kept within a relatively narrow range to avoid the effects of either deficiency or toxicity. Physical and chemical similarities between Cadmium and Zinc allow the interaction of these elements in the environment, possibly causing antagonist effects in which Zinc acts neutralizing the damages caused by Cadmium in the metabolism, or synergistic effects in which Zinc enhances the effects of Cadmium over the metabolism. In this sense, physiological mechanisms to delete, detoxify or compartmentalize the excess of trace-elements are essential for plant survival when exposed to high concentrations of such elements. In order to better understand the responses of the species subjected to Cd and Zn stress, the present study aimed to evaluate Zea mays L (maize) plants sensitive to the contamination by these elements (Organization for Economic Co-operation and Development – OECD, 2006), cultivated in Latosol and Cambisol, using biochemical and ecophysiological analyses. The plants were exposed to doses of Cd and Zn (0.4+14.89, 0.72+28.80, 1.29+48, 2.3+86.64, 4.1+152.64, 13.6+506.89, 24.4+908.61 mg kg-1) during 21 days. We conducted enzymatic and ecophysiological analyses, such as the activity of enzymes SOD, CAT, APX, hydrogen peroxide, lipid peroxidation, chlorophyll content, photosynthetic rate, stomatal conductance and transpiration. The data obtained showed a specific behavior of the maize plants for each analyzed soil. Latosol released higher amounts of Cd to plants, resulting in a greater oxidative damage and other adverse effects. Due to its attributes, especially the higher clay and organic matter content, Cambisol absorbed Cd and Zn in higher proportions, resulting in better plant development.