Lead (Pb) contamination of agricultural soils, and subsequently of crops, has been widely reported. Soybean (Glycine max (L.) Merr.) has been indicated as a plant that accumulates Pb, even in soils that do not exceed the maximum permissible levels. Considering the toxicity of this heavy metal, the aim of the present study was to assess different concentrations of Pb, from low to extremely high (0.25 mM, 1 mM, and 2.5 mM), in soybean seedlings and their tolerance by analyzing morpho-physiological parameters in hydroponic experiments. Soybean seedlings were exposed to control and Pb treatments during 8 days, coinciding with the early growth stages, and the following variables were analyzed: biomass, Pb content in roots, stems and leaves, photosynthetic efficiency, leaf area, biochemical response (antioxidant power, chlorophylls, malondialdehyde), and relative water content of leaves. Results showed that roots accumulated much more Pb than the other organs, with Pb accumulation in roots being saturated even at the lowest Pb concentration, which was reflected in root biomass. Moreover, absorption of culture solutions was lower in Pb treatments, which was also reflected in the lower leaf relative water content. Lead toxicity symptoms in leaves (chlorosis and dark spots, and a decrease of biomass and leaf area, chlorophyll content, and photosynthetic efficiency), and an increase of the oxidative defense system were associated only with the highest Pb concentration (2.5 mM). Our findings support the evidence of soybean as a species tolerant to Pb, showing the effects of toxicity at very high concentrations. | Instituto de Fisiología y Recursos Genéticos Vegetales | Fil: Blanco, Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Instituto Multidisciplinario de Biología Vegetal (IMBIV). Área Contaminación y Bioindicadores; Argentina | Fil: Blanco, Andrés. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina | Fil: Pignata, María L. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Instituto Multidisciplinario de Biología Vegetal (IMBIV). Área Contaminación y Bioindicadores; Argentina | Fil: Pignata, María L. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina | Fil: Lascano, Hernán Ramiro. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Cátedra de Fisiología Vegetal; Argentina | Fil: Lascano, Hernán Ramiro. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Unidad de Estudios Agropecuarios (UDEA); Argentina | Fil: Lascano, Hernán Ramiro. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Fisiología y Recursos Genéticos Vegetales. Argentina | Fil: Rodriguez, Judith H. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Instituto Multidisciplinario de Biología Vegetal (IMBIV). Área Contaminación y Bioindicadores. Argentina | Fil: Rodriguez, Judith H. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina

Glycine max (L.) Merr. (soybean) crop plants have been found to have high lead (Pb) levels in aerial organs; however, knowledge about the processes involved in the incorporation, and subsequent translocation and accumulation of the metal in the plants is scarce. Considering the toxicity of this heavy metal, the aim of the present study was to evaluate Pb uptake and translocation, and their toxic effects on soybean seedlings via experiments of ionic competition with Ca2+ (2.5 mM, Ca:Pb 1:1) and alteration of the transpiration flow [0.25 mM Pb(NO3)2]. The following variables were analyzed: biomass, leaf area (morphological parameters), photosynthetic efficiency, biochemical response (considered physiological stress markers: antioxidant power, chlorophylls, carotenoids, starch, proteins, sugars, and malondialdehyde), and Pb content. Results showed that soybean seedlings can accumulate high Pb concentration in its organs; however, in general, no morpho-physiological Pb stress symptoms were observed, except for lipid peroxidation and antioxidant power. The treatment with Ca ions was not effective in reducing Pb entry into root over time when both Ca and Pb where present in the grow solution. Alteration of the transpiration rate in soybean showed that the air flow increased the consumption of solutions, regardless of the treatments. | Instituto de Fisiología y Recursos Genéticos Vegetales | Fil: Blanco, Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto Multidisciplinario de Biología Vegetal (IMBIV). Área Contaminación y Bioindicadores; Argentina | Fil: Blanco, Andrés. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina | Fil: Pignata, María L. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto Multidisciplinario de Biología Vegetal (IMBIV). Área Contaminación y Bioindicadores; Argentina | Fil: Pignata, María L. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina | Fil: Lascano, Hernán Ramiro. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Cátedra de Fisiología Vegetal; Argentina | Fil: Lascano, Hernán Ramiro. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Estudios Agropecuarios (UDEA); Argentina | Fil: Lascano, Hernán Ramiro. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Fisiología y Recursos Genéticos Vegetales; Argentina | Fil: Salazar, María J. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto Multidisciplinario de Biología Vegetal (IMBIV). Área Contaminación y Bioindicadores; Argentina | Fil: Salazar, María J. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina | Fil: Rodriguez, Judith H. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto Multidisciplinario de Biología Vegetal (IMBIV). Área Contaminación y Bioindicadores; Argentina | Fil: Rodriguez, Judith H. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina