Plasma Membrane Alterations in Phaseolus vulgaris L. Variety CC-25-9-N Induced by Metals/Alteraciones en la membrana plasmatica de Phaseolus vulgaris L. variedad CC-25-9-N inducida por metales: Alteragoes na membrana plasmatica de Phaseolus vulgaris L. variedade CC-25-9-N induzida por metais

It is in the early stages of the vegetative phase, when the plant manifests its greatest susceptibility to sudden changes in environmental conditions and unleashes adaptive pathways that include changes in the structure of cell membranes, as they are the first to respond to damage. The bean (Phaseolus vulgaris L.) is a crop of agricultural interest that can accumulate heavy metals and therefore, the possibility of developing mechanisms of tolerance to this type of stress. For these reasons, the work aimed to determine the existence of changes in the plasma membrane and in the antioxidant activity of leaves in bean plants germinated in presence of heavy metals. Seeds of the variety CC-25-9-N were germinated under controlled conditions with six specific concentrations of [Pb.sup.2+], [Ni.sup.2+] and [Cu.sup.2+] cations. Fifteen days after seed's germination, the tolerance limit, the lethal dose and changes in the permeability of the leaf membranes were determined through electrical conductivity, pH and the activity of total peroxidases and guaiacol peroxidase. The variability in the membrane permeability was checked from differences in the values of the electrical conductivity and the pH in each of the treatments, which depended on the metal and the concentration under study, as well as on the activity of the enzymes analyzed. These results suggest a possible specificity in the plant--metal interaction that implicate different response mechanisms. Keywords: beans, toxic metals, oxidative stress, toxicity, peroxidases. En las primeras etapas de la fase vegetativa es donde la planta manifiesta su mayor susceptibilidad a cambios bruscos en las condiciones del medio, desatándose vías adaptativas que incluyen cambios en la estructura de las membranas celulares, por ser las primeras que responden a un daño. El frijol (Phaseolus vulgaris L.) es un cultivo de interés agrícola que puede acumular metales pesados y, por consiguiente, desarrollar mecanismos de tolerancia a este tipo de estrés. Por estas razones el trabajo tuvo como objetivo determinar la existencia de cambios en la membrana plasmática y en la actividad antioxidante de hojas de plantas de frijol germinadas en presencia de metales pesados. Semillas de la variedad CC-25-9-N fueron germinadas en condiciones controladas en presencia de seis concentraciones específicas para los cationes [Pb.sup.2+], [Ni.sup.2+] y [Cu.sup.2+]. A los 15 días después de la germinación se determinó el límite de tolerancia, la dos