Cadmium causes oxidative damage in Bradyrhizobium sp. strains and peanut plant.

ELIANA BIANUCCI, JESICA RIVADENEIRA, ADRIANA FABRA, STELLA CASTRO,

Carlos Paz

Congreso; IV Congreso Argentino de Microbiologia General; 2009

SAMIGE

Cadmium is one of the most harmful heavy metals in nature and its high toxicity even at low concentration, represents a serious threat to microorganisms and plants of high agronomic value. Its entry in the agricultural soils arises from commonly used practices such as the application of phosphate fertilizers that contain Cd as a trace element. Some of the deleterious effects induced by Cd have been associated with alterations in the oxidative status of the cell. Microorganisms and plants posses both enzymatic and non-enzymatic defence systems to maintain the cellular redox state and to mitigate the damage caused by oxidative stress. The molecule of glutathione (GSH) and the enzymes related to its metabolism glutathione reductase (GR), glutathione peroxidase (GPx) and glutathione S-transferase (GST) are known to be involved in the defence mechanism against heavy metals. In previous works, we studied the effect of Cd on growth and GSH content in <i>Bradyrhizobium</i> sp. strains (peanut microsymbionts). <i>Bradyrhizobium</i> sp. SEMIA6144 was sensitive while <i>Bradyrhizobium</i> sp. NLH25 was tolerant since they grew up to 10 and 30 ìM Cd, respectively. The increase in the GSH content in the tolerant strains suggested that this thiol is involved in tolerance. The objectives of this work were to: 1) dilucidate the role of GR, GPx and GST enzymes in Cd tolerance in <i>Bradyrhizobium</i> sp. strains; 2) evaluate the effect of Cd on peanut growth. The microorganisms were grown in YEM medium supplemented with the maximum Cd concentration that allows them to grow. Plants were grown in Hoagland medium at different Cd concentrations ranging from 0 to 100 ìM. <i>Bradyrhizobium</i> sp. strains showed that GR activity increased only in the tolerant strain; meanwhile GPx activity increased in both strains exposed to Cd. In contrast, GST activity decreased in both strains with Cd. The capacity to maintain GSH/GSSG ratio mediated by the increase of GR activity, could be one of the causes of tolerance in <i>Bradyrhizobium</i> sp. NLH 25. At 10 ìM Cd, peanut growth was affected and an enhance in the concentration of 2-thiobarbituric acid reactive material (lipid peroxidation products) in roots was observed, presumably due to Cd-induced oxidative stress.