Abstract
Seeds have devised sophisticated mechanisms to cope with adverse situations. Among these mechanisms the collectively referred to as redox homeostasis. We have investigated the thioredoxin (Trx)/NADPH/NADPH-dependent thioredoxin reductase (NTR) systems during the pea (Pisum sativum L.) seed germination under heavy metal stress. Cotyledon and embryonic axis were analyzed between 0 and 5 days of germination in the presence or absence of cadmium (Cd). Under Cd stress conditions, NTR activity and Trx h3 and Trx h4 expression were stimulated, while the overall activity of Trx decreased. When incubated with Cd ions in vitro, the disulfide reductase activity of Trx h3 and f isoforms was drastically inhibited, probably through the formation of protein dimers as evidenced by the electrophoresis analysis. The NADPH status was also affected, since Cd treatment provoked an increase in oxidized state of coenzyme as compared to control redox ratio. The contribution of Trx system to the redox regulation during the germination is discussed in relation with the Cd-caused oxidative stress.