Dimethylthiourea, a hydrogen peroxide trap, partially prevents stress effects and ascorbate peroxidase increase in spermidine‐treated maize roots

Inhibition of root growth and accumulation of putrescine caused by exogenous spermidine in roots of maize seedlings (Zea mays L., cv Samodek) were partially prevented by a concomitant treatment with dimethylthiourea (DMTU), that traps H2O2 produced from spermidine by the activity of polyamine oxidase (PAO) in the apoplast. Treatment with spermidine caused a strong increase of ascorbate peroxidase (APX) gene expression, that was induced to a lesser extent by removing spermidine‐generated H2O2 by DMTU. Over‐expression of APX was associated with increased APX activity in spermidine‐treated seedlings whereas the addition of DMTU to spermidine completely prevented spermidine‐induced increase of APX activity. Thus, DMTU permitted the demonstration that exogenous spermidine supplied to maize seedlings causes an oxidative stress and induces APX, a key enzyme of the antioxidant defence mechanism, through H2O2, a spermidine catabolic product.