Protective Effect of Hydrogen Peroxide against Paraquat Toxicity in Young Pea Plants: Possible Role of Endogenous Polyamines

Abstract

Young pea plants grown as a water culture were sprayed with hydrogen peroxide and 24 h later were treated with the herbicide paraquat. The effects of paraquat and H 2 O 2 treatment were investigated on the endogenous concentrations of free proline, and free and conjugated putrescine, spermidine and spermine. Application of PQ increased the free proline and Put, and decreased conjugated and bound polyamines. The results clearly demonstrate the oxidative damages provoked by PQ application. Single treatment with H 2 O 2 provoked considerable decrease in the free fraction of the three PAs studied 2 h after light exposition, but caused an increase in their respective conjugated fractions. Data suggest that PA changes after H 2 O 2 treatment are due to conversion from free to conjugated form. Three hours later free PAs in H 2 O 2 treated-plants reached control levels; however the conjugated remained higher than the control. No alterations were detected in proline concentration after H 2 O 2 treatment. Pretreatment with Н 2 О 2 activated some component of the plant protection mechanisms by causing an alteration in free/conjugated PAs ratio in plants subsequently subjected to PQ treatment. Data concerning PA and proline concentrations in plants treated with both compounds supposed that H 2 O 2 shows a protective role against PQ and improves the plant tolerance to the oxidative stress generated by paraquat.