Does Exogenous Application of Melatonin Ameliorate Lead Toxicity in Eruca vesicaria Plants?

Abstract

Melatonin (N-acetyl-5-methoxytryptamine) is receiving a considerable interest due to its prospected role in alleviating the oxidative stress in plants. Thus a step toward the profitable use of melatonin (ME) in agriculture, our study investigated the exogenous application of ME in Eurica sativa grown in contaminated soil amended with lead nitrate Pb(NO3)2 to produce Pb levels of 350 mg/kg. Melatonin was applied during two periods of plant life by two methods: priming of seeds for 12 hr [0.0 µM/l (P0); 25 µM/l (P1) and 50 µM/l (P2)] and by foliar spray at seedling foliage [0.0 µM/l (F0 and); 25 µM/l (F1) 50 µM/l (F2)]. Rocket plants affected by Pb toxicity reduced significantly the growth characteristics (shoot & root, fresh and dry weight and leaf area/plant), photosynthetic pigments (chlorophyll a, chlorophyll b, carotenoids), photosynthetic activity (4CO2-assimilation), photosynthetic enzymes (phosphoenolpyruvate carboxylase and ribulose-1,5-bisphosphate-carboxylase/oxygenase). Meanwhile, Exogenous application of ME appears to ameliorate toxic effects of lead by improving the above criteria as compared to the control or Pb treated plants. These results showed that ME can promote the growth of Eurica sativa growing in Pb-contaminated soil by stimulating the photosynthetic activity, and the foliar spray method is the optimum at a dose of ME (50 µM/l).