Investigating the effect of methyl jasmonate and melatonin on resistance of Malus crabapple 'Hong Jiu' to ozone stress

Ozone (O-3) is an adverse environmental factor posing damage to ornamental plants. Thus, it is important to seek an effective way of enhancing plant tolerance to O-3-induced damage. Methyl jasmonate (MJ) and melatonin (MT) are plant growth regulators (PGRs) involved in plant abiotic stress responses. In this study, compared with the control group of plants without ozone, the influence of exogenous MJ (0, 10, 50, 100, and 150 mu M) and MT (0, 0.1, 0.5, 2.5, and 12.5 mu M) on the resistance of Malus crabapple 'Hong Jiu' was evaluated under O-3 stress (100 +/- 10 nL/L for 3 h). Our data revealed that levels of MDA were significantly enhanced following O-3 treatment compared with plants without O-3. O-3 induced the activities of antioxidant enzymes and the accumulation of non-enzymatic antioxidants. While lower malondialdehyde (MDA) content, greater activities of antioxidant enzymes, and higher levels of soluble protein and non-enzymatic antioxidants were observed in PGRs-pretreated plants than in non-PGRs-pretreated plants under O-3 stress. Based on the above results and air pollution tolerance index (APTI), an exogenous supply of MJ and MT to Malus crabapple 'Hong Jiu' seedlings was protective for O-3-induced toxicity. The present study provides new insights into the mechanisms of MJ and MT amelioration of O-3-induced oxidative stress damages in Malus crabapple 'Hong Jiu.'