The effect of MeJA on ethylene biosynthesis and induced disease resistance to Botrytis cinerea in tomato

Methyl jasmonate (MeJA), a major derivative of the plant hormone jasmonic acid, plays a critical role in inducing resistance to fungal pathogen. To study the endurance of MeJA-induced resistance and its cause. green mature tomatoes (Solanum esculentum cv. Lichun) were treated with 100 mu M MeJA and nordihydroguaiaretic acid (NDGA, LOX inhibitor) at -35 kPa for 0.5 min and incubated at 25 +/- 1 degrees C, 85-90% RH. Treatment with MeJA reduced disease symptoms in tomato fruit soon after being inoculated with Botrytis cinerea. Lesion size in MeJA-treated fruit was inhibited by 42.5%. 27.9% and 13.9% respectively (P<0.05) in fruit inoculated 1, 3 and 6 d after treatments. At advanced stages (inoculation carried out 9 and 12 d after treatments), no inhibitory effect of MeJA were found. Ethylene biosynthesis was activated in the response of green mature tomatoes to methyl jasmonate with a rapid (I d) and enhanced ethylene peak (0.9 ng kg(-1) FW s(-1)). However the ethylene level was below that of the control from 6 d to 12 d. This rise was closely related with conversion of ACC to ethylene, especially a rise in ACO activity (6 h), which preceded an increase in ACS (12 h) after MeJA treatment. The development of ethylene biosynthesis was accompanied by a significant increase in LOX activity. Two significant O-2(center dot-) peaks (P<0.05) were detected in MeJA-treated fruit during storage (6.18 mu mol g(-1) FW min(-1) at 6 h and 5.68 mu mol g(-1) FW min(-1) at 3 d). The correlations between LOX, and O-2(center dot-) and ACO activities were 0.75, 0.73 respectively (P<0.05). These results indicate that MeJA-induced resistance against B. cinerea is durable, MeJA induces LOX and the superoxide radicals formed by LOX may activate ACO and ethylene biosynthesis. (C) 2009 Published by Elsevier B.V.