Methyl jasmonate-induced defense responses are associated with elevation of 1-aminocyclopropane-1-carboxylate oxidase in Lycopersicon esculentum fruit

It has been known that methyl jasmonate (MeJA) interacts with ethylene to elicit resistance. In green mature tomato fruits (Lycopersicon esculentum cv. Lichun), 0.02 mM MeJA increased the activity of 1-aminocyclopropane-1-carboxylate oxidase (ACO), and consequently influenced the last step of ethylene biosynthesis. Fruits treated with a combination of 0.02 MeJA and 0.02 α-aminoisobutyric acid (AIB, a competitive inhibitor of ACO) exhibited a lower ethylene production comparing to that by 0.02 mM MeJA alone. The increased activities of defense enzymes and subsequent control of disease incidence caused by Botrytis cinerea with 0.2 mM MeJA treatment was impaired by AIB as well. A close relationship (P < 0.05) was found between the activity alterations of ACO and that of chitinase (CHI) and β-1,3-glucanase (GLU). In addition, this study further detected the changes of gene expressions and enzyme kinetics of ACO to different concentrations of MeJA. LeACO1 was found the principal member from the ACO gene family to respond to MeJA. Accumulation of LeACO1/3/4 transcripts followed the concentration pattern of MeJA treatments, where the largest elevations were reached by 0.2 mM. For kinetic analysis, Km values of ACO stepped up during the experiment and reached the maximums at 0.2 mM MeJA with ascending concentrations of treatments. Vmax exhibited a gradual increase from 3 h to 24 h, and the largest induction appeared with 1.0 mM MeJA. The results suggested that ACO is involved in MeJA-induced resistance in tomato, and the concentration influence of MeJA on ACO was attributable to the variation of gene transcripts and enzymatic properties.