Submitted to: Journal of Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/11/2011
Publication Date: 5/21/2011
Citation: Yu, M., Shen, L., Zhang, A., Zheng, J. 2011. Methyl jasmonate-induced defense responses are associated with elevation of 1-aminocyclopropane-1-carboxylate oxidase in Lycopersicon esculentum fruit. Journal of Plant Physiology. 168(15):1820-1827. Interpretive Summary: Environmental signals can induce the biosynthesis of plant hormones. Ethylene is a classic plant hormone responsible for the regulation of plant growth and development. The current study expands earlier findings that the chemical methyl jasmonate (MeJA), a substance used in plant defense and many diverse developmental pathways, induced a defense response closely related to ethylene biosynthesis in plants. By using tomato fruit as a model plant, we demonstrated that an enzyme which catalyses the last step of ethylene biosynthesis is involved in MeJA induced resistance by regulation of certain defense enzymes. This finding will help researchers and growers understand defense mechanisms undertaken by plants during external attack such as drought, chilling, wounding, or pathogen infection. It will also help develop strategies to protect plants from such attacks during plant growth, development, and storage.
Technical Abstract: 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 -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 -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.