Elicitor-induced Oxidative Burst and Phenylpropanoid Metabolism in Pinus radiata Cell Suspension Cultures

A cell wall elicitor preparation from the needle pathogen Dothistroma pini was used to induce defence responses in Pinus radiata cell suspension cultures. Addition of elicitor to cell suspensions induced a rapid, transient burst in the accumulation of H2O2, with maximal response between 20 and 40 min post-elicitation. The protein kinase inhibitors staurosporine and K252a inhibited H2O2 accumulation showing that protein phosphorylation is required in the signal transduction pathway leading to the oxidative burst. Over a more extended time period elicitation of suspension cells lead to the activation of phenylpropanoid biosynthesis. The activity of phenylalanine ammonia-lyase (EC 4.3.1.5), the first enzyme in the phenylpropanoid biosynthetic pathway, increased 8-fold following elicitation with maximal activity 36 h post-elicitation. The activity of cinnamyl alcohol dehydrogenase (EC 1.1.1.195), an enzyme involved in lignin biosynthesis, increased 2.5-fold with maximal response 48–72 h post-elicitation. Thioglycolic acid extractable material increased 2-fold with maximal response 48–72 h post-elicitation, and phloroglucinol–HCl-positive material increased over the same time course. These data show that P. radiata suspension cells are an excellent model system for investigating the biochemistry and enzymology of pathogen defence responses in P. radiata.