Cyclopentenone isoprostanes induced by reactive oxygen species trigger defense gene activation and phytoalexin accumulation in plants

Abstract

Summary: Lipid peroxidation may be initiated either by lipoxygenases or by reactive oxygen species (ROS). Enzymatic oxidation of α‐linolenate can result in the biosynthesis of cyclic oxylipins of the jasmonate type while free‐radical‐catalyzed oxidation of α‐linolenate may yield several classes of cyclic oxylipins termed phytoprostanes in vivo. Previously, we have shown that one of these classes, the E 1‐phytoprostanes (PPE 1), occurs ubiquitously in plants. In this work, it is shown that PPE 1 are converted to novel cyclopentenone A 1‐ and B 1‐phytoprostanes (PPA 1 and PPB 1) in planta. Enhanced formation of PPE 1, PPA 1, and PPB 1 is observed after peroxide stress in tobacco cell cultures as well as after infection of tomato plants with a necrotrophic fungus, Botrytis cinerea. PPA 1 and PPB 1 display powerful biologic activities including activation of mitogen‐activated protein kinase (MAPK) and induction of glutathione‐S‐transferase (GST), defense genes, and phytoalexins. Data collected so far infer that enhanced phytoprostane formation is a general consequence of oxidative stress in plants. We propose that phytoprostanes are components of an oxidant‐injury‐sensing, archaic signaling system that serves to induce several plant defense mechanisms.