B₁-phytoprostanes trigger plant defense and detoxification responses

Phytoprostanes are prostaglandin/jasmonate-like products of nonenzymatic lipid peroxidation that not only occur ubiquitously in healthy plants but also increase in response to oxidative stress. In this work, we show that the two naturally occurring B₁-phytoprostanes (PPB₁) regioisomers I and II (each comprising two enantiomers) are short-lived stress metabolites that display a broad spectrum of biological activities. Gene expression analysis of Arabidopsis (Arabidopsis thaliana) cell cultures treated with PPB ₁-I or -II revealed that both regioisomers triggered a massive detoxification and defense response. Interestingly, expression of several glutathione S-transferases, glycosyl rransferases, and putative ATP-binding cassette transporters was found to be increased by one or both PPB₁ regioisomers, and hence, may enhance the plant's capacity to inactivate and sequester reactive products of lipid peroxidation. Moreover, pretreatment of tobacco (Nicotiana tabacum) suspension cells with PPB₁ considerably prevented cell death caused by severe CuSO₄ poisoning. Several Arabidopsis genes induced by PPB₁, such as those coding for adenylylsulfate reductase, tryptophan synthase β-chain, and PAD3 pointed to an activation of the camalexin biosynthesis pathway that indeed led to the accumulation of camalexin in PPB₁ treated leaves of Arabidopsis. Stimulation of secondary metabolism appears to be a common plant reaction in response to PPB₁. In three different plant species, PPB ₁-II induced a concentration dependent accumulation of phytoalexins that was comparable to that induced by methyl jasmonate. PPB₁-I was much weaker active or almost inactive. No differences were found between the enantiomers of each regioisomer. Thus, results suggest that PPB₁ represent stress signals that improve plants capacity to cope better with a variety of stresses.