THE JASMONATE PATHWAY IS INVOLVED DIFFERENTIALLY IN THE REGULATION OFDIFFERENT DEFENSE RESPONSES IN TOBACCO CELLS

Jasmonic acid, a product of the lipoxygenase (LOX) pathway, has been p roposed to be a signal transducer of defence reactions in plants. We h ave reported previously that methyl jasmonate (WJ) induced accumulatio n of proteinase inhibitors in tobacco cell suspensions (Rickauer et al ., 1992, Plant Physiol Biochem 30: 579-584). The role of this compound in the induction of this and of other defence reactions is further st udied in this paper. Treatment of tobacco cell suspensions with an eli citor from Phytophthora parasitica var. nicotianae induced a rapid and transient increase ill jasmonic acid levels, which was abolished when cells were preincubated with eicosatetraynoic acid (ETYA), an inhibit or of LOX. Pretreatment with ETYA also inhibited the induction of prot einase inhibitors by fungal elicitor, but not by MJ. Linolenic acid, a precursor of jasmonate biosynthesis, induced this defence response, w hereas linoleic acid had no effect. Expression of defence-related gene s encoding proteinase inhibitor II, hydroxyproline-rich or glycine-ric h glycoproteins, glucanase and chitinase, was induced in a basically s imilar manner by fungal elicitor or MJ. However, ETYA did not inhibit, or only partially inhibited, the elicitation of these defence genes. Expression of the sesquiterpene cyclase (5-epi-aristolochene synthase) gene was not induced by MJ, but only by fungal elicitor, and ETYA pre treatment had no effect on this induction. The obtained results indica te that synthesis of jasmonate via the LOX pathway seems to be only pa rt of a complex regulatory mechanism for the onset of many, but not al l, defence reactions.