lnvolvement of de Novo Protein Synthesis, Protein Kinase, Extracellular Ca2+, and Lipoxygenase in Arachidonic Acid lnduction of 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Genes and lsoprenoid Accumulation

A series of inhibitors were tested to determine the participation of de novo protein synthesis, protein kinase activity, extracellular Ca’+, and lipoxygenase adivity in arachidonic acid elicitation of 3hydroxy-3-methylglutaryl coenzyme A reductase (HMCR) gene expression and sesquiterpene phytoalexin biosynthesis in potato (Solanum tuberosum 1. cv Kennebec). Cene-specific probes were used to discriminate effects on the expression of two HMCR genes (hmgl and hmg2) that respond differentially in tuber tissue following wounding or elicitor treatment. lnhibition of protein synthesis with cycloheximide completely blocked arachidonate-induced hypersensitive necrosis and browning, including HMCR gene induction and phytoalexin accumulation. This suggests that proteins necessary for coupling arachidonic acid reception to HMGR mRNA accumulation are either rapidly turned over or not present constitutively and are induced following elicitor treatment. Staurosporin, a potent inhibitor of protein kinases, and ethyleneglycol-bis(& aminoethyl ether)-N,N’-tetraacetic acid, a Ca2+ chelator, inhibited arachidonate-indudion of hmg2 gene expression and phytoalexin accumulation but did not inhibit the wound-induced expression of hmgl. However, staurosporin inhibited arachidonate’s suppression of hmgl gene expression. Eicosatetraynoic acid, a lipoxygenase inhibitor that suppresses elicitor-induced phytoalexin accumulation, also inhibited arachidonate’s suppression of hmgl and induction of hmg2. The results indicate that arachidonate’s suppression of hmgl and adivation of hmg2 depend on a common intermediate or set of intermediates whose generation i s sensitive to the inhibitors tested.