Differential Expression of Genes Encoding Enzymes Involved in Sulfur Assimilation Pathways in Response to Wounding and Jasmonate in Arabidopsis thaliana

Effects of mechanical wounding on levels of transcripts encoding enzymes involved in the sulfur assimilation pathway were examined. RNA blot hybridization showed the sulfate transporter, ATP sulfurylase, adenosine phosphosulfate (APS) kinase, APS reductase and cysteine synthase, all but the first being chloroplastic isozymes differentially responding to wounding, and also to jasmonate, a powerful inducer ofwound responsive gene expression. When plants were exposed to jasmonate, transcripts for APS kinase were increased within 1h after treatment, while those for APS reductase were increased after 3 h. We also found the glucosinolate content to be 2-fold elevated at the latter time point. APS is directed to the secondary metabolic pathway by APS kinase, so that glucosinolates are synthesized, while it is allotted through the action ofAPS reductase to the primary metabolic pathway by which cysteine is synthesized. Consequently, our results suggest that wounded plants primarily deliver available sulfur to synthesize defense-related substances by activating genes involved in the secondary metabolic pathway.