In situ Localization of Phenylpropanoid-Related Gene Expression in Different Tissues of Light- and Dark-Grown Parsley Seedlings

Using in situ R N A hybridization and immunohistochemical techniques, we investigated the tissue-specific and light-dependent expression o f four genes involved in phenylpropanoid metabolism in various parts o f parsley ( Petroselinum crispum) seedlings. The genes encode phenylalanine ammonia-lyase (PAL) and 4-coumarate: Co A ligase (4 CL), two enzymes o f general phenylpropanoid metabolism; chalcone synthase (CHS), the key enzyme o f flavonoid biosynthesis; and bergaptol O-methyltransferase (BMT), a late enzyme o f the furanocoumarin pathway. In young leaves, PAL and 4 CL genes were expressed predominantly and in a coordi­ nated fashion in epidermal cells, young xylem cells o f vascular bundles, and epithelial cells o f oil ducts. The gene(s) encoding BMT was active exclusively in the epithelial cells o f oil ducts, whereas CHS gene expression was largely confined to the epidermis. In shoot and root apices, PAL, 4 CL and CHS m R N A s were detectable at low levels without distinct patterns. The cor­ responding proteins, however, accumulated preferentially in the protoderm and pith meristem o f the shoot apex and in root-cap cells. A gene encoding pathogenesis-related protein 1 (PR 1) was analyzed in roots for comparison and was found to be expressed predominantly in the cortical cells o f root tips. The expression o f all genes investigated was, to a greater or lesser extent, dependent on light conditions and tissue age, with highest levels occurring in newly differentiated, light-exposed tissue. In the leaf epidermis o f seedlings illuminated for 20 h, PAL and CHS m R N A s and proteins, as well as 4 CL protein, were particularly abundant.