IN-SITU LOCALIZATION OF PHENYLPROPANOID BIOSYNTHETIC MESSENGER-RNAS AND PROTEINS IN PARSLEY (PETROSELINUM-CRISPUM)

Using in situ RNA/RNA hybridization, enzyme immunolocalization, and hi stochemical techniques, several phenylpropanoid biosynthetic activitie s and products were localized in tissue sections from various aerial p arts of parsley (Petroselinum crispum) plants at different development al stages. The enzymes and corresponding mRNAs analyzed included two r epresentatives of general phenylpropanoid metabolism: phenylalanine am monia-lyase (PAL) and 4-coumarate:CoA ligase (4CL), and one representa tive each from two distinct branch pathways: chalcone synthase (CHS; f lavonoids) and S-adenosyl-L-methionine: bergaptol O-methyltransferase (BMT; furanocoumarins). In almost all cases, the relative timing of ac cumulation differed greatly for mRNA and protein and indicated short e xpression periods and short half-lives for all mRNAs as compared to th e proteins. PAL and 4CL occurred almost ubiquitously in cell type-spec ific patterns, and their mRNAs and proteins were always coordinately e xpressed, whereas the cell type-specific localization of flavonoid and furanocoumarin biosynthetic activities was to a large extent mutually exclusive. However, the distribution patterns of CHS and BMT, when su perimposed, closely matched those of PAL and 4CL in nearly all tissues analysed, suggesting that the flavonoid and furanocoumarin pathways t ogether consituted a large majority of the total phenylpropanoid biosy nthetic activity. Differential sites of synthesis and accumulation ind icating intercellular translocation were observed both for flavonoids and for furanocoumarins in oil ducts and the surrounding tissue. The w idespread occurrence of both classes of compounds, as well as selected , pathway-specific mRNAs and enzymes, in many cell types of all parsle y organs including various flower parts suggests additional functions beyond the previously established roles of flavonoids in UV protection and furanocoumarins in pathogen defence.