In Situ Localization of Phenylpropanoid Biosynthetic mRNAs and Proteins in Parsley (Petroselinum crispum)

Abstract

Abstract:Using in situ RNA/RNA hybridization, enzyme immunolocalization, and histochemical techniques, several phenylpropanoid biosynthetic activities and products were localized in tissue sections from various aerial parts of parsley (Petroselinum crispum) plants at different developmental stages. The enzymes and corresponding mRNAs analyzed included two representatives of general phenylpropanoid metabolism: phenylalanine ammonia‐lyase (PAL) and 4‐coumarate: CoA ligase (4CL), and one representative each from two distinct branch pathways: chalcone synthase (CHS; flavonoids) and S‐adenosyl‐L‐methionine: bergaptol O‐methyltransferase (BMT; furanocoumarins). In almost all cases, the relative timing of accumulation differed greatly for mRNA and protein and indicated short expression periods and short half‐lives for all mRNAs as compared to the proteins. PAL and 4CL occurred almost ubiquitously in cell type‐specific patterns, and their mRNAs and proteins were always coordinately expressed, 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 superimposed, closely matched those of PAL and 4CL in nearly all tissues analysed, suggesting that the flavonoid and furanocoumarin pathways together consituted a large majority of the total phenylpropanoid biosynthetic activity. Differential sites of synthesis and accumulation indicating intercellular translocation were observed both for flavonoids and for furanocoumarins in oil ducts and the surrounding tissue. The widespread occurrence of both classes of compounds, as well as selected, pathway‐specific mRNAs and enzymes, in many cell types of all parsley organs including various flower parts suggests additional functions beyond the previously established roles of flavonoids in UV protection and furanocoumarins in pathogen defence.