Abstract
Methods involving in situ RNA hybridization, immunohistochemistry, and microspectrophotometry of individual cells were used to localize the mRNA encoding chalcone synthase (the key enzyme of flavonoid biosynthesis), the enzyme protein, and the biosynthetic end products in cross sections of parsley leaves (Petroselinum crispum). The light-dependent, sequential occurrence of all three components was restricted to epidermal cells. The results are in agreement with the putative function of flavonoids (transcriptionally inducible, UV-protective pigments) and suggest that all biosynthetic steps occur in those cells in which the products accumulate.