THE EXPRESSION PATTERN OF ALFALFA FLAVANONE 3-HYDROXYLASE PROMOTER-GUS FUSION IN NICOTIANA-BENTHAMIANNA CORRELATES WITH THE PRESENCE OF FLAVONOIDS DETECTED IN-SITU

Flavanone 3-hydroxylase is an enzyme acting in the central part of the flavonoid biosynthesis pathway. It is generally encoded by a single g ene and seems to have a key position for the regulation in this pathwa y. These two features make a single f3h promoter-gus fusion a suitable tool to study both the f3h expression and the regulation of this path way. We present here the spatial and temporal analysis of the expressi on of an alfalfa flavanone 3-hydroxylase (f3h) promoter-gus fusion int roduced into Nicotiana benthamiana. The Medicago sativa (alfalfa) f3h promoter directed gus expression in flowers, stems, leaves and roots. In flowers, GUS activity was observed in pollen grains, in ovules, in ovary placenta and in the epidermis, medullary parenchyma, trichomes a nd second cortical cellular layer surrounding the vascular bundles of the peduncle. In stems, GUS activity was detected at the same places a s in the peduncle except for the medullary parenchyma. In roots, we fo und GUS staining in root hairs, epidermis and in the vascular bundles of the elongated zone. Finally, in leaves, the f3h promoter expressed essentially in the stalk cells of the multicellular trichomes. The exp ression pattern of the f3h-gus fusion was correlated to the presence o f flavonoids in situ. These data indicate that this construct can be v ery useful to study factors controlling the production of flavonoids.