Organ‐ and Tissue‐specific Biosynthesis of Flavonoids in Seedlings of Oenothera odorata (Onagraceae)

Abstract

AbstractIn developing Oenothera odorata seedlings, phytochrome‐mediated accumulation of various flavonoids (mainly glycosides of cyanidin and quercetin) is detectable, subsequent to a transient induction of the key enzymes of the general phenylpropanoid metabolism, L‐phenylalanine ammonia lyase (PAL) and of flavonoid biosynthesis, chalcone synthase (CHS). Organ‐ and tissue‐specific distribution of these enzymes and of the flavonoid end products was investigated in seedlings, irradiated with continuous far‐red light.Anthocyanins and quercetin glycosides are mainly localized in both the upper and lower epidermis of the cotyledons and to a lesser extent also in the epidermal cell layer of the hypocotyl. An obvious organ‐specific distribution was observed for the anthocyanins: cyanidin‐3,5‐O‐diglucoside accumulates in the epidermal cells of the cotyledons, whereas cyanidin‐3‐O‐glucoside is restricted to the epidermis of the hypocotyl. By contrast the pattern of quercetin glycosides is the same in the cotyledons and in the hypocotyl. The methylated flavonol aglycone 3‐0‐methylquercetin was found to be localized in the seed coat. According to this organ‐ and tissue‐specific pattern of flavonoids, immunochemical and immunohistochemical detection of PAL and CHS revealed a predominant localization of theenzymes in the epidermal layers of the cotyledons and the hypocotyl but also in the cells surrounding the vascular bundles. The role of compartmentation in regulation of flavonoid biosynthesis and putative functions of flavonoid compounds are discussed.