Abstract
Nucleocytoplasmic hybrids derived from the complex-heterozygotes Oenothera berteriana and Oenothera odorata with identical genotypes differing only in their extrachromosomal constitution are a suitable system to study the interrelations between genotype and plasmotype. In the parental form Oenothera odorata and in pairs of reciprocal hybrid seedlings the key enzymes regulating the general phenylpropanoid metabolism (L-phenylalanine ammonia-lyase, PAL) and flavonoid biosynthesis (chalcone synthase, CHS) were examined in relation to flavonoid accumulation using etiolated as well as far-red treated plants. Flavonoids occurring in dark-grown Oenothera seedlings were identified as flavonol aglycones (quercetin; 3-O-methylquercetin) and flavonol glycosides (quercetin-3-O-galactoside; quercetin-3-O-rhamnoside; a quercetin-3-O-glycuronide and a quercetin-3-O-methylglycuronide). Phytochrome mediated irradiation with continuous far-red light induces increased accumulation of the flavonol glycosides and of anthocyanins (cyanidin-3-O-glucoside and cyanidin-3,5-O-diglucoside) in the epidermal tissues of the hypocotyl and of the cotyledons, subsequent to a transient increase in PAL- and CHS synthesis. PAL in Oenothera seedlings is probably regulated by two isoforms with four subunits each, of 75.5 KD (PAL I) and 79.2 KD (PAL II). There is some evidence that only PAL II is involved in flavonoid biosynthesis. Examining far-red treated hybrid seedlings, a directed influence of the extrachromosomal constitution is detectable affecting the synthesis of PAL, CHS and anthocyanins, but not the formation of flavonolglycosides. In darkgrown seedlings only the amount of 3-O-methylquercetin, known to be localized in the testa, seems to be under extranuclear control, but there is no relation to the time courses of PAL- or CHS-accumulation. A model of multiple extranuclear control points affecting flavonoid metabolism in Oenothera seedlings is discussed.
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