title: Growth-promoting nitrogen nutrition affects flavonoid biosynthesis in young apple (Malus domestica Borkh.) leaves.
abstract: Enhanced shoot growth and a decrease in flavonoid concentration in apple trees grown under high nitrogen (N) supply was observed in previous studies, along with increasing scab susceptibility of cultivar "Golden Delicious" after high N nutrition. Several hypotheses have suggested that there is a trade-off between primary and secondary metabolism because of competition for common substrates, but nothing is known about regulation at the enzyme level. In this study, a set of experiments was performed to elucidate the effect of N nutrition on the activities of key enzymes involved in flavonoid biosynthesis (phenylalanine ammonia-lyase [PAL], chalcone synthase/chalcone isomerase [CHS/CHI}, flavanone 3-hydroxylase [FHT], flavonol synthase [FLS], dihydroflavonol 4-reductase [DFR]) and the accumulation of different groups of phenylpropanoids. The inhibition of flavonoid accumulation by high N nutrition could be confirmed, but the influence of N supply on the flavonoid enzymes CHS/CHI, FHT, DFR, and FLS was not evident. However, PAL activity seems to be downregulated, thus forming a bottleneck resulting in a generally decreased flavonoid accumulation. Furthermore, the response of the scab-resistant cultivar "Rewena" to high N nutrition was not as strong as that of the susceptible cultivar "Golden Delicious".
authors.affiliation: Department für Pflanzenwissenschaften, Fachgebiet Obstbau, Technische Universität München-Weihenstephan, Alte Akademie 16, 85350 Freising, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Strissel
authors.forename: H
authors.initials: H
authors.lastname: Halbwirth
authors.forename: U
authors.initials: U
authors.lastname: Hoyer
authors.forename: C
authors.initials: C
authors.lastname: Zistler
authors.forename: K
authors.initials: K
authors.lastname: Stich
authors.forename: D
authors.initials: D
authors.lastname: Treutter
mesh_terms: D018533:Biomass; D005419:Flavonoids / Q000096:biosynthesis*; D027845:Malus / Q000187:drug effects* / Q000201:enzymology / Q000254:growth & development* / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism / Q000494:pharmacology*; D018515:Plant Leaves / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism*; D018520:Plant Shoots / Q000187:drug effects / Q000254:growth & development
chemical_list: D005419:Flavonoids; D009584:Nitrogen