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DOI: 10.1055/s-2005-872989
Georg Thieme Verlag Stuttgart KG · New York
Growth-Promoting Nitrogen Nutrition Affects Flavonoid Biosynthesis in Young Apple (Malus domestica Borkh.) Leaves
Publication History
Received: April 28, 2005
Accepted: October 14, 2005
Publication Date:
02 January 2006 (online)


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”.
Key words
Phenylalanine ammonia-lyase (PAL) - chalcone synthase/chalcone isomerase (CHS/CHI) - flavanone 3-hydroxylase (FHT) - flavonol synthase (FLS) - dihydroflavonol 4-reductase (DFR) - nitrogen nutrition - apple leaf - hydroxycinnamic acids - dihydrochalcones - flavonols - flavanols