Phenylalanine ammonia-lyase activity and phenolic compounds accumulation in nitrogen-deficient Matricaria chamomilla leaf rosettes

Phenylalanine ammonia-lyase (PAL) activity, accumulation of 11 phenolic acids and 3 coumarin-related compounds (herniarin and its glucosidic precursors (Z)- and (E)-2-β-d-glucopyranosyloxy-4-methoxycinnamic acids; umbelliferone), biomass production, plant water content and lipid peroxidation status of Matricaria chamomilla L. leaf rosettes subjected to nitrogen (N) deficiency over 12 days were studied. Both biomass and water content of N-deficient rosettes decreased in comparison to controls, while quantities of most benzoic acids (p-hydroxybenzoic, syringic, vanillic), cinnamic acids (caffeic, chlorogenic, o- and p-coumaric, ferulic), herniarin and (Z)- and (E)-2-β-d-glucopyranosyloxy-4-methoxycinnamic acids increased with prolonged nitrogen deficiency. However, three benzoic derivatives (gallic acid, protocatechuic acid and protocatechuicaldehyde) did not differ significantly from the controls. The content of umbelliferone, a stress metabolite in the leaves of chamomile, was not affected by N deficiency. It thus appears that synthesis of benzoic and cinnamic acids and of coumarins is probably regulated independently. PAL activity was significantly higher in N-deficient leaf rosettes after 4 and 8 days (by 61 and 23%, respectively), but decreased to control level by the end of the experiment. Nevertheless, it can be concluded that this is important biochemical factor contributing to the observed increase of phenolic compounds accumulation by producing nitrogen-free skeletons of t-cinnamate for subsequent pathways of phenylpropanoid metabolism. We also observed that the mechanism of nitrogen deficiency tolerance due to enhanced PAL activity is temporally limited. The non-altered extent of lipid peroxidation expressed as malondialdehyde amounts revealed that membrane integrity was not affected by N deficiency. This phenomenon in correlation to the antioxidative properties of phenolic metabolites is also discussed.