How Changes in Nitrogen Levels Impact Metabolites and Physiological Features of Hypericum androsaemum

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Abstract
Background: The manipulation of mineral nutrition may affect secondary metabolite production and thus determine the nutritional value of food/medicinal plants. Objectives: The present study investigated the impact of nitrogen supply on the production of secondary metabolites and physiological parameters of Hypericum androsaemum plants grown in sand culture. Methods: Four-week plants were irrigated by full-strength Hoagland solution (control), nitrate was reduced to 1/3, and no nitrate was provided for 14 days. Results: The growth of shoots was inhibited by nitrate limitation, but root growth was stimulated. Soluble proteins and water content were significantly affected by nitrate deficiency. Antioxidative enzyme activities (ascorbate peroxidase (APX) and superoxide dismutase (SOD)) were increased due to nitrate deficiency. Treatment of plants with NO3- deficiency caused an increase in total soluble phenols and phenylalanine ammonia-lyase (PAL) activity, while flavonoid content was mainly elevated by NO3- deficiency. At the level of specific metabolites, NO3- deficiency positively affected hypericin and pseudohypericin content but decreased hyperforin content. The expression of the putative gene for hypericin biosynthesis (hyp-1) was up-regulated in response to nitrate deficiency. Conclusions: The results demonstrated that the nitrogen deficiency in the H. androsaemum plant positively affected the antioxidant system, valuable phenols, and secondary metabolites.

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