Influence of nitrogen on the production of hypericins by St. John's wort

The effect of nitrogen supply on the production of 'hypericins' (hypericin and pseudohypericin) in leaves of St. John's wort (Hypericum perforatum L.) was examined with plants grown in sand culture and soil. In sand culture, 56-d growth of St. John's wort plants with decreased nitrogen levels result ed in increased production of hypericins in leaves. A short-term low nitrog en stress in sand culture also resulted in increased production of leaf hyp ericins. While growth in a low nitrogen-containing soil resulted in elevate d levels of hypericins, their production was decreased by supplementation o f the soil with additional nitrogen. Increased production of hypericins in St. John's wort leaves did not require the nitrogen supply to be decreased to levels that resulted in nitrogen deficiency symptoms. Moreover, alterati on in the production of leaf hypericins occurring with changes in nitrogen supply did not alter the concentration ratio of pseudohypericin and hyperic in. Increased production of leaf hypericins was not associated with any sig nificant changes in the number of dark glands on the leaves and only a weak correlation was observed between leaf dark gland number and levels of leaf hypericins. These results are discussed in terms of the biochemistry of na phthodianthrone production by St. John's wort plants and implications for g rowth environment effects during cultivated growth of this medicinal plant. (C) 2000 Editions scientifiques et medicales Elsevier SAS.