Plant–Environment Interactions: Accumulation of Hypericin in Dark Glands of Hypericum perforatum

Abstract

Background and Aims Hypericum perforatum is a perennial herbaceous plant and an extract from this plant has a significant antidepressant effect when administered to humans. The plant is characterized by its secretory glands, also known as dark glands, which are mainly visible on leaves and flowers. The current study evaluates the influence of several environmental factors and developmental stages of the plant on the accumulation and synthesis of hypericin and pseudohypericin (Hy-G), the major bioactive constituents, in H. perforatum plants.Methods The appearance of dark glands on different parts of the plant, under several environmental conditions, was monitored by microscopy. Hy-G concentrations were quantified by high-performance liquid chromatography.Key Results A significant presence of dark glands accompanying the highest concentrations of Hy-G was observed in the stamen tissues more than in any other organ of H. perforatum. A linear relationship between the number of dark glands and net photosynthetic rate of the leaf and Hy-G concentration in the leaf tissue was also established. A very high concentration of Hy-G was measured in the dark-gland tissues, but in the tissues without any dark glands it was almost absent. The presence of emodin, a precursor of Hy-G, at a high concentration in the dark-gland tissues, and its absence in the surrounding tissues was also observed, suggesting that the site of biosynthesis of Hy-G is in the dark-gland cells. A significantly low concentration of Hy-G (occasionally non-detectable) was measured in the xylem sap of the stem tissues. The dark-gland tissues collected from leaves, stems or flowers contained similar concentrations of Hy-G.Conclusions The concentration of Hy-G in various organs of H. perforatum plants is dependent on the number of dark glands, their size or area, not on the location of the dark glands on the plant. The study provides the first experimental evidence that Hy-G is synthesized and accumulates in dark glands.

Sustained Release for St. John?s Wort: A Rational Idea?

“…Beneath the flavonol glycosides rutin, hyperoside, isoquercetrin and quercetrin as major flavonoids, there are also smaller amounts of the flavonol aglycon quercetin as well as biflavonoids such as biapigenin and amentoflavone [5]. Naphtodianthrones namely hypericin and pseudohypericin occur in small amounts up to 0.3% in the flowers and leaves mainly in the dark glands [6]. The occurrence of the phloroglucinol hyperforin in the above ground parts mainly in the transluscent glands [7] is characteristic for SJW.…”

Secondary metabolites in Hypericum species and their distribution in different plant parts

“…depilatum (Cirak et al, 2006). The localization of the secretory structures varies greatly among plant tissues, and for that reason, the levels of phytochemicals in a particular Hypericum tissue depend on the relative abundance of these secretory structures on the harvested material (Zobayed et al, 2006). As a result, organ-dependence of a given chemical is common among Hypericum species and this phenomenon could explain the great variation observed in the chemical contents among the species investigated as well as their different tissues.…”

Phenological changes in the chemical content of wild and greenhouse-grown Hypericum pruinatum: flavonoids

“…These structures are accumulation and/ or synthesis sites for different kinds of phytochemicals; phenolic compounds, including flavonoids, are thought to be synthesized in secretory canals (Ciccarelli et al, 2001). The localization of the secretory structures varies greatly among plant tissues; for that reason, the levels of phytochemicals in a particular Hypericum tissue depend on the relative abundance of these secretory structures in the harvested material (Zobayed et al, 2006). As a result, organ-dependence of a given chemical is common among Hypericum species.…”