Phenotyping the genus Hypericum by secondary metabolite profiling: emodin vs. skyrin, two possible key intermediates in hypericin biosynthesis.

A wide range of compounds that occur in the genus Hypericum are listed as effective drugs of natural origin. The main biological activities of several Hypericum representatives are due to the presence of naphthodianthrones, phloroglucinols, and other diverse groups of secondary metabolites that synergistically contribute to their therapeutic effects. The regulation of biosynthesis of hypericin as the key bioactive naphthodianthrone remains uncertain. Here, we present liquid chromatography mass spectrometry-based phenotyping of 17 Hypericum species, the results of which suggest an important role for skyrin and its derivatives in the polyketide pathway that leads to hypericin formation. Moreover, we report for the first time the presence of new metabolites in the genus Hypericum that are related to classes of anthraquinones, their derivatives, and phloroglucinols. As skyrin and other species of anthraquinones are rarely found in higher plants but frequently occur in fungal microorganisms, the obtained results suggest that further research on the synthesis pathways of hypericin and the role of anthraquinone derivatives in plant metabolism should be carried out. The fact that these compounds are commonly synthesized in endophytic fungi and perhaps there is some similarity in the metabolic pathways between these organisms should also be investigated.

Relation between hypericin content and morphometric leaf parameters in Hypericum spp.: A case of cubic degree polynomial function.

Higher plants often accumulate secondary metabolites in multicellular structures or in secretory reservoirs. Biotechnological production of such compounds by cell cultures lacking proper morphological structures is difficult, therefore possibilities for an efficient increase of their formation by organ cultures are being searched. The genus Hypericum comprises many species that store photoactive and phototoxic naphthodianthrones in the dark nodules on their above-ground parts. To date, the relation between the content of hypericins and their proto-forms accumulated in the nodules, and morphological characters of the plant parts containing these structures has not been sufficiently explained. The content of hypericins and leaf morphology characters were measured in 12 selected diploid seed-derived Hypericum species cultured in vitro. The leaf volume and the volume of the nodules per leaf were calculated. Based on these data, a cubic degree polynomial regression model with high reliability was constructed. The model enables an estimate of the biosynthetic capacity of the cultures, and may be useful in designing the experiments aimed at elicitation of these unique secondary metabolites in shoot cultures of Hypericum spp. An analogous model may be developed for interpretation of experimental results for other plant species which accumulate metabolites in specialized morphological structures.

Interspecific variation in localization of hypericins and phloroglucinols in the genus Hypericum as revealed by desorption electrospray ionization mass spectrometry imaging.

Plants of the genus Hypericum are widely known for their therapeutic properties. The most biologically active compounds of this genus are naphtodianthrones and phloroglucinols. Indirect desorption electrospray ionization mass spectrometry (DESI-MS) imaging allows visualization and localization of secondary metabolites in different plant tissues. This study is focused on localization of major secondary compounds in the leaves of 17 different in vitro cultured Hypericum species classified in 11 sections. Generally, all identified naphtodianthrones, protohypericin, hypericin, protopseudohypericin and pseudohypericin were co-localized in the dark glands of eight hypericin producing species at the site of their accumulation. The known phloroglucinols, hyperforin, adhyperforin, hyperfirin and some new phloroglucinols with m/z [M - H](-) 495 and 569 were localized in the translucent and pale cavities within the leaf in the majority of studied species. The comparison of different Hypericum species revealed an interspecific variation in the distribution of the dark and translucent glands corresponding with the localization of hypericins and phloroglucinols. Moreover, similarities in the localization and composition of the phloroglucinols were observed in the species belonging to the same section. Adding to various quantitative studies focused on the detection of secondary metabolites, this work using indirect DESI-MSI offers additional valuable information about localization of the above-mentioned compounds.