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.

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.Electronic supplementary materialThe online version of this article (10.1007/s00216-018-1384-0) contains supplementary material, which is available to authorized users.

Seedlings of Hypericum perfaroturn L. have produced multiple shoots on RM medium supplemented with 2.22 or 4.40pM BAP. Regenerants were evaluated for variability in several morphological characteristics. A comparison with the control showed significant differences in fresh and dry matter and height of plants, but did not effect branching and the number of glands containing dianthrones.Seeds of Hypericumperforatwn L. (Hypericaceae), cv. Topas were surface sterilized with 5% Chloramine

Meristems of in vitro-grown Hypericum perforatum L. plants were precultured for 3, 10, or 14 days in the presence of 0.5 M mannitol, or 0.076 µM or 0.76 µM abscisic acid, in RM basal liquid culture medium supplemented with 0.5 mg/l 6-benzylaminopurine and subsequently subjected to cryopreservation by the slow freezing method. The survival rate -determined as the percentage of meristems capable of differentiating plantlets -varied between 10% and 48%. Chromosome number stability of the cryopreserved meristems was determined by chromosome counting. The mitotic index of the control did not significantly differ from that of the treated samples.

The hypericin content of in uitro regenerated plants of Hypericum perforaturn L. was determined by spectrophotometry. A significant variability of some of the morphological characters, of the biomass production and the hypericin formation was found within the somaclones of the same genetic origin and among the regenerants of different genotypes. The concentration of BAP which promoted the shoot differentiation did not affect the hypericin content and the gland density. New information on the ultrastructure of hypericin-containing multicellular glands is presented here.