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

Abstract

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.

Occurrence and Distribution of Phytochemicals in the Leaves of 17 In vitro Cultured Hypericum spp. Adapted to Outdoor Conditions

“…Our results are in agreement with the work of Soelberg et al (2007) who used UV-HPLC to detect hyperforin in the translucent glands as well as in minute amounts in dark glands of H. perforatum . In our present study, hyperforin was found to be absent in H. maculatum, H. erectum , and H. tetrapterum , which is in accordance with our earlier study (Kucharíková et al, 2016). This further demonstrates that the accumulation pattern of selected phytochemicals in these in vitro cultured Hypericum spp.…”

“…Their results confirm the localization of hypericin in the dark glands of leaves and petals, and pseudohypericin and protohypericin in the dark glands of leaves of H. perforatum . More recently, we confirmed the localization and/or co-localization of hypericin, pseudohypericin and their protoforms in the dark glands of leaves of the four aforementioned in vitro cultured species belonging to the section Hypericum using indirect DESI-MSI (Kucharíková et al, 2016). …”

“…The species H. rumeliacum is a key representative of the section Drosocarpium , which is known for the presence of hypericin typically localized in numerous bulky dark glands distributed throughout the leaf surface (Kucharíková et al, 2016). In the present study, as anticipated, hypericin, pseudohypericin, and protohypericin were abundantly detected in the dark glands located inside as well as on the edge of the leaves, discerned both from the adaxial and abaxial surfaces.…”

“…Drosocarpium ) and H. tomentosum (sect. Adenosepalum ) (Kucharíková et al, 2016). On the other hand, H. humifusum (sect.…”

“…Recently, we employed matrix-assisted laser desorption/ionization-HRMS (MALDI-HRMS) imaging to reveal, in high spatial resolution with limited sample preparation, the distribution, localization, and subtleties of hypericins and structural analogs and proposed precursors in the secretory as well as non-secretory tissues of three wild-growing Hypericum species ( H. perforatum, H. olympicum , and H. patulum ) (Kusari et al, 2015). More recently, we explored the interspecific variation in localization of hypericins and phloroglucinols as well as some new compounds using indirect DESI-MSI in the leaves of seventeen different in vitro cultured Hypericum species (Kucharíková et al, 2016). This study provided an extensive range of dataset on the localization of major secondary metabolites within leaves of such a broad spectrum of Hypericum species.…”