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Title: The production of hypericins in two selected Hypericum perforatum shoot cultures is related to differences in black gland structure

item LU, CASEY
item Gibson, Donna

Submitted to: Plant Physiology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2006
Publication Date: 1/30/2007
Citation: Kornfeld, A., Kaufman, P.B., Lu, C.R., Gibson, D.M., Bolling, S.F., Warber, S.L., Chang, S., Kirakosyan, A. 2007. The production of hypericins in two selected Hypericum perforatum shoot cultures is related to differences in black gland structure. Plant Physiology and Biochemistry. 45:24-32.

Interpretive Summary: Hypericum perforatum L. (family Hypericaceae), commonly called St. John's wort, is sold as a dietary supplement worldwide. This paper is the last in a series of studies undertaken as part of a Foreign Agricultural Service grant to evaluate germplasm for production of the active principles using cell cultures. The aim of the present study was to determine the portions of the plant involved in biosynthesis via microscopic comparison of two cell lines that vary in production levels. The micrographs revealed that the hypericin and pseudohypericin-containing black glands were located along the margins of the leaves and consisted of a flattened cell sheath surrounded by interior cells that appear to be involved in synthesis. The size of the interior cell mass surrounding the gland correlated with the differences in hypericin/pseudohypericin levels. Since the pricing of St. John's wort is based on the concentration of hypericins and hyperforin, this study may be useful in quickly identifying elite germplasm.

Technical Abstract: In vitro shoot cultures of Hypericum perforatum derived from wild populations grown in Armenia have a wide variation of hypericin and pseudohypericin metabolite content. We found that a germ line denoted as HP3 produces six times more hypericin and fourteen times more pseudohypericin than a second line labeled HP1. We undertook a structural comparison of the two lines (HP1 and HP3) in order to see if there are any anatomical or morphological differences that could explain the differences in production of these economically important metabolites. Analysis by LM (light microscopy), SEM (scanning electron microscopy), and TEM (transmission electron microscopy) reveals that the hypericin/pseudohypericin-containing black glands located along the margins of the leaves consist of a peripheral sheath of flattened cells surrounding a core of interior cells that are typically dead at maturity. The peripheral cells of the HP3 glands appear less flattened than those of the HP1 glands. This may indicate that the peripheral cells are involved in hypericin/pseudohypericin production. Furthermore, we find that these peripheral cells undergo a developmental transition into the gland's interior cells. The fact that the size of the peripheral cells may correlate with metabolite production adds a new hypothesis for the actual site of hypericin synthesis.