Internal secretory structures in Hypericum (Clusiaceae): H. perforatum L. and H. balearicum L.

Abstract

SUMMARYHypericum species have translucent oil cavities; many species also have superficially similar black internal structures. Contradictory descriptions of both structures emerged from 19th century studies, which we review here. Our study of Hypericum perforatum L. leaves and petals shows typical schizogenous translucent oil cavities that develop with a uniseriate epithelium. Black structures, m contrast, are nodules, each composed ot several large cells lacking a central intercellular space and surrounded by a biseriate sheath of flattened cells. Nodule cells accumulate black, granular, but non-resinous contents. The 'streaks' that traverse petals are elongate tubular cavities or nodules, except for some chimerical tubes composed partly of each. Hypericum balearicum L. leaves have bulging, pustular cavities. A large cellular nodule forms first, by non-synchronous cell divisions within the leaf mesophyll, and is surrounded by a sheath of two to three flattened cell layers. The central cells then separate unevenly to form an irregular cavity into which isolated cells and clusters of cells intrude, some of which continue to divide as other cells degenerate. Little or no oil accumulates in the cavity, and the peripheral lining of cells is very irregular to flattened and empty. Both species studied exhibit secretory structures with previously undescribed anatomical features.

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

“…As far as is known, no report is available on the quantification of hypericin or pseudohypericin in the dark glands, although it has been speculated that the dark glands may be the site of accumulation of hypericin or pseudohypericin in H. perforatum plants (McKey, 1979;Curtis and Lersten, 1990;Fornasiero et al, 1998). Moreover, until now, the presence of large numbers of dark glands has been reported only in the petals and leaves (Curtis and Lersten 1990;Fornasiero et al, 1998). In the current study, a significant presence of dark glands (Figs 7 and 8), accompanied by the highest concentrations of Hy-G, has been shown (Fig.…”

“…14A), it is concluded that long-distance transport of photosynthates via the phloem, xylem or apoplastic space occurs. Dark glands are already known to be connected to the minor veins and vein endings, and are surrounded by an irregular vascular reticulum, which typically includes contact with one or more vein endings (Curtis and Lersten, 1990). Moreover, the dark canals located in different organs (Figs 10 and 11), also known to be associated with veins (Curtis and Lersten, 1990), could be a route of transport as proposed by Williams (1954).…”

“…Dark glands are already known to be connected to the minor veins and vein endings, and are surrounded by an irregular vascular reticulum, which typically includes contact with one or more vein endings (Curtis and Lersten, 1990). Moreover, the dark canals located in different organs (Figs 10 and 11), also known to be associated with veins (Curtis and Lersten, 1990), could be a route of transport as proposed by Williams (1954). Multi-vesicular structures in outer flat cells of developed dark glands were investigated by Onelli et al (2002), who showed that the content is similar to the cytoplasm, with ribosome-like structures.…”

“…In contrast, extensive research has been conducted on the anatomical and histological characterization of the dark glands on leaves and petals, starting in the 19th Century (Green, 1884, and references therein; Onelli et al, 2002, Maggi et al, 2004. In several studies, dark glands are proposed as the site where biologically active substances accumulate (McKey, 1979;Curtis and Lersten, 1990;Fornasiero et al, 1998), although no direct evidence of chemical analysis has been presented.…”

“…The major bioactive compound of this plant is the hypericin group (hypericin and pseudohypericin; called Hy-G hereafter), a red naphthodianthrone. Morphologically, H. perforatum plants are characterized by the presence of several types of secretory structures, including translucent glands, dark glands and secretory canals (Curtis and Lersten, 1990;Fornasiero et al, 1998;Bottega et al, 1999). Dark glands, probably first named by Green (1884), are also known as 'nodules' (Curtis and Lersten, 1990) or 'black nodules' (Onelli et al, 2002;Maggi et al, 2004).…”