Ultrastructural studies on the developing secretory nodules of Hypericum perforatum

The secretory nodule of Hypericum perforatum represents a very interesting gland. In fact, many of its active compounds, such as hypericin and hyperforin, are therapeutic agents. We observed, by transmission electron microscopy, the development of the structures, which appeared different from most plant glands, in leaves of H. perforatum. As observed by several authors, they appeared as a solid black cluster of cells without cavities and with some particular cell structures. Generally, young nodules show meristematic features. During development, cellular components degenerate and secrete materials accumulated first in vacuoles and then in a periplasmic space and cell walls. Finally, the cells were filled with black material. The outer flat cells surrounding the nodules appeared morphologically different from the inner cells and showed unusual vesicles in the periplasmic spaces. Ultrastructural observations suggest the secretion of materials could be eccrine.