Relation between hypericin content and morphometric leaf parameters in Hypericum spp.: A case of cubic degree polynomial function.

Higher plants often accumulate secondary metabolites in multicellular structures or in secretory reservoirs. Biotechnological production of such compounds by cell cultures lacking proper morphological structures is difficult, therefore possibilities for an efficient increase of their formation by organ cultures are being searched. The genus Hypericum comprises many species that store photoactive and phototoxic naphthodianthrones in the dark nodules on their above-ground parts. To date, the relation between the content of hypericins and their proto-forms accumulated in the nodules, and morphological characters of the plant parts containing these structures has not been sufficiently explained. The content of hypericins and leaf morphology characters were measured in 12 selected diploid seed-derived Hypericum species cultured in vitro. The leaf volume and the volume of the nodules per leaf were calculated. Based on these data, a cubic degree polynomial regression model with high reliability was constructed. The model enables an estimate of the biosynthetic capacity of the cultures, and may be useful in designing the experiments aimed at elicitation of these unique secondary metabolites in shoot cultures of Hypericum spp. An analogous model may be developed for interpretation of experimental results for other plant species which accumulate metabolites in specialized morphological structures.