Effects of calcium and W-7 on flavonoid accumulation in cell cultures of Hypericum androsaemum L

Hypericum androsaemum L. is a plant found in damp or shady places throughout Europe and has been used in folk medicine owing to the diuretic and hepatoprotective properties of its aerial parts [1]. These biological activities are attributed to the several flavonoids and phenolic acids occurring in the plant.

As reported previously [2], H. androsaemum cell cultures established from hypocotyl-derived callus were able to accumulate small amounts of flavonoids, with the highest levels being observed during the stationary phase (day 14).

Treatment of 11-day-old cultures for 72h with 15 mM CaCl₂ or 5µM calcium ionophore A23187 increased considerably the accumulation of flavonoids and the activity of phenylalanine ammonia-lyase (PAL), a key enzyme of phenolic metabolism assayed according to [3].

Moreover, pre-treatment of cultures with the calmodulin antagonist W-7 (50µM) prevented the Ca²⁺ induced rise in flavonoid contents, but caused no reduction in PAL activity levels. When added alone to control cultures, W-7 by itself significantly stimulated this enzyme activity. Interestingly, a slight enhancement of activity was noticed by adding equivalent concentrations of W-7 to the PAL assay mixture.

These findings suggest a possible involvement of Ca²⁺/calmodulin-dependent processes in the biosynthesis of flavonoids by H. androsaemum cell cultures and indicate that the induction of PAL activity is not correlated with increased accumulation of these compounds.

Acknowledgements: Center of Pharmaceutical Studies

References: 1. Novais, M. et al. (2004)J. Ethnopharmacol. 93: 183–195.

2. Paranhos, A. (2006) Planta Med. 72: 1060–1061.

3. Mori, T. et al. (2001) Plant Sci. 160: 355–360.