Involvement of calcium and cAMP in flavonoid production by cell cultures of Hypericum androsaemum L.

Hypericum androsaemum L. is an herbaceous plant widely distributed throughout Europe which has been used in traditional medicine on account of the diuretic and hepatoprotective properties of its leaves [1]. These biological effects have been ascribed to the different flavonoids and phenolic acids known to be present in this species. Cell suspension cultures established from hypocotyl-derived callus of H. androsaemum were reported [2] to accumulate low amounts of flavonoids, with the highest levels being found during the stationary phase (day 14). More recently [3], it was shown that 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), which is the first committed enzyme in the phenylpropanoid pathway. In similar experiments, the addition of 20µM forskolin (an activator of adenylyl cyclase) or 100µM dibutyryl cAMP (db-cAMP, a membrane-permeable analogue of cAMP) also enhanced the flavonoid levels recorded on day 14, but only the latter treatment caused a significant increase in PAL activity. Moreover, the stimulatory effects of db-cAMP were prevented or markedly inhibited by pretreatment of cells with the calcium channel blocker verapamil (100µM). Taken together, these results suggest that both calcium and cAMP are involved in flavonoid metabolism of H. androsaemum cell cultures.

Acknowledgements: FCT and POCTI/FEDER for financial support

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

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

3. Paranhos, A. (2007) Planta Med. 73: 1017.