Changes induced by gamma ray irradiation on biomass production and secondary metabolites accumulation in Hypericum triquetrifolium Turra callus cultures

The present study investigated the effect of gamma irradiation on biomass formation and yield of pharmacologically relevant secondary metabolites in callus cultures induced from different seedling parts (leaf, stem and root). Calli induction and maintenance were performed on MS medium supplemented with 0.5 mg L-1 IAA and 0.4 mg L-1 TDZ and all parameters were recorded after the third 21 days successive subculture post-elicitation. Fresh callus biomass (FCB) expressed as growth index (Gi) was investigated and the higher Gi value (1109%) was recorded on callus culture from leaf explants and irradiated with 10 Gy dose, as compared to untreated control (757%). H. triquetrifolium callus cultures exhibited quantitatively different phenolic compounds (p-OH-benzoic and chlorogenic acid, epicatechin) and naphtodiantrones (hypericin and pseudohypericin). The chromatographic analysis of callus extracts revealed that after gamma rays elicitation with 10 Gy dose, the higher amount of p-OH-benzoic acid was recorded on calli from leaf explant (4.35 mg 100 g(-1) DW material) while root callus recorded the highest amount of chlorogenic acid (12.91 mg 100 g(-1)) over the control (3.55 mg 100 g(-1) and 10.22 mg 100 g(-1), respectively). The 10 Gy and 20 Gy irradiation doses stimulate the epicatechin accumulation on call from leaf and stem (126.39 and 148.80 mg 100 g(-1)) compared to the control samples (98.81 and 101.72 respectively). In this study, small amount of hypericin and pseudohypericin were identified and quantified on irradiated callus cultures initiated from stem and leaf of Hypericum triquetrifolium, but not in root calli. Callus induced from leaf and irradiated with 10 Gy showed the higher amounts of hypericin and pseudohypericin content (0.29 and 4.00 mg 100 g(-1) DW material). Phytochemical screening carried out on different elicited callus cultures variants reveal, for the first time, the stimulatory effects of gamma irradiation on the production of phenolic compounds and naphtodiantrones in Hypericum triquetrifolium Turra. The results of this study are interesting and offer an innovative approach of elicitation, not yet widely studied for the Hypericum genus.