Tecoma stans is a tropical plant from the Americas. Antioxidant activity and both phenolic compound and flavonoid total content were determined for callus tissue of T. stans cultured in either a set photoperiod or in darkness. Callus lines from three explant types (hypocotyls, stem, and leaf) were established on B5 culture medium supplemented with 0.5 μM 2,4-D and 5.0 μM kinetin. While leaf-derived callus grew slower under a 16-h photoperiod (specific growth rate, μ=0.179 d −1 , t D =3.9 d) than in darkness (μ=0.236 d −1 , t D =2.9 d), it accumulated the highest amount (p<0.05) of both phenolics (86.6±0.01 mg gallic acid equivalents/g) and flavonoids (339.6±0.06 mg catechin equivalents/g). Similarly, antioxidant activity was significantly higher (p<0.05) when callus was cultured in period light than when grown in extended darkness. Antioxidant activity measured with a 2,20-azinobis (3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS)-based assay was 350.5±15.8 mmol Trolox/g extract for callus cultured under a defined photoperiod compared to 129.1±7.5 mmol Trolox/g extract from callus cultured in darkness. Content of phenolic compounds and flavonoids was in agreement with a better antioxidant power (EC 50 =450 μg extract/mg 1,1-diphenyl-2-picrylhydrazyl) and antiradical efficiency. Results of the present study show that calli of T. stans are a source of compounds with antioxidant activity that is favored by culture under a set photoperiod.
Castilleja tenuiflora is a medicinal plant that grows in pine-oak woods primarily in southern and central Mexico. It is highly valued for its medicinal properties, which have been attributed to aucubin-like iridoids. In the present study, we developed an efficient protocol for in vitro shoot proliferation and ex vitro rooting of C. tenuiflora. Using a colorimetric method, we determined total iridoid contents of various different tissues of propagated plants. The shoots were induced from nodal explants cultured on Murashige and Skoog (MS) (1962) medium supplemented with indole-3-butyric acid (IBA) (0 and 0.5 lM) and different concentrations of thidiazuron (TDZ), 6-benzyladenine (BA), or kinetin (KIN) (0-20 lM). Of the cytokinins tested, KIN was more effective for shoot induction than TDZ or BA, and the highest shoot proliferation rate was achieved with 5 lM KIN (4 shoots per explant). Plantlets were rooted on MS medium, nutrient solution, or potting mix, alone or in combination with auxins. The best responses (100% rooting efficiency) were obtained by dipping shoots in half-strength MS medium containing 7.5 lM IBA before transfer to potting mix. On average, each shoot formed 9 roots of 39.3 ± 3.8 mm in length after 21 days. These roots appeared to be more functional than those that developed in nutrient solution, and were associated with a high survival rate (95%) during acclimatization and cultivation in a greenhouse, where flowering occurred after 4 months. Propagated plants accumulated iridoids, thus representing a potential source of pharmacologically useful compounds.
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