Comparison of metabolite levels in callus of Tecoma stans (L.) Juss. ex Kunth. cultured in photoperiod and darkness

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 mu M 2,4-D and 5.0 mu M kinetin. While leaf-derived callus grew slower under a 16-h photoperiod (specific growth rate, mu = 0.179 d(-1), t (D) = 3.9 d) than in darkness (mu = 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 (EC50 = 450 mu g 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.