l-tryptophan decarboxylase activity and tryptamine accumulation in callus cultures of Vinca minor L.

l-tryptophan decarboxylase (TDC, EC 4.1.1.28) catalyses the formation of tryptamine from tryptophan, and therefore it plays a role in terpenoid indole alkaloids biosynthesis. In this study, TDC activity and tryptamine accumulation were monitored in callus cultures of important medicinal plant Vinca minor L. Callus cultures, established from leaf tissues, were incubated on Murashige and Skoog (MS) medium supplemented with 4.4 μM kinetin and different concentrations (0.44, 1.1, 2.2, 4.4 and 6.6 μM) of naphthaleneacetic acid (NAA), and grown either in the dark or under 16 h photoperiod. When the basal enzyme activity of TDC was determined in these cultures, it was 0.5–0.7 nmol tryptamine mg⁻¹ prot. min⁻¹. Moreover, this activity remained linear over time and over protein concentrations, and with optimum pH levels between 6.5 and 7.5, and an optimum temperature of 35°C. The Michaelis–Menten constant (K_m) for l-tryptophan was 1.3 mM. TDC cofactor, pyridoxal-5′-phosphate (1 mM), increased the enzyme activity. During later stages of callus culture growth cycle, an increase in TDC activity was observed, and this activity depended on culture conditions and age of callus cultures. In addition, TDC activity and tryptamine accumulation in callus cultures were strongly enhanced by light treatment.