Antioxidant responses of damiana (Turnera diffusa Willd) to exposure to artificial ultraviolet (UV) radiation in an in vitro model; part I; UV-C radiation.

INTRODUCTION Ultraviolet type C (UV-C) radiation has higher energy than the UV-B radiation and has been less studied because it is completely absorbed by the ozone layer. However, artificial UV-C radiation can generate diverse modifications in the plants. Given that exposure to UV-C for short periods of time increases the antioxidant content, improving the appearance and shelf-life of products, its potential application in postharvest treatments to modify the antioxidant content of medicinal plants, such as damiana (Turnera diffusa), is novel and relevant. OBJECTIVE To determine the effects of UV-C radiation on enzymatic and non-enzymatic antioxidant defenses, as well as oxidative damage levels, in damiana (Turnera diffusa) plants in vitro. RESULTS UV-C radiation decreased superoxide dismutase (SOD, EC 1.15.1.1) and total peroxidases (POX, EC 1.11.1) activities, the concentration of chlorophylls (a and b), carotenes, vitamin C, and total antioxidant capacity. UV-C radiation increased the phenolic compound levels in damiana. Loss of antioxidant defenses was higher in damiana plants exposed to higher UV-C doses and/or for longer periods. This study suggests that UV-C radiation induces oxidative stress, evidenced as increased protein carbonyls and phenolic compound content, in damiana (T. diffusa). CONCLUSION Low dose, short exposure to UV-C stimulates phenolic compound content in damiana. Thus, controlled UV-C treatments could be used as postharvest treatment to increase phenolic compound content in damiana plants.