UV radiation elevates arylalkylamine N-acetyltransferase activity and melatonin content in the two-spotted spider mite, Tetranychus urticae

Ultraviolet (UV) radiation produces reactive oxygen species (ROS) in mammals, where melatonin plays the role of a ROS scavenger. The melatonin synthetic enzyme arylalkylamine N-acetyltransferase (NAT) is a significant element in a possible ROS removal system. Changes in NAT activity and melatonin content were determined in the two-spotted spider mite Tetranychus urticae by irradiating it with monochromatic light using the Okazaki Large Spectrograph at the National Institute for Basic Biology, Okazaki, Japan. The NAT activity and melatonin content were suppressed by blue light (450 nm). No effects of red light (650 nm) on the NAT activity and melatonin content were observed. UV radiation had intensity-dependent dual effects on the NAT activity and melatonin content. In the UV-B (300 nm) treatment, the NAT activity and melatonin content were suppressed at the intensity below 1 μmol m−2 s−1 but elevated when the intensity was as high as 10 μmol m−2 s−1. In the UV-A (350 nm) treatment, the melatonin content was elevated when the intensity was as high as 10 μmol m−2 s−1, though the NAT activity and melatonin content were suppressed at the intensity below 10 and 1 μmol m−2 s−1, respectively. Elevation of the NAT activity and melatonin content by high intensity UV irradiation may indicate that the UV signals initiate melatonin synthesis for ROS removal in mites.