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 (450nm). No effects of red light (650nm) 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 (300nm) treatment, the NAT activity and melatonin content were suppressed at the intensity below 1micromolm(-2)s(-1) but elevated when the intensity was as high as 10micromolm(-2)s(-1). In the UV-A (350nm) treatment, the melatonin content was elevated when the intensity was as high as 10micromolm(-2)s(-1), though the NAT activity and melatonin content were suppressed at the intensity below 10 and 1micromolm(-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.