UV-B Inhibition of Phytochrome-Mediated Anthocyanin Formation in Sinapis alba L. Cotyledons

Abstract

An action spectrum was measured for ultraviolet radiation-induced damage to (inhibition of) phytochrome-induced anthocyanin formation in cotyledons of 40-h-old seedlings. The action spectrum showed maximum effectiveness in the 260 to 280 nanometer waveband with little effect above 295 nanometers. The damaging effect of UV could be photorepaired by subsequent exposure to sunlight or to long wavelength (360 nanometers) UV radiation. Because this form of damage was subject to photorepair (photoreactivation), it was probably caused by the formation of pyrimidine dimers, and the results suggest that it would not be ecologically important even if there were an increase in solar UV due to a decrease in stratospheric ozone levels of about 30%. If a dark period of more than 1 hour intervened between the phytochrome induction and the UV irradiation, the inhibition of the phytochrome induction gradually decreased with increasing dark period.