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

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Abstract
An action spectrum was measured for UV radiation-induced damage to (inhibition of) phytochrome-induced anthocyanin formation in cotyledons of 40-h-old S. alba L. seedlings. The action spectrum showed maximum effectivenes in the 260-280 nm waveband with little effect > 295 nm. The damaging effect of UV could be photorepaired by subsequent exposure to sunlight or to long wavelength (360 nm) UV radiation. Because this form of damage is subject to photorepair (photoreactivation), it is probably due to the formation of pyrimidine dimers, and it would probably be ecologically relevant even if there was an increase in solar UV due to a decrease in stratospheric ozone levels of .apprx. 30%. If a dark period of > 1 h is interspersed between the phytochrome induction and the UV irradiation, the inhibition of the phytochrome induction gradually decreases with increasing dark period.