ULTRAVIOLET ACTION SPECTRA FOR THE INDUCTION AND INHIBITION OF ANTHOCYANIN SYNTHESIS IN BROOM SORGHUM SEEDLINGS

In the first internode of dark-grown seedlings of broom sorghum (Sorghum bicolor Moench) UVB induced anthocyanin synthesis at low fluences, but inhibited it at high fluences. Action spectra for the two UV effects were determined so that the influence of one on the other was reduced as much as possible. The action spectrum for inhibition showed a peak at or below 260 nm and a shoulder at about 28 nm; whereas that for induction had a peak at about 293 nm, confirming a previous result. Wavelengths from about 300 to 350 nm were inductive only and had no inhibitory effect at higher fluences. Inhibition was observable irrespective of the irradiation sequence, and was photoreactivatable. It was, thus, concluded that the UVB photoreceptor proposed for induction was different from that proposed for inhibition of anthocyanin synthesis; the latter being presumably the same as the target of other putatively harmful actions of UV.