Ultraviolet Action Spectrum for Anthocyanin Formation in Broom Sorghum First Internodes

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Abstract
An action spectrum for anthocyanin formation in dark-grown broom sorghum (S. bicolor Moench, cultivars Acme Broomcorn, Sekishokuzairal Fukuyama Broomcorn [Hori Kawazairai, Kokkaku-2 and Sudax]) seedlings was determined over the wavelength range from 260-735 nm. The action peaks were at 290, 650, 385 and 480 nm in descending order of height. The action of the 290-nm peak was not affected by subsequently given far red light [FR], whereas those of the other 3 actin peaks were nullified completely. The nullification of the 385-nm peak action by FR was reversible. When an irradiation at these action peaks was followed by a phytochrome-saturating fluence of red light [R] irradiation, the action of the 290-nm peak remained, whereas that of the 385-nm peak as well as those of the 650- and 480-nm peaks was masked by the action of the 2nd irradiation. Evidently, the 290- and 385-nm action peaks involved different photoreceptors, the latter being phytochrome. The blue light-absorbing photoreceptor as reported to be a prerequisite for phytochrome action in milo sorghum did not exist in the broom sorghums. The action spectrum deprived of the involvement of phytochrome was determined in the UV region by irradiating with FR following monochromatic UV light. The spectrum had a single intense peak at 290 nm and no action at all wavelengths > 350 nm.