A NOVEL EFFECT OF UV-B IN A HIGHER PLANT (SORGHUM VULGARE)

Abstract— Two non-photosynthetic photoreceptors (phytochrome and the usual blue/UV light photoreceptor) were previously found to be involved in light-mediated anthocyanin synthesis in the mesocotyl of Sorghum seedlings (Drumm and Mohr, 1978). The decisive point is that phytochrome can act only after a blue/UV light effect has occurred. On the other hand, the expression of the blue/UV light effect is controlled by phytochrome ('obligatory sequential action'). A strong positive interaction between the blue/UV-A and the UV-B part of the spectrum was found, in addition to the above sequential action: an inductive effect of blue or UV-A light can only express itself fully if short wavelength UV (approximately 300–320nm. UV-B range) is also given, either after the blue/UV-A light or simultaneously. Since even small amounts of the UV-B are strongly effective it is probable that this effect plays a role under natural conditions and may not be considered as a mere laboratory artifact.