PHOTOMORPHOGENIC RESPONSES TO UV-RADIATION .3. A COMPARATIVE-STUDY OFUVB EFFECTS ON ANTHOCYANIN AND FLAVONOID ACCUMULATION IN WILD-TYPE AND AUREA MUTANT OF TOMATO (LYCOPERSICON-ESCULENTUM MILL)

The UV-mediated induction of anthocyanin and UV-absorbing compounds wa s characterized in etiolated hypocotyls of wild-type and aurea (au) mu tant tomato seedlings. Ultraviolet radiation induced significant incre ases of anthocyanin and UV-absorbing compounds in hypocotyls of the au mutant and of its isogenic wild-type, but the differences in the time courses of W-induced pigment accumulation indicate that different pho toregulatory mechanisms are involved for each of these two groups of p igments. It appears that prolonged presence of adequate levels of UVB (290-320 nn) energy and consequently the action of a specific UVB phot oreceptor are indispensable for the photoinduction of anthocyanin accu mulation in UV-irradiated hypocotyl of the au mutant that is missing t he labile phytochrome pool. The large difference found between the wil d-type and the au mutant strongly indicate the involvement of labile p hytochrome as the primary functional photoreceptor for the photoinduct ion of anthocyanin accumulation in wild-type tomato hypocotyls. The UV B photoreceptor could at least partly replace the action of labile phy tochrome (as far as anthocyanin accumulation is concerned) when the fu nctional phytochrome pool is missing as in the au mutant. The general picture of W-mediated induction of total W-absorbing compounds shows o nly a macroscopic difference between wild-type and the au mutant of to mato: the higher initial level (in darkness) of these compounds in the wild-type in contrast to the au mutant. Although there is UV-induced accumulation of UV-absorbing compounds in both genotypes, the levels i n the au mutant never reach that of the wild-type under the same UV ex posure. A UVB photosensor may play a more important role in the photoi nduction of UV-absorbing compounds. Indeed, in the absence of labile p hytochrome, i.e. in the au mutant, a UVB-absorbing photoroceptor alone is able to establish high responsiveness for the UV-induced flavonoid accumulation.