SEVERE SENSITIVITY TO ULTRAVIOLET-RADIATION IN AN ARABIDOPSIS MUTANT DEFICIENT IN FLAVONOID ACCUMULATION .2. MECHANISMS OF UV-RESISTANCE IN ARABIDOPSIS

A mutant Arabidopsis thaliana L., which displays a dramatic increase in sensitivity to ultraviolet-B (UV-B) radiation compared with wild-type plants, has been isolated by chemical mutagenesis. This mutation appears to affect UV-tolerance specifically, since mutant plants are indistinguishable from wild type with respect to their degree of resistance to other forms of stress. The UV-sensitive mutation proved to be recessive and to segregate as a single Mendelian locus. This single gene defect was shown to lead to a block in the synthesis of a group of flavonoids which normally accumulate in developing wild-type Arabidopsis and which increase in concentration when plants are exposed to UV radiation. One of these compounds has been identified as a rhamnosylated derivative of the flavonol, kaempferol. The results suggest that one or more of the flavonoids whose production has been blocked in the UV-sensitive mutant is essential for the protection of Arabinopsis against UV-radiation damage. This constitutes further evidence that flavonoids play an important role in the protection of plants from the damaging effects of UV-B light.