Severe sensitivity to ultraviolet radiation in an Arabidopsis mutant deficient in flavonoid accumulation

An Arabidopsis Mutant Tolerant to Lethal Ultraviolet-B Levels Shows Constitutively Elevated Accumulation of Flavonoids and Other Phenolics

“…Figure 2 shows an assessment of the UV tolerance of mature plants from uvs, wild-type controls, and uvt1 mutants (wild-type background). As previously described (Lois and Buchanan, 1994), under identical UVB irradiation conditions, the uvs mutant showed more pronounced necrotic lesions than the wild type. The uvt1 mutant, however, showed significantly higher UVB tolerance than both uvs and the wild type.…”

“…Normally, wild-type plants accumulate low levels of UV-absorbing pigments, and these levels increase significantly upon UVB exposure. The absorption spectra in Figure 3 are an extension of data presented previously by Lois and Buchanan (1994) and show the normal UV-mediated increase in UV absorption in the region between 260 and 350 nm in wild-type controls, as well as the minimal increase in UV absorption in this region in uvs when plants are exposed to UVB. In contrast, the absorption spectrum of uvt1 shows elevated levels of UV-absorbing pigments prior to UV irradiation.…”

“…To increase our chances of detecting increases in UV tolerance, we used a mutant highly sensitive to UV radiation (uvs), previously isolated in our laboratory, as the genetic background for a new round of ethyl methane sulfonate (EMS)-mediated mutagenesis. As described previously (Lois and Buchanan, 1994), the UV sensitivity of uvs is due to a single recessive lesion in a gene that leads to altered accumulation of UVabsorbing compounds. This mutant does not show the significant increase in absorption in the UV range observed in the wild type upon exposure to UVB radiation.…”

“…It seemed likely then that an increased level of flavonoids in the uvt1 mutant might be responsible for its dark coloration. By the same token, since flavonoids and other UV-absorbing phenolics have been postulated as important UV defense mechanisms (Li et al, 1993;Lois, 1994;Lois and Buchanan, 1994;Landry et al, 1995;Mazza et al, 2000), it appeared possible that the increased UV resistance of uvt1 may be due to the increase in UV-absorbing compounds. To address these questions, we investigated if the levels of these pigments were higher in Figure 1.…”

“…Mutants showing hypersensitivity to UV radiation have been instrumental in laying down the groundwork for our understanding of some of these mechanisms. For example, studies of the transparent testa, fah1, and uvs mutants (Li et al, 1993;Lois and Buchanan, 1994;Landry et al, 1995) have increased our understanding of different aspects of the role of phenolics, including flavonoids and sinapates, in the protection of plants against UV radiation (for review, see Bharti and Khurana, 1997). Mutants deficient in DNA repair (Britt et al, 1993;Jiang et al, 1997;Vonarx et al, 1998) have helped elucidate the involvement of mechanisms of photoreactivation and dark repair of DNA in UV protection.…”