Protection by AET against inactivation of transforming DNA by near-ultraviolet light: action spectrum

An Arabidopsis mutant tolerant to lethal ultraviolet-B levels shows constitutively elevated accumulation of flavonoids and other phenolics

The isolation and characterization of mutants hypersensitive to ultraviolet (UV) radiation has been a powerful tool to learn about the mechanisms that protect plants against UV-induced damage. To increase our understanding of the various mechanisms of defense against UVB radiation, we searched for mutations that would increase the level of tolerance of Arabidopsis plants to UV radiation. We describe a single gene dominant mutation (uvt1) that leads to a remarkable tolerance to UVB radiation conditions that would kill wild-type plants. Pigment analyses show a constitutive increase in accumulation of UV-absorbing compounds in uvt1 that increases the capacity of the leaves to block UVB radiation and therefore is likely to be responsible for the elevated resistance of this mutant to UVB radiation. These increases in absorption in the UV region are due, at least in part, to increases in flavonoid and sinapate accumulation. Expression of chalcone synthase (CHS) mRNA was shown to be constitutively elevated in uvt1 plants, suggesting that the increases in absorption may be a consequence of changes in gene expression. Expression of CHS in uvt1 was shown to be still inducible by UV, indicating that the uvt1 lesion may not affect the UV-mediated regulation of CHS gene expression. Our data support an important role for UV screens in the overall protection of plants to UVB radiation. The uvt1 mutant could prove to be an important tool to elucidate further the exact role of UV-absorbing pigments in UV protection as well as the relative contribution of other mechanisms to the overall tolerance of plants to UV radiation.

Correlation between UVA-induced changes in microviscosity, permeability and malondialdehyde formation in liposomal membrane

The lipid peroxidation, 14C-glucose leakage and microviscosity of liposomal membrane increased linearly with increasing UVA fluence. A positive and highly significant correlation was found between these properties of the UVA-exposed liposomal membrane. The possible involvement of singlet oxygen in the UVA-induced damage of liposomal membrane is discussed.

UVA-induced peroxidation of lipid in the dried film state

Exposure of a dried lipid thin film to UVA produced a dose-dependent linear increase in the three peroxidation products, conjugated diene, lipid hydroperoxide and malondialdehyde (MDA). All three lipid peroxidation products exhibited an inverse dose rate effect. Identical amounts of malondialdehyde were produced when the lipid film was exposed to UVA either directly or through the thickness of the Corning glass on which the film was cast. Antioxidants, alpha-tocopherol, butylated hydroxytoluene (BHT) and the singlet oxygen quencher beta-carotene significantly inhibited the UVA-induced peroxidation of the lipid film. The biological implications of the UVA-induced peroxidation of the dried lipid film are discussed.

The sensitivity of an actinic reticuloid cell strain to near-ultraviolet radiation and its modification by trolox-C, a vitamin E analogue

Near-UV radiation (365 nm)-induced lethality, as measured by colony-forming ability, showed an actinic reticuloid cell strain to be sensitive relative to normal human fibroblasts, when irradiated at 25 degrees C. This effect was not seen after far-UV (254 nm) irradiation. Trolox-C, a water-soluble analogue of vitamin E, incorporated in the pre-irradiation growth medium or in the post-irradiation plating medium, protected the actinic reticuloid cells to the extent that they were as resistant as normal cells. Plating medium containing Trolox-C did not provide differential protection against inactivation of the two cell strains by wavelengths in the far-UV region. The protection provided by Trolox-C, an analogue of the natural antioxidant vitamin E, suggests some free radical involvement in the aetiology of the disease.