ISOLATION OF UVH1, AN ARABIDOPSIS MUTANT HYPERSENSITIVE TO ULTRAVIOLET-LIGHT AND IONIZING-RADIATION

A genetic screen for mutants of Arabidopsis that are hypersensitive to UV light was developed and used to isolate a new mutant designated uv h1. UV hypersensitivity in uvh1 was due to a single recessive trait th at is probably located on chromosome 3. Although isolated as hypersens itive to an acute exposure to UV-C light, uvh1 was also hypersensitive to UV-B wavelengths, which are present in sunlight that reaches the e arth's surface. UV-B damage to both wild-type and uvh1 plants could be significantly reduced by subsequent exposure of UV-irradiated plants to photoreactivating light, showing that photoreactivation of UV-B dam age is important for plant viability and that uvh1 plants are not defe ctive in photoreactivation. A new assay for DNA damage, the Dral assay , was developed and used to show that exposure of wild-type and ovh1 p lants to a given dose of UV light induces the same amount of damage in chloroplast and nuclear DNA. Thus, uvh1 is not defective in a UV prot ective mechanism. uvh1 plants were also found to be hypersensitive to ionizing radiation. These results suggest that uvh1 is defective in a repair or tolerance mechanism that normally provides plants with resis tance to several types of DNA damage.