Spectral quality and genetic background jointly define UVR8-dependent acclimation responses in Arabidopsis

Several laboratories have shown that even UV-naive model plants can acclimate to relatively low doses of supplemental broad-band UV radiation. On the other hand, responses to supplemental narrow-band 311 nm UV-B radiation (outside of the main absorption of UVR8) was applied to study antioxidants responses that were unlike our previous findings in plants exposed to broad-band UV-B or sunlight. The results suggest that signalling pathways activated by 311 nm radiation are distinct from those stimulated by other wavelengths. In this study we are examining the photoreceptor dependence of photosynthetic, antioxidants and epidermal pigment responses. To investigate this, we used photoreceptor deficient Arabidopsis thaliana on Columbia-0 and Wassilewskija backgrounds (uvr8-6 and uvr8-7). Both the broad- and narrow-band UV-B (∼7 kJ m^-2 d^-1 biologically effective dose) was applied to supplement 110 μmol m^-2 s^-1 photosynthetically active radiation for 4 h in the middle of the light period for four days. Our results showed that the photosynthetic yields were modified by broad-band UV, but they were unaffected to 311 nm radiation. However, both uvr8 mutants exhibited altered yields, although to varying degrees. Antioxidant enzyme results show that base values (in the absence of UV) are different not just between wild types, but between the mutants as well. After both UV treatments, enzyme activities displayed significant differences between the wild type and mutant groups. The outcome of our experiments highlights the necessity of studying action spectra of separate UV-B wavelengths in order to understand the complexity of responses to UV radiation.