Figure 1.

The UVR8 dimer/monomer ratio responds to sunflecks in naturally shaded canopies. A and B, The UVR8 dimer/monomer ratio in the wild type (Ws) responds to the UV-B light photon flux density received under sunfleck conditions. Seedlings were grown under deep shade for 7 d, transferred to sunfleck conditions at midday, and harvested 2 h later. Sunfleck conditions were provided by canopies of different height, unfiltered sunlight, and full sunlight filtered by a Mylar film (to reduce UV-B without the other changes caused by natural shade). C and D, The UVR8 dimer/monomer ratio in the wild type (Col-0) and rup1 rup2 mutants during shade and sunflecks. E and F, Time course of the UVR8 dimer/monomer ratio in seedlings grown under deep shade for 7 d, transferred at midday to full sunlight (time = 0), and returned to shade 2 h later. Seedlings that remained as controls under shade are also included and samples were harvested at the indicated times. G, The time courses of UV-B (280–315 nm), PPFD (400–700 nm), and red (645–675 nm)/far-red (715–745 nm; R /FR) ratio during E and F are provided for reference. Data are means ± se of 3 to 4 (A and E) and 10 (C) biological replicates or four canopy light measurements (G). The significance of the regression between dimer/monomer ratio and UV-B photon flux density (A), the effect of rup1 rup2 on the dimer/monomer ratio (C), and the effect of sunflecks on the dimer/monomer ration (E) are indicated. Representative UVR8 protein blots are shown, where the uvr8 mutant is included as negative control and the asterisk denotes an unspecific band (B, D, and F). Quantification of these blots is shown in Supplemental Table S1. Note that no effects of light conditions are observed when samples are denatured (D).