Figure 2.

Low irradiance and low R:FR increase the number of small phyB-NBs in leaf petiole cells. A, Time course of small (diameter ≤ 0.4 µm) and large (diameter > 0.4 µm) phyB-NBs upon transfer to either low irradiance or low R:FR. Data are means ± se of eight plant replicates. The effects of irradiance and R:FR were significant at P < 0.01 and P < 0.0001, respectively (ANOVA). Different letters denote significant differences among means (P < 0.05) in Bonferroni posttests. The inset shows the diameter of the large phyB-NBs after 2-h low irradiance or low R:FR relative to the control under high irradiance and R:FR (in both cases, P < 0.05 compared with the control). B, Representative pictures of phyB-NBs. Bar = 2 µm. C, Plants exposed to low irradiance. Note that changes in phyB-NBs in A and B anticipate leaf angle responses in C. Arabidopsis plants were grown under high-irradiance white light for 2 weeks and transferred to either low irradiance or low R:FR 4 h after the beginning of the photoperiod (time = 0). [See online article for color version of this figure.]