Figure 2.

Primary fluorescence increases over time when transverse stem sections are stored in paraformaldehyde. Transverse sections of A. thaliana stems were stored in 4% paraformaldehyde for 21 days. The same sections cut with a vibratome were observed with UV excitation after 1 (A), 2 (B), 7 (C), and 21 (D) days of incubation in paraformaldehyde. Using a long pass emission filter allows the visualization of primary fluorescence produced by the interfascicular fibers (blue color) and by the plastids located in the cortical parenchyma (red color). Comparison between micrographs (A–D) shows the increase of autofluorescence that occurs over time when the stem sections are stored in paraformaldehyde. Scale bar for (A–D): 30 μm. (E): The measurement of light blue color pixels from the same interfascicular regions of stem sections incubated for 1 and 2 days in 4% paraformaldehyde indicates that the increase of autofluorescence already occurs after 2 days of incubation. The pixel measurement was carried out using ImageJ following the procedure detailed in Supplemental data S2. The micrographs underneath the graph represent the region selected for pixel measurement. For this example, the measurement was done in triplicate. Error bars: SD.