Figure 3.
Wide-field fluorescence microscopy of the mCitrine-AtRCI2A probe in SEs of Arabidopsis (A, B, and E–J) and tobacco (C and D). mCitrine is shown in false-color yellow, aniline blue-stained callose in false-color magenta, and the anti-GFP AlexaFluor 555 conjugate in false-color red. A to D, Live phloem of hand-sectioned Arabidopsis inflorescence stems (A and B) and tobacco source leaf petioles (C and D), showing CCs (dotted outline), SEs, sieve plates (arrowheads), and mCitrine-labeled, nonplasmalemma, SE membrane structures (arrows). The SE and CC on the right side of the sieve plate in B were excised during sectioning and are not visible here. E and F, Methacrylate-embedded cross section of anti-GFP-AlexaFluor 555-stained, SUmCR-transformed Arabidopsis inflorescence stem phloem showing intact mCitrine signal (E) and overlapping AlexaFluor 555 signal (F). Clear SE outlines are visible in both images. G and H, Same as for E and F, but using Arabidopsis plants transformed with the mCitrine-PIP1;3-cDNA construct (line 08). No SE outlines are visible. I, Longitudinal section of a minor vein from a methacrylate-embedded Arabidopsis source leaf. J, Composite image of a longitudinal section of a complete SE from a methacrylate-embedded Arabidopsis inflorescence stem. All bars = 5 μm.