Lignification pattern in Populus tissues selected for qRT-PCR studies. Far left column displays organs and tissues used (Leaf blade, Petiole, bark, Xylem). Middle column shows lignin deposition, visualized under the light microscope after phloroglucine-HCl staining (red color). Right column shows lignin distribution by fluorescent microscopy (autofluorescence). a, b – cross section of leaf vascular bundle, c, d – petiole cross section, e, f – transverse section of stem segment, g, h – secondary xylem from stem. Abbreviations: x – xylem, ph – phloem, s – schlerenchyma. Bars = 100 μm.