Encyclopedia of Experiments: Biological Techniques
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Maule Staining for Lignin - ExperimentTranscript
Lignin is an important structural component in the plant cell wall. It is a polymer composed primarily of syringyl alcohols, or S-lignin units, and guaiacyl alcohols, or, G-lignin units, and a minor population of para-coumaryl alcohols called the H-lignin units.
S-lignin’s content differs in various secondary plant tissues. It is mainly found in the xylary vessels and fibers and interfascicular fibers, where it provides structural support.
To detect the presence of S-lignin, take agarose-embedded dicot stem cross-sections in a tube. Treat the stem sections sequentially with a potassium permanganate staining solution, followed by diluted hydrochloric acid, and, finally, with ammonium hydroxide - a weak base.
During this treatment, the S-Lignin moiety present in the cell wall undergoes a series of changes to finally generate a product that appears red.
The intensity of red coloration is lower in the xylem cells owing to the presence of less S-lignin compared to the interfascicular fibers, which appear a deeper red. Transfer the sections onto a slide, and visualize them under a light microscope.
The variation in red intensity helps to understand the relative ratio of S-lignin in lignified plant tissues.
