phloroglucinolHCl

Phloroglucinol-HCl is a chemical reagent used in histology and plant anatomy to detect lignin in plant cell walls. It is prepared by dissolving phloroglucinol, a 1,3,5-trihydroxybenzene, in concentrated hydrochloric acid, sometimes with a small amount of an organic solvent such as ethanol. The reagent is commonly referred to as the Wiesner test reagent for lignin detection.

In practice, thin sections of plant tissue are treated with the phloroglucinol-HCl solution and examined under light microscopy. Lignified tissues, such as xylem fibers and vessels, develop a characteristic rose-red to reddish color, while non-lignified tissues remain colorless or only weakly tinted.

Mechanism is based on an acid-catalyzed reaction between phloroglucinol and certain lignin-associated aldehyde groups, producing colored chromophores. The color intensity can correlate with lignin content but is not strictly quantitative, and results can be influenced by wood type and sample preparation.

Limitations include its qualitative nature and lack of complete specificity; some tannins and other phenolics may produce color, and certain lignin compositions yield variable results. The reagent can be sensitive to light and air and is typically prepared fresh for use. Proper controls and complementary methods are recommended when interpreting staining outcomes.

Phloroglucinol-HCl remains a classic, rapid screen for lignification in plant tissues and is commonly used in teaching, wood science, and botanical research contexts. It is primarily a qualitative histochemical tool rather than a definitive analytical assay.