Lignin, a complex phenylpropanoid polymer, is primarily deposited in the walls of cells
that have secondary wall thickening, such as tracheary elements and fibers.
Lignin provides mechanical strength to the walls of these sclerenchyma cells. Lignin
is derived from the de-hydrogenative polymerization of the monolignols p-coumaryl alcohol, coniferyl
alcohol, and sinapyl alcohol. These monolignols are synthesized through a phenylpropanoid
In the top part of the stem, where the only sclerenchyma cells present are the xylem vessel
elements, lignin staining is only seen in the xylem. In the middle part of the stem,
another type of sclerenchyma cells - the inter-fascicular fibers is present in addition to xylem cells.
Here lignin is seen in both inter-fascicular fibers and xylem cells. In the lower part
of the stem, more xylem cells and inter-fascicular fibers are formed. Consistently, intense lignin
staining is seen in these sclerenchyma cells too. No lignin staining can be detected in
the cortical cells or the pith parenchyma cells throughout the stems.
Potato Stem of the plant
Double edged razor blade Water
Glass slide Blotting paper
Phloroglucinol Stain (colorless liquid) Petri dish
Using a razor blade cut the potato into a block and make a slit in the middle of the
potato block. Place the stem of the plant in the middle
of the slit made in the potato block. Cut thin sections of the stem along with the
potato block into a Petridish containing water. Using a brush transfer the cut sections of
the stem into a Petridish containing water. Pour few drops of phloroglucinol-HCL stain
into a watch glass using a dropper. Transfer the cut sections of the stem from
the Petridish into the watch glass using a brush.
Take a clean glass slide and pour few drops of water on to the slide. Using a wet brush
transfer the sections from the watch glass onto the slide.
Place a coverslip over the sections on the slide using a forceps.
Remove the excess solution from the edges of the coverslip by touching the side with
a blotting paper and observe the slide under microscope.
The red colour seen in the sections indicate Lignin staining. Lignin staining is heavy
in both xylem cells and inter-fascicular fibers.