Abstract: Roots of pomegranate (Punica
granatum L.), belonging to Punicaceae, were
investigated anatomically to record changes in
tissue development from growth to maturity.
When roots start secondary growth, a protective
tissue called polyderm composed of alternating
suberized and non-suberized cell layers, develop
beyond the endodermis in certain families of
plants including Myrtaceae. Punicaceae family is
not known to develop a polyderm. However, new
layers formed beyond the endodermis during
secondary growth and biopolymer deposition
was observed in their cell walls. The present
study aims to gather more knowledge on this
tissue discovered in pomegranate roots and
cross check whether it is a polyderm or a unique
type of periderm.
Root specimens were sectioned freehand or
with an ultramicrotome after embedding in
Technovit 7100 resin. After staining with
berberine hemisulfate-aniline blue-safranin O,
the root sections were observed under
fluorescent or optical microscopes.
Unlike the polyderm in Myrtaceae roots, in
pomegranate roots, ligno-suberic material
accumulated in every cell layer beyond the
endodermis. The alternating suberized and
non-suberized layers that define the polyderm
were absent. Lignin accumulation in the cell wall
was pronounced in every cell layer of this
outermost tissue and suberin-like
autofluorescence was also observed in the same
layer. We considered this to be a unique feature
typical in pomegranate periderm.
It is possible that accumulating both lignin and
suberin in the same cell layer instead of
alternative layers is more efficient because
metabolic energy is not spent in forming a
separate cell layer. Further experiments are
underway to acknowledge changes in such
biopolymer accumulation in the outermost tissue
in abiotic stress conditions.