The rhizodermis tissue in the root cap was seen to be organized
and well structured (Fig. 1M) in control; but, by contrast and in
spite of showing different expressions of damage, the first bands
of the root cap cells were destroyed by pods (Fig. 1O) and leaves
(Fig. 1P). Also, columella cells containing amyloplasts responsible
for gravity sensing were affected, the columella can also respond
to light as well as pressure of soil particles (Burgos et al., 2004).
This damage at the root cap level indicates that when no such cells
are formed or destroyed, the mucilaginous gel responsible for preventing
dehydration and facilitating penetration of the roots in the
ground, amongst other functions, will not form (Taiz and Zeiger,
2010). Since the meristematic zone is just below the root cap, it was
also damaged, while the apical meristem was left unprotected and
subject to mechanical injury occurring during movement through
the soil’s profile under natural conditions. The meristematic region
in several species, e.g., Arabidopsis thaliana, is about a quarter of
a millimeter long (Taiz and Zeiger, 2010) and the two layers of
cells closest to the apex of the root forms in the dicots (Barlow
et al., 1984). As such, serious affectations in the root cap with
meristem damage interfere with cell division and jeopardize radicle
growth. This is consistent with the inhibition that was detected
in radicle growth of L. sativa and the native species Q. saponaria, H.
aromaticum and Rhodophiala maculata seedlings when subjected
to direct contact and aqueous extracts from different parts of A.
dealbata (Aguilera et al., 2015c).
Observations on the cross-sections cuts at the root hair level
zone in Q. saponaria showed normal structures of cells and tissues
in control (Fig. 2A). However, the micrographs indicated that pods
of A. dealbata inhibited the root hairs formation,