Rp. Sabba et al., Structural and immunocytochemical characterization of the walls of dichlobenil-habituated BY-2 tobacco cells, INT J PL SC, 160(2), 1999, pp. 275-290
BY-2 tobacco cells, grown in the presence of the cellulose biosynthesis inh
ibitor herbicide dichlobenil (DCB), change in morphology from finely disper
sed clumps and filaments to large aggregates after 6 mo. In this article, w
e utilize structural, cytochemical, and immunocytochemical techniques to ch
aracterize the cell wall changes that accompany the habituation of the cell
s to DCB. Wall structure is altered radically in the habituated cells, reve
aling a lamellate structure with no distinct middle lamella, even at cell j
unctions. Plasmodesmata traverse the cell wall by more circuitous routes th
an in the control cells. Habituated cells also produce unusual appositions
of the wall that extend into the cytoplasm. Immunogold localization of vari
ous pectin epitopes reveals a 30-fold-greater density of gold particles det
ected in the walls of habituated cells compared to the controls and less de
nsity when the labeling of the middle lamellae is included. Antiextensin la
beling was also found along the strands of pectic-reactive material, and th
e density of immunogold labeling exhibits a similar increase to that for pe
ctin. Cellulose, detected by cellulase-gold, revealed only 2% of the reacti
vity of the controls, while callose detection was slightly greater compared
to controls. Despite the loss of cellulose, xyloglucan is still detected,
loosely associated with the strands of pectin or trapped between the pectin
lamellae. Cortical microtubule arrays in habituated cells were apparently
normal, despite a virtual absence of cellulose, although callose fibrils di
d parallel this array. These data indicate that long-term habituation to DC
B results in the production of cell walls in which a pectin-extensin networ
k has replaced cellulose as the major component of the cell wall. These cha
nges have profound effects on wall ultrastructure and the gross morphology
of the cultures.