THE PLANT CELL, Vol 2, Issue 3 245-254, Copyright © 1990 by American Society of Plant Biologists
Occurrence and Localization of 9.5 Cellulase in Abscising and Nonabscising Tissues
E. del Campillo, P. D. Reid, R. Sexton and L. N. Lewis
Department of Plant Biology, University of California, Berkeley, California 94720
Nitrocellulose tissue prints immunoblotted with 9.5 cellulase antibody were
used to demonstrate areas of cellulase localization within Phaseolus
vulgaris explants on exposure to ethylene. The 9.5 cellulase was induced in
the distal and proximal abscission zone and in the stem. In both abscission
zones, the 9.5 cellulase was found in the cortical cells of the separation
layer, which develops as a narrow band of cells at the place where fracture
occurs. The enzyme was also found associated with the vascular traces of
the tissues adjacent to the separation layer extending through the first
few millimeters at each side of the separation layer. The two abscission
zones differed in the way that cellulase distributed through the separation
layer as abscission proceeded. In the distal zone, cellulase appeared first
in the cells of the separation layer adjacent to vascular traces and
extended toward the periphery. In the proximal zone, 9.5 cellulase
accumulated first in the cortical cells that lie in the adaxial side and
then extended to the abaxial side. In response to ethylene, 9.5 cellulase
was also induced in the vascular traces of the stem and the pulvinus
without developing a separation layer. The role of 9.5 cellulase in the
vascular traces is unknown. Sodium dodecyl sulfate-polyacrylamide gel
electrophoresis followed by immunoblotting with 9.5 cellulase antibody
identified the same 51-kilodalton protein in both abscising and
nonabscising tissues. Therefore, the determinant characteristic of the
abscission process is the induction of 9.5 cellulase by cortical cells in
the separation layer, and this implies that these cells have a unique
mechanism for initiating 9.5 cellulase synthesis.
