Plant Physiol, October 2002, Vol. 130, pp. 895-903
A Comparison of Oligogalacturonide- and Auxin-Induced
Extracellular Alkalinization and Growth Responses in Roots of Intact
Cucumber Seedlings1
Mark D.
Spiro,*
Jonathan F.
Bowers, and
Daniel J.
Cosgrove
Biology Department, Bucknell University, Lewisburg, Pennsylvania
17837 (M.D.S., J.F.B.); and Root Biology Program and Department of
Biology, The Pennsylvania State University, University Park,
Pennsylvania 16802 (M.D.S., D.J.C.)
Oligogalacturonic acid (OGA) affects plant growth and development
in an antagonistic manner to that of the auxin indole-3-acetic acid
(IAA), the mechanism by which remains to be determined. This study
describes the relationship between IAA and OGA activity in intact
cucumber (Cucumis sativus) seedlings. Both OGA and IAA induced rapid and transient extracellular alkalinization; however, the
characteristics of the OGA and IAA responses differed in their kinetics, magnitude, calcium dependence, and region of the root in
which they induced their maximal response. IAA (1 µM)
induced a saturating alkalinization response of approximately 0.2 pH
unit and a rapid reduction (approximately 80%) in root growth that only partially recovered over 20 h. OGAs, specifically those with a degree of polymerization of 10 to 13, induced a maximal
alkalinization response of 0.48 pH unit, but OGA treatment did not
alter root growth. Saturating concentrations of OGA did not block
IAA-induced alkalinization or the initial IAA-induced inhibition of
root growth but allowed IAA-treated roots to recover their initial
growth rate within 270 min. IAA-induced alkalinization occurs primarily in the growing apical region of the root, whereas OGA induced its
maximal response in the basal region of the root. This study demonstrates that OGA and IAA act by distinct mechanisms and that OGA
does not simply act by inhibition of IAA action. These results also
suggest that IAA-induced extracellular alkalinization is not sufficient
to account for the mechanism by which IAA inhibits root growth.
1
This work was supported in part by the Root
Biology Training Program at the Pennsylvania State University, a unit
of the Department of Energy/National Science Foundation/U.S. Department
of Agriculture Collaborative Research Program in Plant Biology, and in
part by the Department of Energy (grant no.
DE-FG02-84ER13179).
*
Corresponding author; e-mail spiro{at}bucknell.edu; fax
570- 577-3537.
© 2002 American Society of Plant Physiologists
