PLANT PHYSIOLOGY , Vol 105, Issue 2 725-730, Copyright © 1994 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
A Sulfhydryl Reagent Modulates Systemic Signaling for Wound-Induced and Systemin-Induced Proteinase Inhibitor Synthesis
J. Narvaez-Vasquez, M. L. Orozco-Cardenas and C. A. Ryan
Institute of Biological Chemistry, Washington State University, Pullman, Washington 99164-6340
The sulfhydryl group reagent p-chloromecuribenzene sulfonic acid (PCMBS),
an established inhibitor of active apoplastic phloem loading of sucrose in
several plant species, is shown to be a powerful inhibitor of wound-induced
and systemin-induced activation of proteinase inhibitor synthesis and
accumulation in leaves of tomato plants (Lycopersicon esculentum cv
Castlemart). PCMBS, supplied to young tomato plants through their cut
stems, blocks accumulation of proteinase inhibitors in leaves in response
to wounding. The application of systemin directly to fresh wounds enhances
systemic accumulation of proteinase inhibitors to levels higher than
wounding alone. Placed on fresh wounds, PCMBS severely inhibits systemic
induction of proteinase inhibitors, in both the presence and absence of
exogenous systemin. PCMBS inhibition can be reversed by cysteine,
dithiothreitol, and glutathione. Radiolabeled systemin placed on fresh
wounds is readily transported from the wounded leaves to upper leaves.
However, in the presence of PCMBS, radiolabeled systemin is not transported
away from wound sites. Induction of proteinase inhibitor I synthesis by
oligouronides (degree of polymerization [almost equal to] 20), linolenic
acid, or methyl jasmonate was not inhibited by PCMBS. The cumulative data
support a possible role for sulfhydryl groups in mediating the
translocation of systemin from wound sites to distal receptor sites in
tomato plants and further support a role for systemin as a systemic wound
signal.
