PLANT PHYSIOLOGY , Vol 104, Issue 3 945-952, Copyright © 1994 by American Society of Plant Biologists
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PLANT-MICROBE INTERACTIONS |
Involvement of Oxidative Processes in the Signaling Mechanisms Leading to the Activation of Glyceollin Synthesis in Soybean (Glycine max)
N. Degousee, C. Triantaphylides and J. L. Montillet
Departement de Physiologie Vegetale et Ecosystemes, Centre d'Etudes de Cadarache, Commissariat a I' Energie Atomique, F-13108 Saint Paul-Lez-Durance, Cedex, France
The efficiency of hydroperoxides (tert-butyl hydroperoxide, hydrogen
peroxide) and sulfhydryl reagents (iodoacetamide, p-chloromercuribenzene
sulfonic acid) as glyceollin elicitors was examined in relation to
sulfhydryl oxidation, or alteration, and to lipid peroxidation, in 3-d-old
soybean hypocotyl/radicle, Glycine max. These oxidative events were
investigated as possible early steps in the transduction mechanisms leading
to phytoalexin synthesis. Free protein sulfhydryl groups were not modified
after any of the eliciting treatments, thus indicating that immediate
massive protein oxidation or modification cannot be considered a signal
transduction step. Unlike sulfhydryl reagents, which led to a decrease of
the free nonprotein sulfhydryl group (free np-SH) pool under all of the
eliciting conditions, the results obtained with hydroperoxides indicated
that immediate oxidation of the np-SH is not required for the signal
transduction. Moreover, elicitation with 10 mM tertbutyl hydroperoxide did
not lead to further oxidation or to changes in np-SH level during the
critical phase of phenylalanine ammonialyase activation (the first 20 h),
suggesting that np-SH modifications are probably not involved in
hydroperoxide-induced elicitation. On the other hand, all treatments
leading to significant glyceollin accumulation were able to trigger a rapid
(within 2 h) lipid peroxidation process, whereas noneliciting treatments
did not. In addition, transition metals, such as Fe2+ and Cu+, were shown
to stimulate both hydrogen peroxide-induced lipid peroxidation and
glyceollin accumulation, again emphasizing that the two processes are at
least closely linked in soybean. Among the oxidative processes triggered by
activated oxygen species, oxidation of sulfhydryl compounds, or lipid
peroxidation, our results suggest that lipid peroxidation is sufficient to
initiate glyceollin accumulation in soybean. This further supports the
hypothesis that lipid peroxidation could be involved as a step in the
signal cascade that leads to induction of plant defenses.