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PLANTS INTERACTING WITH OTHER ORGANISMS

Effects of Feeding Spodoptera littoralis on Lima Bean Leaves. III. Membrane Depolarization and Involvement of Hydrogen Peroxide¹

Department of Plant Biology and Centre of Excellence CEBIOVEM, University of Turin, I–10125 Turin, Italy (M.E.M, S.B., C.M.B., L.S.C., M.N., V.V., S.Q.); and Max Planck Institute for Chemical Ecology, Bioorganic Chemistry, D–07745 Jena, Germany (A.M., G.-I.A., H.U., W.B.)

In response to herbivore (Spodoptera littoralis) attack, lima bean (Phaseolus lunatus) leaves produced hydrogen peroxide (H₂O₂) in concentrations that were higher when compared to mechanically damaged (MD) leaves. Cellular and subcellular localization analyses revealed that H₂O₂ was mainly localized in MD and herbivore-wounded (HW) zones and spread throughout the veins and tissues. Preferentially, H₂O₂ was found in cell walls of spongy and mesophyll cells facing intercellular spaces, even though confocal laser scanning microscopy analyses also revealed the presence of H₂O₂ in mitochondria/peroxisomes. Increased gene and enzyme activations of superoxide dismutase after HW were in agreement with confocal laser scanning microscopy data. After MD, additional application of H₂O₂ prompted a transient transmembrane potential (V_m) depolarization, with a V_m depolarization rate that was higher when compared to HW leaves. In transgenic soybean (Glycine max) suspension cells expressing the Ca²⁺-sensing aequorin system, increasing amounts of added H₂O₂ correlated with a higher cytosolic calcium ([Ca²⁺]_cyt) concentration. In MD and HW leaves, H₂O₂ also triggered the increase of [Ca²⁺]_cyt, but MD-elicited [Ca²⁺]_cyt increase was more pronounced when compared to HW leaves after addition of exogenous H₂O₂. The results clearly indicate that V_m depolarization caused by HW makes the membrane potential more positive and reduces the ability of lima bean leaves to react to signaling molecules.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Massimo E. Maffei (massimo.maffei{at}unito.it).

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.071993.

^* Corresponding author; e-mail massimo.maffei{at}unito.it; fax 390–112365967.

Received September 29, 2005; returned for revision January 12, 2006; accepted January 12, 2006.

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