Elicitor-induced cell death and phytoalexin synthesis in Daucus carota L. |
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Authors: | Wolfgang Koch Claus Wagner Hanns Ulrich Seitz |
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Institution: | Botanisches Institut der Universit?t Tübingen, Pflanzenphysiologie, Auf der Morgenstelle 1, D-72076 Tübingen, Germany, DE
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Abstract: | Suspension-cultured carrot cells and intact leaves respond to crude and purified protein elicitors from the non-host fungus
Pythium aphanidermatum by activating the general phenylpropanoid pathway and incorporating de-novo-synthesized 4-hydroxybenzoic acid (4-HBA) into
the cell wall. The cultured cells undergo a very rapid elicitor-induced cell death. Both reactions are directly correlated
in their time course and their dose dependency. Cell death in elicitor-treated protoplasts resulted in early membrane damage
and the digestion of DNA into oligonucleosomal fragments. The same pattern of DNA degradation could be induced in protoplasts
by the G-protein activators Mas-7 or mastoparan. In cell cultures, both activators induced a rapid loss of viability without
the activation of the general phenylpropanoid pathway. The elicitor-induced reactions, the loss of viability and the induction
of 4-HBA biosynthesis were blocked by the calcium-channel blocker nifedipine. Neomycin and U73122, two inhibitors of phospholipase
C, blocked the induction of 4-HBA biosynthesis but did not affect the loss in viability. The injection of the elicitor into
the leaves of intact carrot plants confirmed the results obtained with cell cultures with regard to the induction of the hypersensitive
response. The purification of the active compound revealed a 25-kDa protein which triggers both cell death and 4-HBA synthesis.
The signalling pathways to both reactions could be independently blocked or induced.
Received: 27 February 1998 / Accepted: 25 May 1998 |
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Keywords: | : Cell culture (carrot) Cell death Elicitor 4-Hydroxybenzoic acid Hypersensitive response (HR) Pythium |
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