First published online April 9, 2002; 10.1104/pp.010974
Plant Physiol, May 2002, Vol. 129, pp. 103-111
Phospholipase A2 Activity Triggers the
Wound-Activated Chemical Defense in the Diatom Thalassiosira
rotula
Georg
Pohnert*
Max-Planck-Institut für Chemische Ökologie, Winzerlaer
Strasse 10, D-07745 Jena, Germany
The activation of oxylipin-based chemical defense
in the diatom Thalassiosira rotula is initiated by
phospholipases that act immediately after cell damage. This lipase
activity is responsible for the preferential release of free mono- and
polyunsaturated fatty acids. Among these, eicosatetraenoic- and
eicosapentaenoic acid are further converted by lipoxygenases to
reactive defensive metabolites such as the antiproliferative
 , , , -unsaturated aldehydes 2,4-decadienal and
2,4,7-decatrienal. We show that mainly saturated free fatty acids are
present in the intact diatom T. rotula, whereas the
amount of free polyunsaturated eicosanoids is drastically increased in
the first minutes after wounding. Using fluorescent probes, the main
enzyme activity responsible for initiation of the aldehyde-generating
lipase/lipoxygenase/hydroperoxide lyase cascade was characterized as a
phospholipase A2. All enzymes involved in this specific
defensive reaction are active in seawater over several minutes. Thus,
the mechanism allows the unicellular algae to overcome restrictions
arising out of potential dilution of defensive metabolites. Only upon
predation are high local concentrations of aldehydes formed in the
vicinity of the herbivores, whereas in times of low stress, cellular
resources can be invested in the formation of eicosanoid-rich
phospholipids. In contrast to higher plants, which use lipases acting
on galactolipids to release C18 fatty acids for production of
leaf-volatile aldehydes, diatoms rely on phospholipids and the
transformation of C20 fatty acids to form 2,4-decadienal and
2,4,7-decatrienal as an activated defense.
*
E-mail pohnert{at}ice.mpg.de; fax 49-3641-571256.
© 2002 American Society of Plant Physiologists
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