cytochalasin-d and fusicoccin

Programmed cell death (PCD) plays a vital role in plant development and is involved in defence mechanisms against biotic and abiotic stresses. Different forms of PCD have been described in plants on the basis of the cell organelle first involved. In sycamore (Acer pseudoplatanus L.) cultured cells, the phytotoxin fusicoccin (FC) induces cell death. However, only a fraction of the dead cells shows the typical hallmarks of animal apoptosis, including cell shrinkage, chromatin condensation, DNA fragmentation and release of cytochrome c from the mitochondrion. In this work, we show that the scavenging of nitric oxide (NO), produced in the presence of FC, by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) and rutin inhibits cell death without affecting DNA fragmentation and cytochrome c release. In addition, we show that FC induces a massive depolymerization of actin filaments that is prevented by the NO scavengers. Finally, the addition of actin-depolymerizing drugs induces PCD in control cells and overcomes the inhibiting effect of cPTIO on FC-induced cell death. Vice versa, the addition of actin-stabilizing drugs to FC-treated cells partially inhibits the phytotoxin-induced PCD. These results suggest that besides an apoptotic-like form of PCD involving the release of cytochrome c, FC induces at least another form of cell death, likely mediated by NO and independent of cytochrome c release, and they make it tempting to speculate that changes in actin cytoskeleton are involved in this form of PCD.

Topics: Acer; Actin Cytoskeleton; Actins; Apoptosis; Benzoates; Cell Nucleus; Cells, Cultured; Cytochalasin D; Cytochromes c; Cytoskeleton; Depsipeptides; DNA Fragmentation; Glycosides; Hydrogen Peroxide; Imidazoles; Nitric Oxide; Rutin

Actin in guard cells is assembled in a radial pattern when stomata are induced to open under light, but the filaments are disassembled when stomata are closed under darkness or by abscisic acid (S.-O. Eun and Y. Lee, 1997, Plant Physiol. 115: 1491-1498). To test if signals that open stomata commonly generate the polymerized form of actin in guard cells, leaves of Commelina communis L. were treated with a potent stomatal opening agent, fusicoccin, and the actin organization examined by immunolocalization techniques. When stomata were induced to open by fusicoccin, hardly any of the filamentous form of actin was detected; instead, the actin resembled that present in guard cells that had been treated with an antagonist to actin filaments, cytochalasin D, and showed a sharp contrast to the long filaments developed in illuminated guard cells. Furthermore, treatment of illuminated leaves with fusicoccin disintegrated actin filaments that had already been formed in the guard cells. Preincubation of leaves with phalloidin, which interferes with fusicoccin-induced actin depolymerization, delayed fusicoccin-induced opening during the early phase. These observations suggest that the prevention of actin filament formation and/or depolymerization of actin filaments may accelerate the stomatal opening process in response to fusicoccin.

Topics: Actins; Biopolymers; Cytochalasin D; Glycosides; Magnoliopsida; Phalloidine; Plant Leaves