title: Reversible protein phosphorylation regulates the dynamic organization of the pollen tube cytoskeleton: effects of calyculin A and okadaic acid.
abstract: We investigated the cytoskeleton of Lilium longiflorum pollen tubes and examined the effects of the type 2A protein phosphatase (PP2A) inhibitors calyculin A and okadaic acid. An improved method for actin visualization, the simultaneous fixation and staining with rhodamine-labelled phalloidin during microscopical observation, revealed abundant actin filaments of no preferential orientation in the apical clear zone. Microtubules, visualized by indirect immunofluorescence, were mostly absent from the apices of straight-growing pollen tubes but present in those with irregular shape. Double labelling showed that both actin bundles and microtubules had a similar longitudinal or slightly helical orientation in the pollen tube shaft. In the presence of 30 nM calyculin A or okadaic acid, pollen tubes grew very slowly, branched frequently, and contained isolated, randomly oriented, curved actin bundles and microtubules. Treating pollen tubes with calyculin A or okadaic acid after germination arrested growth immediately, reversibly altered the alignment of actin bundles from axial to transverse, and disassembled microtubules. The changes in actin organization caused by the PP2A inhibitors were similar to those observed upon overexpression of AtRop1 (Y. Fu, G. Wu, Z. Yang, Journal of Cell Biology 152: 1019-1032, 2001), suggesting that hyperphosphorylation interferes with the signalling pathway of small GTPases. The effects of the PP2A inhibitors could be ameliorated with nanomolar concentrations of latrunculin B.
authors.affiliation: Institut für Pflanzenphysiologie, Universität Salzburg, Austria. ilse.foissner@sbg.ac.at
authors.forename: Ilse
authors.initials: I
authors.lastname: Foissner
authors.forename: Franz
authors.initials: F
authors.lastname: Grolig
authors.forename: Gerhard
authors.initials: G
authors.lastname: Obermeyer
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D016764:Cell Polarity / Q000187:drug effects / Q000502:physiology; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005306:Fertilization / Q000187:drug effects / Q000502:physiology; D035264:Flowers / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000502:physiology; D027762:Lilium / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D008387:Marine Toxins; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism; D019319:Okadaic Acid / Q000494:pharmacology; D010080:Oxazoles / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D010940:Plant Proteins / Q000187:drug effects / Q000378:metabolism*; D013844:Thiazoles / Q000494:pharmacology; D053778:Thiazolidines
chemical_list: D019086:Bridged Bicyclo Compounds, Heterocyclic; D004791:Enzyme Inhibitors; D008387:Marine Toxins; D010080:Oxazoles; D010940:Plant Proteins; D013844:Thiazoles; D053778:Thiazolidines; D019319:Okadaic Acid; C059041:calyculin A; D010749:Phosphoprotein Phosphatases; C037068:latrunculin B