title: The role of actin filaments in the gravitropic response of snapdragon flowering shoots.
abstract: The involvement of the actin and the microtubule cytoskeleton networks in the gravitropic response of snapdragon ( Antirrhinum majus L.) flowering shoots was studied using various specific cytoskeleton modulators. The microtubule-depolymerizing drugs tested had no effect on gravitropic bending. In contrast, the actin-modulating drugs, cytochalasin D (CD), cytochalasin B (CB) and latrunculin B (Lat B) significantly inhibited the gravitropic response. CB completely inhibited shoot bending via inhibiting general growth, whereas CD completely inhibited bending via specific inhibition of the differential flank growth in the shoot bending zone. Surprisingly, Lat B had only a partial inhibitory effect on shoot bending as compared to CD. This probably resulted from the different effects of these two drugs on the actin cytoskeleton, as was seen in cortical cells. CD caused fragmentation of the actin cytoskeleton and delayed amyloplast displacement following gravistimulation. In contrast, Lat B caused a complete depolymerization of the actin filaments in the shoot bending zone, but only slightly reduced the amyloplast sedimentation rate following gravistimulation. Taken together, our results suggest that the actin cytoskeleton is involved in the gravitropic response of snapdragon shoots. The actin cytoskeleton within the shoot cells is necessary for normal amyloplast displacement upon gravistimulation, which leads to the gravitropic bending.
authors.affiliation: Department of Postharvest Science of Fresh Produce, Agricultural Research Organization, The Volcani Center, 50250 Bet Dagan, Israel.
authors.forename: Haya
authors.initials: H
authors.lastname: Friedman
authors.forename: Jan W
authors.initials: JW
authors.lastname: Vos
authors.forename: Peter K
authors.initials: PK
authors.lastname: Hepler
authors.forename: Shimon
authors.initials: S
authors.lastname: Meir
authors.forename: Abraham H
authors.initials: AH
authors.lastname: Halevy
authors.forename: Sonia
authors.initials: S
authors.lastname: Philosoph-Hadas
mesh_terms: D000199:Actins / Q000378:metabolism*; D032161:Antirrhinum / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002748:Chlorpropham / Q000494:pharmacology; D003571:Cytochalasin B / Q000494:pharmacology; D015638:Cytochalasin D / Q000494:pharmacology; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D035264:Flowers / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018522:Gravitropism / Q000187:drug effects; D008768:Methylmethacrylates / Q000494:pharmacology; D018520:Plant Shoots / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013844:Thiazoles / Q000494:pharmacology; D053778:Thiazolidines; D013997:Time Factors
chemical_list: D000199:Actins; D019086:Bridged Bicyclo Compounds, Heterocyclic; D008768:Methylmethacrylates; D013844:Thiazoles; D053778:Thiazolidines; D002748:Chlorpropham; D015638:Cytochalasin D; C060877:Dakril 4B; D003571:Cytochalasin B; C037068:latrunculin B; D004121:Dimethyl Sulfoxide