title: The apical actin fringe contributes to localized cell wall deposition and polarized growth in the lily pollen tube.
abstract: In lily (Lilium formosanum) pollen tubes, pectin, a major component of the cell wall, is delivered through regulated exocytosis. The targeted transport and secretion of the pectin-containing vesicles may be controlled by the cortical actin fringe at the pollen tube apex. Here, we address the role of the actin fringe using three different inhibitors of growth: brefeldin A, latrunculin B, and potassium cyanide. Brefeldin A blocks membrane trafficking and inhibits exocytosis in pollen tubes; it also leads to the degradation of the actin fringe and the formation of an aggregate of filamentous actin at the base of the clear zone. Latrunculin B, which depolymerizes filamentous actin, markedly slows growth but allows focused pectin deposition to continue. Of note, the locus of deposition shifts frequently and correlates with changes in the direction of growth. Finally, potassium cyanide, an electron transport chain inhibitor, briefly stops growth while causing the actin fringe to completely disappear. Pectin deposition continues but lacks focus, instead being delivered in a wide arc across the pollen tube tip. These data support a model in which the actin fringe contributes to the focused secretion of pectin to the apical cell wall and, thus, to the polarized growth of the pollen tube.
authors.affiliation: Department of Biology, University of Massachusetts, Amherst, Massachusetts 01003 (C.M.R., P.K.H.); andSchool of Natural Science, Hampshire College, Amherst, Massachusetts 01002 (L.J.W.).
authors.forename: Caleb M
authors.initials: CM
authors.lastname: Rounds
authors.affiliation: Department of Biology, University of Massachusetts, Amherst, Massachusetts 01003 (C.M.R., P.K.H.); andSchool of Natural Science, Hampshire College, Amherst, Massachusetts 01002 (L.J.W.) hepler@bio.umass.edu.
authors.forename: Peter K
authors.initials: PK
authors.lastname: Hepler
authors.affiliation: Department of Biology, University of Massachusetts, Amherst, Massachusetts 01003 (C.M.R., P.K.H.); andSchool of Natural Science, Hampshire College, Amherst, Massachusetts 01002 (L.J.W.).
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Winship
mesh_terms: D000199:Actins / Q000378:metabolism*; D019521:Body Patterning; D020126:Brefeldin A; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002473:Cell Wall / Q000378:metabolism*; D027762:Lilium / Q000254:growth & development* / Q000378:metabolism; D010368:Pectins / Q000378:metabolism*; D053205:Pollen Tube / Q000254:growth & development*; D011190:Potassium Cyanide; D053778:Thiazolidines
chemical_list: D000199:Actins; D019086:Bridged Bicyclo Compounds, Heterocyclic; D053778:Thiazolidines; D020126:Brefeldin A; D010368:Pectins; C037068:latrunculin B; D011190:Potassium Cyanide