Poster: Cytoskeleton: Structure & Function

Abs # 1114: Actin polymerization drives reverse fountain motility in pollen tubes

Presenter:	Hepler, Peter K., hepler@bio.umass.edu
Authors	Hepler, Peter K. (A)   Cardenas, Luis  (A)   Wilsen, Kathleen L (A)
Affiliations:	(A): University of Massachusetts

Actin polymerization contributes to the control of pollen tube growth (Gibbon, et al., 1999; Vidali et al., 2001; Cárdenas et al., in preparation). Treatment of pollen tubes with latrunculin B (Lat-B), which inhibits actin polymerization, blocks oscillatory growth, and reduces the extent of the clear zone. Streaming continues, but exhibits a circulatory rather than reverse fountain pattern. Here we employ jasplakinolide (Jas), a sponge cyclic peptide that promotes polymerization and stabilizes microfilaments. Although Jas (2 µM) also inhibits oscillatory growth, in contrast to Lat-B, it blocks streaming in the shank of the tube, and induces reverse fountain motility in a swollen apical domain. In medial optical section the motility pattern appears as oppositely rotating circles, reminiscent of an "egg beater". That Jas promotes actin polymerization in the apical domain is supported by the appearance of prominent patches of F-actin, indicated either by fluorescent phalloidin or GFP-talin, and by the marked reduction in G-actin, as revealed by a fluorescent analog of DNAse. Ion imaging further indicates that Jas reduces the tip-focused calcium gradient. However, the alkaline band intensifies in the swollen apex and is spatially localized with the reverse fountain streaming activity. Given the ability of Jas to block actomyosin-dependent streaming, while promoting actin polymerization, our results support the idea that reverse fountain motility in the apex is driven by actin polymerization. Gibbon BC, Kovar DR, Staiger CJ. 1999. Plant Cell 11: 2349-2363. Vidali L, McKenna ST, Hepler PK. 2001. Molec. Biol. Cell 12: 2534-2545. Supported by grants from the NSF (MCB-0077599; DBI-9970191).