The existence and possible function of actin at the tip of growing pollen tubes has been controversial, with results differing depending on the fixation or visualization techniques. Now Fu et al. (page 1019) have used the actin-binding protein talin, linked to an enhanced green fluorescent protein (GFP), to detect sparse and transient short actin bundles (SABs) in pollen tips . They also use mutant and overproduced Rop1At to implicate this pollen-specific Rho GTPase in the control of SAB formation and polarized tip growth.
The SABs oscillate in abundance every 60–75 s, with SABs disappearing at the peak of a tube's calcium transient and growth spurt. Fu et al. suggest that phosphatidylinositol-4,5-bisphosphate [PIP(2)] production stimulated by Rop1At might control all of these variables. First, a direct inhibition of profilin by PIP(2) would permit actin polymerization, allowing actin-based delivery of vesicles...
