A POTENTIAL SIGNALING ROLE FOR PROFILIN IN POLLEN OF PAPAVER RHOEAS

Regulation of pollen tube growth is known to involve alterations in in tracellular calcium levels and phosphoinositide signaling, although th e mechanisms involved are unclear. However, it appears likely that pol lination events involve a complex interplay between signaling pathways and components of the actin cytoskeleton in pollen. In many eukaryoti c cells, actin binding proteins function as stimulus-response modulato rs, translating signals into alterations in the cytoplasmic architectu re. In this study, we examined whether profilin, which is a member of this class of signaling intermediate, might play a similar role in pol len. We have analyzed the functional properties of native profilin fro m pollen of Papaver rhoeas and have investigated the effects of profil in on the phosphorylation of pollen proteins in vitro by adding a slig ht excess of profilin to cytosolic pollen extracts. We present clear e vidence that profilin interacts with soluble pollen components, result ing in dramatic alterations in the phosphorylation of several proteins . We also show, albeit in vitro, the involvement of profilin in modula ting the activity of a signaling component(s) affecting protein phosph orylation. Our data, which suggest that pollen profilin can regulate a ctin-based cytoskeletal protein assembly and protein kinase or phospha tase activity, indicate a possible role for the involvement of profili n in signaling pathways that may regulate pollen tube growth.