Profilin is associated with the plasma membrane in microspores and pollen

In higher plants, a large number of isoforms for the actin monomer-binding protein profilin have been identified, whereas other organisms express only few profilins. Furthermore, plant profilin isoforms are expressed in a tis sue-specific manner. These observations raise questions concerning function al and locational differences between isoforms of plant profilins. In this paper, we introduce three polyclonal antisera and one monoclonal antibody d eveloped against purified pollen profilins from Zea mays and against recomb inant maize profilin. Immunoblot analyses of native profilins and four reco mbinant maize pollen profilin isoforms show that three of the antibodies di splay a preference for certain isoforms. In situ immunofluorescence of poll en of Zea mays and two developmental stages of microspores of Betula pumila indicates that all antibodies label plasma membrane-associated domains. Th us, we show that at least some profilin isoforms are located at a distinct subcellular domain within developing microspores and, less distinctly, in m ature pollen. This contrasts previously reported uniform distributions thro ughout the cytoplasm of mature pollen and pollen tubes. The results are dis cussed in light of the large number of profilins co-expressed in plants and with reference to accumulating evidence for functional differences between profilin isoforms.