XVI International Botanical Congess

Profilin, a monomeric actin binding protein, is a complex regulator of actin polymerization. In maize pollen, profilin is present at intracellular concentrations >100 µM and is equimolar with actin. The Kd for native pollen actin binding to profilin predicts that the majority of actin in pollen is in a profilin­actin complex. This was supported by measuring F-actin levels with a fluorescent phalloidin-binding assay. At least 5 different profilin transcripts are present in maize pollen. Pollen profilins fall into at least two classes based on their functional properties, they differ in the ability to bind to monomeric actin and poly-L-proline. The latter property presumably reflects the ability to interact with proline-rich proteins that might alter profilins subcellular location or function. Our data suggest that profilin is a major regulator of pollen actin organization and that multiple profilin isoforms perform distinct functions in pollen.