Signalling and the cytoskeleton of pollen tubes of Papaver rhoeas

Abstract

Self-incompatibility (SI) is a genetically controlled system used by many flowering plants to prevent self-pollination, often by the inhibition of pollen tube growth. The importance of cytosolic free calcium, [Ca2+](i), for the regulation of pollen tube growth is well known. We have established, using calcium imaging, that the SI response in Papaver rhoeas L. pollen involves a calcium-mediated intracellular signalling pathway. Tip growth of cells is dependent upon a typical configuration of the actin cytoskeleton, which is controlled by actin binding proteins. In animal cells, the actin-binding protein, profilin, is thought to act as a key intermediate between signalling pathways and actin rearrange ments. Profilin is an abundant component of pollen. To better understand the signalling cascades that modulate pollen tip growth and actin dynamics, we are investigating a possible signalling role for profilin. We have demonstrated that profilin modulates the phosphorylation of pollen proteins in vitro. This implicates a role for profilin in altering protein kinase or phosphatase activity. Furthermore, we demonstrate for the first time that profilin from pollen can be phosphorylated in vitro. This provides compelling evidence that profilin interacts with signalling pathways in angiosperms. Finally, we demonstrate that in the SI response, the actin cytoskeleton of incompatible pollen tubes is dramatically rearranged. Our data strongly support a role for the cytoskeleton and actin-binding proteins interacting with signalling pathways involved in the regulation of pollen tube growth. (C) 2000 Annals of Botany Company.