Inhibition of actin polymerization by LatB affects endocytosis and secretion both in the apex and in the subapical regions of tobacco pollen tubes

The pollen tube is a tip growing cell that plays a fundamental role in the fertilization process of higher plants. Pollen tube growth is based on transport and accumulation of secretory vesicles. The incorporation of new segments of PM largely exceeds the quantity of membrane required for the extension, so the excess of PM must be removed by endocytosis. Recent studies showed internalization of subapical PM domains that were mainly recycled to exocytosis through the Golgi apparatus and a second mainly degradative pathway. The movements of the endomembrane system during the pollen tube growth depends on the concerted action and integrity of the cytoskeleton. In this study we disturb the system of cortical actin filaments using Latrunculin B to verify modifications in endocytosis, using specific FM dyes in time-lapse experiments and by ultrastructural experiments using charged Nanogold. Our results demonstrate that the system of cortical microfilaments determines a strong reduction of endocytosis and consequently the alteration of recycling through the Golgi, the inhibition of degradative pathways, and changes in the secretion pattern at the tip PM.