Endocytosis in tobacco pollen tubes: Visualisation and measurement of plasma membrane retrieval,during different gravity conditions indicates gravity-dependence of endocytosis

We studied the effect of microgravity on endocytosis in growing tobacco pollen tubes by measuring the plasma membrane retrieval employing the fluorescent phospholipid bis-Bodipy FL C-11- phosphatidylcholine as marker. Time course experiments under 1xg conditon revealed a localised and relatively fast plasma membrane retrieval in the pollen tube tip region within the first minutes after lipid application. The rate of endocytotic bis-Bodipy FL C-11- PC-modified plasma membrane retrieval is inhibited by hyper-g conditions achieved by centrifugal forces. In contrast, during the mug phase of a parabolic rocket flight the retrieval of the fluorescently-marked plasma membrane is distinctly enhanced. Our results show that mug exerts an unspecific physiological response in pollen tubes, most likely involving the cytoskeleton as inhibitor experiments indicate under 1xg condition.