Analysis of fluid-phase endocytosis in (intact) plant cells

Endocytosis is a continuous process at the plasma membrane at least of all eukaryotic cells. Regardless of the molecular machinery, which drives the formation and uptake of endocytic vesicles, it is reasonable to assume that this process inevitably collects external fluid. Hence, at least for the majority of apoplastic solutes, the endocytosis of the fluid phase is likely to be an inevitable process. Due to its independence from the molecular machinery and low selectivity with respect to the cargo, it is thus perfectly suited to be used as a tracer to follow the activity of all endocytic events. Here we describe simple protocols based on fluorescence microscopy, which yield quantitative information about endocytic vesicle sizes-with sub-diffraction accuracy-as well as the size exclusion limits for these uptake routes.