Clathrin-Independent Endocytosis Contributes to Uptake of Glucose into BY-2 Protoplasts.

In eukaryotic cells several pathways for the internalisation of plasma membrane proteins and extracellular cargo molecules exist. These endocytic pathways can be grouped into clathrin-dependent and clathrin-independent endocytosis. While the former one has been described to be involved in a variety of cellular processes in plants, the latter one has so far only been identified in animal and yeast cells. Here we show that internalisation of fluorescent glucose into BY-2 cells leads to accumulation of the sugar into compartments of the endocytic pathway. This endocytic uptake of glucose was not blocked by ikarugamycin (IKA), an inhibitor of clathrin-dependent endocytosis, suggesting a role for clathrin-independent endocytosis in glucose uptake. Investigations of fusion and fission of single vesicles by membrane capacitance measurements revealed a stimulation of endocytic activity by extracellular glucose. Glucose stimulated fission of vesicles was not affected by addition of IKA or block of clathrin coat formation by transient over-expression HUB1 (C-terminal part of the clathrin heavy chain). These data demonstrate that clathrin-independent endocytosis does exist in plant cells. This pathway may represent a common mechanism for the uptake of external nutrients. © 2011 The Authors. The Plant Journal© 2011 Blackwell Publishing Ltd