Retrograde vesicles from the vacuole regulate tonoplast surface area and volume during fluid-phase endocitosis

Trabajo presentado en el International Plant Membrane Biology Congress, celebrado en Adelaida del 19 al 24 de eptiembre de 2010.

During transport of external solutes from the apoplast to the vacuole by fluid-phase endocytosis (FPE), endocytic vesicles me rge with the tonoplast to release their contents. The merging of endocytic vesicles with the vacuole generates in a larger surface area/volume ratio, resulting in an increase volume and dilution of vacuolar contents. To concentrate solutes, a mechanism(s) to reduce tonoplast surface area must exist. We investigated possible means of tonoplast rearrangement during FPE using red beet hypocotyls for their red and fluorescent vacuolar pigment, which would identify any structure of vacuolar origin. When incubated 200 mM sucrose, cells took up sucrose in part by endocytosis. Increase in 24 mM sucrose content by endocytic sucrose uptake implicated a 2% increase in vacuolar volume and a 14% increase in tonoplast membrane surface area. During endocytosis, we observed the formation of vacuolar originating structures of various sizes as demonstrated by confocal laser scanning microscopy. Therefore, to counteract the disproportionate addition of membrane and fluids to the vacuole, cells generate exocytic vesicles. Exocytic vesicles re-establish surface area/volume ratio allowing for the concentration of solutes within the vacuole.

Peer Reviewed