Lipid droplets in onion epidermal cells: interactions with the nucleus

Lipid droplets are abundant in adaxial epidermal cells in onion (Allium cepa). Its presumptive functions are energy storage, cellular metabolism and organellar coordination, but how cells integrate lipid droplet dynamics with nuclei remains unknown. Here, we analyzed lipid droplet occurrence and distribution in fresh preparations of hydrated white onion and red onion epidermal cells through differential interference contrast (DIC) microscopy and assess the inter-organellar connection through these oil bodies. Large extensions of membrane-bound cytoplasmic organelles were found to interact with the nuclear envelope, and these peripheral tubular structures were found to transport lipid droplets. The lipid content of vesicles could be confirmed by BODIPY493/503 staining and confocal microscopy, whereas Lugol staining allowed visualization of a wide membranal network that extends throughout the cell. Thus, lipid droplet dynamics may account for the regulation of the nuclear shape and/or function and membrane interactions enable the transport of lipid droplets among organelles in onion bulb epidermal cells.