title: Lipid body biogenesis and the role of microtubules in lipid synthesis in Ornithogalum umbellatum lipotubuloids.
abstract: Lipid bodies present in lipotubuloids of Ornithogalum umbellatum ovary epidermis take the form of a lens between leaflets of ER (endoplasmic reticulum) membrane filled with a highly osmiophilic substance. The two enzymes, DGAT1 [DAG (diacylglycerol) acyltransferase 1] and DGAT2 (DAG acyltransferase 2), involved in this process are synthesized on rough ER and localized in the ER near a monolayer surrounding entities like lipid bodies. After reaching the appropriate size, newly formed lipid bodies transform into mature spherical lipid bodies filled with less osmiophilic content. They appear to be surrounded by a half-unit membrane, with numerous microtubules running adjacently in different directions. The ER, no longer continuous with lipid bodies, makes contact with them through microtubules. At this stage, lipid synthesis takes place at the periphery of lipid bodies. This presumption, and a hypothesis that microtubules are involved in lipid synthesis delivering necessary components to lipid bodies, is based on strong arguments: (i) silver grains first appear over microtubules after a short [3H]palmitic acid incubation and before they are observed over lipid bodies; (ii) blockade of [3H]palmitic acid incorporation into lipotubuloids by propyzamide, an inhibitor of microtubule function; and (iii) the presence of gold grains above the microtubules after DGAT1 and DGAT2 reactions, as also near microtubules after an immunogold method that identifies phospholipase D1.
authors.affiliation: Department of Cytophysiology, University of Łodz, Pomorska 141143, 90236 Łodz, Poland. kwiat@biol.uni.lodz.pl
authors.forename: Maria
authors.initials: M
authors.lastname: Kwiatkowska
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Popłońska
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Wojtczak
authors.forename: Dariusz
authors.initials: D
authors.lastname: Stępiński
authors.forename: Justyna Teresa
authors.initials: JT
authors.lastname: Polit
mesh_terms: D001549:Benzamides / Q000494:pharmacology; D051048:Diacylglycerol O-Acyltransferase / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D035264:Flowers / Q000378:metabolism; D002479:Inclusion Bodies / Q000378:metabolism; D008055:Lipids / Q000096:biosynthesis*; D050155:Lipogenesis; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism*; D031442:Ornithogalum / Q000201:enzymology / Q000378:metabolism*; D010739:Phospholipase D / Q000378:metabolism
chemical_list: D001549:Benzamides; D008055:Lipids; C001059:pronamide; D051048:Diacylglycerol O-Acyltransferase; D010739:Phospholipase D; C106801:phospholipase D1