title: Origin of β-carotene-rich plastoglobuli in Dunaliella bardawil.
abstract: The halotolerant microalgae Dunaliella bardawil accumulates under nitrogen deprivation two types of lipid droplets: plastoglobuli rich in β-carotene (βC-plastoglobuli) and cytoplasmatic lipid droplets (CLDs). We describe the isolation, composition, and origin of these lipid droplets. Plastoglobuli contain β-carotene, phytoene, and galactolipids missing in CLDs. The two preparations contain different lipid-associated proteins: major lipid droplet protein in CLD and the Prorich carotene globule protein in βC-plastoglobuli. The compositions of triglyceride (TAG) molecular species, total fatty acids, and sn-1+3 and sn-2 positions in the two lipid pools are similar, except for a small increase in palmitic acid in plastoglobuli, suggesting a common origin. The formation of CLD TAG precedes that of βC-plastoglobuli, reaching a maximum after 48 h of nitrogen deprivation and then decreasing. Palmitic acid incorporation kinetics indicated that, at early stages of nitrogen deprivation, CLD TAG is synthesized mostly from newly formed fatty acids, whereas in βC-plastoglobuli, a large part of TAG is produced from fatty acids of preformed membrane lipids. Electron microscopic analyses revealed that CLDs adhere to chloroplast envelope membranes concomitant with appearance of small βC-plastoglobuli within the chloroplast. Based on these results, we propose that CLDs in D. bardawil are produced in the endoplasmatic reticulum, whereas βC-plastoglobuli are made, in part, from hydrolysis of chloroplast membrane lipids and in part, by a continual transfer of TAG or fatty acids derived from CLD.
authors.affiliation: Departments of Biological Chemistry and.
authors.forename: Lital
authors.initials: L
authors.lastname: Davidi
authors.forename: Eyal
authors.initials: E
authors.lastname: Shimoni
authors.forename: Inna
authors.initials: I
authors.lastname: Khozin-Goldberg
authors.forename: Ada
authors.initials: A
authors.lastname: Zamir
authors.forename: Uri
authors.initials: U
authors.lastname: Pick
mesh_terms: D000595:Amino Acid Sequence; D015153:Blotting, Western; D002247:Carbon Isotopes; D002734:Chlorophyll / Q000378:metabolism; D000460:Chlorophyta / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D002736:Chloroplasts / Q000378:metabolism / Q000648:ultrastructure; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D022083:Cytoplasmic Structures / Q000378:metabolism* / Q000648:ultrastructure; D005227:Fatty Acids / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D007091:Image Processing, Computer-Assisted; D008055:Lipids / Q000737:chemistry*; D008969:Molecular Sequence Data; D009584:Nitrogen / Q000172:deficiency; D010078:Oxazines / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D021381:Protein Transport; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013997:Time Factors; D014054:Tomography; D014280:Triglycerides / Q000378:metabolism; D019207:beta Carotene / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D005227:Fatty Acids; D008055:Lipids; D010078:Oxazines; D010940:Plant Proteins; D012333:RNA, Messenger; D014280:Triglycerides; D019207:beta Carotene; D002734:Chlorophyll; D009584:Nitrogen; C044808:nile red