Structural correlates of cytoplasmic and chloroplast lipid body synthesis in Chlamydomonas reinhardtii and stimulation of lipid body production with acetate boost.
Light microscopy and deep-etch electron microscopy were used to visualize triacylglyceride (TAG)-filled lipid bodies (LBs) of the green eukaryotic soil alga Chlamydomonas reinhardtii, a model organism for biodiesel production. Cells growing in nitrogen-replete media contain small cytoplasmic lipid bodies (α-cyto-LBs) and small chloroplast plastoglobules. When starved for N, β-cyto-LB formation is massively stimulated. β-Cyto-LBs are intimately associated with both the endoplasmic reticulum membrane and the outer membrane of the chloroplast envelope, suggesting a model for the active participation of both organelles in β-cyto-LB biosynthesis and packaging. When sta6 mutant cells, blocked in starch biosynthesis, are N starved, they produce β-cyto-LBs and also chloroplast LBs (cpst-LBs) that are at least 10 times larger than plastoglobules and eventually engorge the chloroplast stroma. Production of β-cyto-LBs and cpst-LBs under the conditions we used is dependent on exogenous 20 mM acetate. We propose that the greater TAG yields reported for N-starved sta6 cells can be attributed to the strain's ability to produce cpst-LBs, a capacity that is lost when the mutant is complemented by a STA6 transgene. Provision of a 20 mM acetate "boost" during N starvation generates sta6 cells that become so engorged with LBs-at the expense of cytoplasm and most organelles-that they float on water even when centrifuged. This property could be a desirable feature for algal harvesting during biodiesel production.
Department of Biology, Washington University, St. Louis, MO 63130, USA.
Carrie
C
Goodson
Robyn
R
Roth
Zi Teng
ZT
Wang
Ursula
U
Goodenough
D016825:Chlamydomonas reinhardtii / Q000254:growth & development / Q000378:metabolism* / Q000648:ultrastructure; D002736:Chloroplasts / Q000378:metabolism* / Q000648:ultrastructure; D003470:Culture Media / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism* / Q000648:ultrastructure; D050356:Lipid Metabolism; D009584:Nitrogen / Q000378:metabolism; D053141:Organelle Size; D015388:Organelles / Q000378:metabolism; D019347:Potassium Acetate / Q000378:metabolism*; D014280:Triglycerides / Q000378:metabolism
D003470:Culture Media; D014280:Triglycerides; D019347:Potassium Acetate; D009584:Nitrogen