Molecular Plant Advance Access originally published online on September 19, 2008
Molecular Plant 2008 1(6):925-937; doi:10.1093/mp/ssn046
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The Ultrastructure of a Chlamydomonas reinhardtii Mutant Strain Lacking Phytoene Synthase Resembles that of a Colorless Alga
a Department of Plant and Microbial Biology, 111 Koshland Hall, University of California, Berkeley, CA 94720–3102, USA
b Electron Microscope Laboratory, 26 Giannini Hall, University of California, Berkeley, CA 94720–3330, USA
1 To whom correspondence should be addressed. E-mail kustu{at}nature.berkeley.edu, fax (510) 642-4995, tel. (510) 643-9308.
Chlamydomonas reinhardtii strains lacking phytoene synthase, the first enzyme of carotenoid biosynthesis, are white. They lack carotenoid pigments, have very low levels of chlorophyll, and can grow only heterotrophically in the dark. Our electron and fluorescence microscopic studies showed that such a mutant strain (lts1-204) had a proliferated plastid envelope membrane but no stacks of thylakoid membranes within the plastid. It accumulated cytoplasmic compartments that appeared to be autophagous vacuoles filled with membranous material. The lts1 mutants apparently lacked pyrenoid bodies, which normally house ribulose bisphosphate carboxylase–oxygenase (Rubisco), and accumulated many starch granules. Although these mutant strains cannot synthesize the carotenoid and carotenoid-derived pigments present in the phototactic organelle (eyespot), the mutant we examined made a vestigial eyespot that was disorganized and often mislocalized to the posterior end of the cell. The absence of a pyrenoid body, the accumulation of starch, and the disorganization of the eyespot may all result from the absence of thylakoids. The ultrastructure of lts1 mutant strains is similar to but distinct from that of previously described white and yellow mutant strains of C. reinhardtii and is similar to that of naturally colorless algae of the Polytoma group.
2 These authors contributed equally to this work and should both be considered first author.