Transfer of proteins from the chloroplast to vacuoles in Chlamydomonas reinhardtii (Chlorophyta): A pathway for degradation

Hyoungshin Park, Laura L. Eggink, Robert Roberson, J. Kenneth Hoober

Research output: Contribution to journalArticle

33 Scopus citations

Abstract

Several chloroplast proteins were detected by immunoelectron microscopy within dense granules in cytoplasmic vacuoles in the alga Chlamydomonas reinhardtii Dangeard. Transfer from chloroplast to vacuoles of two major, pulse-labeled polypeptides, the large subunit of rubisco and the α subunit of ATPase, which are synthesized on chloroplast ribosomes, was demonstrated by the recovery of these polypeptides in vacuolar granules over a several-hour time period. The ultrastructure of cryofixed algal cells was examined to search for structures that would provide insight into the transfer of chloroplast proteins to vacuoles. Micrographs showed that the two membranes of the envelope were appressed, with no detectable intermembrane space, over most of the chloroplast surface. Protrusions of the outer membrane of the envelope were occasionally found that enclosed stroma, with particles similar in size to chloroplast ribosomes, but generally not thylakoid membranes. These observations suggest that chloroplast material, especially the stromal phase, was extruded from the chloroplast in membrane-bound structures, which then interacted with Golgi-derived vesicles for degradation of the contents by typical lysosomal activities. A protein normally targeted to vacuoles through the endomembrane system for incorporation into the cell wall was detected in Golgi structures and vacuolar granules but not the chloroplast.

Original languageEnglish (US)
Pages (from-to)528-538
Number of pages11
JournalJournal of Phycology
Volume35
Issue number3 II
DOIs
StatePublished - Jun 1999

Keywords

  • Chlamydomonas reinhardtii
  • Chlorophyta
  • Chloroplast development
  • Chloroplast envelope
  • Chloroplast protrusions
  • Cryofixation
  • Immunoelectron microscopy
  • Ultrastructure
  • Vacuoles

ASJC Scopus subject areas

  • Aquatic Science
  • Plant Science

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