INTERACTION OF CHLOROPLAST AND VACUOLES IN CHLAMYDOMONAS

Proteins synthesized within the chloroplast of Chlamydomonas reinhardtii were recovered in granules within vacuoles (Park et al., J. Phycol. 35,528‐538, 1999). Apoproteins of light‐harvesting complexes, synthesized in the cytosol in excess of the capacity of the chloroplast to synthesize chlorophyll...

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Bibliographic Details
Published in:Journal of phycology 2000-12, Vol.36 (s3), p.53-53
Main Authors: Park, H., Roberson, R.W., Eggink, L. L., Hoober, J.K.
Format: Article
Language:English
Subjects:
Chlamydomonas reinhardtii
Freshwater
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Summary:Proteins synthesized within the chloroplast of Chlamydomonas reinhardtii were recovered in granules within vacuoles (Park et al., J. Phycol. 35,528‐538, 1999). Apoproteins of light‐harvesting complexes, synthesized in the cytosol in excess of the capacity of the chloroplast to synthesize chlorophyll, also were recovered in vacuolar granules. The ultrastructure of conventionally‐ and cryo‐fixed cells revealed protuberances of the chloroplast envelope outer membrane that contained stroma‐like material and also connections between the outer membrane and vacuolar membrane. Transfer of proteins via these structures to vacuoles appeared to be a pathway for degradation of chloroplast material. Purified granules contained polyphosphate as the major component, which seemed to protect proteins in the vacuole from breakdown. A predominant 70 kDa protein in purified granules accumulated in the cell wall of wild‐type cells and in granules of wall‐deficient cells, as revealed by immunolocalization. This protein entered vacuoles via small vesicles from Golgi, which probably also introduced degradative enzymes into this compartment. Vacuoles thus apparently serve as lysosome‐like structures as well as secretory vesicles. The membranes of the chloroplast envelope in cryo‐fixed green cells were tightly appressed except where the inner membrane invaginated or the outer membrane protruded into the cytosol. Whereas conventional fixation showed lack of appression of thylakoid membranes in a chlorophyll b‐less mutant, these membranes appeared as large grana in images of cryofixed cells. The enhanced images obtained with cryofixation allowed substantial refinement of our knowledge of the ultrastructure of these algal cells.
ISSN:0022-3646
1529-8817
DOI:10.1046/j.1529-8817.1999.00001-158.x