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Plant Physiol, September 2001, Vol. 127, pp. 90-96
Chloroplast Protein Translocon Components atToc159 and atToc33
Are Not Essential for Chloroplast Biogenesis in Guard Cells and Root
Cells1
Tien-Shin
Yu and
Hsou-min
Li*
Institute of Molecular Biology, Academia Sinica, Taipei 11529, Taiwan
Protein import into chloroplasts is mediated by a protein import
apparatus located in the chloroplast envelope. Previous results indicate that there may be multiple import complexes in Arabidopsis. To
gain further insight into the nature of this multiplicity, we analyzed
the Arabidopsis ppi1 and ppi2 mutants,
which are null mutants of the atToc33 and atToc159 translocon proteins,
respectively. In the ppi2 mutant, in contrast to the
extremely defective plastids in mesophyll cells, chloroplasts in guard
cells still contained starch granules and thylakoid membranes. The
morphology of root plastids in both mutants was similar to that in wild
type. After prolonged light treatments, root plastids of both mutants
and the wild type differentiated into chloroplasts. Enzymatic assays indicated that the activity of a plastid enzyme was reduced only in
leaves but not in roots. These results indicated that both the
ppi1 and ppi2 mutants had functional root
and guard cell plastids. Therefore, we propose that import complexes
are cell type specific rather than substrate or plastid specific.
1
This work was supported by the National Science
Council (grant no. NSC 89-2321-B-001-005 to H.-m.L.) and by
Academia Sinica of Taiwan (grant to H.-m.L.).
*
Corresponding author; e-mail mbhmli{at}ccvax.sinica.edu.tw; fax
886-2-2782-6085.
© 2001 American Society of Plant Physiologists
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