Poster: Organelle Biogenesis

Abs # 1135: Isolation and characterization of chloroplast morphological mutants of Arabidopsis thaliana

Presenter:	Nakanishi, Hiromitsu , t02h212@tmail.shinshu-u.ac.jp
Authors	Nakanishi, Hiromitsu  (A)   Uchikawa, Shouji  (A)   Tsuji, Takashi  (B)   Taguchi, Goro  (A)   Kojima, Mineo  (A) (C)  Kaneko, Yasuko  (B)   Hayashida, Nobuaki  (A)
Affiliations:	(A): Gene Research Center, Shinshu University (B): Dept. of Regulation Biology, Fac. Sci., Saitama University (C): Dept. Appl. Biol., Fac. Text. Sci. Technol., Shinshu University

There are presumed to be 3,662 genes encoding products that carry chloroplast targeting signals in the Arabidopsis genome. The function of more than 80% of these genes remains yet to be determined. It is very likely that color mutants have abnormalities in chlorophyll biosynthesis or in the developmental steps of the chloroplast. We have collected and analyzed color mutants of Arabidopsis to study chloroplast biogenesis. A total of 77 color mutant lines were selected from a mutant library generated by EMS mutagenesis. Some lines exhibiting abnormalities in chloroplast morphology were screened by microscopic observation of the isolated protoplasts. Two of them were analyzed in more detail by electron microscopy. One was that of a variegated leaf phenotype, which develops white sectors on the leaf during growth. Electron microscopic observation indicated that the chloroplasts in the green sectors had a structure similar to that of wild type though some of them had fewer thylakoid membranes, while the plastids in the white sectors were vacuolated and did not have well developed thylakoid membranes. The abnormalities may be due to a lack of some components that are important in the development or maintenance system of the chloroplasts. In the other line of mutants, the size and shape of chloroplasts were irregular. These mutants contained enlarged chloroplasts with diameter up to twice that of wild type chloroplasts, and tiny chloroplasts in the same cells. The machinery controlling correct division of chloroplasts may be missing. Further electron microscopic observation revealed that the arrangement and direction of thylakoid membranes were distorted and the stromal area was abnormally expanded. The regulatory mechanism for membrane organization appears to be mutated.