Algae. 2003; 18(2): 121-127.
Gold Immunolocalization of Rubisco and Rubisco Activase in Pyrenoid of Chlamydomonas reinhardtii
Peimin He*, Dabing Zhang1, Gengyun Chen2, Qigen Liu and Weining Wu
Shanghai Fisheries University, Shanghai 200090, 1Agriculture Institute of Shanghai, Shanghai 20106 and 2Shanghai Institute of Plant Physiology, Chinese Academy of Science, Shanghai 200433, China
The pyrenoid ultrastructure and distribution of ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco) and Rubisco activase in the chloroplasts of Chlamydomonas reinhardtii was studied using the immunogold localization technology with electron microscopy. there were several tubular thylakoids invading in the pyrenoid matrix to form several spokewise channels. The connections between pyrenoid matrix and stroma of chloroplast were the partial of channels. The starch sheath surrounding the pyrenoid was separated into several parts by the connections in transection. Some thylakoids were packed together near the connections in one side of the pyrenoid. Those special structures might be used to transport substance between pyrenoid and stroma of With the antibody raised against the large subunits of Rubisco from C. protothecoides, the result of the gold immunolocalization of Rubisco in Chlamydomonas reinhardtii showed most of the gold particles heavily labeled the pyrenoid matrix, as well as the starch sheath matrix, and very few in the stroma of choroplasts. The gold particle density was 880.00 ± 164.32, 190.00 ± 152.39 and 9.60 ± 5.37 ㎛〈sup〉-2〈/sup〉in pyrenoid matrix, starch sheath and stroma region of choroplast respectively (background: 5.67 ± 1.53 ㎛〈sup〉-2〈/sup〉). 99.59% of the total Rubiscos was calculated to be concentrated in the pyrenoid matrix and starch sheath by spatial densities. The gold immunolocalization of Rubisco activase also showed that Rubisco activase was mainly concentrated in the periphery of the pyrenoid and the starch sheath (the density was as high as 229.69 ± 96.96 ㎛〈sup〉-2〈/sup〉). There were very few gold particles located in the stroma of chloroplasts. These results indicated that pyrenoid surface and starch sheath was the site for Rubisco activation and CO₂ fixation, which supported the suggestion that pyrenoids perform photosynthesis function.
Keywords : Chlamydomonas reinhardtii, gold immunolocalization, pyrenoid, Rubisco, Rubisco activase, ultrastructure