Poster: Organelle Biogenesis

Abs # 1132: Demonstration of plastid DNA and photoinduction of photosynthetic proteins in Prototheca wickerhamii by immunoelectron microscopy

Presenter:	Osafune, Tetsuaki , osafune@ny.tokai.or.jp
Authors	Osafune, Tetsuaki  (A)   Aoki, Shigeji  (B)   Schwartzbach, Steven D (C)
Affiliations:	(A): Department of Life Sciences, Nippon Sport Science University (B): Advance Research Center, Nippon Dental University at Niigata (C): Microbiology and Molecular Cell Sciences, University of Memphis

The presence of plastids has been accepted as morphologically crucial evidence for classifying the Prototheca species as green algae. In the present study, immunoelectron microscopy was used to identify plastid DNA and to examine the light regulated expression of two photosynthetic plastid proteins in a clinical isolate of Prototheca wickerhamii. P. wickerhamii plastids contained starch grains enclosed by a double-membrane. Membranous lamella-like structures developed in the plastids of cells grown in the light. Deposition of anti-DNA immunogold particles showed the presence of DNA in the plastids. The chloroplast DNA encoded large subunit of the CO₂-fixing enzyme, ribulose-1, 5-bisphosphate carboxylase (RuBisCO), was found in plastids of cells grown in either the light or dark. The nuclear DNA encoded small subunit of RuBisCO was found distributed in both the cytoplasm and plastids. The apoprotein of the light-harvesting chlorophyll a/b-binding protein of photosystem II (LHCP II), a nuclear encoded thylakoid protein, was also detected in both the cytoplasm and plastids of cells grown in the light but was not detected in cells grown in the dark. Although the genus Prototheca has lost the ability to synthesize chlorophyll, it has retained the ability to synthesize at least some chloroplast proteins in response to light exposure. The metabolic role if any of RuBisCO remains to be determined.