Poster: Organelle biogenesis

Abs # 632: Regulation of chloroplast synthesis by a light-mediated phosphoinositide system

Presenter:	Lyman, harvard , hlyman@notes.cc.sunysb.edu
Authors	Regan, kristin  (A) (A)  Lyman, harvard  (A) (A)
Affiliations:	(A): State University of New York at Stony Brook

In most higher plants and algae nuclear-coded chloroplast proteins are synthesized on free ribosomes and delivered in a post-translational manner, in Euglena proteins are transported in a co-translational manner through ER and Golgi.Previous work in our laboratory established that light triggers a phosphoinositide system generating IP₃ IP₃ opens Calcium channels leading to interactions between calcium-binding proteins and a cascade of cellular events. This cascade of signaling events triggers the release of vesicles from the Golgi and mediates transport to the outer membrane of the chloroplast. We investgated the effect of the Calcium channel inhibitor, Cadmium Chloride on the biogenesis of the chloroplast. Previous studies showed Cadmium Chloride inhibited chlorplast synthesis in a reversible manner. This inhibition results in an inhibition of protein transit to the chloroplast The kinetics of inhibition and reversal were determined. Cells washed at 12 and 24 hours of illumination showed a reversal of inhibition whilecells washed at 36 hours showe incomplete reversal. At concentrations above 175ul, there was no reversal of inhibition. One explanation for this result is that proteins are trapped within the endoplasmic reticulum and the trans-Golgi network due to the lack of Calcium to signal the transport of vesicles to the outer membrane of the chloroplast. Calcium has been implictaed in vesicle formation, transport and fusion with target membrane. Future research will be on the role of Calcium in vesicleformation and transport. Grant for this research was funded by Howard Hughes Medical Institute Howard Hughes Medical Institute, grant #52003052, 2003