The Effect Of Light On Expression Of Pea Chloroplast Genes

Abstract

The purpose of this research project was to determine whether light affects on the expression of certain chloroplast-encoded proteins of the pea ATP synthase complex. The proteins studied were the alpha and beta subunits of the CF ₁ portion of the ATP synthase. Dark-germinated pea seedlings were exposed to varying periods of light from 0 to 48 hours in length. Following light exposure, chlorophyll and total protein assays were run on harvested leaf tissue. The proteins in extracts of leaf tissue were separated by SDS polyacrylamide gel electrophoresis and then subjected to Western blotting. The synthase subunits were detected on the Western blot by reaction with specific rabbit antibodies; the antigen-antibody complex was visualized by a color reaction utilizing a second antibody enzyme conjugate. Both the concentration of chlorophyll and of total protein in the leaf tissue rose with longer periods of light exposure. The alpha and beta subunits were both detected in the etiolated leaves of the seedlings which did not receive any light. The level of the beta subunit remained about the same until the seedlings had received 24 hours of light at which point the level showed a marked increase. At 48 hours of light, the beta protein level declined. However, the amount of the alpha subunit did not change noticeably with increasing light exposure.