Electrophoretic studies of light-induced charge in spinach chloroplasts

Stable-flow free-boundary electrophoresis of isolated spinach chloroplasts was performed in various buffered saline solutions, in the light and dark. The chloroplasts were negatively charged, and the absolute value of their electrophoretic mobility was about 15% larger in the light than in the dark. This light-induced mobility increase could be abolished by 3-(3,4-dichlorophenyl)-1,1-dimethylurea, a finding confirmed by conventional microelectrophoresis. The increase appeared to be unaffected by uncouplers of photophosphorylation or by a cyclic electron carrier, in distinction to light-induced shrinkage or ion translocation. Contrary to light-induced swelling, the mobility increase was observed under low light intensity and was lost upon mechanical disruption of the chloroplasts. A physical rather than metabolic mechanism appears most consistent with all the observations.