| Abstract: | The concentration and absorption of methylphenazinium cations (MP+) in suspensions of pea chloroplasts are simultaneously lowered during rapid (approximately 10s) illumination. The light-induced changes of absorption and concentration of MP+ reveal similar sensitivity towards some inhibitors and uncouplers and are determined by MP+ uptake by the thylakoids. The time-course of light-induced MP+ uptake was found to be modified in the presence of dithioerythritol, Mg2+ and ATP, i. e. under conditions which induce the ATPase activity and ATP hydrolysis in chloroplasts. The kinetic curve of light-induced MP+ uptake under these conditions consists of a relatively fast (approximatley 10 s) and a slow (approximately 10 min) components. The slow ATP-dependent component of MP+ uptake is enhanced by low concentrations of gramicidin and is completely inhibited by the energy transfer inhibitor--dicyclohexylcarbodiimide. The data obtained suggest that the light-induced energization of the chloroplast membrane is accompanied by the transport of MP+ into the thylakoids against the electrical potential and concentration gradients. |
