EVIDENCE FOR THE INVOLVEMENT OF GLYCOLATE SYNTHESIS IN THE STIMULATION OF GLYCERATE UPTAKE BY LIGHT IN ISOLATED-CHLOROPLASTS

The glycerate/glycollate (Glc) translocator in chloroplasts of C3 plants mediates the initial export of glycollate from and the final import of glycerate into the chloroplasts during photorespiration. Glycerate uptake into oat (Avena sativa L.) chloroplasts was stimulated by light. Studies with a single-layer (SL) and a stable double-layer (SDL) silicone oil system indicated that this light stimulatory effect was caused, at least in part, by glycollate synthesised during the pre-illumination period. Firstly, preincubation with glycerate and glycollate increased [C-14]glycerate uptake to an extent similar to the stimulation by light. Secondly, [C-14)glycerate uptake was not inhibited by 3-(3',4'-dichlorophenyl)-1,1-dimethylurea and carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone when it was measured in a short time (2 s) in the SDL system. Thirdly, inhibition of ribulose 1,5-bisphosphate oxygenation (and so glycollate synthesis) by KCN abolished the observed stimulation of [C-14]glycerate uptake in the light.