Balance between Metabolite Accumulation and Transport in Relation to Photosynthesis by Isolated Spinach Chloroplasts

Abstract
The relationship between the rate of orthophosphate (Pi) transport into the stroma and the rate of CO2 fixation by intact chloroplasts was investigated. High Pi concentrations in the medium lead to a depletion of stromal metabolites, due to excessive Pi transport into the stroma, resulting in the inhibition of CO2 fixation. This inhibitory effect of Pi is released by inhibitors of Pi transport, such as pyrophosphate, citrate or pyridoxal-5-phosphate. The latter compound appeared to be specially valuable in inhibiting Pi transport without affecting stromal reactions.