Abstract
A chloroplast fraction isolated from Acetabularia mediterrania carries on photosynthesis at rates essentially equal to those of whole cells. Electron and phase contrast microscopy reveals that the chloroplasts are intact and well preserved. Preparations contain no identifiable peroxisomes, but some cytoplasmic and mitochondrial contamination is present. Photosynthesis and CO(2) production in light by chloroplast preparations are in many respects similar to that of bean leaves, although the measured rates are somewhat lower. Respiration and photosynthesis of chloroplast preparations and whole cells of Acetabularia is essentially similar except that cells have a strong dark-type respiration which continues in light and is CO(2) dependent, the substrate being mainly recent photosynthate. The data suggest that chloroplasts are the site of photorespiration.