AbstractThe stromal pH of chloroplasts contained in wheat leaf protoplasts was determined by incubating the protoplast suspension with radioactively labelled DMO, followed by rapid subcellular fractionation and measurement of the radioactivity in the separated chloroplast fraction. The stromal pH was found to be about 8.0 upon illumination and 7.6 in darkness. These results demonstrate that light‐dependent stromal pH changes, which have been found earlier in isolated chloroplasts, also occur in a plant cel