Assay of photosynthetic oxygen evolution from single protoplasts.

A semiquantitative assay for light-dependent O(2) evolution by a single mesophyll protoplast is described. The assay indicator is the density of aerotactic bacteria (Pseudomonas aeruginosa, ATCC 10145; ;Engelmann experiment') attracted to the protoplast. Quantification is by dark field microphotometry. The sensitivity is about 50 femtomoles O(2) per protoplast per minute. The results demonstrate the biphasic nature of O(2) evolution of a single protoplast during photosynthetic induction. Computerized data acquisition yields traces which, until a steady state of photosynthetic O(2) evolution is reached, are identical to ordinary O(2) electrode traces.