Dark Release of CO(2) from Higher Plant Leaves.

A study was conducted with 48 species of the amount of (14)CO(2) released during the first minute of dark following fixation of (14)CO(2) in the light. Light fixation periods varied from 5 to 60 seconds. The species examined included both monocots and dicots and represented C(4), C(3), and Crassulacean acid metabolism (CAM) photosynthetic types.Total CO(2) uptake was determined as the sum of soluble (14)C (ethanol and water), insoluble (14)C, and (14)CO(2) released during the first minute of dark. Insoluble (14)C made up a very small percent of the total. The percent of soluble (14)C increased with fixation time in C(4) species, while the percent of (14)CO(2) released in the dark decreased. C(3) species released a very small percent of (14)CO(2) in the dark, and this percent remained relatively constant with time of (14)CO(2) fixation whereas C(4) species released a higher percent initially and this percent declined with time of fixation. CAM species were similar to C(4) species.The species are grouped according to the (14)CO(2) released during the first minute of dark with light labeling times of 5 and 60 seconds. These comparisons are shown to separate C(3) from C(4) and CAM species. Further, the data suggest that the origin of the CO(2) in the dark release of C(4) plants is quite different from that of C(3) plants.