Chlorophyll a Fluorescence as a Quantitative Probe of Photosynthesis: Effects of Co₂ Concentration During Gas Transients on Chlorophyll Fluorescence in Spinach Leaves

SUMMARY The relationship between changes in chlorophyll a fluorescence and changes in CO 2 concentration in spinach leaves is analyzed. The height of the fluorescence excursion, when plotted against the CO 2 concentration during the transient, results in a hyperbola. When these data are replotted on an inverse‐reciprocal plot, an apparent K m (CO 2 ) for the fluorescence transient can be obtained which closely approximates the K m (CO 2 ) for carbon assimilation under similar conditions. Transitions in CO 2 concentration at 2 % O 2 result in deviation from this hyperbolic relationship, reducing the apparent K m (CO 2 ) for this process. The relationship between carbon assimilation and chlorophyll fluorescence is discussed with reference to the two components of fluorescence quenching. This technique raises the possibility that chlorophyll fluorescence could be used as a quantitative as well as a qualitative tool in plant screening.