Some effects of changes in gas phase on the steady-state chlorophyll a fluorescence exhibited by illuminated leaves

Abstract

Excursions in chlorophyll fluorescence were obtained under continuous illumination by changing the composition of the atmosphere surrounding pieces of spinach leaf. Removal of CO$_{2}$ caused a transient rise and a subsequent fall to a new quasi-steady-state level. This response could be interrupted at any time by readmission of air, and similar but smaller excursions could be initiated by decreasing the CO$_{2}$ concentration. The effect was then proportional to the decrease in CO$_{2}$ whereas the steady-state value was related to the final CO$_{2}$ concentration. The excursions promoted by the decrease in CO$_{2}$ concentration were enhanced if O$_{2}$ was simultaneously decreased from 20 to 2%. Responses to changes in O$_{2}$ concentration in the absence of CO$_{2}$, to increases in CO$_{2}$ concentration alone, and to pulses of CO$_{2}$ and O$_{2}$ in a N$_{2}$ atmosphere, are also described. The results are discussed in relation to changes in NADPH and ATP brought about by photosynthetic carbon assimilation and its regulatory mechanisms.