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

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Abstract
Excursions in chlorophyll fluorescence were obtained under continuous illumination by changing the composition of the atmosphere surrounding pieces of spinach leaf. Removal of CO2caused 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 CO2concentration. The effect was then proportional to the decrease in CO2whereas the steady-state value was related to the final CO2concentration. The excursions promoted by the decrease in CO2concentration were enhanced if O2was simultaneously decreased from 20 to 2%. Responses to changes in O2concentration in the absence of CO2, to increases in CO2concentration alone, and to pulses of CO2and O2in a N2atmosphere, 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.

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