Some effects of CO2concentration and decreased O2concentration on induction fluorescence in leaves

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Abstract
A procedure is described that permits spinach leaves to display secondary fluorescence kinetics when illuminated in air at 20 °C. The initial peak in chlorophyllafluorescence is then followed by a fall to a quasi-steady state (S), a rise to a new peak (M) and a final fall to a terminal steady-state value (T). These kinetics can be modified by changing the periods of light and darkness before measurement. The M peak is abolished by exposure to CO2-free air and greatly modified by exposure to 5 % CO2. In 2% O2the period of darkness immediately before illumination needs to be lengthened if secondary kinetics are to be observed. The results are discussed in relation to the probable impact of photosynthetic carbon assimilation on fluorescence-quenching mechanisms.