Some effects of CO 2 concentration and decreased O 2 concentration on induction fluorescence in leaves

Abstract

A procedure is described that permits spinach leaves to display secondary fluorescence kinetics when illuminated in air at 20.degree. C. The initial peak in chlorophyll a fluorescence 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% O2 the 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 C assimilation on fluorescence-quenching mechanisms.