Beans grown under intermittent light (1 msec polychromatic intense light flash every 15 min during cultivation in darkness) do not show photosynthetic oxygen production and variable fluorescence emission immediately after the administration of continuous light for the first time. However, a weak light preillumination is enough to sensitize the leaf in such a way that an actinic illumination then provokes quite normal oxygen production behaviour, as well as variable fluorescence emission. Kinetic studies show that both oxygen production criteria (oxygen outburst and induction kinetics of oxygen production) and variable fluorescence emission criteria (position and intensity of the emission peaks) change in the same way as a function of the amount of light given during the preillumination period.

We conclude that the induction of oxygen evolution and the induction of variable fluorescence in flashed leaves are correlated phenomena regulated by a weak light intensity multiquantum mechanism.