Characteristics of prompt and delayed fluorescence from spinach chloroplasts.

Effects of ferricyanide, dichlorophenyldimethylurea (DCMU), and uncouplers of phosphorylation on the prompt and delayed fluorescences from spinach chloroplasts are described. Any factor that affects the yield of prompt fluorescence will similarly influence the intensity of delayed fluorescence. This idea, recently investigated by Lavorel, should be expressed in terms of a "live" component of fluorescence; that is, the component from chlorophyll associated with the photochemical traps of System II. Some of the effects of ferricyanide and DCMU on delayed fluorescence can then be explained in terms of effects on the yield of prompt fluorescence. From the internal consistency of the explanation, applied to various observations, a judgment can be made that most of the prompt fluorescence observed initially when dark-adapted chloroplasts are first illuminated is "dead," coming from chlorophyll not associated with trap II. The live fluorescence is represented almost entirely by the time-varying component that develops during illumination. The observed intensity of delayed fluorescence can be divided by the yield of live prompt fluorescence to give an intrinsic delayed fluorescence. This intrinsic delayed fluorescence is proportional to the square root of exciting light intensity (as long as the excitation is not saturating) and decays with second order kinetics. This behavior may reflect the photochemical formation and second order dissipation of an oxidized product of Photosystem II.