Changes in the room-temperature emission spectrum of chlorophyll during fast and slow phases of the Kautsky effect in intact leaves

Changes in the room-temperature emission spectrum of chlorophyll (Chl) were analyzed using fast diode-array recordings during the Kautsky effect in mature and in greening barley leaves. In mature leaves, the comparison of F-O (basal level of fluorescence yield at transient O) and F-M (maximum level of fluorescence yield at transient M) spectra showed that the relative amplitude of total variable fluorescence was maximal for the 684 nm Photosystem II (PSII) band and minimal for the 725 nm Photosystem I band. During the increase from F-O to F-M, a progressive redshift of the spectrum of variable fluorescence occurred. This shift reflected the different fluorescence rise kinetics of different layers of chloroplasts inside the leaf. This was verified by simulating the effect of screening on the emission spectrum of isolated chloroplasts and by experiments on greening leaves with low Chl content. In addition, experiments performed at different greening stages showed that the presence of uncoupled Chl at early-greening stages and light-harvesting complex II (LHCII) at later stages have detectable but minor effects on the shape of room-temperature emission spectra. When strong actinic light was applied to mature green leaves, the slow fluorescence yield, which declined from F-M to FT (steady-state level of fluorescence yield at transient T), was accompanied by a slight redshift of the 684 nm PSII band because of nonphotochemical quenching of short-wavelength-emitting Chl ascribed to LHCII.