[en] Room temperature absorbance and 77 K fluorescence measurements were used in order to identify Pchlide and Chlide spectral forms involved in protochlorophyllide photoreduction in greening leaves of barley. Pchlide(650) (the subscript refers to the in vivo absorbance maximum of the pigment) is the main photoactive Pchlide throughout the first 8 h of greening. Its photoreduction triggers a succession of Chl(ide) spectral forms that are identical to those normally found after photoreduction in unirradiated leaves. After an actinic radiation pulse, Chlide(684) appears within 2 s from an intermediate at shorter wavelength and is transformed to Chlide(672) in less than 2 min. The time-scale of the shifts is remarkably shorter than in unirradiated leaves, which is consistent with the acceleration of Chi accumulation during greening. Pchlide(630) and Pchlide(640) act as precursors of Pchlide(650) during its regeneration, which exhibits a marked inhibition at temperatures above 30 degrees C.
