Photoactive protochlorophyllide regeneration in cotyledons and leaves fromhigher plants

Chorophyll accumulation during greening implies the continuous transformati on of photoactive protochlorophyllide (Pchlide) to chlorophyllide, Since th is reaction is a light-dependent step, the study of regeneration of photoac tive Pchlide under a continuous illumination is difficult. Therefore this p rocess is best studied on etiolated plants during a period of darkness foll owing the initial photoreduction of photoactive Pchlide, In this study, the regeneration process has been studied using spinach cotyledons, as well as barley and bean leaves, illuminated by a single saturating flash. The rege neration was characterized using 77 K fluorescence emission and excitation spectra and high-performance liquid chromatography. The fluorescence data i ndicated that the same spectral forms of photoactive Pchlide are regenerate d by different pathways: (1) photoactive Pchlide regeneration starts immedi ately after the photoreduction through the formation of a nonphotoactive Pc hlide form, emitting fluorescence at approximately 651 nm, This form is sim ilar to the large aggregate of photoactive Pchlide present before the illum ination, but it contains oxidized form of nicotinamide adenine dinucleotide phosphate, instead of the reduced form (NADPH), in the ternary complexes; and (2) after the dislocation of the large aggregates of chlorophyllide-lig ht-dependent NADPH:Pchlide a photooxidoreductase-NADPH ternary complexes, t he regeneration occurs at the expense of the several nonphotoactive Pchlide spectral forms present before the illumination.