Biosynthesis of chlorophyll of photosystem II reaction centers in plant leaves in early stages of etiolation

Spectral methods were used to study the sequences of chlorophyll biosynthes is reactions in etiolated pea, bean, and maize plants in early stages (3-4 days) of growth. For these juvenile plants, along with the reaction chain k nown for mature (7-9 day-old) plants, a new reaction chain was found which started with phototransformation of the long-wavelength form PChld 686/676 into PChld 653/648. (PChld 653/648 differs from the main known precursor fo rm PChld 655/650). The subsequent photoreduction of PChld 653/648 leads to the formation of Chld 684/676, which is transformed into Chi 688/680 in the course of a dark reaction. After completion of this reaction, fast (20-30 sec) quenching of the fluorescence of the reaction product is observed with the formation of non-fluorescent Chi 680. The reaction accompanied by pigm ent fluorescence quenching is absent in pea mutants with depressed function of Photosystem II reaction centers. This suggests that the newly found rea ction chain leads to the formation of chlorophyll of the Photosystem II rea ction center.