PHOTOREDUCTION OF PROTOCHLOROPHYLLIDE TO CHLOROPHYLLIDE IN 2-D-OLD DARK-GROWN BEAN (PHASEOLUS-VULGARIS CV COMMODORE) LEAVES - COMPARISON WITH 10-D-OLD DARK-GROWN (ETIOLATED) LEAVES

Two-d-old leaves which do not contain prolamellar bodies synthesize active protochlorophyllide in darkness. When protochlorophyllide is photoreduced by one intense white flash, a main chlorophyllide species emitting at 690 nm is formed. After the photoreduction, the emission maximum is shifted to 675 nm within 5 s. This result suggests that in young leaves, chlorophyllide formed after one flash is quickly released from the active site of NADPH: protochlorophyllide oxidoreductase. This interpretation is strenghtened by time-resolved fluorescence measurements at room temperature, showing that 675 nm emitting chlorophyllide does not transfer excitation energy to the 696 nm emitting chlorophyllide which is formed in very low amount. In 10-d-old bean leaves, the 690 nm chlorophyllide emitting species formed after one short flash undergoes the well-known rapid and Shibata spectral shifts. The 675 nm emitting chlorophyllide appears only as a shoulder. At both ages, the fluorescence intensity of the active protochlorophyllide strongly decreases during and after photoreduction, suggesting rapid modifications in the close environment of the pigment.