CHANGES OF CHLOROPHYLL(IDE) FLUORESCENCE YIELD INDUCED BY A SHORT LIGHT-PULSE AS A PROBE TO MONITOR THE EARLY STEPS OF ETIOPLAST PHOTOTRANSFORMATION IN DARK-GROWN LEAVES

The fluorescence yield of chlorophyll(ide) (ChI[ide]) excited by weak modulated light was recorded at room temperature during a 2 h period a fter a short actinic light pulse that transformed all photoactive prot ochlorophyllide in dark-grown barley leaves. A typical pattern of fluo rescence yield variations was found whatever the age of the leaf but w ith age-dependent changes in rates. Its successive phases were related to the Chl(ide) spectral shifts observed in low-temperature emission spectra. The fluorescence yield started at a high level and strongly d eclined during the formation of Chlide(695) from Chlide(688) within a few seconds. It increased to a transient maximum during the Shibata sh ift (15-25 min) that resulted in ChI(ide)(682). A final, slow decrease to a steady state occurred during the final red shift to ChI(685). Pr etreatments with delta-aminolevulinic acid, chloramphenicol or 1,10-ph enanthroline resulted in correlated modifications of Chl(ide) fluoresc ence yield transients and shifts of the low-temperature Chl(ide) emiss ion band. The complex response of the final decrease phase of the fluo rescence yield to these compounds suggests that it results both from t he assembly of photosynthetic Chi proteins and from the reorganization of the etioplast membrane system. From these results it is concluded that continuous recordings of CN(ide) fluorescence yield after a short light pulse represent a useful tool to monitor the kinetics of pigmen t-protein organization and primary thylakoid assembly triggered by Pch lide photoreduction.