FORMATION OF LONG-WAVELENGTH CHLOROPHYLLIDE (CHLIDE695) IS REQUIRED FOR THE ASSEMBLY OF PHOTOSYSTEM-II IN ETIOLATED BARLEY LEAVES

Chlorophyll(ide) spectroscopic properties and Photosystem II assembly, monitored by 77 K variable fluorescence, were studied in etiolated ba rley leaves as a function of the extent of protochlorophyllide photore duction by a single millisecond light flash of different intensities. Variable fluorescence, measured 2 hours after the flash, was only dete cted when the extent of phototransformation was higher than a threshol d value of 0.4. Its development paralleled the formation of a chloroph yll emission component at 685 nm, which itself derived from long-wavel ength chlorophyllide with an emission maximum at 695 nm. At low flash intensities, short-wavelength chlorophyllide forms preferentially accu mulated and no Photosystem II fluorescence was detected after 2 hours. Chlorophyllide esterification was independent of the extent of photot ransformation. These results suggested that the formation of long-wave length chlorophyllide was essential for further assembly of Photosyste m II. This interpretation was strengthened by the observed inhibition of both long-wavelength chlorophyllide formation and of variable fluor escence development in leaves treated with 6-aminolevulinic acid or in untreated leaves subjected to repeated flashes of low intensity.