Protection of native chlorophyll(ide) forms ans of photosystem II against photodamage during early stages of chloroplast differentiation

The resistance of chlorophyllide to intense light and the integration of chlorophyll to photosystems have been studied during the early stages of the greening process in etiolated bean or barley leaves. The possible role of NADPH-protochlorophyllide-oxidoreductase in chlorophyllide protection is discussed on the basis of chlorophyllide absorbance data during photodegradation and of chlorophyllide fluorescence lifetime measurements. Free chlorophyll during continuous greening was evaluated through fluorescence spectroscopy and fluorescence lifetime measurements in isolated etiochloroplasts. Its relative amount was maximum after 2 hours and decreased rapidly to a low level in parallel to photosystem II variable fluorescence development. Photosystem II mediated electron transport was compared in etiochloroplasts from flashed leaves before or after photoactivation of the water-splitting system. The effects of exogenous quinones on rapid fluorescence transients suggest the occurrence of a cyclic electron flow in water-splitting deficient photosystem II.