Chlorophyll synthesis in green leaves and isolated chloroplasts of barley (Hordeum vulgare)

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Abstract
The photoreduction of protochlorophyllide was studied in leaves and isolated chloroplasts of barley. Leaves of plants which had been preilluminated for varying lengths of time were incubated with [14C]‐δ‐ aminolevulinic acid for 2 h in the dark. The subsequent photoreduction of [14C]‐protochlorophyllide was analyzed by high performance liquid chromatography of pigments extracted from illuminated leaves and plastids. The plastids used in this study were isolated in the dark from leaves at the end of the 2 h labelling period. Three major results were obtained: The extent of protochlorophyllide reduction in vivo was rapidly reduced as a function of the preillumination period. In 24 h preilluminated plants only a small fraction of the radioactively labelled protochlorophyllide was reduced during the subsequent light period. The amount of NADPH‐protochlorophyllide oxidoreductase (EC 1.6.99.‐) present in plastids of fully‐green plants was drastically reduced relative to levels in plastids of dark‐grown plants as estimated by the methods of immunoblotting of plastid proteins and immunogold labelling of ultrathin sections of the leaf tissue. In etiolated plants light seemed to affect the reduction of protochlorophyllide directly through the excitation of protochlorophyllide. In fully green plants, however, light also affected chlorophyll formation indirectly by the supply of NADPH via photosynthetic electron transport.