Chlorophyll Synthetase and Chloroplast tRNA glu are Present in Heat-Bleached, Ribosome-Deficient Plastids

Abstract

Summary Heat-bleached, plastid-ribosome deficient primary leaves of rye ( Secale cereale ) and oat ( Avena sativa ) were investigated for the presence of chloroplast tRNA glu and chlorophyll synthetase. In spite of the ribosome deficiency, tRNA glu is found in substantial amounts in bleached rye plastids. This result is discussed with regard to the coding site (nucleus or chloroplast) of chloroplast RNA polymerase. Chlorophyll synthetase is present with nearly normal or partially (30-40%) reduced activity in bleached leaf tissue compared with normal green primary leaves. It is concluded that this enzyme is encoded by a nuclear gene. The transcription of this gene should (almost) not be affected by the action of a postulated plastid factor triggering the expression of certain nuclear genes in correspondence with the development of photosynthetically active chloroplasts. The low content of chlorophyll in leaves developed at elevated temperature is obviously not caused by a deficiency in chloroplast tRNA glu or chlorophyll synthetase activity.