On the protein-synthesizing system of chloroplasts

Hybridization of leucyl-transfer ribonucleic Acid isoacceptors from green leaves with nuclear and chloroplast deoxyribonucleic Acid

Chromatographically distinct isoacceptors of leucyl-tRNA from mature bean leaves were all observed to hybridize with bean chloroplast and nuclear DNA in a ratio similar to that exhibited by the unfractionated leucyl-tRNA. Under the same hybridization conditions, maize tRNA failed to form a stable hybrid with bean DNA, and levels of hybridization between bean-leaf leucyl-tRNA and nuclear or chloroplast DNAs from tobacco and maize were relatively small.

Chloroplast and cytoplasmic low-molecular-weight ribonucleic acid components of the leaf of Vicia faba L

1. A method for the extraction of plant nucleic acids and their separation on methylated-serum-albumin-kieselguhr columns is described. It is demonstrated that the characteristics of the elution profiles of material from the same source are consistently reproducible. 2. Major dissimilarities were found in the elution profiles of nucleic acids from root and from leaves of Vicia faba L. These dissimilarities were confirmed by polyacrylamide-gel electrophoresis. 3. Four distinct types of low-molecular-weight RNA were demonstrated to be present in leaves, clearly distinguished by their behaviour when chromatographed on methylated-serum-albumin-kieselguhr columns. (a) Both cytoplasmic and chloroplast ribosomes contained a low-molecular-weight RNA, and these components were distinct from each other. (b) The chloroplast possessed a unique ;soluble' RNA (i.e. RNA that is not precipitated by centrifugal forces that sediment ribosomes) which was not present in the rest of the cell. (c) A soluble component, probably transfer RNA, was found in both the chloroplasts and in the cytoplasm. 4. The components distinguishable by methylated-serum-albumin-kieselguhr column chromatography could not be distinguished by sucrose-density-gradient centrifugation.

Protein synthesis in tomato fruit locule tissue: The sites of synthesis and the pathway of carbon into protein

The net increase in total protein during development of tomato fruit locule tissue has been further investigated with respect to the sites of protein synthesis within the cells. The results point to the plastids as being the major sites of protein synthesis. This is supported by radioisotope experiments in which labelled carbon from bicarbonate has been show to appear in protein at a higher rate than exogenously supplied amino acid. Isolated plastids incorporate carbon from bicarbonate, glucose and pyruvate into protein, and it is suggested that the pathway of carbon into protein involves photosynthetic pathways. The results are discussed with reference to possible differences between protein synthesis in plastids, and protein synthesis in the cytoplasm of plant cells.

[The action of phytochrome and actinomycin D on chlorophyll a formation in mustard seedlings (Sinapis alba L.)]

In the mustard seedling chlorophyll a synthesis under white light is enhanced by a pretreatment with far-red which maintains a low but virtually stationary concentration of active phytochrome (=P730) (Fig. 1) during the period of irradiation (4 hours). - On the other hand chlorophyll a synthesis is inhibited or delayed by relatively low concentrations of Actinomycin D(=Act) (Fig. 2)The inhibitory action of Act (on a percent basis) is exactly the same with and without a far-red pre-irradiation (Fig. 3). Act in relatively low doses (5 or 10 μg/ml) greatly extends the lag-phase of chlorophyll synthesis; however, these doses do not influence the effect of the far-red pretreatment on the rate of chlorophyll synthesis when it finally takes place (Fig.4,5,6). The data presented in this paper indicate that Act does not inhibit protochlorophyll synthesis as such; we have rather to conclude that Act inhibits the de novo synthesis of some specific structural proteins which are prerequisites of chlorophyll accumulation and maintenance in the plastids (Table 1). Synthesis of these structural proteins seems to be under the control of phytochrome too.It is concluded that those genes which are already in function are relatively resistant to Act (e. g. those genes which are needed for protochlorophyll synthesis) whereas potentially active genes (e. g. those which code some specific structural proteins of the plastids) are very sensitive to Act. -A similar conclusion has been reached in an earlier paper in connection with phytochrome-induced antocyanin synthesis (LANGE and MOHR, 1965). Our argumentation is further supported by SCHOPFER's data on control of ascorbate synthesis in the mustard seedling by phytochrome and Act (SCHOPFER, 1966).