Ribosomale RNA und thylakoidmembranen in piastiden von chlorophylldefektmutanten der gerste

The deficiency of soluble proteins and plastid ribosomal RNA in the albino pollen plantlets of rice

The components of soluble protein and ribosomal RNA in green and albino pollen plantlets of rice were studied by means of polyacrylamide gel electrophoresis. The results were as follows: (1) Soluble protein: the soluble proteins in green pollen plantlets may be fractionated into 15 bands of varying intensities in which the highest content and the most prominent one is band 3 (fraction I protein). Band 3, however, is nearly absent in albino pollen plantlets. (2) Ribosomal RNA (rRNA): rRNA of high molecular weight in green pollen plantlets may be fractionated into 4 bands, i.e. 25S RNA and 18S RNA in cytoplasmic ribosomes, and 23S RNA and 16S RNA in plastid ribosomes. Little or no 23S RNA and 16S RNA, however, is found in albino pollen plantlets. Together with the evidence obtained by other workers, it is suggested that albino forms of pollen plantlets is caused by the impairment of DNA.

Biochemical differentiation of plastids and other organelles in rye leaves with a high-temperature-induced deficiency of plastid ribosomes

1. In developing rye (Secale cereale L.) leaves the formation of plastidic ribosomes was selectively prevented in light as well as in darkness, when the seedlings were grown at an elevated temperature of 32° instead of 22° where normal development ocurred. Plastid ribosome deficient parts of lightgrown leaves were chlorotic at 32°. - 2. At both temperatures the leaves contained under all conditions (light or dark, on H2O or nutrient solution) equal or very similar amounts of total amino nitrogen. In light, the contents of total protein and dry weight were lower at 32° than at 22°, especially when the plants were grown on nutrient solution. - 3. Mitochondrial marker enzymes had normal or even higher activities in 32°-grown leaves. Respiration rates were similar for segments of leaves grown on water in light either at 32° or at 22° but by 20-30% lower for 32°-grown plants when they had been raised in darkness or on nutrient solution. In contrast to 22°-grown tissue, respiration of 32°-grown leaf segments was rather insensitive to KCN. Comparative inhibitor studies indicated the presence of both the cyanide-sensitive and the cyanide-insensitive pathway of respiration in 32°-grown leaves. - 4. Leaf microbody marker enzymes were present in leaves grown at 32°. From chlorotic parts of 32°-light-grown leaves a typical microbody fraction was isolated on sucrose densitygradients. - 5. Leaves of seedlings grown at 32° contained only very low levels of ribulosediphosphate carboxylase activity and of fraction I protein. Photosynthetic (14)CO2-fixation of such leaves was only a few per cent of that observed in normal leaves, and no photosynthetic oxygen evolution was observed in chlorotic leaf segments. However, ten other soluble enzymes which are exclusively or partially localized in chloroplasts reached high activities under all conditions at 32° (Table 4). - 6. From chlorotic parts of 32°-light-grown leaves as well as from etiolated 32°-grown leaves a fraction of intact plastids was isolated and purified by sucrose gradient centrifugation which contained several soluble chloroplast enzymes. From the results we conclude that cytoplasmic protein synthesis must contribute a functional chloroplast envelope including the mechanism for the recognition and uptake of chloroplast proteins which are synthesized on cytoplasmic ribosomes.

Two-dimensional gel electrophoresis of ribosomal proteins from streptomycin-sensitive and streptomycin-resistant mutants of Chlamydomonas reinhardi

Ribosomal proteins from three mutant strains of Chlamydomonas reinhardi were analysed and compared by one-dimensional and two-dimensional gel electrophoresis. One mutant was streptomycin-sensitive the other two were streptomycin-resistant, one with a Mendelian the other with a non-Mendelian pattern of inheritance. In the 30-S subunits of chloroplast ribosomes approximately 25 proteins are found and in the 50-S subunits 34 proteins. The 40-S subunits of cytoplasmic ribosomes contain about 31 proteins and the 60-S subunits 44 proteins. The molecular weights of most proteins in all subunits are in the range of 10 000 to 35 000. However, the 60-S subunits contain in addition a protein of molecular weight 50 000 and the 30-S subunits show 6-7 bands of molecular weights from 50 000 to 83 000. The proteins of the cytoplasmic 80-S ribosomes or of their subunits from all three mutants are electrophoretically identical. The proteins of the 70-S organellar ribosomes and both of their subunits show distinct differences between the three strains. Our results indicate that organellar ribosomal proteins are in part controlled by nuclear DNA and in part by organellar DNA.

Selective inhibition of mesophyll chloroplast development in some C4-pathway species by low night temperature

Exposure of plants of Sorghum bicolor L. line E 1287 and hybrid NK 145, of Digitaria smutsii Stapf, and of Paspalum dilatatum L.-grasses having the C4 pathway of photosynthesis-to temperatures of 4°, 2.5°, 2.5° and-3°, respectively, for a single night caused the formation within 36 h of transverse, irreversibly chlorotic bands on emerging leaves. Chlorosis was associated with the presence of chlorophyll-deficient, structurally abnormal plastids in most mesophyll cells, whereas chloroplasts in adjacent bundle-sheath cells were green and possessed a normal lamellar structure. The ultrastructure of other organelles in the chlorotic mesophyll cells appeared normal and the levels of cytoplasmic rRNA, non-plastid lipids and isocitrate dehydrogenase were similar or slightly higher in chlorotic compared with green lamina. The content of chloroplast rRNA and plastid lipids in the chlorotic tissue was low. Activities of all C4-pathway enzymes examined were lower in the chlorotic tissue but phosphopyruvate carboxylase, NADP-malate dehydrogenase and adenylate kinase were reduced to a greater extent than ribulose diphosphate carboxylase, fructose diphosphate aldolase and malic enzyme. The region of emerging leaves that contained mesophyll plastids susceptible to low temperature was identified and the stages of plastid ontogeny below, within and above this region examined. During normal differentiation rapid increases in plastid size and in the content of chloroplast rRNA, chlorophyll, plastid lipids and in the activities of C4-pathway enzymes occur at a developmental stage subsequent to that at which plastids are susceptible to low temperature.