Influence of darkness on insulin binding in the unicellular algae Acetabularia mediterranea]

Culture of Acetabularia in darkness increases the number of membrane receptor sites to insulin. This increase has not been observed with anucleated parts of algae. It may be concluded that induction of insulin receptor sites depends on the presence of the cell nucleus.     

Rna transport from the nucleus to the cytoplasm in Acetabularia mediterranea]

The biosynthesis of nuclear RNA, its transport from the nucleus to the cytoplasm and distribution in the cytoplasm were studied in Acetabularia mediterranea under different light conditions. It was shown that the nuclear RNA incorportate 3H-uracil more rapidly in the darkness and the transport of labeled RNA from the nucleus slowed down after the transfer of plants in the cold medium in the darkness. To study the distribution of nuclear RNA in the cytoplasm, the 3H-uracil labeled nuclei were transplanted in the rhizoids of unlabeled plants, the dikaryons obtained were kept for different time in the light and in the darkness and the content of 3H-RNA was determined in different stem regions. It was shown that the transport of 3H-RNA in the cytoplasm is slowed down in the darkness and it is distributed by the basal-apical gradient. RNA is rapidly accumulated in the apical stem zone in the light and redistributed afterwards in the basal stem zones. The problem of relationship between the polarity and nuclear RNA distribution in Acetabularia is discussed.     

Betacyanin biosynthesis in the isolated hypocotyls bei Acetabularia mediterranea

Summary Isolated hypocotyls synthesize betacyanin after light exposure in Amaranthus caudatus L. Pigment synthesizing capacity is reduced in the hypocotyls with increased incubation of seedlings in dark after 24h. External feeding of precursors of betacyanin L-tyrosine and DOPA enhances pigment synthesis in the isolated hypocotyls to equal that of intact hypocotyls. Cotyledons are probably the source of precursors while both cotyledons and hypocotyls are the sites of betacyanin synthesis. Betacyanin synthesizing capacity is progressively lost from the base of the hypocotyl and precursors could not induce pigment synthesis in these regions.     

Intracellular transport of nuclear ribosomal RNA in Acetabularia mediterranea]

The ribosomal RNA transport from a nucleus to a perinuclear cytoplasm and its following distribution in the cytoplasm of Acetabularia mediterranea cells were studied using transplantation of RNA-labeled rhizoid into unlabeled stalk. In addition rifamycin treatment was used for inhibition of cytoplasmic RNA synthesis. Acetabularia nuclei contain the stable RNA fractions similar to those present in some other eukaryotes. Nuclear 25S and 17S ribosomal RNA rapidly enter the rhizoid cytoplasm whereas the following trasfer of them to other regions of the cell is a very slow process. Within two days only an insignificant part of 25S and 17S ribosomal RNA is transferred from the rhizoid to the stalk and is distributed there over the base-apical gradient. No preferential transfer of the nuclear ribosomal RNA to the apical region was observed.     

Some pathways of biosynthesis and degradation of polyphosphates from green algae Acetabularia mediterranea]

The activity of ATP: polyphosphate phosphotransferase was detected in free-cellular extracts of Acetabularia mediterranea. The enzyme activity in cells originally deficient in phosphorus and subsequently transferred into the phosphate-containing medium increases 5-10-fold as compared to normal. Polyphosphate degradation in A. mediterranea is probably produced by polyphosphatase, which was also detected in the free-cellular extract. It was shown that the polyphosphatase activity has two pH optima, i.e. 4.5 and 7.5, and is considerably increased when the cells are transferred into the phosphate-free medium. It is assumed that high-molecular polyphosphates involved in A. Mediterranea metabolism are responsible for regulation of orthophosphate and ATP level in the cells by ATP: polyphosphate phosphotransferase and polyphosphatase.     

Polar distribution of RNA in the cytoplasm of Acetabularia mediterranea]

The distribution of total RNA and its individual fractions in two regions of Acetabularia mediterranea stem during regeneration was investigated. During regeneration of both the nuclear and enucleated cells, RNA concentration increases in the cytoplasm of growth zone whereas it changes insignificantly in the central stem region. A study of the qualitative RNA composition in the same stem regions has shown that during regeneration high molecular weight RNA fractions (main peaks - 0,56-10(6) and 1.04-10(6) Dalton) are found in the growth zone and are practically absent from the central cell region. Low molecular weight RNA (supposedly, tRNA and products of RNA destruction) are present in both the cell regions under study.     

Photic induction of polar growth in enucleated fragments of Acetabularia mediterranea]

The process of induction of polarity in enucleated fragments (EF) of Acetabularia mediterranea has been studied by the method of local illumination. A device is described which allows to illuminate one part of EF at 2, 500 lx and another at 5 lx. The local illumination of a part of EF during 10-24 hrs was shown to polarize with a high probability the subsequent growth and formation of caps at the subsequent uniform illumination. Using the method of successive illumination and darkening of apical and basal portions of EF, it was shown that the initial stages of induction were partially reversible and the complete determination of polarity took place after the initiation of the cap anlage. After the short-term induction by light (2500 lx), the darkening of the growth zone inhibits completely the process of cap initiation, but already at 100 lx the EF previously induced at 2 500 lx are initiated and grow. While using the local illumination of grafts of EF from two species, A. crenulata and A. mediterranea, with their subsequent fragmentation and the analysis of cap morphology, it was shown that the induction of polar growth did not provide the directed transport of the factors controlling morphogenesis to the future growth zone.     

Ultrathin structure of normally growing and regenerating cells of Acetabularia mediterranea]

The ultrastructure of nucleus and cytoplasm in regenerating cells of Acetabularia mediterranea differs from that in normally growing ones: the nucleus of regenerating cells form numerous outgrowths; the cortical layer of nucleolus disintegrates markedly; the emission of nucleolar material in the nucleoplasm is observed. In the cytoplasm the portion of active chloroplasts increases and a great number of tubular fibrils appears. In the cytoplasm of regenerating cells the Golgi dictyosomes occur more frequently and the vesicles at their ends are larger than in that of normally growing cells. The changes of macromolecular organization of the nucleus and cytoplasm in question observed at the earlier stages of regeneration (2--12 hrs) suggest the increase of metabolic activity of cells.