Between-year variation in flowering and fruit set in frost-prone and frost-sheltered populations of dioecious Rubus chamaemorus

Summary The flowering and fruiting patterns of the dioecious perennial herb Rubus chamaemorus L. were studied in frost-prone (open) and frost-sheltered (Shaded) habitats in northern Sweden over 6 years. The number of ramets with flower buds, the proportion of flower buds that opened, and fruit set varied markedly between years. In the frost-prone populations, the occurrence or absence of detrimental frosts during the development of flowers and fruit could explain much of the variation, both in the proportion of flower buds that developed into flowers, and in fruit set. In the frost-sheltered populations, most female flowers that did not develop into fruit aborted without any signs of physical damage and before any ovules had begun to enlarge. Flower mortality caused by herbivores feeding on reproductive parts was commonly low, but reached values higher than 10% in one of the shaded populations. Hand-pollination increased the proportion of ovules producing seeds in the mature fruits by about 20%, and in one year also increased fruit set significantly in one population. Fruit-producing female ramets had a higher mortality and a lower probability of flowering in the subsequent year than male ramets and non-fruiting female ramets. In R. chamaemorus, the conditions for fruit maturation are highly unpredictable at the time of flower initiation. It is suggested that the apparent over-initiation of flower buds is advantageous, as it allows the plant to attain a high reproductive success in years favourable for flowering and fruit development.     

Enzyme patterns during substrate shifts between phenol,acetate and glucose in continuous culture of Trichosporon cutaneum

Summary The soil yeast Trichosporon cutaneum was grown in continuous culture on phenol, acetate or glucose as sole carbon source. The activities of enzymes participating in the tricarboxylic acid cycle, glyoxylate cycle, 3-oxoadipate pathway, pentose phosphate pathway and glycolysis were determined in situ during shifts of carbon sources. Cells grown on phenol or glucose contained basal activity of the glyoxylate-cycle-specific isocitrate lyase. The derepression of the glyoxylate cycle enzymes was partly hindered in the presence of phenol but not in the presence of low levels of glucose. Phenol and glucose caused repression of isocitrate lyase. In the presence of either phenol or glucose, acetate accumulation in the medium increased. However, part of the supplied acetate was utilized simultaneously with phenol or glucose, the utilization rate of either carbon source being reduced in the presence of the other carbon source. Acetate caused repression but not inactivation of the phenol-degrading enzymes, phenol hydroxylase and catechol 1,2-dioxygenase. The simultaneous utilization of phenol and other carbon sources in continuous culture as well as the observed repression-derepression patterns of the involved enzymes reveal T. cutaneum to be an organism of interest for possible use in decontamination processes. Offprint requests to: H. Y. Neujahr Offprint requests to: H. Y. Neujahr     

Studies on the assembly of apo B-100-containing lipoproteins in HepG2 cells

The relationship between apoB-100 and the membrane of the endoplasmic reticulum (ER) has been studied by a combination of pulse-chase methodology and subcellular fractionation. HepG2 cells were pulse-labeled with [35S]methionine for 3 min and chased with cold methionine for periods between 0 and 20 min. ApoB-100 and albumin, present in the membrane as well as in the luminal content of the ER vesicles, were isolated after each chase period. The results indicated that apoB-100 was cotranslationally bound to the membrane of the ER, and from this membrane-bound form, was transferred to the lumen after a delay of 10-15 min. Albumin was, as could be expected for a typical secretory protein, cotranslationally sequestered in the lumen of the ER. Apo-B-100-containing lipoproteins present in the microsomal lumen were analyzed by ultracentrifugation in a sucrose gradient. ApoB-100 occurred on rounded particles in three density regions: (i) d 1.1065-1.170 g/ml (Fraction I), (ii) d 1.011-1.045 g/ml (Fraction II), and (iii) d less than 1.011 g/ml (Fraction III). Fraction I, isolated from cells cultured in the absence of oleic acid, contained a homogenous population of particles with a mean diameter of approximately 200 A. Fraction I isolated from cells cultured in the presence of oleic acid was slightly more heterogeneous and had a mean diameter of approximately 250 A. Fractions II and III had mean diameters of 300 and 500 A, respectively. Cholesterol esters and triacylglycerol were the quantitatively dominating lipid constituents of all three fractions. Pulse-chase experiments indicated that Fraction I contained the newly assembled lipoproteins. With increasing chase time, the apoB-100 radioactivity was redistributed from Fraction I to Fractions II and III, indicating that Fraction I is converted into Fractions II and III during the intracellular transfer. Particles corresponding to Fractions II and III were by far the most abundant lipoproteins found in the medium. The results presented support the possibility of a sequential assembly of apoB-100-containing lipoproteins.     

Histochemistry and ultrastructure of adrenergic and acetylcholinesterase-containing nerves supplying follicles and endocrine cells in the guinea-pig ovary

Summary With the use of an anti-human S-100 protein antibody, it was possible to reveal a characteristic cell type in the anterior lobe of the normal human pituitary. These cells, so-called folliculo-stellate cells, were present in all pituitaries studied but their number varied from one gland to another. Immunoreactive cells, isolated or grouped, were arranged close to various secretory granulated cells. Especially by use of double immunoenzymatic labeling, it was evident that these cells are spatially related either to somatotropes, prolactin cells and corticotropes, or to glycoprotein-containing cells. Such immunoreactive cells were rare or absent in pseudo-follicular arrangements of secretory granulated cells. Since it is now possible to identify this cell type by light microscopy and since no reliable functional significance is known, it seems more advisable to term this cell type stellate cell instead of folliculostellate cell.     

Stability of solvent formation in Clostridium acetobutylicum during repeated subculturing

Summary Clostridium acetobutylicum ATCC 824 was submitted to repeated subculturing at 24-hour intervals for 218 days. The organism retained its ability to form solvents, although the fermentation slowly became increasingly acidogenic during the first 200 days. Except for the initial spore inoculum, the cultures were not subjected to heat shocking between the serial transfers. When the inoculum volume was doubled from 3.3% to 6.7% after 200 days of subculturing, the product formation pattern quickly shifted back from acids to primarily butanol. Acetone production also resumed after being undetectable for more than 50 days. The relative formation of acetate and ethanol remained nearly constant throughout the experiments, while the formation of butyrate mirrored that of butanol.     

Identification of the stable free radical tyrosine residue in ribonucleotide reductase.

The small subunit of iron-dependent ribonucleotide reductases contains a stable organic free radical, which is essential for enzyme activity and which is localized to a tyrosine residue. Tyrosine-122 in the B2 subunit of Escherichia coli ribonucleotide reductase has been changed into a phenylalanine. The mutation was introduced with oligonucleotide-directed mutagenesis in an M13 recombinant and verified by DNA sequencing. Purified native and mutant B2 protein were found to have the same size, iron content and iron-related absorption spectrum. The sole difference observed is that the mutant protein lacks tyrosyl radical and enzymatic activity. These results identify Tyr122 of E. coli protein B2 as the tyrosyl radical residue. An expression vector was constructed for manipulation and expression of ribonucleotide reductase subunits. It contains the entire nrd operon with its own promoter in a 2.3-kb fragment from pBR322. Both the B1 and the B2 subunits were expressed at a 25-35 times higher level as compared to the host strain.     

Isolation and characterization of a 23 kDa protein essential for photosynthetic oxygen evolution

A 23 kDa protein has recently been demonstrated to participate in photosynthetic oxygen evolution by reconstitution experiments on inside-out thylakoid vesicles (Åkerlund H-E, Jansson C and Andersson B (1982) Biochim Biophys Acta 681:1–10). Here we describe the isolation of the 23 kDa protein from a spinach chloroplast extract using ion-exchange chromatography. The protein was obtained in a yield of 25% and with less than 1% of contaminating proteins. The ability of the protein to stimulate oxygen evolution in inside-out thylakoids was preserved throughout the various fractionation steps. The isolated protein was highly water soluble and appeared as a monomer. Its isoelectric point was at pH=7.3. The amino acid composition showed a high content of polar amino acids, resulting in a polarity index of 49%. The isolated protein lacked metals and other prosthetic groups. Its function as a catalytic or regulating subunit in the oxygen evolving complex is discussed.     

Peptides with NH2-terminal tryptophan in the adenohypophysis

Summary In the mammalian pituitary formaldehyde-ozone treatment induces strong fluorescence in the cells of the pars intermedia and moderate to strong fluorescence in numerous cells of the pars distalis. Maximum excitation is at 370–375 nm and maximum emission at 495–505 nm. The properties of the cellular fluorescence are indistinguishable from those of tryptamine or peptides with NH₂-terminal tryptophan. From chemical analysis such peptides seem to occur abundantly in the mammalian pituitary. The concentration of these peptides agrees very well with the number and fluorescence intensity of the cells in all species studied. Furthermore, the tryptophyl peptides in the various parts of the pig pituitary have a distribution quite parallel to that of the fluorescent cells. As we have failed to detect tryptamine in the pituitary, we conclude that the formaldehyde-ozone-induced fluorescence in the adenohypophysis reflects the presence of tryptophyl peptides.This study was supported by grants from the Swedish Medical Research Council (04X-1007; 04X-3764), the Ford Foundation, Harald and Greta Jeanssons stiftelse and Riksföreningen mot Cancer (660-K73-01X).For brevity occasionally referred to as tryptophyl peptides.