Growth, dry matter partitioning, and diurnal activities of RuBP carboxylase in citrus seedlings maintained at two levels of CO2

The long-term response of citrus rootstock seedlings to CO₂ enrichment was examined in Carrizo estrange ( Poncirua trifoliata (L.) Raf. x Citrus sinensis (L.) Osbeck] and Swingle citrumelo ( P. trifoliate x C. parodist Macf.]. Plaotlets 14 weeks old were transferred to outdoor controlled-environment chambers and maintained for 5 months from Feb. 14 to July 21. During this period, new growth (cm) of citrange and citrumelo shoots at 660 μl1⁻¹ was 94 and 69% greater, respectively, than at 330 μ1 1⁻¹. Total dry weight of both rootstock shoots had increased by over 100%. Growth of few species is affected this markedly by elevated CO₂ levels.
More carbon was partitioned to above-ground organs in CO₂-enriched citrus seedlings. Stem dry matter per unit length was also 32 and 44% greater in citrange and citrumelo, respectively. Total leaf area was increased by 124% in citrange and 85% in citrumelo due to greater leaf number and size. Variations in overall relative growth rate appeared to be related to the rapid, sequential, flush-type growth in citrus, in which an entire shoot segment with its associated leaves remains an active sink until fully expanded. RuBP carboxylase (EC 4.1.1.39) activity in leaves of recently-expanded flushes was higher in citrumelo plants grown at 660 vs 330 μ1 1⁻¹ CO₂ and changed diurnally for citrange (but not citrumelo) leaves at both CO₂ levels. The results are consistent with the hypothesis that positive long-term effects of CO² enrichment may be greater in species or during growth periods where sink capacity for carbon utilization is high.     

Primeval cells: Possible energy-generating and cell-division mechanisms

Summary It is proposed that the first entity capable of adaptive Darwinian evolution consisted of a liposome vesicle formed of (1) abiotically produced phospholipidlike molecules; (2) a very few informational macromolecules; and (3) some abiogenic, lipid-soluble, organic molecule serving as a symporter for phosphate and protons and as a means of high-energy-bond generation. The genetic material had functions that led to the production of phospholipidlike materials (leading to growth and division of the primitive cells) and of the carrier needed for energy transduction. It is suggested that the most primitive exploitable energy source was the donation of 2H⁺+2e^– at the external face of the primitive cell. The electrons were transferred (by metal impurities) to internal sinks of organic material, thus creating, via a deficit, a protonmotive force that could drive both the active transport of phosphate and high-energy-bond formation.This model implies that proton translocation in a closed-membrane system preceded photochemical or electron transport mechanisms and that chemically transferable metabolic energy was needed at a much earlier stage in the development of life than has usually been assumed. It provides a plausible mechanism whereby cell division of the earliest protocells could have been a spontaneous process powered by the internal development of phospholipids. The stimulus for developing this evolutionary sequence was the realization that cellular life was essential if Darwinian survival of the fittest was to direct evolution toward adaptation to the external environment.     

Immunoreactive and biologically active somatostatin in human and sheep milk

The presence of immunoreactive and biologically active somatostatin in sheep and human milk has been demonstrated. Milk somatostatin exhibits similar chromatographic behavior to that of synthetic somatostatin-14 on both reversed-phase C18 and cation-exchange high-performance liquid chromatography columns. Milk, in contrast to plasma, contains only somatostatin-14-like material. Milk somatostatin was capable of inhibiting the basal and the prostaglandin-induced release of growth hormone from anterior pituitary cell cultures in a pattern similar to synthetic somatostatin-14. The concentrations of the peptide, as determined by radioimmunoassay, were found to be 113 pg/ml in human milk and 150 +/- 4.8 pg/ml (mean +/- range) in sheep milk. These values are severalfold higher than the corresponding concentration of the peptide in the plasma of these species. These findings are analogous to our previous observations concerning two other hypothalamic hormones, luliberin and thyroliberin [Baram, T., Koch, Y., Hazum, E. and Fridkin, M. (1977) Science (Wash. DC) 198, 300-302]. The high concentration of somatostatin and other neuropeptides in milk implies either an active concentrating mechanism in the mammary gland or an additional extrahypothalamic source for the synthesis and release of these peptides.     

Expression of acetylcholinesterase gene(s) in the human brain: molecular cloning evidence for cross-homologous sequences

The regulation of acetylcholinesterase (AChE) in the human brain has been approached at the level of the genome. A human DNA fragment of the length of 2 600 nucleotides was isolated from a human genomic library. This DNA fragment, designated Huache 1R, bears sequence homology to a DNA fragment from the vicinity of the Drosophila Ace region, that controls AChE biosynthesis (Soreq et al., 1985). Polyadenylated RNA from human brain was hybridized with Huache 1R DNA, eluted and microinjected into Xenopus oocytes in the absence or presence of 35S-methionine. The hybrid-selected RNA induced the biosynthesis of active AChE in the oocytes. Immunoprecipitation of labeled oocyte proteins with monoclonal antibodies against human AChE (Fambrough et al., 1982) resulted in the selective precipitation of an 85 000 Mr induced protein, with a similar size to that of the subunit of human brain AChE. These findings show that the Huache 1R DNA hybridizes with human brain AChEmRNA. The Huache 1R fragment was employed to select a collection of 12 homologous phage-cloned human genomic DNA fragments with different restriction patterns. A cDNA library in pBR322 plasmids was prepared from polyadenylated RNA isolated from embryonic brain. This library was also screened using labeled Huache 1R DNA as a probe. Forty-two out of 37 000 colonies were found positive. Several of these were selected for further analyses. Hybrid-selection experiments using DNA from two of the positive plasmid clones showed that these cDNAs also hybridize with AChEmRNA from human brain. DNA blot hybridization revealed homologies between these cDNA chains and the original Huache 1 fragment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cellular location of origin and terminus of replication in Bacillus subtilis.

The origin of replication of Bacillus subtilis 168 trp thy dna-1 (temperature-sensitive initiation mutant) was labeled with [3H]thymidine. Analysis of labeled cells by autoradiography revealed that most of the radioactivity was associated with cell pole areas. To label the terminus, cells that had initiated were treated with chloramphenicol to inhibit cell growth and division but to allow continued DNA synthesis. These cells were then labeled with [3H]thymidine at a time when chromosome replication was nearly complete. The distribution of radioactivity was similar to that observed in origin-labeled cells. In contrast, exponentially growing cells that were labeled for a brief time at the permissive temperature showed a random distribution of radioactivity. These data indicate that the origin and terminus of replication are located at cell poles.     

G inversion in bacteriophage Mu DNA is stimulated by a site within the invertase gene and a host factor

The Gin function of bacteriophage Mu catalyzes inversion of the G DNA segment, thus switching the host range of Mu phage particles. This site-specific recombination event takes place between inverted repeat sequences (IR) that border the G segment. Sequences in the Mu beta region extending approximately from position 118 to 178 are essential for efficient inversion. In cis this region, termed sis, stimulates inversion about 15-fold. Neither the relative orientation of sis with respect to the IR sequences nor the distance to IR substantially influences the stimulatory effect. For full activity purified Gin protein must be supplemented with crude host factor from E. coli K12. We suggest that, in addition to Gin, a DNA-binding host protein is required for efficient G inversion.     

Selective protection of in vitro synthesized cDNA against nucleases by incorporation of phosphorothioate-analogues.

The conditions for the stepwise synthesis of single- (ss) and double-stranded (ds) cDNA using thio-analogues instead of dNTPs are described in this paper. RNA of paramyxovirus Sendai (strain 6/94) serves as template in these experiments. The increased resistance of this alpha S-modified cDNA against several nucleases, like S1-Nuclease, DNase I, Exonuclease III, snake venom Phosphodiesterase (PDE) and the combination of DNase I and PDE is demonstrated.     

Insertion and fate of the cell wall in Bacillus subtilis

Cell wall assembly was studied in autolysin-deficient and -sufficient strains of Bacillus subtilis. Two independent probes, one for peptidoglycan and the other for surface-accessible teichoic acid, were employed to monitor cell surface changes during growth. Cell walls were specifically labeled with N-acetyl-D-[3H]glucosamine, and after growth, autoradiographs were prepared for both cell types. The locations of silver grains revealed that label was progressively lost from numerous sites on the cell cylinders, whereas label was retained on the cell poles, even after several generations. In the autolysin-deficient and chain-forming strain, it was found that the distance between densely labeled poles approximately doubled after each generation of growth. In the autolysin-sufficient strain, it was found that the numbers of labeled cell poles remained nearly constant for several generations, supporting the premise that completed septa and poles are largely conserved during growth. Fluorescein-conjugated concanavalin A was also used to determine the distribution of alpha-D-glucosylated teichoic acid on the surfaces of growing cells. Strains with temperature-sensitive phosphoglucomutase were used because in these mutants, glycosylation of cell wall teichoic acids can be controlled by temperature shifts. When the bacteria were grown at 45 degrees C, which stops the glucosylation of teichoic acid, the cells gradually lost their ability to bind concanavalin A on their cylindrical surfaces, but they retained concanavalin A-reactive sites on their poles. Discrete areas on the cylinder, defined by the binding of fluorescent concanavalin A, were absent when the synthesis of glucosylated teichoic acid was inhibited during growth for several generations at the nonpermissive temperature. When the mutant was shifted from a nonpermissive to a permissive temperature, all areas of the cylinder became able to bind the labeled concanavalin A after about one-half generation. Old cell poles were able to bind the lectin after nearly one generation at the permissive temperature, showing that new wall synthesis does occur in the cell poles, although it occurs slowly. These data, based on both qualitative and quantitative experiments, support a model for cell wall assembly in B. subtilis, in which cylinders elongate by inside-to-outside growth, with degradation of the stress-bearing old wall in wild-type organisms. Loss of wall material, by turnover, from many sites on the cylinder may be necessary for intercalation of new wall and normal length extension. Poles tend to retain their wall components during division and are turned over much more slowly.     

Intracellular CBG-like molecules in the rat pituitary

The localization of transcortin (CBG) in pituitary cells of the rat was investigated using the peroxydase-antiperoxydase (PAP) technique. A rabbit antiserum against purified rat plasma transcortin was used as the primary antiserum. Transcortin-like (CBG-like) immunoreactive products were found in the cytoplasma of certain cells in the anterior pituitary, but not in the intermediate lobe and weakly in the posterior pituitary. It is postulated that the CBG-like molecules participate in the cellular uptake process of corticosterone, thereby modulating the feedback signal of this steroid on pituitary function.