Adaptation of the Photosynthetic Apparatus to Irradiance in Dunaliella tertiolecta: A Kinetic Study

The time course of adaptation from a high to a low photon flux density was studied in the marine chlorophyte Dunaliella tertiolecta. A one-step transition from 700 to 70 micromole quanta per square meter per second resulted in a reduction of doubling rate from 1.1 to 0.4 per day within 24 hours, followed by a slower accumulation of photosynthetic pigments, light harvesting antenna complexes, Photosystem II reaction centers and structural lipids that constitute the thylakoid membranes. Photoregulated changes in the biochemical composition of the thylakoid proteins and lipids were functionally accompanied by decreases in the minimal photosynthetic quantum requirement and photosynthetic capacity, and an increase in the minimal turnover time for in vivo electron transport from water to CO₂. Analysis of de novo synthesis of thylakoid membranes and proteins indicates that a high light to low light transition leads to a transient in carbon metabolism away from lipid biosynthesis toward the synthesis of the light harvesting antenna protein complexes, accompanied by a slower restoration rate of reaction centers and thylakoid membranes. This pattern of sequential synthesis of light harvesting complexes followed by reaction centers and membranes, appears to optimize light harvesting capabilities as cells adapt to low photon flux densities.     

Control of Continuous Irradiation Injury on Potatoes with Daily Temperature Cycling

Two controlled-environment experiments were conducted to determine the effects of temperature fluctuations under continuous irradiation on growth and tuberization of two potato (Solanum tuberosum L.) cultivars, Kennebec and Superior. These cultivars had exhibited chlorotic and stunted growth under continuous irradiation and constant temperatures. The plants were grown for 4 weeks in the first experiment and for 6 weeks in the second experiment. Each experiment was conducted under continuous irradiation of 400 micromoles per square meter per second of photosynthetic photon flux and included two temperature treatments: constant 18°C and fluctuating 22°C/14°C on a 12-hour cycle. A common vapor pressure deficit of 0.62 kilopascal was maintained at all temperatures. Plants under constant 18°C were stunted and had chlorotic and abscised leaves and essentially no tuber formation. Plants grown under the fluctuating temperature treatment developed normally, were developing tubers, and had a fivefold or greater total dry weight as compared with those under the constant temperature. These results suggest that a thermoperiod can allow normal plant growth and tuberization in potato cultivars that are unable to develop effectively under continuous irradiation.     

Discrimination between closely related Triticeae species using genomic DNA as a probe

Summary Labelled total genomic DNA was used as a probe in combination with blocking DNA to discriminate between taxonomically closely related species in the genera Hordeum and Secale. Discrimination was possible both by Southern hybridization to size-fractionated restriction enzyme digests of genomic DNA and by in situ hybridization to chromosome preparations. To distinguish between two species (e.g. H. vulgare and H. bulbosum), genomic DNA from one species was used as the labelled probe, while unlabelled DNA from the other species was applied at a much higher concentration as a block. The blocking DNA presumably hybridized to sequences in common between the block and the labelled probe, and between the block and DNA sequences on the membrane or chromosomes in situ. If so, mainly species-specific sequences would remain as sites for probe hybridization. These species-specific sequences are dispersed and represent a substantial proportion of the genome (unlike many cloned, species-specific sequences). Consequently, rapid nonradioactive methods detected probe hybridization sites satisfactorily. The method was able to confirm the parentage of hybrid plants. It has potentially wide application in plant breeding for the detection of alien DNA transfer, and it can be easily adapted to many species.     

Cloning and expression of Clostridium acetobutylicum ATCC 824 acetoacetyl-coenzyme A:acetate/butyrate:coenzyme A-transferase in Escherichia coli

Coenzyme A (CoA)-transferase (acetoacetyl-CoA:acetate/butyrate:CoA-transferase [butyrate-acetoacetate CoA-transferase] [EC 2.8.3.9]) of Clostridium acetobutylicum ATCC 824 is an important enzyme in the metabolic shift between the acid-producing and solvent-forming states of this organism. The purification and properties of the enzyme have recently been described (D. P. Weisenborn, F. B. Rudolph, and E. T. Papoutsakis, Appl. Environ. Microbiol. 55:323-329, 1989). The genes encoding the two subunits of this enzyme have been cloned by using synthetic oligodeoxynucleotide probes designed from amino-terminal sequencing data from each subunit of the CoA-transferase. A bacteriophage lambda EMBL3 library of C. acetobutylicum DNA was prepared and screened by using these probes. Subsequent subcloning experiments established the position of the structural genes for CoA-transferase. Complementation of Escherichia coli ato mutants with the recombinant plasmid pCoAT4 (pUC19 carrying a 1.8-kilobase insert of C. acetobutylicum DNA encoding CoA-transferase activity) enabled the transformants to grow on butyrate as a sole carbon source. Despite the ability of CoA-transferase to complement the ato defect in E. coli mutants, Southern blot and Western blot (immunoblot) analyses showed that neither the C. acetobutylicum genes encoding CoA-transferase nor the enzyme itself shared any apparent homology with its E. coli counterpart. Polypeptides of Mr of the purified CoA-transferase subunits were observed by Western blot and maxicell analysis of whole-cell extracts of E. coli harboring pCoAT4. The proximity and orientation of the genes suggest that the genes encoding the two subunits of CoA-transferase may form an operon similar to that found in E. coli.(ABSTRACT TRUNCATED AT 250 WORDS)     

Production of fumonisin B1 by Fusarium moniliforme NRRL 13616 in submerged culture

Fumonisin B1, a recently discovered mycotoxin, was synthesized by submerged cultures of Fusarium moniliforme NRRL 13616 grown for 29 days at 28 degrees C and 220 rpm in a basal salts medium (pH 5.0) supplemented with 90 g of glucose per liter and 3.5 g of ammonium sulfate per liter. Under these culture conditions, 74 +/- 23 micrograms of fumonisin B1 per ml was produced by 29-day-old F. moniliforme NRRL 13616 cultures. Fumonisin B1 was detected in liquid culture extracts by high-performance thin-layer chromatography. Fumonisin B1 was confirmed and quantitated by gas chromatography and gas chromatography-mass spectral analysis of the trimethylsilyl derivative. The use of a defined medium for producing fumonisin B1 in a submerged culture facilitates its isolation and provides an excellent method for conducting biosynthetic studies.     

A new microcomputer-controlled neutron activation and analysis system

A microcomputer-controlled irradiation and measurement system and a microprocessor-controlled sample changer have been installed at the SLOWPOKE-2 Facility at the Royal Military College of Canada (RMC). These systems can provide the gamut of instrumental neutron activation analysis (INAA) techniques for the analyst. Custom software has been created for system control, data acquisition, and off-line spectral analysis using programs that incorporate Gaussian peak-fitting methods of analysis. The design and use of the equipment is discussed, and the performance is illustrated with results obtained from the analysis of marine sediment and biological reference materials.     

Secretion of a platelet-derived growth factor homologue by rat alveolar macrophages exposed to particulates in vitro

Lung macrophages secrete a homologue of platelet-derived growth factor (PDGF) which induces the proliferation of fibroblasts in vitro. In previous studies, we showed that such a PDGF homologue is produced by rat alveolar macrophages and that rat lung fibroblasts have specific receptors for the macrophage-derived PDGF. In this study, we demonstrate the biological and physicochemical properties of the growth factor, as well as the time-related production of this factor following macrophage activation in vitro by organic and inorganic particles. Alveolar macrophages (AMs) collected by saline lavage from the lungs of rats were cultured in serum-free Dulbecco's modified Eagle's medium (SF-DMEM) for varying periods of time up to 72 h. The SF-DMEM "conditioned" by the AMs was used to treat early passage rat lung fibroblasts (RLFs), which were rendered quiescent by culturing in 2% platelet-poor plasma (PPP). Alveolar macrophage conditioned media (AMCM) in the presence of PPP caused increases in the number of fibroblasts, the percent of labeled fibroblast nuclei and tritiated [3H]thymidine incorporation. AMCM alone caused no detectable changes in fibroblast growth rate. These results indicate that AMs release a "competence-like" growth factor. The AMs were left untreated or were exposed to opsonized zymosan, carbonyl iron spheres or chrysotile asbestos fibers. Macrophages attached to a plastic substrate spontaneously produced the factor, and subsequent addition of the organic and inorganic particles to the macrophage cultures significantly increased the fibroblast-stimulating activity of the AMCM. The growth factor was stable after concentration (100-fold), lyophilization and reconstitution.(ABSTRACT TRUNCATED AT 250 WORDS)     

Time-dependent changes in cardiovascular regulation caused by chronic tobacco smoke exposure

The purpose of this study was to determine whether chronic tobacco smoke exposure for less than 2 mo alters cardiovascular regulation. One group of male Sprague-Dawley rats was administered tobacco smoke from low-nicotine cigarettes (group A, 1 mg/cigarette) for 4-6 wk, while a second group (B) served as a sham control by receiving only puffs of room air. Reflex adjustments in mean arterial blood pressure (MAP) after bilateral common carotid occlusion (BCCO) were compared between the two groups. In the anesthetized control state, no significant difference existed for the cardiovascular parameters measured in the two groups. However, MAP increases after BCCO were significantly greater in the smoke-treated animals (P less than 0.05) compared with the sham-treated group. At 10, 20, 30, and 40 s after BCCO, MAP increases above preocclusion values were 66, 45, 42, and 38% for group A and 35, 26, 24, and 22% for group B, respectively. Additionally, the time required to reach maximum MAP after BCCO was significantly less (P less than 0.05) for the smoke-treated vs. sham-treated animals (8.5 +/- 0.2s for group A, 11.2 +/- 0.3s for group B). MAP changes during BCCO were significantly different (P less than 0.05) between the treatment groups after cervical vagotomy. It is concluded that chronic tobacco smoke exposure in experimental animals for periods as short as 4-6 wk alters the reflex regulation of the cardiovascular system.     

Localization of Sites in the Tail Domain of the Middle Molecular Mass Neurofilament Subunit Phosphorylated by a Neurofilament-Associated Kinase and by Casein Kinase I

Abstract: We have shown previously that a neurofilament (NF)-associated kinase (NFAK) extracted from chicken NF preparations phosphorylates selectively the middle molecular mass NF subunit (NF-M). Here we show that the major kinase activity in NFAK is indistinguishable from enzymes of the casein kinase I (CKI) family based on the following criteria: (1) inhibition of NFAK phosphorylation by the selective CKI inhibitor CKI-7, (2) the similarity in substrate specificity of NFAK and authentic CKI, (3) the correspondence of two-dimensional phosphopeptide maps of NF-M phosphorylated in vitro by NFAK with those generated by CKI under similar conditions, and (4) immunological cross-reactivity of NFAK with an antibody raised against CKI. We have also identified Ser⁵⁰², Ser⁵²⁸, and Ser⁵³⁶ as phosphorylation sites by NFAK/CKI in vitro, each of which is also phosphorylated in vivo. All three serines are found in peptides with CKI phosphorylation consensus sequences, and Ser⁵²⁸ and Ser⁵³⁶ and flanking amino acids are highly conserved in higher vertebrate NF-M sequences. Neither Ser⁵⁰² nor Ser⁵³⁶ has been identified previously as NF-M phosphorylation sites.     

Chronic In Vivo Sodium Azide Infusion Induces Selective and Stable Inhibition of Cytochrome c Oxidase

Abstract: The effect of chronic subcutaneous infusion of sodium azide on the activity of mitochondrial respiratory chain enzymes was investigated in Sprague-Dawley rats. Treatment with ∼1 mg/kg/h sodium azide induced chronic, partial inhibition of cytochrome c oxidase, whereas the activities of respiratory complexes I and III were not significantly affected. The inhibition of cytochrome c oxidase was evident by 7 days after infusion began, and the effect was stable for at least 3 weeks. The selectivity of azide for cytochrome c oxidase is discussed in the context of other findings of azide effects on enzymes. The results of the present study indicate that the sodium azide infusion paradigm described here provides a useful tool for the evaluation of selective and stable cytochrome oxidase inhibition in vivo.