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PubMed2004

Amino acid requirement of growing pigs depending on amino acid efficiency and level of protein deposition 1st communication: lysine.

The study was conducted to evaluate the variability of efficiency of lysine utilisation in different feed proteins for growing pigs including wheat, unprocessed soybean flakes (SF), hydrothermal processed SF, corn gluten meal (CGM), two batches of soybean protein concentrate (SPC-1, SPC-2), different batches of peas (Pisum sativum) and field beans (Vicia faba). Data about efficiency of lysine are important for further conclusions related to lysine requirement in dependence on level of daily protein deposition. In N-balance studies 161 growing barrows (40-65 kg BW) of the genotype [Piétrain x (Duroc x Landrace)] were randomly allotted into 23 experimental treatments (n = 7) with diets in which lysine was the first limiting amino acid. Data from the N-balance trials were used to calculate efficiency of lysine and consequently lysine requirement based on an exponential N-utilisation model. Results from the present studies indicate that efficiency of lysine in different feed proteins varies in a very wide range and this variation greatly affected the calculated lysine requirement. Therefore, the variation in efficiency of lysine should be taken into account in requirement calculations and consequently in diet formulation for pigs. The results of model calculation for the lysine requirement depending on daily protein deposition (130, 145 and 160 g/d) and efficiency of lysine are given for different standards for comparison (g x kg(-0.67) x d(-1), g x d(-1) and percentage of lysine in the diet). The calculated lysine requirement of growing barrows (50 kg BW) corresponding to an average lysine efficiency was 15.5, 18.0 and 21.1 g/d for daily protein deposition of 130, 145 and 160 g, respectively. The results of the model calculation for 145 or 160 g daily protein deposition are in agreement with actual studies and recommendations of NRC (1998) and DLG (2002) for lysine supply.

Animal Feed↗

PubMed1987

Mechanical efficiency and metabolic cost as measures of learning a novel gross motor task.

"Efficiency, " or economy of movement with respect to energy expended in achieving the goal of the task, is implicit in many definitions of skilled performance. This study examined changes in mechanical efficiency and transport efficiency on a novel gross motor skill. The subjects were 5 physically fit adult males who were asked to perform 20 3-min trials walking on hands and feet (crawling) on a motor-driven treadmill at constant speed (0.76 m/s). Transport efficiency, the metabolic cost of transporting the body mass a given distance at constant speed, improved significantly over practice trials. Mechanical efficiency, derived from the mechanical power output of individual body segments, showed an overall improvement of 13.7% by the last day of practice. Even though this improvement was not statistically significant it appears to be greater than that expected due to physiological training effects. The efficiency measures correlated significantly with changes in limb kinematics. It was concluded that with practice subjects tailored their movement pattern to produce energy efficient adaptations to task constraints. These findings provide empirical support for theoretical perspectives that have emphasized biological principles in the organization of motor coordination and control.

Journal Article↗

PubMedDate not supplied

Lipoplex size determines lipofection efficiency with or without serum.

In order to identify factors affecting cationic liposome-mediated gene transfer, the relationships were examined among cationic liposome/DNA complex (lipoplex)-cell interactions, lipoplex size and lipoplex-mediated transfection (lipofection) efficiency. It was found that lipofection efficiency was determined mainly by lipoplex size, but not by the extent of lipoplex-cell interactions including binding, uptake or fusion. In addition, it was found that serum affected mainly lipoplex size, but not lipoplex-cell interactions, which effect was the major reason behind the inhibitory effect of serum on lipofection efficiency. It was concluded that, in the presence or absence of serum, lipoplex size is a major factor determining lipofection efficiency. Moreover, in the presence or absence of serum, lipoplex size was found to affect lipofection efficiency by controlling the size of the intracellular vesicles containing lipoplexes after internalization, but not by affecting lipoplex-cell interactions. In addition, large lipoplex particles showed, in general, higher lipofection efficiency than small particles. These results imply that, by controlling lipoplex size, an efficient lipid delivery system may be achieved for in vitro and in vivo gene therapy.

Cations↗

PubMed2001

Theoretical and observational assessments of flare efficiencies.

Flaring of waste gases is a common practice in the processing of hydrocarbon (HC) materials. It is assumed that flaring achieves complete combustion with relatively innocuous byproducts such as CO2 and H2O. However, flaring is rarely successful in the attainment of complete combustion, because entrainment of air into the region of combusting gases restricts flame sizes to less than optimum values. The resulting flames are too small to dissipate the amount of heat associated with 100% combustion efficiency. Equations were employed to estimate flame lengths, areas, and volumes as functions of flare stack exit velocity, stoichiometric mixing ratio, and wind speed. Heats released as part of the combustion process were then estimated from a knowledge of the flame dimensions together with an assumed flame temperature of 1200 K. Combustion efficiencies were subsequently obtained by taking the ratio of estimated actual heat release values to those associated with 100% complete combustion. Results of the calculations showed that combustion efficiencies decreased rapidly as wind speed increased from 1 to 6 m/sec. As wind speeds increased beyond 6 m/sec, combustion efficiencies tended to level off at values between 10 and 15%. Propane and ethane tend to burn more efficiently than do methane or hydrogen sulfide because of their lower stoichiometric mixing ratios. Results of theoretical predictions were compared to nine values of local combustion efficiencies obtained as part of an observational study into flaring activity conducted by the Alberta Research Council (ARC). All values were obtained during wind speed conditions of less than 4 m/sec. There was generally good agreement between predicted and observed values. The mean and standard deviation of observed combustion efficiencies were 68 +/- 7%. Comparable predicted values were 69 +/- 7%.

Air Pollutants↗

PubMed1989

Calculating concentration of inhaled radiolabeled particles from external gamma counting: external counting efficiency and attenuation coefficient of thorax.

We determined the overall external counting efficiency of radiolabeled particles deposited in the sheep lung. This efficiency permits the noninvasive calculation of the number of particles and microcuries (microCi) from gamma-scintillation lung images of the live sheep. Additionally, we have calculated the attenuation of gamma radiation (120 keV) by the posterior chest wall and the gamma-scintillation camera collection efficiency of radiation emitted from the lung. Four methods were employed in our experiments: (1) by light microscopic counting of discrete carbonized polystyrene particles with a count median diameter (CMD) of 2.85 microns and tagged with cobalt-57 (57Co), we delineated a linear relationship between the number of particles and the emitted counts per minute (cpm) detected by well scintillation counting; (2) from this conversion relationship we determined the number of particles inhaled and deposited in the lungs by scintillation counting fragments of dissected lung at autopsy; (3) we defined a linear association between the number of particles or microcuries contained in the lung and the emitted radiation as cpm detected by a gamma scintillation camera in the live sheep prior to autopsy (external counting efficiency); and (4) we compared the emitted radiation from the lungs of the live sheep to that of whole excised lungs in order to calculate the attenuation coefficient (ac) of the chest wall. The mean external counting efficiency was 4.00 X 10(4) particles/cpm (5.1 X 10(-3) microCi/cpm), the camera collection efficiency was 1 cpm/10(4) disintegrations per minute (dpm), and the ac had a mean of 0.178/cm. The external counting efficiency remained relatively constant over a range of particles and microcuries, permitting a more general use of this ratio to estimate number of particles or microcuries depositing after inhalation in a large mammalian lung if a similarly collimated gamma camera system is used.

Animals↗

PubMed1991

Efficiency of acetylcholine receptor subunit assembly and its regulation by cAMP.

Assembly of nicotinic acetylcholine receptor (AChR) subunits was investigated using mouse fibroblast cell lines stably expressing either Torpedo (All-11) or mouse (AM-4) alpha, beta, gamma, and delta AChR subunits. Both cell lines produce fully functional cell surface AChRs. We find that two independent treatments, lower temperature and increased intracellular cAMP can increase AChR expression by increasing the efficiency of subunit assembly. Previously, we showed that the rate of degradation of individual subunits was decreased as the temperature was lowered and that Torpedo AChR expression was acutely temperature sensitive, requiring temperatures lower than 37 degrees C. We find that Torpedo AChR assembly efficiency increases 56-fold as the temperature is decreased from 37 to 20 degrees C. To determine how much of this is a temperature effect on degradation, mouse AChR assembly efficiencies were determined and found to be only approximately fourfold more efficient at 20 than at 37 degrees C. With reduced temperatures, we can achieve assembly efficiencies of Torpedo AChR in fibroblasts of 20-35%. Mouse AChR in muscle cells is also approximately 30% and we obtain approximately 30% assembly efficiency of mouse AChR in fibroblasts (with reduced temperatures, this value approaches 100%). Forskolin, an agent which increases intracellular cAMP levels, increased subunit assembly efficiencies twofold with a corresponding increase in cell surface AChR. Pulse-chase experiments and immunofluorescence microscopy indicate that oligomer assembly occurs in the ER and that AChR oligomers remain in the ER until released to the cell surface. Once released, AChRs move rapidly through the Golgi membrane to the plasma membrane. Forskolin does not alter the intracellular distribution of AChR. Our results indicate that cell surface expression of AChR can be regulated at the level of subunit assembly and suggest a mechanism for the cAMP-induced increase in AChR expression.

Acetylglucosaminidase↗

PubMed1999

High-efficiency transfer of cystic fibrosis transmembrane conductance regulator cDNA into cystic fibrosis airway cells in culture using lactosylated polylysine as a vector.

To find more efficient vectors for the transfer of CFTR cDNA, lactosylated polylysine was explored for transfer into airway epithelial cells in primary culture. The efficacy and high efficiency of transfection were shown by several criteria: expression of both mRNA and protein for CFTR and the functional correction of the Cl- channel activity. Using specific combinations of agents to enhance the transfection, an efficiency of 90% was obtained as detected by in situ hybridization with digoxigenin-labeled probes generated against exon 14 of CFTR. The highest efficiency was observed by adding E5CA peptide (10 microg) and 5% glycerol to the transfection mixture. The degree of transfection could be controlled by the enhancing agents, thus modulating the efficiency of transfection. The highest level of transfection efficiency is equivalent to that reported for viral vectors. None of the agents or their combinations in the concentrations used were cytotoxic to the primary cells. Antibody pAb3145 was used to detect the expression of the CFTR protein in the cells. When an N-terminal GFP-CFTR fusion gene was used to transfect the CF cells a functional correction of the CFTR Cl- channel was detected by patch-clamp electrophysiology. The high efficiency of CFTR gene transfer with lactosylated polylysine leads to the conclusion that lactosylated polylysine is a promising vector to transfer the CFTR gene into human airway cells in culture.

Base Sequence↗

PubMed2006

Physical collection efficiency of filter materials for bacteria and viruses.

The purpose of this study was to determine the physical collection efficiency of commercially available filters for collecting airborne bacteria, viruses, and other particles in the 10-900 nm (nanometer) size range. Laboratory experiments with various polytetrafluoroethylene (PTFE), polycarbonate (PC) and gelatin filters in conjunction with Button Inhalable samplers and three-piece cassettes were undertaken. Both biological and non-biological test aerosols were used: Bacillus atrophaeus, MS2, polystyrene latex (PSL), and sodium chloride (NaCl). The B.atrophaeus endospores had an aerodynamic diameter of 900 nm, whereas MS2 virion particles ranged from 10 to 80 nm. Monodisperse 350 nm PSL particles were used as this size was believed to have the lowest filtration efficiency. NaCl solution (1% weight by volume) was used to create a polydisperse aerosol in the 10-600 nm range. The physical collection efficiency was determined by measuring particle concentrations size-selectively upstream and downstream of the filters. The PTFE and gelatin filters showed excellent collection efficiency (>93%) for all of the test particles. The PC filters showed lower collection efficiency for small particles especially <100 nm. Among the tested filters, the lowest collection efficiencies, 49 and 22%, were observed for 1 and 3-microm pore size PC filters at the particle sizes of 47 and 63 nm, respectively. The results indicate that the effect of filter material is more significant for the size range of single virions than for bacteria. The effect of filter loading was examined by exposing filters to mixtures of PSL particles, which aimed at mimicking typical indoor dust levels and size distributions. A 4-h loading did not cause significant change in the physical collection efficiency of the tested filters.

Air Microbiology↗

PubMed1998

Mutational analysis of the RNA pseudoknot involved in efficient ribosomal frameshifting in simian retrovirus-1.

Mutational effects on frameshifting efficiency of the RNA pseudoknot involved in ribosomal frameshifting in simian retrovirus-1 (SRV-1) have been investigated. The primary sequence and the proposed secondary structure of the SRV-1 pseudoknot are similar to those of other efficient frameshifting pseudoknots in mouse mammary tumor virus (MMTV) and feline immunodeficiency virus (FIV), where an unpaired adenine nucleotide intercalates between stem 1 and stem 2. In SRV-1 pseudoknot, the adenine nucleotide in between stem 1 and stem 2 has a potential to form an A*U base pair with the last uridine nucleotide in the loop 2, resulting in a continuous A-form helix with coaxially stacked stem 1 and stem 2. To test whether this A*U base pairing and coaxial stacking of stem 1 and stem 2 is absolutely required for efficient frameshifting in SRV-1, a series of mutants changing this potential A.U base pair to either G.C base pair or A.A, A.G, A.C, G.A, G.G mismatch is generated, and their frameshifting efficiencies are investigated in vitro using rabbit reticulocyte lysate translation assay. The frameshifting abilities of these mutant pseudoknots are similar to that of the wild-type pseudoknot, suggesting that the A*U base pair in between stem 1 and stem 2 is not necessary to promote efficient frameshifting in SRV-1. These results reveal that coaxial stacking of stem 1 and stem 2 with a Watson-Crick A.U base pair in between two stems is not a required structural feature of the pseudoknot for promoting efficient frameshifting in SRV-1. Our mutational data suggest that SRV-1 pseudoknot adopts similar structural features common to other efficient frameshifting pseudoknots as observed in MMTV and FIV.

Animals↗

PubMed2006

Natural anti-Gal and Salmonella-specific antibodies in bile and plasma of hens differing in diet efficiency.

Specific anti-Salmonella enteritidis (SE) and natural anti-alpha-gal epitope (Galalpha1-3Galbeta-1-4GlcNAc-R; anti-Gal) antibodies were measured in plasma sample pools and individual bile specimens obtained from hens differing in diet efficiency. More SE somatic (O) and flagellar (H) antibodies were found in plasma pools from efficient hens (R-) compared with nonefficient hens (R+) after oral challenge with live SE. Mean titers of somatic agglutinins in bile were 2.3 in R- hens and 1.9 in R+ hens (P = 0.06) following live challenge. Salmonella enteritidis antibodies were also found in bile of nonchallenged hens of both types but their levels were not significantly different. Flagellar (H) agglutinin scores were higher in SE-challenged hens compared with nonchallenged hens (3.1 vs. 2.1; P < or = 0.004) but efficiency types did not differ. Bile also contained high titers of the anti-Gal antibody indicated by the agglutination of glutaraldehyde-stabilized rabbit erythrocytes. The average titer of all SE-nonexposed hens was 9.0 corresponding to 1:5,120 when corrected for the initial dilution and expressed in conventional terms. Salmonella enteritidis exposure was associated with higher anti-Gal titers. The average anti-Gal titer for all SE-exposed hens was 10.0, corresponding to 1:10,240 in conventional terms; this difference was significant (P < or = 0.016). Diet efficiency type-associated differences in anti-Gal titers were not significant. Collectively, our data indicate that diet efficiency status is not associated with compromised Salmonella-specific immune responses. Rather it appears that the immune responses of diet efficient hens (R-) are also more efficient. This is because R- hens produced higher levels of O- and H-type antibody only as the result of direct exposure to living SE. On the contrary, R+ hens produced H-type antibody because of challenge with heat-killed SE, a circumstance that will not result in disease. Moreover, the hen type difference does not seem to occur at the expense of innate immunity as measured by anti-Gal antibody levels.

Animal Feed↗

PubMed1975

Efficiency of muscular work: some clinical implications.

The concept of mechanical efficiency is briefly reviewed. Biochemical considerations set a maximum potential efficiency of 25 percent, but, in some instances, storage of energy in elastic tissue may yield a higher apparent efficiency. Comparisons of efficiency between normal and handicapped individuals can be made in terms of the oxygen cost of specific activities, or, if due regard is paid to the effects of the primary disease, the simpler indexes of pulse rate and ventilation may be used. Measurements of efficiency can be helpful in improving the working technique of both the healthy individual and the handicapped person, Useful gains of efficiency can result only if tasks initially have an efficiency substantially below the theoretical ultimate of 25 percent.

Adenosine Triphosphate↗

PubMed1996

No effect of cycling experience on leg cycle ergometer efficiency.

Estimates of muscular efficiency in competitive and recreational cyclists at similar work intensities and cycling frequencies were examined. Twelve healthy college-age male nonsmoker volunteers were grouped as either competitive (CC; N = 6) or recreational (RC; N = 6) cyclists based upon previous cycling experience. Subjects were studied at pedaling frequencies of 50 and 80 rpm during bouts of graded and submaximal endurance (75% VO2peak) exercise. Between rest and 250 W, we observed no intergroup differences in VO2 (energy input) at either 50 or 80 rpm. Estimates of whole body (gross) muscular efficiency ranged from 15% to 24% in competitive and 13% to 22% in recreational cyclists at 50 rpm but were not different. Delta (delta) efficiencies ranged from 20% to 34% in competitive and from 21% to 28% in recreational cyclists. Delta efficiency decrease from 27% to 21% in competitive cyclists, from 25% to 21% in recreational cyclists as a function of pedaling frequency, and was not different between groups. Competitive cyclists rode longer at both 50 rmp (27 +/- 5 min vs 14 +/- 2 min; P < 0.05) and 80 rpm (35 +/- 4 min vs 20 +/- 4 min; P < 0.05). At 50 rpm (3.08 +/- 0.02 l.min-1 vs 2.78 +/- 0.05 l.min-1; P < 0.01) and 80 rpm (3.14 +/- 0.01 l.min-1 vs 2.7 +/- 0.04 l.min-1; P < 0.001), the mean VO2 was also greater in competitive cyclists. Although both groups showed superior endurance at 80 compared with 50 rpm and total work was approximately double competitive cyclists at each pedaling frequency, we observed no differences in whole body muscular efficiency during sustained exercise at 75% VO2peak. Our results suggested that previous cycling experience was of minor importance when comparing cycle ergometer efficiency between these two groups. The increased endurance at higher pedaling frequencies during submaximal exercise is not explained by altered muscular efficiency.

Adolescent↗

PubMed2002

Wheelchair propulsion technique and mechanical efficiency after 3 wk of practice.

PURPOSE: Differences in gross mechanical efficiency between experienced and inexperienced wheelchair users may be brought about by differences in propulsion technique. The purpose of this experiment was to study changes in propulsion technique (defined by force application, left-right symmetry, intercycle variability, and timing) and gross mechanical efficiency during a 3-wk wheelchair practice period in a group of novice able-bodied nonwheelchair users. METHODS: Subjects were randomly divided over an experimental group (N = 10) and a control group (N = 10). The experimental group received a 3-wk wheelchair practice period (3.wk-1, i.e., 9 practice trials) on a computer-controlled wheelchair ergometer, whereas the control group only participated in trials 1 and 9. During all nine practice trials, propulsion technique variables and mechanical efficiency were measured. RESULTS: No significant differences between the groups were found for force application, left-right symmetry, and intercycle variability. The push frequency and negative power deflection at the start of the push phase diminished significantly in the experimental group in contrast to the control group (P < 0.05). Work per cycle, push time, cycle time, and mechanical efficiency increased. CONCLUSION: The practice period had a favorable effect on some technique variables and mechanical efficiency, which may indicate a positive effect of improved technique on mechanical efficiency. Although muscle activation and kinematic segment characteristics were not measured in the present study, they may also impact mechanical efficiency. No changes occurred over time in most force application parameters, left-right symmetry, and intercycle variability during the 3-wk practice period; however, these variables may change on another time scale.

Acceleration↗

PubMed2004

Effect of wheelchair stroke pattern on mechanical efficiency.

OBJECTIVE: To investigate the effect of different wheelchair stroke patterns on efficiency and propulsion technique (force application and timing). DESIGN: Inexperienced, able-bodied subjects were randomly divided into two velocity groups (1.11 m/sec [n = 13] and 1.39 m/sec [n = 11]). An external (medium) load was set at 0.23 N/kg. Subjects performed four 4-min exercise blocks on a wheelchair ergometer. The first block was performed with a freely chosen movement pattern of the hand. Thereafter, the pumping, semicircular, or single-looping over propulsion pattern were performed in a counterbalanced order. Gross mechanical efficiency and propulsion technique variables were measured with Oxycon Alpha and an instrumented wheelchair ergometer. RESULTS: A significant difference was found for mechanical efficiency, with pumping showing the highest efficiency and semicircular the lowest efficiency, regardless of velocity. Timing variables and negative power deflections before and after the push phase showed significant differences between the stroke patterns. CONCLUSIONS: Pumping is the energetically most efficient stroke pattern in contrast to the semicircular pattern in this subject group. Propulsion technique could not explain the difference in efficiency.

Adult↗

PubMed2003

In vivo efficiency of four commercial monopolar radiofrequency ablation systems: a comparative experimental study in pig liver.

RATIONALE AND OBJECTIVES: To evaluate the efficiency of 4 radiofrequency (RF) systems by assessing the amount of delivered energy for each thermal induced lesion after perfusion mediated RF ablation and to compare the influence of perfusion mediation types on the energy efficiency. METHODS: A total of 43 ablations in 16 male landrace pigs with 4 RF devices were performed strictly according to the manufacturers' instructions. Total absorbed energy was computed and then related to 3D volumetry obtained after histopathological evaluation. Sixteen ablations were performed under physiological liver perfusion and 27 ablations with occlusion of portal vein, hepatic artery, or both vessels. Energy efficiency values of the RF systems for different vascular occlusion techniques were compared and analyzed by a nonparametrical rank sum test. RESULTS: Under physiological perfusion, the average energy delivered to produce 1-cm3 lesion size was calculated to 1650 +/- 929, 3097 +/- 389, 8312 +/- 2068, and 5493 +/- 2306 Watt x s/cm3 for the Berchtold, Radionics, Radiotherapeutics, and RITA system, respectively. After perfusion-mediated RF ablation, artery occlusion was not as effective as portal vein occlusion, which reduced the energy to 587 +/- 148, 869 +/- 276, and 903 +/- 394 Watt. s/cm3 for the Berchtold, Radionics, and Radiotherapeutics system, respectively. The occlusion of vessels, portal vein, and artery or portal vein alone increased the energy efficiency compared with physiological liver perfusion or occlusion of the artery (P = 0,003). CONCLUSIONS: Under physiological liver perfusion the open perfused system and the internally cooled system provided the best efficiency values with lowest standard deviations. The energy efficiency was increased markedly for all systems after occlusion of the portal vein either alone or in combination with arterial occlusion. Occlusion of the hepatic artery did not improve the efficiency.

Animals↗

PubMed2003

Zinc efficiency is correlated with enhanced expression and activity of zinc-requiring enzymes in wheat.

Zinc (Zn) is an essential micronutrient for plants. The ability of plants to maintain significant yields under low Zn is termed Zn efficiency (ZE) and its genetic and mechanistic basis is still not well understood. Previously, we showed that root Zn uptake did not play a role in ZE. In the current study, Zn-efficient and -inefficient wheat (Triticum aestivum) genotypes were grown for 13 d in chelate buffer nutrient solutions at low (0.1 pM), sufficient (150 pM), and high (1 microM) Zn(2+) activities and analyzed for root-to-shoot translocation of Zn, subcellular leaf Zn distribution, and activity and expression of the Zn-requiring enzymes in leaves. No correlation between ZE and Zn translocation to the shoot was found. Furthermore, total and water-soluble concentrations of leaf Zn were not associated with ZE, and no differences in subcellular Zn compartmentation were found between Zn-efficient and -inefficient genotypes. However, the expression and activity of the Zn-requiring enzymes copper (Cu)/Zn superoxide dismutase (SOD) and carbonic anhydrase did correlate with differences in ZE. Northern analysis suggested that Cu/ZnSOD gene expression was up-regulated in the Zn-efficient genotype, Kirgiz, but not in inefficient BDME. Under Zn deficiency stress, the very Zn-efficient genotype Kirgiz and moderately Zn-efficient Dagdas exhibited an increased activity of Cu/ZnSOD and carbonic anhydrase when compared with Zn-inefficient BDME. These results suggest that Zn-efficient genotypes may be able to maintain the functioning of Zn-requiring enzymes under low Zn conditions; thus, biochemical Zn utilization may be an important component of ZE in wheat.

Biological Transport↗

PubMed2005

Light enables a very high efficiency of carbon storage in developing embryos of rapeseed.

The conversion of photosynthate to seed storage reserves is crucial to plant fitness and agricultural production, yet quantitative information about the efficiency of this process is lacking. To measure metabolic efficiency in developing seeds, rapeseed (Brassica napus) embryos were cultured in media in which all carbon sources were [U-14C]-labeled and their conversion into CO2, oil, protein, and other biomass was determined. The conversion efficiency of the supplied carbon into seed storage reserves was very high. When provided with 0, 50, or 150 micromol m(-2) s(-1) light, the proportion of carbon taken up by embryos that was recovered in biomass was 60% to 64%, 77% to 86%, and 85% to 95%, respectively. Light not only improved the efficiency of carbon storage, but also increased the growth rate, the proportion of 14C recovered in oil relative to protein, and the fixation of external 14CO2 into biomass. Embryos grown at 50 micromol m(-2) s(-1) in the presence of 5 microM 1,1-dimethyl-3-(3,4-dichlorophenyl) urea (an inhibitor of photosystem II) were reduced in total biomass and oil synthesis by 3.2-fold and 2.8-fold, respectively, to the levels observed in the dark. To explore if the reduced growth and carbon conversion efficiency in dark were related to oxygen supplied by photosystem II, embryos and siliques were cultured with increased oxygen. The carbon conversion efficiency of embryos remained unchanged when oxygen levels were increased 3-fold. Increasing the O2 levels surrounding siliques from 21% to 60% did not increase oil synthesis rates either at 1,000 micromol m(-2) s(-1) or in the dark. We conclude that light increases the growth, efficiency of carbon storage, and oil synthesis in developing rapeseed embryos primarily by providing reductant and/or ATP.

Brassica rapa↗

PubMed2006

Translation efficiencies of synonymous codons are not always correlated with codon usage in tobacco chloroplasts.

Codon usage in chloroplasts is different from that in prokaryotic and eukaryotic nuclear genomes. However, no experimental approach has been made to analyse the translation efficiency of individual codons in chloroplasts. We devised an in vitro assay for translation efficiencies using synthetic mRNAs, and measured the translation efficiencies of five synonymous codon groups in tobacco chloroplasts. Among four alanine codons (GCN, where N is U, C, A or G), GCU was the most efficient for translation, whereas the chloroplast genome lacks tRNA genes corresponding to GCU. Phenylalanine and tyrosine are each encoded by two codons (UUU/C and UAU/C, respectively). Phenylalanine UUC and tyrosine UAC were translated more than twice as efficiently than UUU and UAU, respectively, contrary to their codon usage, whereas translation efficiencies of synonymous codons for alanine, aspartic acid and asparagine were parallel to their codon usage. These observations indicate that translation efficiencies of individual codons are not always correlated with codon usage in vitro in chloroplasts. This raises an important issue for foreign gene expression in chloroplasts.

Amino Acid Sequence↗