Wavelength dependency of light-induced effects on photoperiodic clock in the migratory blackheaded bunting (Emberiza melanocephala)

The effects of light wavelength on photoperiodic clock were determined in the migratory male blackheaded bunting (Emberiza melanocephala). We constructed an action spectrum for photoperiodic induction (body fattening, gain in body mass, and gonadal recrudescence) by exposing birds for 4.5 weeks to 13 h light per day (L:D = 13:11 h) of white (control), blue (450 nm), or red (640 nm) color at irradiances ranging from 0.028 to 1.4Wm(-2). The threshold light irradiance for photoinduction was about 10-fold higher for blue, compared to red and white light. Phase-dependent effects of light wavelength on the photoperiodic clock were further examined in the next two sets of skeleton photoperiods (SKPs). In the first set of SKPs, birds were exposed for four weeks to asymmetrical light periods (L:D:L:D= 6:6:1:11 h) at 0.25+/-0.01 W m(-2); two light periods applied were of the same (450nm: blue:blue, B:B; 640nm, red:red, R:R) or different (blue:red, B:R or red:blue, R:B) wavelengths, or of white:white (W:W, controls). Photoperiodic induction occurred under R:R and B:R, but not under B:B and R:B light conditions; the W:W condition induced an intermediate response. The second set of SKPs used symmetrical light periods (L:D:L:D = 1:11:1:11 h), and measured effects also on the activity rhythm. Birds were first exposed to one of the four SKPs (R:R, B:B, R:B, or B:R) for three weeks, subsequently were released into dim constant light (LLdim; approximately 0.01 Wm(-2), the night light used in an L:D cycle) for two weeks, and then were returned to respective SKPs for another three weeks. Activity was greater in the R:R compared to B:B, and in B:R compared to R:B light condition. Zugunruhe (intense nighttime activity, indicating migratory restlessness in a caged situation) developed under the R:R and B:R, but not the B:B and R:B, light condition. Under LLdim, all birds free-ran with a period >24h, the Zugunruhe had a circadian period longer than the daytime activity, and the re-entrainment to SKPs was influenced by the position of light periods relative to circadian phase of the activity rhythm. Photoperiodic induction at the end of 8 weeks was found in the R:R and B:R, but not in B:B, light conditions; in the R:B condition only one bird had initiated testes. Taken together, these results suggest that in the blackheaded bunting, the circadian photoperiodic clock is differentially responsive to light wavelengths; this responsiveness is phase-dependent, and the development of Zugunruhe reflects a true circadian function. Wavelength-dependent response of the photoperiodic clock could be part of an adaptive strategy in evolution of the seasonality in reproduction and migration among photoperiodic species under wild conditions.     

Wavelength Dependency of Light-Induced Effects on Photoperiodic Clock in the Migratory Blackheaded Bunting (Emberiza melanocephala)

The effects of light wavelength on photoperiodic clock were determined in the migratory male blackheaded bunting (Emberiza melanocephala). We constructed an action spectrum for photoperiodic induction (body fattening, gain in body mass, and gonadal recrudescence) by exposing birds for 4.5 weeks to 13 h light per day (L:D = 13:11 h) of white (control), blue (450 nm), or red (640 nm) color at irradiances ranging from 0.028 to 1.4 W m^?2. The threshold light irradiance for photoinduction was about 10-fold higher for blue, compared to red and white light. Phase-dependent effects of light wavelength on the photoperiodic clock were further examined in the next two sets of skeleton photoperiods (SKPs). In the first set of SKPs, birds were exposed for four weeks to asymmetrical light periods (L:D:L:D = 6:6:1:11 h) at 0.25 ± 0.01 W m^?2; two light periods applied were of the same (450 nm: blue:blue, B:B; 640 nm, red:red, R:R) or different (blue:red, B:R or red:blue, R:B) wavelengths, or of white:white (W:W, controls). Photoperiodic induction occurred under R:R and B:R, but not under B:B and R:B light conditions; the W:W condition induced an intermediate response. The second set of SKPs used symmetrical light periods (L:D:L:D = 1:11:1:11 h), and measured effects also on the activity rhythm. Birds were first exposed to one of the four SKPs (R:R, B:B, R:B, or B:R) for three weeks, subsequently were released into dim constant light (LL_dim; ?0.01 W m^?2, the night light used in an L:D cycle) for two weeks, and then were returned to respective SKPs for another three weeks. Activity was greater in the R:R compared to B:B, and in B:R compared to R:B light condition. Zugunruhe (intense nighttime activity, indicating migratory restlessness in a caged situation) developed under the R:R and B:R, but not the B:B and R:B, light condition. Under LL_dim, all birds free-ran with a period >24 h, the Zugunruhe had a circadian period longer than the daytime activity, and the re-entrainment to SKPs was influenced by the position of light periods relative to circadian phase of the activity rhythm. Photoperiodic induction at the end of 8 weeks was found in the R:R and B:R, but not in B:B, light conditions; in the R:B condition only one bird had initiated testes. Taken together, these results suggest that in the blackheaded bunting, the circadian photoperiodic clock is differentially responsive to light wavelengths; this responsiveness is phase-dependent, and the development of Zugunruhe reflects a true circadian function. Wavelength-dependent response of the photoperiodic clock could be part of an adaptive strategy in evolution of the seasonality in reproduction and migration among photoperiodic species under wild conditions.     

Synthesis and reactivity of coordinatively unsaturated osmium and ruthenium stannyl complexes

Treatment of MHCl(CO)(PPh₃)₃ (M=Ru, Os) with (CH₂=CH)SnR₃ is a good general route to the coordinatively unsaturated osmium and ruthenium stannyl complexes M(SnR₃)Cl(CO)(PPh₃)₂ (1: M=Ru, R=Me; 2: M=Ru, R = n-butyl; 3: M=Ru, R = p-tolyl; 4: M=Os, R=Me). These coordinatively unsaturated complexes readily add CO and CN-p-tolyl to form the coordinatively saturated compounds M(SnR₃)Cl(CO)L(PPh₃)₂ (5: M=Ru, R=Me, L=CO; 6: M=;Ru, R = n-butyl, L=CO; 7: M=Ru, R = p-tolyl, L=CO; 8: M=Os, R=Me, L=CO; 9: M=Ru, R=Me, L=CN-p-tolyl; 10: M=Ru, R = n-butyl, L=CN-p-tolyl; 11: M=Os, R=Me, L=CN-p-tolyl). In addition, the chloride ligand in Ru(SnR₃)Cl(CO)(PPh₃)₂ proves to be labile and treatment with the potentially bidentate anionic ligands, dimethyldithiocarbamate or diethyldithiocarbamate, affords the coordinatively saturated compounds Ru(SnR₃)(η²-S₂CNR′₂)(CO)(PPh₃)₂ (12: R=Me, R′ = Me; 13: R=Me, R′ = Et; 14: R = n-butyl, R′ = Me; 15: R = p-tolyl, R′ = Me; 16: R = p-tolyl, R′ = Et). Chloride is also displaced by carboxylates forming the six-coordinate compounds Ru(SnR₃)(η²-O₂CR′)(CO)(PPh₃)₂ (17: R=Me, R′ = H; 18: R=Me, R′ = Me; 19: R=Me, R′ = Ph; 20: R = n-butyl, R′ = Me; 21: R = p-tolyl, R′ = Me). IR and ¹H NMR spectral data for all the new compounds and ³¹P and ¹¹⁹Sn NMR spectral data for selected compounds are reported.     

Myofilament mechanical performance is enhanced by R403Q myosin in mouse myocardium independent of sex

Male but not female mice carrying a single R403Q missense allele for cardiac alpha-myosin heavy chain (M-alphaMHC(R403Q/+) and F-alphaMHC(R403Q/+), respectively) develop significant hypertrophic cardiomyopathy (HCM) compared with male and female wild-type mice (M-alphaMHC(+/+) and F-alphaMHC(+/+), respectively) after approximately 30 wk of age. We tested the hypothesis that myofilament mechanical performance differs between M-alphaMHC(R403Q/+) and F-alphaMHC(R403Q/+) at younger ages (10-20 wk) and could account for sex differences in HCM development. The sensitivity of chemically skinned myocardial strips to Ca(2+) activation (pCa(50)) was significantly (P < 0.05) enhanced in male mice independent of genotype (M-alphaMHC(R403Q/+): 5.70 +/- 0.06, M-alphaMHC(+/+): 5.63 +/- 0.05, F-alphaMHC(R403Q/+): 5.57 +/- 0.03, F-alphaMHC(+/+): 5.54 +/- 0.04) by two-way ANOVA, whereas maximum developed tension was significantly enhanced in alpha-MHC(R403Q/+) independent of sex (M-alphaMHC(R403Q/+): 29.3 +/- 2.3, M-alphaMHC(+/+): 26.0 +/- 1.4, F-alphaMHC(R403Q/+): 30.2 +/- 2.1, F-alphaMHC(+/+): 26.2 +/- 1.2 mN/mm(2)). The frequency of maximum work generated by sinusoidal length perturbation was significantly higher in alphaMHC(R403Q/+) mice than in sex-matched controls (M-alphaMHC(R403Q/+): 2.26 +/- 0.47, M-alphaMHC(+/+): 1.29 +/- 0.18, F-alphaMHC(R403Q/+): 3.21 +/- 0.33, F-alphaMHC(+/+): 2.52 +/- 0.36 Hz). Unloaded shortening velocity was significantly enhanced in alphaMHC(R403Q/+) and in female mice (M-alphaMHC(R403Q/+): 2.26 +/- 0.47, M-alphaMHC(+/+): 1.29 +/- 0.18, F-alphaMHC(R403Q/+): 3.21 +/- 0.33, F-alphaMHC(+/+): 2.52 +/- 0.36 muscle lengths/s), and normalized mechanical power, calculated from the tension-velocity relationship, was significantly enhanced in alphaMHC(R403Q/+) independent of sex (M-alphaMHC(R403Q/+): 60 +/- 2 10(-3), M-alphaMHC(+/+): 37 +/- 3 10(-3), F-alphaMHC(R403Q/+): 57 +/- 3 10(-3), F-alphaMHC(+/+) 25 +/- 3 10(-3) muscle lengths/s x normalized tension). We did not find a statistically significant sex x mutation interaction for any measure of myofilament performance. Therefore, sarcomeric incorporation of the R403Q myosin similarly enhanced left ventricular myofilament mechanical performance in both male and female mice. The sex-dependent development of HCM due to the R403Q myosin may then be inhibited by female sex hormones, which may additionally underlie the observed sex differences for pCa(50) and unloaded shortening velocity.     

Unique quadruplex structure and interaction of an RNA aptamer against bovine prion protein

RNA aptamers against bovine prion protein (bPrP) were obtained, most of the obtained aptamers being found to contain the r(GGAGGAGGAGGA) (R12) sequence. Then, it was revealed that R12 binds to both bPrP and its β-isoform with high affinity. Here, we present the structure of R12. This is the first report on the structure of an RNA aptamer against prion protein. R12 forms an intramolecular parallel quadruplex. The quadruplex contains G:G:G:G tetrad and G(:A):G:G(:A):G hexad planes. Two quadruplexes form a dimer through intermolecular hexad–hexad stacking. Two lysine clusters of bPrP have been identified as binding sites for R12. The electrostatic interaction between the uniquely arranged phosphate groups of R12 and the lysine clusters is suggested to be responsible for the affinity of R12 to bPrP. The stacking interaction between the G:G:G:G tetrad planes and tryptophan residues may also contribute to the affinity. One R12 dimer molecule is supposed to simultaneously bind the two lysine clusters of one bPrP molecule, resulting in even higher affinity. The atomic coordinates of R12 would be useful for the development of R12 as a therapeutic agent against prion diseases and Alzheimer''s disease.     

Tissue transglutaminase contributes to disease progression in the R6/2 Huntington's disease mouse model via aggregate-independent mechanisms

Huntington's disease (HD) is caused by an expansion of CAG repeats within the huntingtin gene and is characterized by intraneuronal mutant huntingtin protein aggregates. In order to determine the role of tissue transglutaminase (tTG) in HD aggregate formation and disease progression, we cross-bred the R6/2 HD mouse model with a tTG knockout mouse line. R6/2 mice that were tTG heterozygous knockouts (R6/2 : tTG+/-) and tTG homozygous knockouts (R6/2 : tTG-/-) showed a very similar increase in aggregate number within the striatum compared with R6/2 mice that were wild-type with respect to tTG (R6/2 : tTG+/+). Interestingly, a significant delay in the onset of motor dysfunction and death occurred in R6/2 : tTG-/- mice compared with both R6/2 : tTG+/+ and R6/2 : tTG+/- mice. As aggregate number was similarly increased in the striatum of both R6/2 : tTG+/- and R6/2 : tTG-/- mice, whereas only R6/2 : tTG-/- mice showed delayed disease progression, these data suggest that the contribution of tTG towards motor dysfunction and death in the R6/2 mouse is independent of its ability to negatively regulate aggregate formation. Moreover, the combined results from this study suggest that the formation of striatal huntingtin aggregates does not directly influence motor dysfunction or death in this HD mouse model.     

The influence of R:FR ratio on the growth, photosynthesis and rooting ability of Terminalia spinosa Engl. and Triplochiton scleroxylon K. Schum

Stockplants of the tropical hardwoods Terminalia spinosa Engl, and Triplochiton scleroxylon K. Schum were grown in a controlled environment under red:far-red (R:FR) ratios ranging from 0.5-3.1. In both species, rates of shoot height increment were higher (P < 0.05) under the low R:FR ratios as a result of increased internode elongation. In Terminalia spinosa , specific leaf area (SLA) was also significantly higher under lower R:FR ratios, values ranging from 175 to 210 cm² g^-1 in the 3.1 and 0.9 treatments respectively. No effect of R:FR ratio on SLA was recorded in Triplochiton scleroxylon. Pre-severance photo-synthetic rate, stomatal conductance and water-use efficiency were increased under the higher R:FR ratios in Terminalia spinosa , rates of photosynthesis ranging between 2.68-4.59 μmol m^-2 s^-1 in the 0.5 and 3.1 R:FR treatments respectively. Gas exchange rates of Triplochiton scleroxylon were unaffected by R:FR treatment. These contrasting responses to variation in R:FR ratio were associated with differences in rooting ability. In Terminalia spinosa , significantly higher percentage rooting was recorded in the cuttings from the 3.1 R:FR treatment than from 0.5, with values of 93.7% and 77.5% recorded respectively. R:FR ratio also affected rooting percentages of Triplochiton scleroxylon , but in this case, higher rooting percentages were recorded in the lower R:FR ratios, values ranging from 31.1–54.1% in the 3.0 and 0.5 R.FR treatments respectively. This difference in rooting response is attributed to the contrasting effects of R:FR ratio on the leaf and stem morphology of the two species. The implications of these results for stockplant management are discussed.     

Genetic and nucleotide sequence analysis of the gene htdA, which regulates conjugal transfer of IncHI plasmids.

IncHI plasmids are naturally repressed for conjugative transfer and do not allow efficient propagation of the IncH pilus-specific phage Hgal. Transposons Tn7, Tn5, and TnlacZ were inserted into IncHI plasmids R478, R477-1, and R27, respectively, leading to the isolation of several plasmid mutants which exhibited increased levels of transfer and also permitted good lysis with phage Hgal. A 4.3-kb HindIII fragment from R478 reversed both phenotypic effects of derepression for the R477-1::Tn5 and the R478::Tn7 derivatives, pKFW99 and pKFW100, respectively. Exonuclease III deletions of this fragment and nucleotide sequence analysis indicated that the gene responsible for transfer repression, named here htdA, encoded a polypeptide of 150 amino acids. Cloning and sequence analysis of pDT2454 (R27::TnlacZ) revealed that the transposon had inserted into an open reading frame (ORF) which had an 83% amino acid identity with the R478 htdA gene. Maxicell analysis showed both the R27 and R478 HtdA products had molecular masses of 19.9 kDa. Conjugation experiments showed that the cloned htdA determinants caused a significant reduction of the transfer frequencies of wild-type R478 and R27 plasmids. Examination of both R478 derepressed mutants, pKFW100 and pKFW101, indicated that both transposon insertions occurred upstream of the htdA ORF. The results suggest that HtdA is a regulatory component of IncH plasmid transfer and also show that the region upstream of the htdA ORF is involved in transfer repression. The locations of the htdA determinants were identified on the plasmid maps of R27 and R478.     

pH dependence of the hydrolysis of hippuric acid esters by carboxypeptidase A.

The pH dependence (pH 4.5-10.5) of the hydrolysis of seven hippuric acid esters (C6H5CONHCH2C-O2CR1R2CO2H: 1a: R1 = R2 = H; 1b: R1 = R2 = CH3; 1c: R1 = H, R2 = p-ClC6H4; 1d: R1 = H, R2 = C2H5; 1e: R1 = H, R2 = (CH3)2CHCH2; 1f: R1 = H, R2 = C6H5; 1g: R1 = H, R2 = C6H5CH2) by bovine carboxypeptidase A has been investigated, and the pH dependence of the substrate activation of 1a-c and the substrate inhibition of 1d-g have been compared. For all seven esters the catalytically productive binding of the first substrate molecule depends on enzymatic pKa values of 6.0 and 9.1. For 1d, 1e, and 1g the rate of hydrolysis (k2app) of this complex is pH independent, whereas for 1f k2app depends on a pKa of 5.9. The rate of hydrolysis (k3app) of the 1:2 enzyme-substrate complex (ES2) is pH independent for 1d-g, but for 1a-c k3app depends on the following pKa values: 1a, 6.1 and 9.1; 1b, 5.4; 1c, 6.6. The pH dependences of k2app for 1f and k3app for 1c are rationalized by the presence of catalytically nonproductive species. Equivalent ES2 species are believed to be productive for 1c-g; however, the productive ES2 species for 1b must be quite different.     

Tn4351 transposes in Bacteroides spp. and mediates the integration of plasmid R751 into the Bacteroides chromosome.

The gene for resistance to erythromycin and clindamycin, which is carried on the conjugative Bacteroides plasmid, pBF4, has been shown previously to be part of an element (Tn4351) that transposes in Escherichia coli. We have now introduced Tn4351 into Bacteroides uniformis 0061 on the following two suicide vectors: (i) the broad-host-range IncP plasmid R751 (R751::Tn4351) and (ii) pSS-2, a chimeric plasmid which contains 33 kilobases of pBF4 (including Tn4351) cloned into the IncQ plasmid RSF1010 and which is mobilized by R751. When E. coli HB101, carrying either R751::Tn4351 or R751 and pSS-2, was mated with B. uniformis under aerobic conditions, Emr transconjugants were detected at a frequency of 10(-6) to 10(-5) (R751::Tn4351) or 10(-8) to 10(-6) (R751 and pSS-2). In matings involving pSS-2, all Emr transconjugants contained simple insertions of Tn4351 in the chromosome, whereas in matings involving R751::Tn4351, about half of the Emr transconjugants had R751 cointegrated with Tn4351 in the chromosome. Of the Emr transconjugants, 13% were auxotrophs. Bacteroides spp. which had R751 cointegrated with Tn4351 in the chromosome did not transfer R751 or Tn4351 to E. coli HB101 or to isogenic B. uniformis, nor did the intergrated R751 mobilize pE5-2, an E. coli-Bacteroides shuttle vector that contains a transfer origin that is recognized by R751.     

Effect of interrepetition rest on power output in the power clean

The effect of interrepetition rest (IRR) periods on power output during performance of multiple sets of power cleans is unknown. It is possible that IRR periods may attenuate the decrease in power output commonly observed within multiple sets. This may be of benefit for maximizing improvements in power with training. This investigation involved 10 college-aged men with proficiency in weightlifting. The subjects performed 3 sets of 6 repetitions of power cleans at 80% of their 1 repetition maximum with 0 (P0), 20 (P20), or 40 seconds (P40) of IRR. Each protocol (P0, P20, P40) was performed in a randomized order on different days each separated by at least 72 hours. The subjects performed the power cleans while standing on a force plate with 2 linear position transducers attached to the bar. Peak power, force, and velocity were obtained for each repetition and set. Peak power significantly decreased by 15.7% during P0 in comparison with a decrease of 5.5% (R1: 4,303 ± 567 W, R6: 4,055 ± 582 W) during P20 and a decrease of 3.3% (R1: 4,549 ± 659 W, R6: 4,363 ± 476 W) during P40. Peak force significantly decreased by 7.3% (R1: 2,861 ± 247 N, R6: 2,657 ± 225 N) during P0 in comparison with a decrease of 2.7% (R1: 2,811 ± 327 N, R6: 2,730 ± 285 N) during P20 and an increase of 0.4% (R1: 2,861 ± 323 N, R6: 2,862 ± 280 N) during P40. Peak velocity significantly decreased by 10.2% (R1: 1.97 ± 0.15 m·s(-1), R6: 1.79 ± 0.11 m·s(-1)) during P0 in comparison with a decrease of 3.8% (R1: 1.89 ± 0.13 m·s(-1), R6: 1.82 ± 0.12 m·s(-1)) during P20 and a decrease of 1.7% (R1: 1.93 ± 0.17 m·s(-1), R6: 1.89 ± 0.14 m·s(-1)) during P40. The results demonstrate that IRR periods allow for the maintenance of power in the power clean during a multiple set exercise protocol and that this may have implications for improved training adaptations.     

Three- and four-repeat tau regulate the dynamic instability of two distinct microtubule subpopulations in qualitatively different manners. Implications for neurodegeneration

The microtubule-associated protein tau is implicated in the pathogenesis of many neurodegenerative diseases, including fronto-temporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), in which both RNA splicing and amino acid substitution mutations in tau cause dominantly inherited early onset dementia. RNA-splicing FTDP-17 mutations alter the wild-type approximately 50:50 3-repeat (3R) to 4-repeat (4R) tau isoform ratio, usually resulting in an excess of 4R tau. To examine further how splicing mutations might cause dysfunction by misregulation of microtubule dynamics, we used video microscopy to determine the in vitro behavior of individual microtubules stabilized by varying amounts of human 4R and 3R tau. At low tau:tubulin ratios (1:55 and 1:45), all 3R isoforms reduced microtubule growth rates relative to the no-tau control, whereas all 4R isoforms increased them; however, at a high tau:tubulin ratio (1:20), both 4R and 3R tau increased the growth rates. Further analysis revealed two distinct subpopulations of growing microtubules in the absence of tau. Increasing concentrations of both 4R and 3R tau resulted in an increase in the size of the faster growing subpopulation of microtubules; however, 4R tau caused a redistribution to the faster growing subpopulation at lower tau:tubulin ratios than 3R tau. This modulation of discrete growth rate subpopulations by tau suggests that tau causes a conformational shift in the microtubule resulting in altered dynamics. Quantitative and qualitative differences observed between 4R and 3R tau are consistent with a "microtubule misregulation" model in which abnormal tau isoform expression results in the inability to properly regulate microtubule dynamics, leading to neuronal death and dementia.     

Rhizobium selenireducens sp. nov.: A Selenite-Reducing α-Proteobacteria Isolated From a Bioreactor

A Gram-negative, nonpigmented bacterium designated strain B1 was isolated from a laboratory bioreactor that reduced selenate to elemental red selenium (Se(0)). 16S rRNA gene-sequence alignment identified the isolate as a Rhizobium sp. belonging to the Rhizobium clade, which includes R. daejeonense, R. giardinii, R. undicola, R. larrymoorei, R. radiobacter, R. rubi, and R. vitis. R. radiobacter and R. rubi are its closest relatives as indicated by 16S rRNA gene-sequence alignments, which differ from strain B1 by 2.6% and 2.8%, respectively. Within this group, strains that show variances > 0.8% to 2.2% have been classified as different species. The major cellular fatty acids present in the B1 strain were C16:0 (1.8%), C18:0 (3.38%), 18:0 3-OH (1.6%), 18:1 omega7c (86.8%), 19:0 cycloomega8c (1.5%), and summed features 2 (3.8%) and 3 (1.2%). The large amount of 18:1 omega7c present is constant with members of this group of bacteria, but the small amounts of 16:0, 19:0 cycloomega8c, and summed feature 3 shows variance from R. radiobacter and R. rubi. The strain's phenotypic and biochemical characteristics are consistent with its placement in this genus.     

Synthesis of 4-denitro-4-azido-chloramphenicol: A photochemically activatable analog of chloramphenicol

The synthesis of 4-denitro-4-azido-chloramphenicol is described. Phthalylation of d-threo-(1R:2R)-1-(4-nitrophenyl)-2-amino-1,3-propanediol with N-ethoxy-carbonyl-phthalimide yields d-threo-(1R:2R)-1-(4-nitrophenyl)-2-phthaloylamino-1.3-propanediol. On catalytic hydrogenation, the latter compound is converted to d-threo-(1R:2R)-1-(4-aminophenyl)-2-phthaloylamino-1.3-propanediol, diazotization of which, followed by displacement of the diazonium group by azide ion, gives d-threo-(1R:2R)-1-(4-azidophenyl)-2-phthaloylamino-1.3-propanediol. Hydrazine dephthalylates that compound to give d-threo-(1R:2R)-1-(4-azidophenyl)-2-amino-1.3-propanediol. By esterification of this azide with methyl dichloroacetate d-threo-(1R:2R)-1-(4-azidophenyl)-2-dichloroacetylamino-1.3-propanediol, “4-denitro-4-azido-chloramphenicol” is formed. This substance photolyses on irradiation with uv light to a reactive nitrene, which is expected to form covalent linkages at its ribosomal binding site, and thus, help to elucidate the mode of action of the antibiotic chloramphenicol in protein biosynthesis.     

Bulb Development in Onion (Allium cepa L.) II. The Influence of Red: Far-red Spectral Ratio and of Photon Flux Density

Bulb development was followed in four onion cultivars growingin controlled environments under 17 h days in factorial combinationsof photon-flux densities (PFD) of 111 and 333 µmol m^–2s^–1 with red: far-red spectral ratios (R : FR) of 2.88and 1.41. A PFD of 111with R : FR of 0.86 was used in a secondexperiment. The lower the R : FR or the higher the PFD the higherthe mean bulbing ratio and the ratio of bulb plus sheath toleaf blade dry weight and the earlier the bulb swelling. LowerR : FR accelerated scale initiation as did the higher PFD underR : FR 2.88 but not under R : FR 1.41. In high PFD bulb swellingoccurred before scale initiation because many sheaths of bladedleaves thickened, but in low PFD and low R : FR bulb swellingand scale initiation were concurrent. In the low PFD a low R: FR increased soluble carbohydrate concentrations in sheathsand scales compared to high R : FR. In high PFD, soluble carbohydrateconcentrations did not vary with R : FR and were higher thanunder low PFD. Onion, Allium cepa L., bulb, photon flux density, red: far-red ratio, light spectral quality, soluble carbohydrate     

Density-dependent regulation of ramet recruitment by the red:far-red ratio of solar radiation: a field evaluation with the bunchgrass Schizachyrium scoparium

Depressions in the red to far-red ratio (R:FR) of solar radiation arising from the selective absorption of R (600–700 nm) and scattering of FR (700–800 nm) by chlorophyll within plant canopies may function as an environmental signal directly regulating axillary bud growth and subsequent ramet recruitment in clonal plants. We tested this hypothesis in the field within a single cohort of parental ramets in established clones of the perennial bunchgrass, Schizachyrium scoparium. The R:FR was modified near leaf sheaths and axillary buds at the bases of individual ramets throughout the photoperiod without increasing photosynthetic photon flux density (PPFD) by either (1) supplementing R beneath canopies to raise the naturally low R:FR or (2) supplementing FR beneath partially defoliated canopies to suppress the natural R:FR increase following defoliation. Treatment responses were assessed by simultaneously monitoring ramet recruitment, PPFD and the R:FR beneath individual clone canopies at biweekly intervals over a 12-week period. Neither supplemental R nor FR influenced the rate or magnitude of ramet recruitment despite the occurrence of ramet recruitment in all experimental clones. In contrast, defoliation with or without supplemental FR beneath clone canopies reduced ramet recruitment 88% by the end of the experiment. The hypothesis stating that the R:FR signal directly regulates ramet recruitment is further weakened by evidence demonstrating that (1) the low R:FR-induced suppression of ramet recruitment is only one component of several architectural modifications exhibited by ramets in response to the R:FR signal (2) immature leaf blades, rather than leaf sheaths or buds, function as sites of R:FR perception on individual ramets, and (3) increases in the R:FR at clone bases following partial canopy removal are relatively transient and do not override the associated constraints on ramet recruitment resulting from defoliation. A depressed R:FR is probably of greater ecological significance as a signal of competition for light in vegetation canopies than as a density-dependent signal which directly regulates bud growth and ramet recruitment.     

Regulation of the photosynthetic capacity of primary bean leaves by the red:far-red ratio and photosynthetic photon flux density of incident light

The main objective of the present work was to examine the effects of the red:far-red ratio (R:FR) prevailing during leaf development on the photosynthetic capacity of mature leaves. Plants of Phaseolus vulgaris L. cv. Balin de Albenga were grown from time of emergence in a controlled environment room, 25 ± 3°C, 12-h photoperiod, with different light treatments:a) high photosynthetic photon flux density (PPFD) = 800 μmol m⁻¹ s⁻¹+ high R:FR= 1.3;b) low PPFD= 300 μmol m⁻² s⁻¹+ high R:FR= 1.3; c) high PPFD=800 μmol m⁻² s⁻¹+ low R:FR= 0.7; d) low PPFD= 300 μmol m⁻²s⁻¹+ low R:FR=0.7. With an R:FR ratio of 1.3, a decrease in irradiance during leaf growth reduced photosynthesis when measured at moderate to high PPFD; but when measured at low PPFD, leaves expanded under low irradiance actually had photosynthesis rates higher than those of leaves grown in high irradiance. A low R:FR ratio during development reduced the photosynthetic capacity of the leaves. In leaves expanded under R:FR = 0.7 and high irradiance photosynthesis was reduced by 42 to 89%, depending on the PPFD at which measurements were made, whereas for leaves developed at R:FR = 0.7 and low irradiance photosynthesis decreased by 21 to 24%, compared to leaves under R:FR = 1.3 and similar irradiance. The reduced photosynthetic capacity under R:FR = 0.7 and high irradiance. In natural environments, leaves may experience low R:FR conditions temporarily during their development, and this may affect their future photosynthetic capacity in full sunlight.