Regulation of Photosynthetic Rate of Two Sunflower Hybrids under Water Stress

The effect of short-term water stress on photosynthesis of two sunflower hybrids (Helianthus annuus L. cv Sungro-380 and cv SH-3622), differing in productivity under field conditions, was measured. The rate of CO₂ assimilation of young, mature leaves of SH-3622 under well-watered conditions was approximately 30% greater than that of Sungro-380 in bright light and elevated CO₂; the carboxylation efficiency was also larger. Growth at large photon flux increased assimilation rates of both hybrids. The changes in leaf composition, including cell numbers and sizes, chlorophyll content, and amounts of total soluble and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) protein, and in Rubisco activity and amount of ribulose-1,5-bisphosphate (RuBP) were determined to assess the factors regulating the differences in assimilation of the hybrids at high and low water potentials. The amounts of chlorophyll, soluble protein, Rubisco protein and the initial activity of Rubisco and its activation state did not differ significantly between hybrids. However, unstressed leaves of SH-3622 had more, smaller cells per unit area and 60% more RuBP per unit leaf area than that of Sungro-380. Water stress developing over 4 days decreased the assimilation of both hybrids similarly. Changes in the amounts of chlorophyll, soluble and Rubisco protein, and Rubisco activity and activation state were small and were not sufficient to explain the decrease in photosynthesis; neither was decreased stomatal conductance (or stomatal “patchiness”). Reduction of photosynthesis per unit leaf area from 25 to 5 micromoles CO₂ per square meter per second in both hybrids was caused by a decrease in the amount of RuBP from approximately 130 to 40 micromoles per square meter in SH-3622 and from 80 to 40 micromoles per square meter in Sungro. Differences between hybrids and their response to water stress is discussed in relation to control of RuBP regeneration.     

Interactions of racemic mefloquine and its enantiomers with P-glycoprotein in an immortalised rat brain capillary endothelial cell line, GPNT

The brain distribution of the enantiomers of the antimalarial drug mefloquine is stereoselective according to the species. This stereoselectivity may be related to species-specific differences in the properties of some membrane-bound transport proteins, such as P-glycoprotein (P-gp). The interactions of racemic mefloquine and its individual enantiomers with the P-glycoprotein efflux transport system have been analysed in immortalised rat brain capillary endothelial GPNT cells. Parallel studies were carried out for comparison in human colon carcinoma Caco-2 cells. The cellular accumulation of the P-glycoprotein substrate, [(3)H]vinblastine, was significantly increased both in GPNT cells and in Caco-2 cells when treated with racemic mefloquine and the individual enantiomers. In GPNT cells, the (+)-stereoisomer of mefloquine was up to 8-fold more effective than its antipode in increasing cellular accumulation of [(3)H]vinblastine, while in Caco-2 cells, both enantiomers were equally effective. These results suggest that racemic mefloquine and its enantiomers are effective inhibitors of P-gp. Furthermore, a stereoselective P-glycoprotein inhibition is observed in rat cells but not in human cells. The efflux of [(14)C]mefloquine from GPNT cells was decreased when the cells were incubated with the P-gp modulators, verapamil, cyclosporin A or chlorpromazine, suggesting that MQ could be a P-gp substrate.     

Role of the yiaR and yiaS genes of Escherichia coli in metabolism of endogenously formed L-xylulose

Genes yiaP and yiaR of the yiaKLMNOPQRS cluster of Escherichia coli are required for the metabolism of the endogenously formed L-xylulose, whereas yiaS is required for this metabolism only in araD mutants. Like AraD, YiaS was shown to have L-ribulose-5-phosphate 4-epimerase activity. Similarity of YiaR to several 3-epimerases suggested that this protein could catalyze the conversion of L-xylulose-5-phosphate into L-ribulose-5-phosphate, thus completing the pathway between L-xylulose and the general metabolism.     

Stereospecific versus nonstereospecific assessments for the bioequivalence of two formulations of racemic chlorpheniramine

Chlorpheniramine (chlorphenamine, CPAM) is a racemic antihistaminic H1 drug containing two enantiomers. The aim of this study was to assess the bioequivalence of two formulations (reference and Vietnamese-tested formulation) of racemic chlorpheniramine combined with phenylpropanolamine in an open-labeled, randomized, crossover two-period study, after administration of 8 mg of racemic chlorpheniramine in 12 healthy Vietnamese subjects. First, dissolution of both formulations was tested in vitro according to USP requirements. Then the 12 subjects received both formulations after an overnight fast and a 7-day wash-out period. Plasma samples were collected up to 168 h. Plasma concentrations of total chlorpheniramine and its individual enantiomers were determined with a validated chiral HPLC method and pharmacokinetic parameters were estimated using model-independent analysis. For the reference formulation, Cmax and AUC values were higher for (+)S-chlorpheniramine ((+)S-CPAM) compared to (-)R-chlorpheniramine ((-)R-CPAM) (13.3 vs. 6.8 ng/ml and 409 vs. 222 ng/ml/h, respectively) while Clt/F and Vd/F were lower (9.8 vs. 17.6 l/h and 321 vs. 627 l, respectively). No difference was observed for Tmax, t(1/2), and MRT. Pharmacokinetic parameters were similar for the reference and the Vietnamese-tested formulation. Bioequivalence was assessed by Schuirmann test, as recommended by the current FDA and European Community criteria. Dissolution tests showed that both formulations were equivalent. A nonstereospecific, but not a stereospecific, approach indicated bioequivalence between the formulations.     

The effect of long-term administration of low oral doses of chlormadinone acetate on heat cycles and ovarian functions in beef heifers

Chlormadinone acetate (CAP) was given orally for 42 days to four groups of 15 regularly cycling Hereford heifers in Central Mexico (19°N, altitude 2200 m). The CAP doses (0.625; 1.25 and 2.5 mg/day per animal) represent 1/16th, 1/8th and 1/4th, respectively, of the cycle synchronizing dose of 10 mg. Heat was observed for 1 hour at 06.00, 12.00 and 18.00 h and animals in heat were rectally palpated at 6 h intervals until ovulation had occurred. Observations continued for the duration of the treatment period and 26 days thereafter. CAP treatment had significant effects. With 2.5 mg, occurrence of the next heat was delayed in 8 and inhibited in 6 animals; nine animals had synchronized heat after CAP withdrawal; five animals did not ovulate but developed luteinized follicles; animals not cycling had prolonged periods of vulvar swelling. With 1.25 mg CAP, most animals continued cycling, but estrous intervals were prolonged and 3 animals developed luteinized follicles. With 0.625 mg CAP, only a slight prolongation in estrous intervals and of the heat periods was observed.Individual differences in response to CAP were marked in all treatment groups. CAP at the higher doses interfered with mechanisms of ovulation and was partially effective in preventing heat and follicular development.In cycling animals the length of the cycle, the duration of heat and the daily variations of the onset of heat were within reported limits. The interval between disappearance of heat symptoms and ovulations (21.23 h) was about twice that reported in the literature. Ovulations followed a daily rhythm with a major peak between 24.00 and 0.600 h and a minor elevation between 12.00 and 18.00 h.     

Disruptive viability selection on adult exploratory behaviour in eastern chipmunks

Heterogeneous forces of selection associated with fluctuating environments are recognized as important factors involved in the maintenance of inter‐individual phenotypic variance within populations. Consistent behavioural differences over time and across situations (e.g. personality) are increasingly cited as examples of individual variation observed within populations. However, the suggestion that heterogeneous selective pressures target different animal personalities remains largely untested in the wild. In this 5‐year study, we investigated the dynamics of viability selection on a personality trait, exploration, in a population of eastern chipmunks (Tamias striatus) experiencing substantial seasonal variations in weather conditions and food availability associated with masting trees. Contrary to our expectations, we found no evidence of fluctuating selection on exploration. Instead, we found strong disruptive viability selection on adult exploration behaviour, independent of seasonal variations. Individuals with either low or high exploration scores were almost twice as likely to survive over a 6‐month period compared with individuals with intermediate scores. We found no evidence of viability selection on juvenile exploration. Our results highlight that disruptive selection might play an important role in the maintenance of phenotypic variance of wild populations through its effect on different personality types across temporally varying environmental conditions.     

Ocean Acidification Has Multiple Modes of Action on Bivalve Larvae

Ocean acidification (OA) is altering the chemistry of the world’s oceans at rates unparalleled in the past roughly 1 million years. Understanding the impacts of this rapid change in baseline carbonate chemistry on marine organisms needs a precise, mechanistic understanding of physiological responses to carbonate chemistry. Recent experimental work has shown shell development and growth in some bivalve larvae, have direct sensitivities to calcium carbonate saturation state that is not modulated through organismal acid-base chemistry. To understand different modes of action of OA on bivalve larvae, we experimentally tested how pH, P_CO2, and saturation state independently affect shell growth and development, respiration rate, and initiation of feeding in Mytilus californianus embryos and larvae. We found, as documented in other bivalve larvae, that shell development and growth were affected by aragonite saturation state, and not by pH or P_CO2. Respiration rate was elevated under very low pH (~7.4) with no change between pH of ~ 8.3 to ~7.8. Initiation of feeding appeared to be most sensitive to P_CO2, and possibly minor response to pH under elevated P_CO2. Although different components of physiology responded to different carbonate system variables, the inability to normally develop a shell due to lower saturation state precludes pH or P_CO2 effects later in the life history. However, saturation state effects during early shell development will carry-over to later stages, where pH or P_CO2 effects can compound OA effects on bivalve larvae. Our findings suggest OA may be a multi-stressor unto itself. Shell development and growth of the native mussel, M. californianus, was indistinguishable from the Mediterranean mussel, Mytilus galloprovincialis, collected from the southern U.S. Pacific coast, an area not subjected to seasonal upwelling. The concordance in responses suggests a fundamental OA bottleneck during development of the first shell material affected only by saturation state.     

Infectious bursal disease virus uptake involves macropinocytosis and trafficking to early endosomes in a Rab5‐dependent manner

Infectious bursal disease virus (IBDV) internalization is sparsely known in terms of molecular components of the pathway involved. To describe the cell biological features of IBDV endocytosis, we employed perturbants of endocytic pathways such as pharmacological inhibitors and overexpression of dominant‐negative mutants. Internalization analysis was performed quantifying infected cells by immunofluorescence and Western blot detection of the viral protein VP3 at 12 h post‐infection reinforced by the analysis of the capsid protein VP2 localization after virus uptake at 1 h post‐infection. We compared IBDV infection to the internalization of well‐established ligands with defined endocytic pathways: transferrin, cholera‐toxin subunit B and dextran. To describe virus endocytosis at the morphological level, we performed ultrastructural studies of viral internalization kinetics in control and actin dynamics‐blocked cells. Our results indicate that IBDV endocytic internalization was clathrin‐ and dynamin‐independent, and that IBDV uses macropinocytosis as the primary entry mechanism. After uptake, virus traffics to early endosomes and requires exposure to the low endocytic pH as well as a functional endocytic pathway to complete its replication cycle. Moreover, our results indicate that the GTPase Rab5 is crucial for IBDV entry supporting the participation of the early endosomal pathway in IBDV internalization and infection of susceptible cells.     

Correlation of LNCR rasiRNAs expression with heterochromatin formation during development of the holocentric insect Spodoptera frugiperda

Repeat-associated small interfering RNAs (rasiRNAs) are derived from various genomic repetitive elements and ensure genomic stability by silencing endogenous transposable elements. Here we describe a novel subset of 46 rasiRNAs named LNCR rasiRNAs due to their homology with one long non-coding RNA (LNCR) of Spodoptera frugiperda. LNCR operates as the intermediate of an unclassified transposable element (TE-LNCR). TE-LNCR is a very invasive transposable element, present in high copy numbers in the S. frugiperda genome. LNCR rasiRNAs are single-stranded RNAs without a prominent nucleotide motif, which are organized in two distinct, strand-specific clusters. The expression of LNCR and LNCR rasiRNAs is developmentally regulated. Formation of heterochromatin in the genomic region where three copies of the TE-LNCR are embedded was followed by chromatin immunoprecipitation (ChIP) and we observed this chromatin undergo dynamic changes during development. In summary, increased LNCR expression in certain developmental stages is followed by the appearance of a variety of LNCR rasiRNAs which appears to correlate with subsequent accumulation of a heterochromatic histone mark and silencing of the genomic region with TE-LNCR. These results support the notion that a repeat-associated small interfering RNA pathway is linked to heterochromatin formation and/or maintenance during development to establish repression of the TE-LNCR transposable element. This study provides insights into the rasiRNA silencing pathway and its role in the formation of fluctuating heterochromatin during the development of one holocentric organism.