Root growth dynamics of Nicotiana attenuata seedlings are affected by simulated herbivore attack

Many studies demonstrate resource-based trade-offs between growth and defence on a large timescale. Yet, the short-term dynamics of this growth reaction are still completely unclear, making it difficult to explain growth-defence trade-offs mechanistically. In this study, image-based non-destructive methods were used to quantify root growth reactions happening within hours following simulated herbivore attack. The induction of wound reactions in Nicotiana attenuata in the seedling stage led to transiently decreased root growth rates. Application of the oral secretion of the specialist herbivore Manduca sexta to the leaves led to a transient decrease in root growth that was more pronounced than if a mere mechanical wounding was imposed. Root growth reduction was more pronounced than leaf growth reduction. When fatty acid-amino acid conjugates (FACs) were applied to wounds, root growth reduction occurred in the same intensity as when oral secretion was applied. Timing of the transient growth reduction coincided with endogenous bursts of jasmonate (JA) and ethylene emissions reported in literature. Simulation of a wound response by applying methyl jasmonate (MeJA) led to more prolonged negative effects on root growth. Increased nicotine concentrations, trichome lengths and densities were observed within 72 h in seedlings that were treated with MeJA or that were mechanically wounded. Overall, these reactions indicate that even in a very early developmental stage, the diversion of plant metabolism from primary (growth-sustaining) to secondary (defence-related) metabolism can cause profound alterations of plant growth performance.     

Continuous asymmetric ketone reduction processes with recombinant Escherichia coli

The reduction of methyl acetoacetate was carried out in continuously operated biotransformation processes catalyzed by recombinant Escherichia coli cells expressing an alcohol dehydrogenase from Lactobacillus brevis. Three different cell types were applied as biocatalysts in three different cofactor regeneration approaches. Both processes with enzyme-coupled cofactor regeneration catalyzed by formate dehydrogenase or glucose dehydrogenase are characterized by a rapid deactivation of the biocatalyst. By contrast the processes with substrate-coupled cofactor regeneration by alcohol dehydrogenase catalyzed oxidation of 2-propanol could be run over a period of 7 weeks with exceedingly high substrate and cosubstrate concentrations of up to 2.5 and 2.8 mol L(-1), respectively. Even under these extreme conditions, the applied biocatalyst showed a good stability with only marginal leakage of intracellular cofactors.     

The seasonal activity and the effect of mechanical bending and wounding on the PtCOMT promoter in Betula pendula Roth

In this study, 900-bp (signed as p including nucleotides –1 to –886) and partly deleted (signed as dp including nucleotides –1 to –414) COMT (caffeate/5-hydroxyferulate O-methyltransferase) promoters from Populus tremuloides Michx. were fused to the GUS reporter gene, and the tissue-specific expression patterns of the promoters were determined in Betula pendula Roth along the growing season, and as a response to mechanical bending and wounding. The main activity of the PtCOMTp- and PtCOMTdp-promoters, determined by the histochemical GUS assay, was found in the developing xylem of stems during the 8th–13th week and in the developing xylem of roots in the 13th week of the growing season. The GUS expression patterns did not differ among the xylem cell types. The PtCOMT promoter-induced GUS expression observed in phloem fibres suggests a need for PtCOMT expression and thus syringyl (S) lignin synthesis in fibre lignification. However, the PtCOMTdp-promoter induced GUS expression in stem trichomes, which may contribute to the biosynthesis of phenylpropanoid pathway-derived compounds other than lignin. Finally, a strong GUS expression was induced by the PtCOMT promoters in response to mechanical stem bending but not to wounding. The lack of major differences between the PtCOMTp- and PtCOMTdp-promoters suggests that the deleted promoter sequence (including nucleotides −415 to −886) did not contain a significant regulatory element contributing to the GUS expression in young B. pendula trees.     

Glycoprotein-surfactant interactions: a calorimetric and spectroscopic investigation of the phytase-SDS system

The interactions of sodium dodecyl sulfate (SDS) and two glyco-variants of the enzyme phytase from Peniophora lycii were investigated. One variant (Phy) was heavily glycosylated while the other (dgPhy) was enzymatically deglycosylated. Effects at 24 degrees C of titrating SDS to Phy and dgPhy were studied by Isothermal Titration Calorimetry (ITC) and Synchrotron Radiation Circular Dichroism (SRCD) spectroscopy. Comparisons of results for the two variants were used to elucidate glycan-surfactant interrelationships. The CD spectra suggested that both the native and the SDS-denatured states of the two variants were mutually similar, and hence that the denaturation process was structurally equivalent for the two glyco-variants. The denatured state was far from fully unfolded and probably retained a substantial content of native-like structure. Furthermore, it was found that the glycans brought about only a small increase in the resistance towards SDS induced denaturation. The SDS concentration required to denature half of the protein molecules differed less than 1 mM for the two variants. The affinity for SDS of both variants was unusually low. The amount of bound SDS (w/w) at different stages of the binding isotherm was 3-10 times lower than that reported for the most previously investigated globular proteins. Analysis of the relative affinity of the glycan and peptide moieties suggested that the carbohydrates bind much less surfactant. At saturation, glycans adsorbed about half as much SDS (in g/g) as the peptide moiety of Phy and about five times less than average proteins.     

Progress towards a DNA-based model system for the study of electron spin-spin interactions

A DNA-based model system is described for studying electron spin-spin interactions between a paramagnetic metal ion and a nitroxide spin label. The modified base deoxythymidine-EDTA (dT-EDTA) chelates the divalent or trivalent metal ion and produces a new feature in the circular dichroism (CD) spectra that makes it possible to monitor local DNA melting. Based on the results of optical and electron paramagnetic resonance (EPR) experiments, we find that the terminus of the DNA duplex that incorporates dT-EDTA and the spin-label melts at a higher temperature than the rest of the DNA duplex. EPR microwave progressive power saturation experiments performed at 77 K are consistent with the specific binding of Dy(III) at the EDTA site and an intramolecular dipole-dipole interaction between the nitroxide spin-label and the chelated Dy(III). This model system should be suitable for studying the relaxation properties of metal ions by saturation-recovery EPR.     

Alpha-Adrenergic receptor responsiveness is preserved during prolonged exercise

Our laboratory has previously reported a decline in sympathetic nervous system restraint of skeletal muscle blood flow during prolonged mild-intensity exercise. This decline may be explained by a decrease in alpha(1)- and alpha(2)-adrenergic receptor responsiveness over time. Thus the purpose of the present study was to investigate the effect of exercise duration on alpha(1)- and alpha(2)-adrenergic receptor responsiveness during prolonged constant-load exercise. Mongrel dogs (n = 6) were instrumented chronically with transit-time flow probes on the external iliac arteries and an indwelling catheter in a branch of the femoral artery. On separate days, flow-adjusted doses of selective alpha(1)- (phenylephrine) alpha(2)-adrenergic-receptor (clonidine) agonists, and tyramine (to evoke endogenous norepinephrine release) were infused following 5, 30 and 50 min of mild-intensity treadmill exercise (3 miles/h), with hindlimb blood flow (HBF) and mean arterial pressure (MAP) monitored continuously. Vascular conductance (VC) was calculated as HBF/MAP. While the dogs ran on the treadmill at 3 miles/h, infusion of phenylephrine resulted in similar decreases in VC after 5 [73% (SD 10)], 30 [76% (SD 9)], and 50 [73% (SD 10)] min of exercise. Infusion of the alpha(2)-agonist clonidine also produced similar decreases in VC after 5 [58% (SD 10)], 30 [58% (SD 11)], and 50 [53% (SD 12)] min of exercise. Infusion of tyramine resulted in similar decreases in VC after 5 [55% (SD 15)], 30 [51% (SD 10)], and 50 [50% (SD 7)] min of exercise. These results demonstrate that alpha(1)- and alpha(2)-adrenergic receptor responsiveness to infusion of selective alpha(1)- and alpha(2)-adrenergic-receptor agonists and endogenous norepinephrine release (tyramine) does not decline during prolonged mild-intensity exercise. Thus a decrease in alpha-adrenergic receptor responsiveness over time does not appear to be responsible for the decrease in sympathetic restraint of muscle blood flow during prolonged exercise.     

Semaphorin-1a controls receptor neuron-specific axonal convergence in the primary olfactory center of Drosophila

In the olfactory system of Drosophila, 50 functional classes of sensory receptor neurons (ORNs) project in a highly organized fashion into the CNS, where they sort out from one another and converge into distinct synaptic glomeruli. We identified the transmembrane molecule Semaphorin-1a (Sema-1a) as an essential component to ensure glomerulus-specific axon segregation. Removal of sema-1a in ORNs does not affect the pathfinding toward their target area but disrupts local axonal convergence into a single glomerulus, resulting in two distinct targeting phenotypes: axons either intermingle with adjacent ORN classes or segregate according to their odorant receptor identity into ectopic sites. Differential Sema-1a expression can be detected among neighboring glomeruli, and mosaic analyses show that sema-1a functions nonautonomously in ORN axon sorting. These findings provide insights into the mechanism by which afferent interactions lead to synaptic specificity in the olfactory system.     

Genetic interaction of Gsc and Dkk1 in head morphogenesis of the mouse

Mouse embryos lacking Gsc and Dkk1 function display severe deficiencies in craniofacial structures which are not found in either Dkk1 homozygous null or Gsc homozygous null mutant embryos. Loss of Gsc has a dosage-related effect on the severity of head truncation phenotype in Dkk1 heterozygous embryos. The synergistic effect of these mutations in enhancing head truncation provides direct evidence of a genetic interaction between Gsc and Dkk1, which display overlapping expression in the prechordal mesoderm. In the absence of Gsc activity, the expression of Dkk1, WNT genes and a transgenic reporter for WNT signalling are altered. Our results show that Gsc and Dkk1 functions are non-redundant in the anterior mesendoderm for normal anterior development and Gsc may influence Wnt signalling as a negative regulator.     

Atomic-resolution crystal structure of the antiviral lectin scytovirin

The crystal structures of the natural and recombinant antiviral lectin scytovirin (SVN) were solved by single-wavelength anomalous scattering and refined with data extending to 1.3 A and 1.0 A resolution, respectively. A molecule of SVN consists of a single chain 95 amino acids long, with an almost perfect sequence repeat that creates two very similar domains (RMS deviation 0.25 A for 40 pairs of Calpha atoms). The crystal structure differs significantly from a previously published NMR structure of the same protein, with the RMS deviations calculated separately for the N- and C-terminal domains of 5.3 A and 3.7 A, respectively, and a very different relationship between the two domains. In addition, the disulfide bonding pattern of the crystal structures differs from that described in the previously published mass spectrometry and NMR studies.     

Reproduction and longevity: secrets revealed by C. elegans

What is the relationship between reproduction and longevity? Evolutionary biology suggests that reproduction exacts a cost in somatic maintenance, a cost that reduces longevity. The frequent occurrence of this tradeoff between life span and fecundity, both due to experimental manipulations as well as natural variation, suggest that the mechanism might be conserved during evolution. Until recently, little was known about the mechanistic details of how reproduction might regulate life span. Here we discuss recent advances in our understanding of the regulation of life span by reproductive signaling, focusing on studies using Caenorhabditis elegans.