Pre- and Posttranslational Regulation of β-Endorphin Biosynthesis in the CNS: Effects of Chronic Naltrexone Treatment

Abstract: There appear to be two anatomically distinct β-endorphin (βE) pathways in the brain, the major one originating in the arcuate nucleus of the hypothalamus and a smaller one in the area of the nucleus tractus solitarius (NTS) of the caudal medulla. Previous studies have shown that these two proopiomelanocortin (POMC) systems may be differentially regulated by chronic morphine treatment, with arcuate cells down-regulated and NTS cells unaffected. In the present experiments, we examined the effects of chronic opiate antagonist treatment on βE biosynthesis across different CNS regions to assess whether the arcuate POMC system would be regulated in the opposite direction to that seen after opiate agonist treatment and to determine whether different βE-containing areas might be differentially regulated. Male adult rats were administered naltrexone (NTX) by various routes for 8 days (subcutaneous pellets, osmotic minipumps, or repeated intraperitoneal injections). Brain and spinal cord regions were assayed for total βE-ir, different molecular weight immunoreactive β-endorphin (βE-ir) peptides, and POMC mRNA. Chronic NTX treatment, regardless of the route of administration, reduced total βE-ir concentrations by 30–40% in diencephalic areas (the arcuate nucleus, the remaining hypothalamus, and the thalamus) and the midbrain, but had no effect on βE-ir in the NTS or any region of the spinal cord. At the same time, NTX pelleting increased POMC mRNA levels in the arcuate to ～ 140% of control values. These data suggest that arcuate POMC neurons are up-regulated after chronic NTX treatment (whereas NTS and spinal cord systems remain unaffected) and that they appear to be under tonic inhibition by endogenous opioids. Chromatographic analyses demonstrated that, after chronic NTX pelleting, the ratio of full length βE_1–31 to more processed βE-ir peptides (i.e., βE_1–27 and βE_1–26) tended to increase in a dose-dependent manner in diencephalic areas. Because βE_1–31 is the only POMC product that possesses opioid agonist properties, and βE_1–27 has been posited to function as an endogenous anatgonist of βE_1–31, the NTX-induced changes in the relative concentrations of βE_1–31 and βE_1–27/βE_1–26 may represent a novel regulatory mechanism of POMC cells to alter the opioid signal in the synapse.     

Modelling C3 photosynthesis: A sensitivity analysis of the photosynthetic carbon-reduction cycle

A model of the C ₃ photosynthetic system is developed which describes the sensitivity of the steadystate rate of carbon dioxide assimilation to changes in the activity of several enzymes of the system. The model requires measurements of the steady-state rate of carbon dioxide assimilation, the concentrations of several intermediates in the photosynthetic system, and the concentration of the active site of ribulose 1,5-bisphosphate carboxyalse/oxygenase (Rubisco). It is shown that in sunflowers (Helianthus annuus L.) at photon flux densities that are largely saturating for the rate of photosynthesis, the steady-stete rate of carbon dioxide assimilation is most sensitive to Rubisco activity and, to a lesser degree, to the activities of the stromal fructose, 6-bisphosphatase and the enzymes catalysing sucrose synthesis. The activities of sedoheptulose 1,7-bisphosphatase, ribulose 5-phosphate kinase, ATP synthase and the ADP-glucose pyrophosphorylase are calculated to have a negligible effect on the flux under the high-light conditions. The utility of this analysis in developing simpler models of photosynthesis is also discussed.Abbreviations c _i intercellular CO₂ concentration - C _infP ^supJ control coefficient for enzyme P with respect to flux J - DHAP dihydroxyacetonephosphate - E4P erythrose 4-phosphate - F6P fructose 6-phosphate - FBP fructose 1,6-bisphosphate - FBPase fructose 1,6-bisphosphatase - G3P glyceraldehyde 3-phosphate - G1P glucose 1-phosphate - G6P glucose 6-phosphate - Pi inorganic phosphate - PCR photosynthetic carbon reduction - PGA 3-phosphoglyceric acid - PPFD photosynthetically active photon flux density - R _n ^J response coefficient for effector n with respect to flux J - R5P ribose 5-phosphate - Rubisco ribulose 1,5-bisphosphate carboxylase/oxygenase - Ru5P ribulose 5-phosphate - RuBP ribulose 1,5-bisphosphate - S7P sedoheptulose 7-phosphate - SBP sedoheptulose 1,7-bisphosphate - SBPase sedoheptulose 1,7-bisphosphatase - SPS sucrose-phosphate synthase - Xu5P xylulose 5-phosphate - _n ^P elasticity coefficient for effector n with respect to the catalytic velocity of enzyme P This research was funded by an Australian Research Council grant to I.E.W. and was undertaken during a visity by K.A.M. to the James Cook University of North Queensland. The expert help of Glenys Hanley and Mick Kelly is greatly appreciated.     

Expression of the Acc1 Gene-Encoded Acetyl-Coenzyme A Carboxylase in Developing Maize (Zea mays L.) Kernels

A mutation (Acc1-S2) in the structural gene for maize (Zea mays L.) acetyl-coenzyme A carboxylase (ACCase) that significantly reduces sethoxydim inhibition of leaf ACCase activity was used to investigate the gene-enzyme relationship regulating ACCase activity during oil deposition in developing kernels. Mutant embryo and endosperm ACCase activities were more than 600-fold less sensitive to sethoxydim inhibition than ACCase in wild-type kernel tissues. Moreover, in vitro cultured mutant kernels developed normally in the presence of sethoxydim concentrations that inhibited wild-type kernel development. The results indicate that the Acc1-encoded ACCase accounts for the majority of ACCase activity in developing maize kernels, suggesting that Acc1-encoded ACCase functions not only during membrane biogenesis in leaves but is also the predominant form of ACCase involved in storage lipid biosynthesis in maize embryos.     

Prediction of near-term climate change impacts on UK wheat quality and the potential for adaptation through plant breeding

Wheat is a major crop worldwide, mainly cultivated for human consumption and animal feed. Grain quality is paramount in determining its value and downstream use. While we know that climate change threatens global crop yields, a better understanding of impacts on wheat end-use quality is also critical. Combining quantitative genetics with climate model outputs, we investigated UK-wide trends in genotypic adaptation for wheat quality traits. In our approach, we augmented genomic prediction models with environmental characterisation of field trials to predict trait values and climate effects in historical field trial data between 2001 and 2020. Addition of environmental covariates, such as temperature and rainfall, successfully enabled prediction of genotype by environment interactions (G × E), and increased prediction accuracy of most traits for new genotypes in new year cross validation. We then extended predictions from these models to much larger numbers of simulated environments using climate scenarios projected under Representative Concentration Pathways 8.5 for 2050–2069. We found geographically varying climate change impacts on wheat quality due to contrasting associations between specific weather covariables and quality traits across the UK. Notably, negative impacts on quality traits were predicted in the East of the UK due to increased summer temperatures while the climate in the North and South-west may become more favourable with increased summer temperatures. Furthermore, by projecting 167,040 simulated future genotype–environment combinations, we found only limited potential for breeding to exploit predictable G × E to mitigate year-to-year environmental variability for most traits except Hagberg falling number. This suggests low adaptability of current UK wheat germplasm across future UK climates. More generally, approaches demonstrated here will be critical to enable adaptation of global crops to near-term climate change.     

The complex genome and adaptive evolution of polyploid Chinese pepper (Zanthoxylum armatum and Zanthoxylum bungeanum)

Zanthoxylum armatum and Zanthoxylum bungeanum, known as ‘Chinese pepper’, are distinguished by their extraordinary complex genomes, phenotypic innovation of adaptive evolution and species-special metabolites. Here, we report reference-grade genomes of Z. armatum and Z. bungeanum. Using high coverage sequence data and comprehensive assembly strategies, we derived 66 pseudochromosomes comprising 33 homologous phased groups of two subgenomes, including autotetraploid Z. armatum. The genomic rearrangements and two whole-genome duplications created large (~4.5 Gb) complex genomes with a high ratio of repetitive sequences (>82%) and high chromosome number (2n = 4x = 132). Further analysis of the high-quality genomes shed lights on the genomic basis of involutional reproduction, allomones biosynthesis and adaptive evolution in Chinese pepper, revealing a high consistent relationship between genomic evolution, environmental factors and phenotypic innovation. Our study provides genomic resources and new insights for investigating diversification and phenotypic innovation in Chinese pepper, with broader implications for the protection of plants under severe environmental changes.     

Glycosylation sites identified by solid-phase Edman degradation: O-linked glycosylation motifs on human glycophorin A

The human red blood cell sialoglycoprotein, glycophorin A (GpA),contains a ‘mucin-like’ extensively O-glycosylatedextracellular domain which carries the MN blood group antigens.We have revised the sites of O-glyccsylation in the extracellulardomain of GpA by automated solid-phase Edman degradation, whichallowed positive identification and quantitation of O-glycosylatedSer and Thr residues, as well as the single N-glycosylationsite. One N-linked and 16 O-linked sites were identified. Carbohydratewas absent on Ser 1, Ser14, Ser15, Ser23, Thr28 and Thr58 inGpA. We propose that the glycosyltransferases present in erythrocytesrecognize specific flanking sequences around potential O-glycosylationsites. All 16 O-glycosylation sites are explained on the basisof four motifs. Three motifs are associated with Thr-glycosylation:Xaa—Pro—Xaa—Xaa where at least one Xaa = Thr;Thr—Xaa—Xaa—Xaa where at least one Xaa = Thr;Xaa—Xaa—Thr—Xaa where at least one X = Argor Lys. The fourth motif is associated with Ser-glycosylation:Ser—Xaa—Xaa—Xaa where at least one Xaa = Ser.These simple rules explain the glycosylation (or lack of it)on 21 of 22 Ser/Thr in the extracellular domain of GpA. glycophorin A O-glycosylation motif solid-phase Edman degradation     

Peatlands as scientific archives of past biodiversity

Peat bogs preserve past biodiversity in a way which is unique among ecosystems, but the full realization of this, and the exploitation of the various records which are archived in the stratified layers of peat, is only now beginning. Present knowledge of peat formation in ombrotrophic or rain-fed bogs is reviewed and the many advantages of such systems as proxy-data sources are summarized. Some results of recent work involving pollen analysis and human impact, pollution histories, volcanic ash layers, plant macrofossils and the prospects for a detailed proxy-climate record are presented. The present vegetation of such bogs is only a very partial view of their past biodiversity; the conservation of the peat that remains must have a high priority.     

THE FLAGELLAR APPARATUS OF HYMENOMONAS CORONATA (PRYMNESIOPHYTA)1

The ultrastructure of Hymenomonas coronata Mills was reinvestigated to determine the microarchitecture of the flagellar apparatus. Cell morphology and flagellar apparatus structure are very similar to those of Pleurochrysis. Some important variations occur. First, a crystalline root (= compound root) is absent on microtubular root 1. Second, a two-stranded microtubular root emanates at a right angle from microtubular root 2. Third, a fibrous root emanates from the dorsal region between the basal bodies and extends to the cell's right, paralleling microtubular root 3. These similarities and variations in flagellar apparatus characters are discussed in reference to known variations in the Prymnesiophyta.