Reaction wood – a key cause of variation in cell wall recalcitrance in willow

Background

The recalcitrance of lignocellulosic cell wall biomass to deconstruction varies greatly in angiosperms, yet the source of this variation remains unclear. Here, in eight genotypes of short rotation coppice willow (Salix sp.) variability of the reaction wood (RW) response and the impact of this variation on cell wall recalcitrance to enzymatic saccharification was considered.

Results

A pot trial was designed to test if the ‘RW response’ varies between willow genotypes and contributes to the differences observed in cell wall recalcitrance to enzymatic saccharification in field-grown trees. Biomass composition was measured via wet chemistry and used with glucose release yields from enzymatic saccharification to determine cell wall recalcitrance. The levels of glucose release found for pot-grown control trees showed no significant correlation with glucose release from mature field-grown trees. However, when a RW phenotype was induced in pot-grown trees, glucose release was strongly correlated with that for mature field-grown trees. Field studies revealed a 5-fold increase in glucose release from a genotype grown at a site exposed to high wind speeds (a potentially high RW inducing environment) when compared with the same genotype grown at a more sheltered site.

Conclusions

Our findings provide evidence for a new concept concerning variation in the recalcitrance to enzymatic hydrolysis of the stem biomass of different, field-grown willow genotypes (and potentially other angiosperms). Specifically, that genotypic differences in the ability to produce a response to RW inducing conditions (a ‘RW response’) indicate that this RW response is a primary determinant of the variation observed in cell wall glucan accessibility. The identification of the importance of this RW response trait in willows, is likely to be valuable in selective breeding strategies in willow (and other angiosperm) biofuel crops and, with further work to dissect the nature of RW variation, could provide novel targets for genetic modification for improved biofuel feedstocks.

     

Now I know my ABC. A systems neurochemistry and functional metabolomic approach to understanding the GABAergic system

Here, we describe use of a reductionist brain model, the brain tissue slice, to generate snapshots of functional metabolism in response to a pharmacological (GABAergic) perturbation. Tissue slices prepared from Guinea pig cerebral cortex were incubated for 1 h in the presence of [3-¹³C]-pyruvate and ligands with affinity for GABA receptors. The resultant patterns of ¹³C flux and metabolite levels were measured by ¹³C/¹H NMR spectroscopy, generating 'metabolic fingerprints' for each ligand. Effects of agonists and effectors at GABA receptors (A, B, and C types) were examined, compared to those of exogenous GABA and evaluated using multivariate statistical models. Data clusterings did not directly correlate with GABA receptor types but produced at least five distinct groups ranked according to their affinity for GABA. As our experimental model retains, to a large extent, the structure and function of normal brain tissue, the generated database can be used to assess GABAergic ligands and make unique inferences relevant to their modes of action in brain.     

Rapid Assessment of Avoidable Blindness in the Occupied Palestinian Territories

Background

There are no recent data on the prevalence and causes of blindness in the Occupied Palestinian Territories. The aim of our study was to estimate the prevalence and causes of blindness and visual impairment in the population aged 50 years and above in the Occupied Palestinian Territories using the Rapid Assessment of Avoidable Blindness (RAAB) survey method.

Methods and Findings

Clusters of 40 people who were 50 years and above were selected with probability proportionate to size using a multistage cluster random sampling method. Participants received a comprehensive ophthalmic examination in their homes, including visual acuity testing by one of three experienced ophthalmologists. The principal cause for visual loss was determined by an experienced ophthalmologist using portable diagnostic instruments. Information about previous cataract surgery, satisfaction with surgery and barriers to cataract surgery were collected. The prevalence of self-reported diabetes was also determined. The prevalence of bilateral blindness (VA<3/60 in the better eye with available correction) was 3.4% (95% CI: 2.7–4.0), 2.0% (95% CI: 1.4–2.5) for severe visual impairment (VA≥3/60 and <6/60), and 7.4% (95% CI: 6.4–8.3) for visual impairment (VA≥6/60 and <6/18). Avoidable causes (i.e. cataract, refractive error, aphakia, surgical complications, corneal scarring and phthysis) accounted for 80.0% of bilateral blindness, severe visual impairment (70.7%) and visual impairment (86.2%). Cataract was the main cause of blindness (55.0%). The prevalence of blindness was higher in Gaza (4.9%, 95% CI: 3.7–6.1%) than in the West Bank (2.5%, 95% CI: 1.9–3.1%) and among women (4.3%,95% CI: 3.3–5.2%) compared to men (2.2%,95%CI:1.5–2.9%). Among people who had undergone cataract surgery in the past, only 54.5% of eyes obtained a good outcome (VA≥6/18), 23.2% had a borderline outcome (VA<6/18 and ≥6/60) and 22.3% had a poor outcome (VA<6/60) with available correction. The prevalence of self-reported diabetes mellitus in ≥50 year age group was 26.4% (95% CI: 24.9–27.9).

Conclusions

The prevalence of blindness suggests that significant numbers of people in the Occupied Palestinian Territories exist who do not access eye care - predominantly women and those residing in Gaza. Programmes need to focus on maximizing the use of current services by these excluded groups.     

Human cytoplasmic serine hydroxymethyltransferase is an mRNA binding protein

The 5' untranslated region (UTR) of the human cytoplasmic serine hydroxymethyltransferase (cSHMT) message is alternatively spliced, creating a full-length 5' UTR (LUTR) encoded within exons 1-3 and a shorter UTR (SUTR) that results from excision of exon 2. The role of the 5' UTRs in cSHMT expression was investigated by fusing the cSHMT 5' UTRs to the 5' end of the luciferase gene. Human cSHMT protein at 10 microM inhibits in vitro translation of cSHMT 5' UTR-luciferase fusion mRNA templates by more than 90%, but does not inhibit translation of the luciferase message lacking the UTR. Translation inhibition is independent of amino acid and folate substrate binding to the cSHMT enzyme. The cSHMT SUTR-luciferase mRNA binds to the cSHMT.glycine.5-formyltetrahydrofolate ternary complex with an apparent K(d) of 10 microM. Gel mobility shift assays demonstrate that the human cSHMT protein binds to the cSHMT LUTR-luciferase fusion mRNA in the presence and absence of glycine and 5-formyltetrahydrofolate pentaglutamate. The fusion cSHMT SUTR-luciferase message at 65 microM inhibits the cSHMT-catalyzed cleavage of allothreonine as a partial mixed type inhibitor, reducing both k(cat) and K(m) by 40 and 75%, respectively, while tRNA has no effect on cSHMT catalysis. These studies indicate that the cSHMT protein can bind mRNA, and displays increased affinity for the 5' untranslated region of its mRNA.     

Arabidopsis species hybrids in the study of species differences and evolution of amphiploidy in plants

It is estimated that 5 million years of evolution separate Arabidopsis thaliana from its close relative Arabidopsis lyrata. The two taxa differ by many characteristics, and together they exemplify the differentiation of angiosperms into self-fertilizing and cross-fertilizing species as well as annual and perennial species. Despite their disparate life histories, the two species can be crossed to produce viable and vigorous hybrids exhibiting heterotic effects. Although pollen sterile, the hybrids produce viable ovules and were used as female parent in backcrosses to both parental species. The resulting backcross plants exhibited transgressive variation for a number of interesting developmental and growth traits as well as negative nuclear/cytoplasmic interactions. Moreover, the genesis of a fertile amphidiploid neospecies, apparently by spontaneous somatic doubling in an interspecific hybrid, was observed in the laboratory. The mechanisms responsible for the generation of amphiploids and the subsequent evolution of amphiploid genomes can now be studied through direct observation using the large arsenal of molecular tools available for Arabidopsis.     

LiCl-induced flavor avoidance compared between rats and mice using a nondeprivation protocol

The present studies examine some parameters involved in flavor avoidance learning, using LiCl to induce malaise, in a novel nondeprivation protocol that allows direct comparison between rats and mice. The procedure involves daily presentation of a gelatin dessert that contains carbohydrate (Polycose) and a distinctive food flavor. Regular chow is additionally available at all times. Both rats and mice showed robust intakes of these gels with little change of gram intake as concentration of Polycose was varied in the range 2-30%; at the highest concentration, the caloric yield was approximately 7% of normal daily intake in both species. Rats that were injected on three occasions with LiCl (0.75 meq/kg) 1 h after consumption of a flavored gel formed a complete and sustained conditioned flavor avoidance (CFA). In a two-flavor discrimination protocol, in which a second flavor was followed by injections of saline, rats showed complete avoidance of the LiCl-paired flavor and partial avoidance of the saline-paired flavor. Mice injected on three occasions with LiCl (6 meq/kg) 1 h after intake of a flavored gel formed a partial CFA; a more complete CFA was formed when there was no delay between removal of the flavor and the injection. Using this no-delay protocol, mice, like rats, showed avoidance of a saline-paired flavor in a two-flavor discrimination protocol, and the CFA was strong when the dose of LiCl was reduced to that used in rats (0.75 meq/kg). In comparable protocols, mice thus are able to form complete CFAs using low doses of LiCl that are comparable to CFAs observed in rats, but the interval between flavor and sickness over which associative learning can occur may be shorter in mice.     

Characterization of the PGI2/IP system in cultured rat mesangial cells

Mesangial cells play an important role in glomerular function. They are an important source of cyclooxygenase (COX)-derived arachidonic acid metabolites, including prostaglandin E(2) and prostacyclin. Prostacyclin receptor (IP) mRNA was amplified from cultured mesangial cell total RNA by RT-PCR. While the prostaglandin E(2) receptor subtype EP(2) was not detected, EP(1,3,4) mRNA was amplified. Also, IP protein was noted in mesangial cells, proximal tubules, inner medullary collecting ducts, and the inner and outer medulla. But no protein was detected in whole cortex preparations. Prostacyclin analogues: cicaprost and iloprost, increased cAMP levels in mesangial cells. On the other hand, arginine-vasopressin and angiotensin II increased intracellular calcium in mesangial cells, but cicaprost, iloprost and prostaglandin E(2) had no effect. Moreover, a 50% inhibition of cicaprost- and iloprost-cAMP stimulation was observed upon mesangial cell exposure to 25 and 35 mM glucose for 5 days. But no change in IP mRNA was observed at any glucose concentration or time exposure. Although 25 mM glucose had no effect on COX-1 protein levels, COX-2 was increased up to 50%. In contrast, PGIS levels were reduced by 50%. Thus, we conclude that the prostacyclin/IP system is present in cultured rat mesangial cells, coupling to a cAMP stimulatory pathway. High glucose altered both enzymes in the PGI(2) synthesis pathway, increasing COX-2 but reducing PGIS. In addition, glucose diminished the cAMP response to prostacyclin analogues. Therefore, glucose attenuates the PGI(2)/IP system in cultured rat mesangial cells.