Accurate measurement of body weight and food intake in environmentally enriched male Wistar rats

Laboratory animals are crucial in the study of energy homeostasis. In particular, rats are used to study alterations in food intake and body weight. To accurately record food intake or energy expenditure it is necessary to house rats individually, which can be stressful for social animals. Environmental enrichment may reduce stress and improve welfare in laboratory rodents. However, the effect of environmental enrichment on food intake and thus experimental outcome is unknown. We aimed to determine the effect of environmental enrichment on food intake, body weight, behavior and fecal and plasma stress hormones in male Wistar rats. Singly housed 5–7‐week‐old male rats were given either no environmental enrichment, chew sticks, a plastic tube of 67 mm internal diameter, or both chew sticks and a tube. No differences in body weight or food intake were seen over a 7‐day period. Importantly, the refeeding response following a 24‐h fast was unaffected by environmental enrichment. Rearing, a behavior often associated with stress, was significantly reduced in all enriched groups compared to controls. There was a significant increase in fecal immunoglobulin A (IgA) in animals housed with both forms of enrichment compared to controls at the termination of the study, suggesting enrichment reduces hypothalamo‐pituitary‐adrenal (HPA) axis activity in singly housed rats. In summary, environmental enrichment does not influence body weight and food intake in singly housed male Wistar rats and may therefore be used to refine the living conditions of animals used in the study of energy homeostasis without compromising experimental outcome.     

The strigolactone germination stimulants of the plant-parasitic Striga and Orobanche spp. are derived from the carotenoid pathway

The seeds of parasitic plants of the genera Striga and Orobanche will only germinate after induction by a chemical signal exuded from the roots of their host. Up to now, several of these germination stimulants have been isolated and identified in the root exudates of a series of host plants of both Orobanche and Striga spp. In most cases, the compounds were shown to be isoprenoid and belong to one chemical class, collectively called the strigolactones, and suggested by many authors to be sesquiterpene lactones. However, this classification was never proven; hence, the biosynthetic pathways of the germination stimulants are unknown. We have used carotenoid mutants of maize (Zea mays) and inhibitors of isoprenoid pathways on maize, cowpea (Vigna unguiculata), and sorghum (Sorghum bicolor) and assessed the effects on the root exudate-induced germination of Striga hermonthica and Orobanche crenata. Here, we show that for these three host and two parasitic plant species, the strigolactone germination stimulants are derived from the carotenoid pathway. Furthermore, we hypothesize how the germination stimulants are formed. We also discuss this finding as an explanation for some phenomena that have been observed for the host-parasitic plant interaction, such as the effect of mycorrhiza on S. hermonthica infestation.     

Analysis of detergent-resistant membranes in Arabidopsis. Evidence for plasma membrane lipid rafts

The trafficking and function of cell surface proteins in eukaryotic cells may require association with detergent-resistant sphingolipid- and sterol-rich membrane domains. The aim of this work was to obtain evidence for lipid domain phenomena in plant membranes. A protocol to prepare Triton X-100 detergent-resistant membranes (DRMs) was developed using Arabidopsis (Arabidopsis thaliana) callus membranes. A comparative proteomics approach using two-dimensional difference gel electrophoresis and liquid chromatography-tandem mass spectrometry revealed that the DRMs were highly enriched in specific proteins. They included eight glycosylphosphatidylinositol-anchored proteins, several plasma membrane (PM) ATPases, multidrug resistance proteins, and proteins of the stomatin/prohibitin/hypersensitive response family, suggesting that the DRMs originated from PM domains. We also identified a plant homolog of flotillin, a major mammalian DRM protein, suggesting a conserved role for this protein in lipid domain phenomena in eukaryotic cells. Lipid analysis by gas chromatography-mass spectrometry showed that the DRMs had a 4-fold higher sterol-to-protein content than the average for Arabidopsis membranes. The DRMs were also 5-fold increased in sphingolipid-to-protein ratio. Our results indicate that the preparation of DRMs can yield a very specific set of membrane proteins and suggest that the PM contains phytosterol and sphingolipid-rich lipid domains with a specialized protein composition. Our results also suggest a conserved role of lipid modification in targeting proteins to both the intracellular and extracellular leaflet of these domains. The proteins associated with these domains provide important new experimental avenues into understanding plant cell polarity and cell surface processes.     

Somatic hypermutation at A.T pairs: polymerase error versus dUTP incorporation

Somatic hypermutation of immunoglobulin genes occurs at both C.G pairs and A.T pairs. Mutations at C.G pairs are created by activation-induced deaminase (AID)-catalysed deamination of C residues to U residues. Mutations at A.T pairs are probably produced during patch repair of the AID-generated U.G lesion, but they occur through an unknown mechanism. Here, we compare the popular suggestion of nucleotide mispairing through polymerase error with an alternative possibility, mutation through incorporation of dUTP (or another non-canonical nucleotide).     

The POLARIS peptide of Arabidopsis regulates auxin transport and root growth via effects on ethylene signaling

The rate and plane of cell division and anisotropic cell growth are critical for plant development and are regulated by diverse mechanisms involving several hormone signaling pathways. Little is known about peptide signaling in plant growth; however, Arabidopsis thaliana POLARIS (PLS), encoding a 36-amino acid peptide, is required for correct root growth and vascular development. Mutational analysis implicates a role for the peptide in hormone responses, but the basis of PLS action is obscure. Using the Arabidopsis root as a model to study PLS action in plant development, we discovered a link between PLS, ethylene signaling, auxin homeostasis, and microtubule cytoskeleton dynamics. Mutation of PLS results in an enhanced ethylene-response phenotype, defective auxin transport and homeostasis, and altered microtubule sensitivity to inhibitors. These defects, along with the short-root phenotype, are suppressed by genetic and pharmacological inhibition of ethylene action. PLS expression is repressed by ethylene and induced by auxin. Our results suggest a mechanism whereby PLS negatively regulates ethylene responses to modulate cell division and expansion via downstream effects on microtubule cytoskeleton dynamics and auxin signaling, thereby influencing root growth and lateral root development. This mechanism involves a regulatory loop of auxin-ethylene interactions.     

Strigol: biogenesis and physiological activity

The role played by molecules of the strigolactone family in stimulating the germination of seeds of parasitic weeds of the genera Striga, Orobanche and Alectra has never been clearly elucidated. The biogenesis of these unusual terpenoid lactones, originally identified in minute quantities in the root exudates of a small number of host plants and two or three "false hosts", also remains obscure. These lactones, as the chemical signals which initiate the life cycle of Striga, are consequently at the forefront of the Striga research effort. This paper reviews recent key discoveries relating to the biosynthesis and mode of action of strigolactones, and summarises the evidence suggesting that these molecules may be far more widely distributed and have a greater physiological significance than has hitherto been appreciated.     

Caenorhabditis elegans senses bacterial autoinducers

Pseudomonas aeruginosa uses virulence factors controlled by quorum sensing (QS) to kill Caenorhabditis elegans. Here we show that C. elegans is attracted to the acylated homoserine lactones (AHSLs) that mediate QS in P. aeruginosa. Our data also indicate that C. elegans can distinguish AHSLs and may use them to mediate aversive or attractive learning.