Extrafloral nectaries as a deterrent mechanism against seed predators in the chemically protected weed Crotalaria pallida (Leguminosae)

Abstract In several plants, extrafloral nectaries (EFN) are located close to the reproductive structures, suggesting that ants may act as a defence against specialized seed predators that overcome chemical defences. Alternatively, ants may also deter herbivores in a generalized manner, thereby protecting the whole plant. In this work, we examined the relationship between the chemically protected weed Crotalaria pallida Ait. (Leguminosae) that bears EFN, its specialized seed predator, the larvae of the arctiid moth Utetheisa ornatrix L. (Arctiidae) and ants. We tested two hypotheses related to the type of deterrence caused by ants. The Seed Predator Deterrence Hypothesis predicts that ant deterrence is directed primarily towards herbivores that destroy seeds and other reproductive structures, without attacking herbivores on vegetative structures. The General Deterrence Hypothesis states that ants are general in their effects, equally deterring herbivores in vegetative and reproductive structures. Our results supported the predictions of the Seed Predator Deterrence Hypothesis, namely, that (i) ant activity on EFN was related to the vulnerability of reproductive structures to attack by U. ornatrix; (ii) ant patrolling was restricted almost entirely to racemes; (iii) ants removed termites used as baits more frequently on racemes than on leaves; and (iv) U. ornatrix larvae were often expulsed from the racemes. These results indicate that EFN can act as another deterrent mechanism in chemically protected plants by promoting the expulsion of specialist seed predators.     

Prediction of indirect interactions in proteins

Background  

Both direct and indirect interactions determine molecular recognition of ligands by proteins. Indirect interactions can be defined as effects on recognition controlled from distant sites in the proteins, e.g. by changes in protein conformation and mobility, whereas direct interactions occur in close proximity of the protein's amino acids and the ligand. Molecular recognition is traditionally studied using three-dimensional methods, but with such techniques it is difficult to predict the effects caused by mutational changes of amino acids located far away from the ligand-binding site. We recently developed an approach, proteochemometrics, to the study of molecular recognition that models the chemical effects involved in the recognition of ligands by proteins using statistical sampling and mathematical modelling.     

Summer spawning of Porites lutea from north-western Australia

Most coral species off Australia??s west coast spawn in the austral autumn (March?CApril), with a few species also spawning in the southern spring or early summer (November?CDecember). This is the reverse timing to spawning recorded off Australia??s east coast. Porites lutea, a gonochoric broadcast spawner that is common on Australia??s west coast, is shown here to spawn in the months of November or December, as it does on Australia??s east coast. Spawning occurred between 2 and 5 nights after full moon, with the majority of spawning activity on night 3. Gametes developed over three to four months with rapid development in the last two weeks before spawning. Zooxanthellae were typically observed in mature oocytes, only a week before spawning so their presence may provide a useful indicator of imminent spawning.     

Conserved polar residues in transmembrane domains V, VI, and VII of free fatty acid receptor 2 and free fatty acid receptor 3 are required for the binding and function of short chain fatty acids

FFA2 and FFA3 are closely related G protein-coupled receptors that bind and respond to short chain fatty acids. (FFA2 and FFA3 are the provisional International Union of Pharmacology designations for the receptors previously called GPR43 and GPR41, respectively.) Sequence comparisons between these two receptors and alignments with the related G protein-coupled receptor FFA1, linked to homology modeling based on the atomic level structure of bovine rhodopsin, indicated the potential for polar residues within the transmembrane helix bundle to play important roles in ligand recognition and function. In both FFA2 and FFA3, mutation of either an arginine at the top of transmembrane domain V or a second arginine at the top of transmembrane domain VII eliminated the function of a range of short chain fatty acids. Mutation of a histidine in transmembrane domain VI, predicted to be in proximity to both the arginine residues, also eliminated function in many but not all assay formats. By contrast, mutation of a histidine in transmembrane domain IV, predicted to be lower in the binding pocket, modulated function in some assays of FFA3 function but had limited effects on the function of acetate and propionate at FFA2. Interestingly, wild type FFA3 responded to caproate, whereas FFA2 did not. Mutation of the transmembrane domain IV histidine eliminated responses of FFA3 to caproate but resulted in a gain of function of FFA2 to this six-carbon fatty acid. These data demonstrate the importance of positively charged residues in the recognition and/or function of short chain fatty acids in both FFA2 and FFA3. The development of small molecule ligands that interact selectively with these receptors will allow further details of the binding pockets to be elucidated.     

Lectin histochemistry of normal human gastric mucosa

Information about the saccharides expressed in gastric mucosa is mostly limited to the glycan content of gastric mucins and there are only a few studies of the glycoprofiling of the constituent cells and their components. Knowledge of the glycan expression of normal gastric mucosa is necessary for the interpretation of the significance of changes of expression in disease. A lectin histochemical study of normal human gastric (body) mucosa was performed using 27 lectins chosen to probe for a wide range of oligosaccharide sequences within several categories of glycoprotein glycans. There were marked differences in staining reactions in the various microanatomical structures of the mucosa, particularly between pits and glands with the former more closely resembling the surface epithelium. A notable feature was the degree of difference in the staining between a substantial sub-population of cells within the neck region and the epithelium of both the pits and glands. These neck cells resembled the pit cells with some lectins, glandular cells with some others and neither with some other lectins. Overall, the differences between the pit, gland and neck epithelia were diverse and numerous, and could not be explained by altered activity of a small set of glycosyltransferases. Widespread alterations of glycans must have occurred (affecting terminal and internal parts of their structures) and the very different glycotypes of the pit, neck and gland epithelia are, therefore, suggestive of the existence of three cell lineages within normal gastric epithelium. Published in 2004. This revised version was published online in July 2006 with corrections to the Cover Date.     

Metabolic relationships of the isolated fractions of the pectic substances of actively growing sycamore cells

1. d-Glucose and l-arabinose serve as precursors of the pectic polysaccharides of sycamore suspension-callus tissue. 2. The rates and characteristics of the incorporation of radioactive sucrose, glucose and mesoinositol by sycamore callus tissue have been compared and shown to be different. 3. The time-course of the incorporation of radioactive glucose into the major fractions within the cells has been determined. Approx. 7-10% of the radioactivity incorporated is present in the whole pectin of the cells. 4. A study of the continuous incorporation of radioactive glucose showed that the neutral arabinan-galactan fraction of the pectin quickly became saturated with the radioactive label. During the incorporation of radioactivity from a pulse of radioactive glucose the neutral fraction became progressively less labelled, with a corresponding increase in the radioactivity of the weakly acidic pectinic acid, which is known to contain neutral sugars. 5. When the cells were exposed to a pulse of radioactive l-arabinose, the label accumulated first in the neutral fraction and then after 4hr. it passed to the weakly acidic pectinic acid with a corresponding decrease in the radioactivity of the neutral fraction. 6. The product that was initially labelled during the first hour of exposure of the cells in the stationary phase to radioactive glucose was identified as an incompletely methylated galacturonan in which the radioactivity was present in the anhydrogalacturonide residues. This polysaccharide probably acts as the precursor of the polyuronide portions of both the strongly acidic and weakly acidic pectinic acids. 7. The observations are discussed in relation to the structure of the pectic substances and their function in cell growth and development. A tentative model for their metabolic relationship is put forward.