Dynamics of intracellular mannan and cell wall folding in the drought responses of succulent Aloe species

Plants have evolved a multitude of adaptations to survive extreme conditions. Succulent plants have the capacity to tolerate periodically dry environments, due to their ability to retain water in a specialized tissue, termed hydrenchyma. Cell wall polysaccharides are important components of water storage in hydrenchyma cells. However, the role of the cell wall and its polysaccharide composition in relation to drought resistance of succulent plants are unknown. We investigate the drought response of leaf‐succulent Aloe (Asphodelaceae) species using a combination of histological microscopy, quantification of water content, and comprehensive microarray polymer profiling. We observed a previously unreported mode of polysaccharide and cell wall structural dynamics triggered by water shortage. Microscopical analysis of the hydrenchyma cell walls revealed highly regular folding patterns indicative of predetermined cell wall mechanics in the remobilization of stored water and the possible role of homogalacturonan in this process. The in situ distribution of mannans in distinct intracellular compartments during drought, for storage, and apparent upregulation of pectins, imparting flexibility to the cell wall, facilitate elaborate cell wall folding during drought stress. We conclude that cell wall polysaccharide composition plays an important role in water storage and drought response in Aloe.     

Untangling the Echiniscus Gordian knot: paraphyly of the “arctomys group” (Heterotardigrada: Echiniscidae)

The genus Echiniscus C.A.S. Schultze, 1840, one of the earliest established and speciose tardigrade genera, has been hypothesized to be polyphyletic. Moreover, the presence or absence of trunk appendages, the type of cuticular sculpturing and body colour have been argued to hold taxonomic significance at the genus level in Echiniscus-line taxa. Here, by combining morphological and genetic analyses, we demonstrate that the so-called “arctomys group”, i.e. Echiniscus spp. lacking trunk appendages, comprises numerous separate evolutionary lineages within the family Echiniscidae. As a result, we erect five new echiniscid genera: Barbaria gen. nov. , presumably of Neotropical (Gondwanan) origin, previously classified as the Echiniscus bigranulatus group; the pantropical and subtropical Kristenseniscus gen. nov. (the tessellatus group), characterized by a peculiar subdivision of dorsal plates; Claxtonia gen. nov. (the wendti group), with large and evident endocuticular pillars in the form of polygons; Nebularmis gen. nov. (the reticulatus group), with an elusive dorsal sculpturing; and Viridiscus gen. nov. (the viridis group), with body colour ranging from light green through brownish to even almost black. Additionally, we briefly address appendaged Echiniscus s.s. and divide the genus into several groups based on dorsal plate sculpturing and suggest that these could also represent separate supraspecific entities.     

A model of the transition state in the alkaline phosphatase reaction

A high resolution crystal structure of Escherichia coli alkaline phosphatase in the presence of vanadate has been refined to 1.9 A resolution. The vanadate ion takes on a trigonal bipyramidal geometry and is covalently bound by the active site serine nucleophile. A coordinated water molecule occupies the axial position opposite the serine nucleophile, whereas the equatorial oxygen atoms of the vanadate ion are stabilized by interactions with both Arg-166 and the zinc metal ions of the active site. This structural complex supports the in-line displacement mechanism of phosphomonoester hydrolysis by alkaline phosphatase and provides a model for the proposed transition state in the enzyme-catalyzed reaction.     

Response of NADPH-Diaphorase-Exhibiting Neurons in the Medullar Reticular Formation to High Spinal Cord Injury

1. The effect of hemisection of the cervical spinal cord on NADPH-diaphorase staining in the reticular nuclei of the rabbit medulla was investigated using histochemical technique.2. A quantitative assessment of somal and neuropil NADPH-diaphorase staining was made by an image analyzer in a selected area of each reticular nucleus of the rabbit medulla.3. On the 7th postsurgery day, the highest up-regulation of somatic NADPH-diapho- rase staining was observed in regions regulating cardiorespiratory processes; however, the highest increase of neuropil NADPH-diaphorase staining was found in the reticular nuclei modulating the tonus of postural muscles.4. The degeneration of non-NADPH-diaphorase-stained neurons was detected throughout the reticular formation of the medulla, but the extent of neuronal death did not correlate with the up-regulation of the NADPH-diaphorase staining in the reticular nuclei of the medulla.5. The findings provide evidence that NADPH-diaphorase-exhibiting neurons are refractory to the hemisection of the cervical spinal cord and that the neuronal up-regulation of NADPH-diaphorase at the medullar level is probably not a causative factor leading to the death of the reticulospinal neurons.     

Structure–function relationships of four compression wood types: micromechanical properties at the tissue and fibre level

The mechanisms behind compressive stress generation in gymnosperms are not yet fully understood. Investigating the structure–function relationships at the tissue and cell level, however, can provide new insights. Severe compression wood of all species lacks a S3 layer, has a high microfibril angle in the S2 layer and a high lignin content. Additionally, special features like helical cavities or spiral thickenings appear, which are not well understood in terms of their mechanical relevance, but need to be examined with regard to evolutionary trends in compression wood development. Thin compression wood foils and isolated tracheids of four gymnosperm species [Ginkgo biloba L., Taxus baccata L., Juniperus virginiana L., Picea abies (L.) Karst.] were investigated. The tracheids were isolated mechanically by peeling them out of the solid wood using fine tweezers. In contrast to chemical macerations, the cell wall components remained in their original condition. Tensile properties of tissue foils and tracheids were measured in a microtensile apparatus under wet conditions. Our results clearly show an evolutionary trend to a much more flexible compression wood. An interpretation with respect to compressive stress generation is discussed.     

Factors influencing glycosylation of Trichoderma reesei cellulases. II: N-glycosylation of Cel7A core protein isolated from different strains

A systematic analysis of the N-glycosylation of the catalytic domain of cellobiohydrolase I (Cel7A or CBH I) isolated from several Trichoderma reesei strains grown in minimal media was performed. Using a combination of chromatographic, electrophoretic, and mass spectrometric methods, the presence of glucosylated and phosphorylated oligosaccharides on the three N-glycosylation sites of Cel7A core protein (from T. reesei strains Rut-C30 and RL-P37) confirms previous findings. With N-glycans isolated from other strains, no end-capping glucose could be detected. Phosphodiester linkages were however found in proteins from each strain and these probably occur on both the alpha1-3 and the alpha1-6 branch of the high-mannose oligosaccharide tree. Evidence is also presented for the occurrence of mannobiosyl units on the phosphodiester linkage. Therefore the predominant N-glycans on Cel7A can be represented as (ManP)(0-1)GlcMan(7-8)GlcNAc2 for the hyperproducing Rut-C30 and RL-P37 mutants and as (Man(1-2)P)(0-1-2)Man(5-6-7)GlcNAc2 for the wild-type strain and the other mutants. As shown by ESI-MS, random substitution of these structures on the N-glycosylation sites explains the heterogeneous glycoform population of the isolated core domains. PAG-IEF separates up to five isoforms, resulting from posttranslational modification of Cel7A with mannosyl phosphodiester residues at the three distinct sites. This study clearly shows that posttranslational phosphorylation of glycoproteins is not atypical for Trichoderma sp. and that, in the case of the Rut-C30 and RL-P37 strains, the presence of an end-capped glucose residue at the alpha1-3 branch apparently hinders a second mannophoshoryl transfer.     

Increased release of serotonin from rat ileum due to dexfenfluramine

Plasma levels of serotonin are elevated in primary pulmonary hypertension even after bilateral lung transplantation, suggesting a possible etiologic role. Serotonin is released primarily from the small intestine. Anorectic agents, such as dexfenfluramine, which can cause pulmonary hypertension, are known to inhibit potassium channels in vascular smooth muscle cells. We examined the hypothesis that dexfenfluramine may stimulate release of serotonin from the ileum by inhibition of K+ channels. In an isolated loop of rat ileum perfused with a physiological salt solution, the administration of dexfenfluramine, its major metabolite D-norfenfluramine, the potassium channel blocker 4-aminopyridine (5 mM), and caffeine (30 mM) increased serotonin levels in the venous effluent. Potassium chloride (60 mM) tended to increase serotonin levels. In genetically susceptible individuals, dexfenfluramine may induce pulmonary hypertension by increasing cytosolic calcium in enterochromaffin cells of the small intestine, thus releasing serotonin and causing vasoconstriction. This work indicates that dexfenfluramine and its major metabolite d-norfenfluramine can increase serotonin release from the small intestine.     

The Effect of Cauda Equina Constriction on Nitric Oxide Synthase Activity

Nitric oxide synthase (NOS) activity was studied in the gray and white matter regions of the spinal cord 2 and 5 days after multiple cauda equina constrictions of the central processes of L7-Co5 dorsal root ganglia neurons. The results show considerable differences in enzyme activity in the thoracic, upper lumbar, lower lumbar, and sacral segments. Increased NOS activity was observed at 2 days after multiple cauda equina constrictions in the dorsal, lateral, and ventral columns of the lower lumbar segments and in the ventral column of the upper lumbar segments. The values returned to control levels within 5 postconstriction days. In the lateral columns of thoracic segments taken 2 and 5 days after surgery, NOS activity was enhanced by 54% and 55% and in the upper lumbar segments by 130% and 163%, respectively. Multiple cauda equina constrictions performed surgically for 2 and 5 days caused a significant increase in NOS activity predominantly in the gray matter regions of thoracic segments. A quite different response was found 5 days postconstriction in the upper lumbar segments, where the enzyme activity was significantly decreased in the dorsal horn, intermediate zone, and ventral horn. No such extreme differences could be seen in the lower lumbar segments, where NOS activity was significantly enhanced only in the ventral horn. The data correspond with a higher number of NOS immunoreactive somata, quantitatively evaluated in the ventral horn of the lower lumbar segments at 5 days after multiple cauda equina constrictions. While the great region-dependent heterogeneity in NOS activity seen 2 and 5 days after multiple cauda equina constrictions is quite apparent and suggestive of an active role played by nitric oxide in neuroprotective or neurotoxic processes occurring in the gray and white matter of the spinal cord, the extent of damage or the degree of neuroprotection caused by nitric oxide in compartmentalized gray and white matter in this experimental paradigm would be possible only using longer postconstriction periods.     

Changes in glycosidase activities during galactoglucomannan oligosaccharide inhibition of auxin induced growth

The inhibition of 2,4-D-induced elongation growth by galactoglucomannan oligosaccharides (GGMOs) in pea stem segments (Pisum sativum L. cv. Tyrkys) after 18 h of incubation results in changes of extracellular, intracellular and cell wall glycosidase activities (beta-D-glucosidase, beta-D-mannosidase, beta-D-galactosidase, beta-D-xylosidase, alpha-D-galactosidase, and alpha-L-arabinosidase). GGMOs lowered the glycosidase activities in the extracellular fraction, while in the cell wall fractions their activities were markedly increased. The intracellular enzyme alpha-d-galactosidase increased while the beta-d-galactosidase decreased in activity in response to the GGMO treatment. Extracellular enzymes showed low values of activities in comparison with intracellular and cell wall glycosidases. It is evident that GGMOs can alter auxin induced elongation and glycosidase activities in different compartments of the cell, however, the mode and site of their action remains unclear.     

Veterinary parasitic vaccines: pitfalls and future directions

Most available antiparasitic drugs are safe, cheap and highly effective against a broad spectrum of parasites. However, the alarming increase in the number of parasite species that are resistant to these drugs, the issue of residues in the food chain and the lack of new drugs stimulate development of alternative control methods in which vaccines would have a central role. Parasite vaccines are still rare, but there are encouraging signs that their number will increase in the next decade. The modern paradigm is that an understanding of parasite genes will lead to the identification of useful antigens, which can then be produced in recombinant systems developed as a result of the huge investment in biotechnology. However, we should also continue to devote efforts to basic research on the host-parasite interface.