EnzMet™: An Enzymatic Metallography Reagent for Accurately Delineating Neuronal Boundaries for Segmenting Gap Junction-Coupled Neurons in their Three-dimensional Space

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 - August 2, 201

Influence of nanostructured ceria support on platinum nanoparticles for methanol electrooxidation in alkaline media

The catalytic activity of platinum (Pt) nanoparticles (NPs) towards methanol electrooxidation in alkaline media was demonstrated to be dependent on their interactions with their nanostructured ceria support. Ceria nanorods (NRs) with diameters of 5 to 10 nm and lengths of 15 to 50 nm as well as ceria NPs with diameters of 2 to 6 nm were applied as supports for similarly sized Pt NPs with diameters of 2 to 5 nm. Cyclic voltammetry data showed that Pt NPs supported on ceria NPs exhibited a 2-to-5-fold higher catalytic current density versus ceria NRs. X-ray photoelectron spectroscopic data indicated that Pt NPs deposited onto ceria NRs were disproportionally composed of oxidized species (Pt2+, Pt4+ and Pt–O–M) rather than Pt0 while Pt NPs on ceria NPs mainly consisted of Pt0. Stronger metal-support interactions between Pt NPs and ceria NRs are postulated to induce preferential oxidation of Pt NPs and consequently decrease the catalytic sites and overall activity

A Model for the Development of the Rhizobial and Arbuscular Mycorrhizal Symbioses in Legumes and Its Use to Understand the Roles of Ethylene in the Establishment of these two Symbioses

We propose a model depicting the development of nodulation and arbuscular mycorrhizae. Both processes are dissected into many steps, using Pisum sativum L. nodulation mutants as a guideline. For nodulation, we distinguish two main developmental programs, one epidermal and one cortical. Whereas Nod factors alone affect the cortical program, bacteria are required to trigger the epidermal events. We propose that the two programs of the rhizobial symbiosis evolved separately and that, over time, they came to function together. The distinction between these two programs does not exist for arbuscular mycorrhizae development despite events occurring in both root tissues. Mutations that affect both symbioses are restricted to the epidermal program. We propose here sites of action and potential roles for ethylene during the formation of the two symbioses with a specific hypothesis for nodule organogenesis. Assuming the epidermis does not make ethylene, the microsymbionts probably first encounter a regulatory level of ethylene at the epidermis–outermost cortical cell layer interface. Depending on the hormone concentrations there, infection will either progress or be blocked. In the former case, ethylene affects the cortex cytoskeleton, allowing reorganization that facilitates infection; in the latter case, ethylene acts on several enzymes that interfere with infection thread growth, causing it to abort. Throughout this review, the difficulty of generalizing the roles of ethylene is emphasized and numerous examples are given to demonstrate the diversity that exists in plants

A Stimulatory Role for Cytokinin in the Arbuscular Mycorrhizal Symbiosis of Pea

The arbuscular mycorrhizal (AM) symbiosis between terrestrial plants and AM fungi is regulated by plant hormones. For most of these, a role has been clearly assigned in this mutualistic interaction; however, there are still contradictory reports for cytokinin (CK). Here, pea plants, the wild type (WT) cv. Sparkle and its mutant E151 (Pssym15), were inoculated with the AM fungus Rhizophagus irregularis. E151 has previously been characterized as possessing high CK levels in non-mycorrhizal (myc-) roots and exhibiting high number of fungal structures in mycorrhizal (myc+) roots. Myc- and myc+ plants were treated 7, 9, and 11 days after inoculation (DAI) with synthetic compounds known to alter CK status. WT plants were treated with a synthetic CK [6-benzylaminopurine (BAP)] or the CK degradation inhibitor INCYDE, whereas E151 plants were treated with the CK receptor antagonist PI-55. At 13 DAI, plant CK content was analyzed by mass spectrometry. The effects of the synthetic compounds on AM colonization were assessed at 28 (WT) or 35 (E151) DAI via a modified magnified intersections method. The only noticeable difference seen between myc- and myc+ plants in terms of CK content was in the levels of nucleotides (NTs). Whereas WT plants responded to fungi by lowering their NT levels, E151 plants did not. Since NTs are thought to be converted into active CK forms, this result suggests that active CKs were synthesized more effectively in WT than in E151. In general, myc+ and myc- WT plants responded similarly to INCYDE by lowering significantly their NT levels and increasing slightly their active CK levels; these responses were less obvious in BAP-treated WT plants. In contrast, the response of E151 plants to PI-55 depended on the plant mycorrhizal status. Whereas treated myc- plants exhibited high NT and low active CK levels, treated myc+ plants displayed low levels of both NTs and active CKs. Moreover, treated WT plants were more colonized than treated E151 plants. We concluded that CKs have a stimulatory role in AM colonization because increased active CK levels were paralleled with increased AM colonization while decreased CK levels corresponded to reduced AM colonization

Ethylene supports colonization of plant roots by the mutualistic fungus Piriformospora indica

The mutualistic basidiomycete Piriformospora indica colonizes roots of mono- and dicotyledonous plants, and thereby improves plant health and yield. Given the capability of P. indica to colonize a broad range of hosts, it must be anticipated that the fungus has evolved efficient strategies to overcome plant immunity and to establish a proper environment for nutrient acquisition and reproduction. Global gene expression studies in barley identified various ethylene synthesis and signaling components that were differentially regulated in P. indica-colonized roots. Based on these findings we examined the impact of ethylene in the symbiotic association. The data presented here suggest that P. indica induces ethylene synthesis in barley and Arabidopsis roots during colonization. Moreover, impaired ethylene signaling resulted in reduced root colonization, Arabidopsis mutants exhibiting constitutive ethylene signaling, -synthesis or ethylene-related defense were hyper-susceptible to P. indica. Our data suggest that ethylene signaling is required for symbiotic root colonization by P. indica

Vacuolar organization in the nodule parenchyma is important for the functioning of pea root nodules

Different models have been proposed to explain the operation of oxygen diffusion barrier in root nodules of leguminous plants. This barrier participates in protection of oxygen-sensitive nitrogenase, the key enzyme in nitrogen fixation, from inactivation. Details concerning structural and biochemical properties of the barrier are still lacking. Here, the properties of pea root nodule cortical cells were examined under normal conditions and after shoot removal. Microscopic observations, including neutral red staining and epifluorescence investigations, showed that the inner and outer nodule parenchyma cells exhibit different patterns of the central vacuole development. In opposition to the inner part, the outer parenchyma cells exhibited vacuolar shrinkage and formed cell wall infoldings. Shoot removal induced vacuolar shrinkage and formation of infoldings in the inner parenchyma and uninfected cells of the symbiotic tissue, as well. It is postulated that cells which possess shrinking vacuoles are sensitive to the external osmotic pressure. The cells can give an additional resistance to oxygen diffusion by release of water to the intercellular spaces

Influence of nanostructured ceria support on platinum nanoparticles for methanol electrooxidation in alkaline media

The catalytic activity of platinum (Pt) nanoparticles (NPs) towards methanol electrooxidation in alkaline media was demonstrated to be dependent on their interactions with their nanostructured ceria support. Ceria nanorods (NRs) with diameters of 5 to 10 nm and lengths of 15 to 50 nm as well as ceria NPs with diameters of 2 to 6 nm were applied as supports for similarly sized Pt NPs with diameters of 2 to 5 nm. Cyclic voltammetry data showed that Pt NPs supported on ceria NPs exhibited a 2-to-5-fold higher catalytic current density versus ceria NRs. X-ray photoelectron spectroscopic data indicated that Pt NPs deposited onto ceria NRs were disproportionally composed of oxidized species (Pt2+, Pt4+ and Pt–O–M) rather than Pt0 while Pt NPs on ceria NPs mainly consisted of Pt0. Stronger metal-support interactions between Pt NPs and ceria NRs are postulated to induce preferential oxidation of Pt NPs and consequently decrease the catalytic sites and overall activity