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

Arbuscular mycorrhizal community structure on co-existing tropical legume trees in French Guiana

Aims We aimed to characterise the arbuscular mycorrhizal fungal (AMF) community structure and potential edaphic determinants in the dominating, but poorly described, root-colonizing Paris-type AMF community on co-occurring Amazonian leguminous trees. Methods Three highly productive leguminous trees (Dicorynia guianensis, Eperua falcata and Tachigali melinonii were targeted) in species-rich forests on contrasting soil types at the Nouragues Research Station in central French Guiana. Abundant AMF SSU rRNA amplicons (NS31-AM1 & AML1-AML2 primers) from roots identified via trnL profiling were subjected to denaturing gradient gel electrophoresis (DGGE), clone library sequencing and phylogenetic analysis. Results Classical approaches targeting abundant SSU amplicons highlighted a diverse root-colonizing symbiotic AMF community dominated by members of the Glomeraceae. DGGE profiling indicated that, of the edaphic factors investigated, soil nitrogen was most important in influencing the AMF community and this was more important than any host tree species effect. Conclusions Dominating Paris-type mycorrhizal leguminous trees in Amazonian soils host diverse and novel taxa within the Glomeraceae that appear under edaphic selection in the investigated tropical forests. Linking symbiotic diversity of identified AMF taxa to ecological processes is the next challenge ahead

Collaborative innovation and open innovation

Consumers’ demand for products has moved, since the eighties, toward products customized to personal needs. This change has incited firms to work closely with other organizations and especially customers, in order to anticipate better the future needs, inducing a growth in external relationships of firms. This trend is still at work in most of industries in which lead users impulse evolution in products. In consequence, the collaborative process continues to increase. At the same time, the efficiency of the production by in-house R&D of firms’ decreases to such an extent that following Chesbrough (2003), many scholars advise firms to access knowledge externally and to develop innovation with an open process of development: the open innovation model. They incite firms to use all the external sources which are available to be the first to introduc ..

Paleo-erosion rates in Central Asia since 9 Ma: A transient increase at the onset of Quaternary glaciations?

Erosion is a fundamental player of the interactions existing between internal geodynamics and climate, in particular through its influence on the carbon dioxide budget. However, long term (> Ma) erosion rates, estimated indirectly from sediment budget, remain poorly constrained. While some studies suggest that worldwide erosion rates increased at the Plio-Pleistocene climatic transition (~4–2 Ma), the validity of this observation and its significance is a matter of debate due to potential biases of the sedimentary record and to the influence of sea level fall on the global sedimentary flux to marginal basins. In the present study, we estimate erosion rates over the last ~9 Ma using in situ produced cosmogenic ^(10)Be concentrations measured in magnetostratigraphically dated continental sediments. We focus on an intracontinental endorheic watershed draining the northern Tianshan in Central Asia, a key region regarding the ongoing debate. While erosion rates between 0.1 and 1 mm·yr^(−1) are derived from most of our record, they reach values as high as ~2.5 mm·yr^(−1) from 2.5 to 1.7 Ma. Then, after 1.7 Ma, recent andmodern erosion rates fell below 1 mm·yr^(−1). This temporary increase is correlated with the onset of Quaternary ice ages and suggests that global climate had a significant and transient impact on erosion

Interactions between arbuscular mycorrhizal fungi and a mycorrhiza-defective mutant tomato: does a noninfective fungus alter the ability of an infective fungus to colonise the roots - and vice versa?

We have investigated whether inoculation of a mycorrhiza-defective mutant (rmc) of tomato (Lycopersicon esculentum) with an individual arbuscular mycorrhizal (AM) fungal species affects subsequent colonisation by another AM fungal species that has different infectivity when presented alone. Inoculum was provided by leek (Allium porrum) growing in 'nurse pots' into which rmc seedlings were planted, and between which they were subsequently transferred

WHEN IS FREQUENT FACE-TO-FACE CONTACT NECESSARY IN INNOVATION? A COMPARATIVE STUDY OF TWO DISTRIBUTED PRODUCT DEVELOPMENT PROJECTS

This paper combines the concept of technological modularity from the product-development literature with the concept of brokers from literature about communities of practice to explain why some innovation project teams require frequent face-to-face interactions to efficiently co-create new technologies, whereas others do not. The explanation is explored through a comparative case-study analysis of two distributed product-development projects in the European software and telecommunications industries. These case-study projects traversed several geographical sites in Norway, Germany, Greece, England and the Netherlands as well various communities of practice related to a number of distinct technological specialisations. The method involved participative observations and 40 in-depth interviews with key project members, managers and consultants.International innovation projects, Face-to-face interactions, ICT, Communities of practice, Technological modularity,

Colonization patterns in a mycorrhiza-defective mutant tomato vary with different arbuscular-mycorrhizal fungi

Interactions between a mycorrhiza-defective tomato (Lycopersicon esculentum) mutant, rmc, and different species of arbuscular mycorrhizal (AM) fungi were investigated and compared with those with the wild-type cv. 76R. Both cv. 76R and rmc were challenged with Glomus intraradices, G. mosseae, G. coronatum, G. versiforme, G. etunicatum, G. fasciculatum, Gigaspora margarita and Scutellospora calospora using a nurse pot inoculation system. Cv. 76R demonstrated normal colonization patterns for all fungal species. By contrast, the development of different fungal species with rmc was impaired at different steps. Development of G. intraradices, G. etunicatum and G. fasciculatum was arrested on the root surface. However, G. mosseae, G. coronatum, G. margarita and S. calospora frequently penetrated the root epidermis, but colonization of the cortex was rare. G. versiforme achieved relatively normal colonization in rmc compared with the other species. This is the first report on the variation of colonization patterns in a mycorrhiza-defective mutant by different species of AM fungi, and highlights the need for previously described mutants in legumes to be challenged by more than one fungus. © New Phytologist (2001)